[[boot-features]]
= Spring Boot Features
include::attributes.adoc[]

This section dives into the details of Spring Boot.
Here you can learn about the key features that you may want to use and customize.
If you have not already done so, you might want to read the "<<getting-started.adoc#getting-started>>" and "<<using-spring-boot.adoc#using-boot>>" sections, so that you have a good grounding of the basics.



[[boot-features-spring-application]]
== SpringApplication
The `SpringApplication` class provides a convenient way to bootstrap a Spring application that is started from a `main()` method.
In many situations, you can delegate to the static `SpringApplication.run` method, as shown in the following example:

[source,java,indent=0]
----
	public static void main(String[] args) {
		SpringApplication.run(MySpringConfiguration.class, args);
	}
----

When your application starts, you should see something similar to the following output:

[indent=0,subs="attributes"]
----
  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::   v{spring-boot-version}

2019-04-31 13:09:54.117  INFO 56603 --- [           main] o.s.b.s.app.SampleApplication            : Starting SampleApplication v0.1.0 on mycomputer with PID 56603 (/apps/myapp.jar started by pwebb)
2019-04-31 13:09:54.166  INFO 56603 --- [           main] ationConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6e5a8246: startup date [Wed Jul 31 00:08:16 PDT 2013]; root of context hierarchy
2019-04-01 13:09:56.912  INFO 41370 --- [           main] .t.TomcatServletWebServerFactory : Server initialized with port: 8080
2019-04-01 13:09:57.501  INFO 41370 --- [           main] o.s.b.s.app.SampleApplication            : Started SampleApplication in 2.992 seconds (JVM running for 3.658)
----

By default, `INFO` logging messages are shown, including some relevant startup details, such as the user that launched the application.
If you need a log level other than `INFO`, you can set it, as described in <<boot-features-custom-log-levels>>.
The application version is determined using the implementation version from the main application class's package.
Startup information logging can be turned off by setting `spring.main.log-startup-info` to `false`.
This will also turn off logging of the application's active profiles.

TIP: To add additional logging during startup, you can override `logStartupInfo(boolean)` in a subclass of `SpringApplication`.



[[boot-features-startup-failure]]
=== Startup Failure
If your application fails to start, registered `FailureAnalyzers` get a chance to provide a dedicated error message and a concrete action to fix the problem.
For instance, if you start a web application on port `8080` and that port is already in use, you should see something similar to the following message:

[indent=0]
----
	***************************
	APPLICATION FAILED TO START
	***************************

	Description:

	Embedded servlet container failed to start. Port 8080 was already in use.

	Action:

	Identify and stop the process that's listening on port 8080 or configure this application to listen on another port.
----

NOTE: Spring Boot provides numerous `FailureAnalyzer` implementations, and you can <<howto.adoc#howto-failure-analyzer,add your own>>.

If no failure analyzers are able to handle the exception, you can still display the full conditions report to better understand what went wrong.
To do so, you need to <<boot-features-external-config,enable the `debug` property>> or <<boot-features-custom-log-levels,enable `DEBUG` logging>> for `org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener`.

For instance, if you are running your application by using `java -jar`, you can enable the `debug` property as follows:

[indent=0,subs="attributes"]
----
	$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug
----



[[boot-features-lazy-initialization]]
=== Lazy Initialization
`SpringApplication` allows an application to be initialized lazily.
When lazy initialization is enabled, beans are created as they are needed rather than during application startup.
As a result, enabling lazy initialization can reduce the time that it takes your application to start.
In a web application, enabling lazy initialization will result in many web-related beans not being initialized until an HTTP request is received.

A downside of lazy initialization is that it can delay the discovery of a problem with the application.
If a misconfigured bean is initialized lazily, a failure will no longer occur during startup and the problem will only become apparent when the bean is initialized.
Care must also be taken to ensure that the JVM has sufficient memory to accommodate all of the application's beans and not just those that are initialized during startup.
For these reasons, lazy initialization is not enabled by default and it is recommended that fine-tuning of the JVM's heap size is done before enabling lazy initialization.

Lazy initialization can be enabled programmatically using the `lazyInitialization` method on `SpringApplicationBuilder` or the `setLazyInitialization` method on `SpringApplication`.
Alternatively, it can be enabled using the configprop:spring.main.lazy-initialization[] property as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  main:
	    lazy-initialization: true
----

TIP: If you want to disable lazy initialization for certain beans while using lazy initialization for the rest of the application, you can explicitly set their lazy attribute to false using the `@Lazy(false)` annotation.



[[boot-features-banner]]
=== Customizing the Banner
The banner that is printed on start up can be changed by adding a `banner.txt` file to your classpath or by setting the configprop:spring.banner.location[] property to the location of such a file.
If the file has an encoding other than UTF-8, you can set `spring.banner.charset`.
In addition to a text file, you can also add a `banner.gif`, `banner.jpg`, or `banner.png` image file to your classpath or set the configprop:spring.banner.image.location[] property.
Images are converted into an ASCII art representation and printed above any text banner.

Inside your `banner.txt` file, you can use any of the following placeholders:

.Banner variables
|===
| Variable | Description

| `${application.version}`
| The version number of your application, as declared in `MANIFEST.MF`.
  For example, `Implementation-Version: 1.0` is printed as `1.0`.

| `${application.formatted-version}`
| The version number of your application, as declared in `MANIFEST.MF` and formatted for display (surrounded with brackets and prefixed with `v`).
  For example `(v1.0)`.

| `${spring-boot.version}`
| The Spring Boot version that you are using.
  For example `{spring-boot-version}`.

| `${spring-boot.formatted-version}`
| The Spring Boot version that you are using, formatted for display (surrounded with brackets and prefixed with `v`).
  For example `(v{spring-boot-version})`.

| `${Ansi.NAME}` (or `${AnsiColor.NAME}`, `${AnsiBackground.NAME}`, `${AnsiStyle.NAME}`)
| Where `NAME` is the name of an ANSI escape code.
  See {spring-boot-module-code}/ansi/AnsiPropertySource.java[`AnsiPropertySource`] for details.

| `${application.title}`
| The title of your application, as declared in `MANIFEST.MF`.
  For example `Implementation-Title: MyApp` is printed as `MyApp`.
|===

TIP: The `SpringApplication.setBanner(...)` method can be used if you want to generate a banner programmatically.
Use the `org.springframework.boot.Banner` interface and implement your own `printBanner()` method.

You can also use the configprop:spring.main.banner-mode[] property to determine if the banner has to be printed on `System.out` (`console`), sent to the configured logger (`log`), or not produced at all (`off`).

The printed banner is registered as a singleton bean under the following name: `springBootBanner`.

[NOTE]
====
The `${application.version}` and `${application.formatted-version}` properties are only available if you are using Spring Boot launchers.
The values won't be resolved if you are running an unpacked jar and starting it with `java -cp <classpath> <mainclass>`.

This is why we recommend that you always launch unpacked jars using `java org.springframework.boot.loader.JarLauncher`.
This will initialize the `application.*` banner variables before building the classpath and launching your app.
====



[[boot-features-customizing-spring-application]]
=== Customizing SpringApplication
If the `SpringApplication` defaults are not to your taste, you can instead create a local instance and customize it.
For example, to turn off the banner, you could write:

[source,java,indent=0]
----
	public static void main(String[] args) {
		SpringApplication app = new SpringApplication(MySpringConfiguration.class);
		app.setBannerMode(Banner.Mode.OFF);
		app.run(args);
	}
----

NOTE: The constructor arguments passed to `SpringApplication` are configuration sources for Spring beans.
In most cases, these are references to `@Configuration` classes, but they could also be references to XML configuration or to packages that should be scanned.

It is also possible to configure the `SpringApplication` by using an `application.properties` file.
See _<<boot-features-external-config>>_ for details.

For a complete list of the configuration options, see the {spring-boot-module-api}/SpringApplication.html[`SpringApplication` Javadoc].



[[boot-features-fluent-builder-api]]
=== Fluent Builder API
If you need to build an `ApplicationContext` hierarchy (multiple contexts with a parent/child relationship) or if you prefer using a "`fluent`" builder API, you can use the `SpringApplicationBuilder`.

The `SpringApplicationBuilder` lets you chain together multiple method calls and includes `parent` and `child` methods that let you create a hierarchy, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/builder/SpringApplicationBuilderExample.java[tag=hierarchy]
----

NOTE: There are some restrictions when creating an `ApplicationContext` hierarchy.
For example, Web components *must* be contained within the child context, and the same `Environment` is used for both parent and child contexts.
See the {spring-boot-module-api}/builder/SpringApplicationBuilder.html[`SpringApplicationBuilder` Javadoc] for full details.



[[boot-features-application-availability]]
=== Application Availability
When deployed on platforms, applications can provide information about their availability to the platform using infrastructure such as https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/[Kubernetes Probes].
Spring Boot includes out-of-the box support for the commonly used "`liveness`" and "`readiness`" availability states.
If you are using Spring Boot's "`actuator`" support then these states are exposed as health endpoint groups.

In addition, you can also obtain availability states by injecting the `ApplicationAvailability` interface into your own beans.



[[boot-features-application-availability-liveness-state]]
==== Liveness State
The "`Liveness`" state of an application tells whether its internal state allows it to work correctly, or recover by itself if it's currently failing.
A broken "`Liveness`" state means that the application is in a state that it cannot recover from, and the infrastructure should restart the application.

NOTE: In general, the "Liveness" state should not be based on external checks, such as <<production-ready-features.adoc#production-ready-health, Health checks>>.
If it did, a failing external system (a database, a Web API, an external cache) would trigger massive restarts and cascading failures across the platform.

The internal state of Spring Boot applications is mostly represented by the Spring `ApplicationContext`.
If the application context has started successfully, Spring Boot assumes that the application is in a valid state.
An application is considered live as soon as the context has been refreshed, see <<boot-features-application-events-and-listeners, Spring Boot application lifecycle and related Application Events>>.



[[boot-features-application-availability-readiness-state]]
==== Readiness State
The "`Readiness`" state of an application tells whether the application is ready to handle traffic.
A failing "`Readiness`" state tells the platform that it should not route traffic to the application for now.
This typically happens during startup, while `CommandLineRunner` and `ApplicationRunner` components are being processed, or at any time if the application decides that it's too busy for additional traffic.

An application is considered ready as soon as application and command-line runners have been called, see <<boot-features-application-events-and-listeners, Spring Boot application lifecycle and related Application Events>>.

TIP: Tasks expected to run during startup should be executed by `CommandLineRunner` and `ApplicationRunner` components instead of using Spring component lifecycle callbacks such as `@PostConstruct`.



[[boot-features-application-availability-managing]]
==== Managing the Application Availability State
Application components can retrieve the current availability state at any time, by injecting the `ApplicationAvailability` interface and calling methods on it.
More often, applications will want to listen to state updates or update the state of the application.

For example, we can export the "Readiness" state of the application to a file so that a Kubernetes "exec Probe" can look at this file:

[source,java,indent=0]
----
    @Component
	public class ReadinessStateExporter {

		@EventListener
	    public void onStateChange(AvailabilityChangeEvent<ReadinessState> event) {
			switch (event.getState()) {
		    case ACCEPTING_TRAFFIC:
			    // create file /tmp/healthy
			break;
		    case REFUSING_TRAFFIC:
		    	// remove file /tmp/healthy
			break;
		    }
	    }

	}
----

We can also update the state of the application, when the application breaks and cannot recover:

[source,java,indent=0]
----
    @Component
	public class LocalCacheVerifier {

	    private final ApplicationEventPublisher eventPublisher;

	    public LocalCacheVerifier(ApplicationEventPublisher eventPublisher) {
            this.eventPublisher = eventPublisher;
	    }

	    public void checkLocalCache() {
	    	try {
	    		//...
	    	}
	    	catch (CacheCompletelyBrokenException ex) {
	    		AvailabilityChangeEvent.publish(this.eventPublisher, ex, LivenessState.BROKEN);
	    	}
	    }

	}
----

Spring Boot provides <<production-ready-features.adoc#production-ready-kubernetes-probes,Kubernetes HTTP probes for "Liveness" and "Readiness" with Actuator Health Endpoints>>.
You can get more guidance about <<deployment.adoc#cloud-deployment-kubernetes,deploying Spring Boot applications on Kubernetes in the dedicated section>>.



[[boot-features-application-events-and-listeners]]
=== Application Events and Listeners
In addition to the usual Spring Framework events, such as {spring-framework-api}/context/event/ContextRefreshedEvent.html[`ContextRefreshedEvent`], a `SpringApplication` sends some additional application events.

[NOTE]
====
Some events are actually triggered before the `ApplicationContext` is created, so you cannot register a listener on those as a `@Bean`.
You can register them with the `SpringApplication.addListeners(...)` method or the `SpringApplicationBuilder.listeners(...)` method.

If you want those listeners to be registered automatically, regardless of the way the application is created, you can add a `META-INF/spring.factories` file to your project and reference your listener(s) by using the `org.springframework.context.ApplicationListener` key, as shown in the following example:

[indent=0]
----
	org.springframework.context.ApplicationListener=com.example.project.MyListener
----

====

Application events are sent in the following order, as your application runs:

. An `ApplicationStartingEvent` is sent at the start of a run but before any processing, except for the registration of listeners and initializers.
. An `ApplicationEnvironmentPreparedEvent` is sent when the `Environment` to be used in the context is known but before the context is created.
. An `ApplicationContextInitializedEvent` is sent when the `ApplicationContext` is prepared and ApplicationContextInitializers have been called but before any bean definitions are loaded.
. An `ApplicationPreparedEvent` is sent just before the refresh is started but after bean definitions have been loaded.
. An `ApplicationStartedEvent` is sent after the context has been refreshed but before any application and command-line runners have been called.
. An `AvailabilityChangeEvent` is sent right after with `LivenessState.CORRECT` to indicate that the application is considered as live.
. An `ApplicationReadyEvent` is sent after any <<boot-features-command-line-runner,application and command-line runners>> have been called.
. An `AvailabilityChangeEvent` is sent right after with `ReadinessState.ACCEPTING_TRAFFIC` to indicate that the application is ready to service requests.
. An `ApplicationFailedEvent` is sent if there is an exception on startup.

The above list only includes ``SpringApplicationEvent``s that are tied to a `SpringApplication`.
In addition to these, the following events are also published after `ApplicationPreparedEvent` and before `ApplicationStartedEvent`:

- A `WebServerInitializedEvent` is sent after the `WebServer` is ready.
  `ServletWebServerInitializedEvent` and `ReactiveWebServerInitializedEvent` are the servlet and reactive variants respectively.
- A `ContextRefreshedEvent` is sent when an `ApplicationContext` is refreshed.

TIP: You often need not use application events, but it can be handy to know that they exist.
Internally, Spring Boot uses events to handle a variety of tasks.

NOTE: Event listeners should not run potentially lengthy tasks as they execute in the same thread by default.
Consider using <<boot-features-command-line-runner,application and command-line runners>> instead.

Application events are sent by using Spring Framework's event publishing mechanism.
Part of this mechanism ensures that an event published to the listeners in a child context is also published to the listeners in any ancestor contexts.
As a result of this, if your application uses a hierarchy of `SpringApplication` instances, a listener may receive multiple instances of the same type of application event.

To allow your listener to distinguish between an event for its context and an event for a descendant context, it should request that its application context is injected and then compare the injected context with the context of the event.
The context can be injected by implementing `ApplicationContextAware` or, if the listener is a bean, by using `@Autowired`.



[[boot-features-web-environment]]
=== Web Environment
A `SpringApplication` attempts to create the right type of `ApplicationContext` on your behalf.
The algorithm used to determine a `WebApplicationType` is the following:

* If Spring MVC is present, an `AnnotationConfigServletWebServerApplicationContext` is used
* If Spring MVC is not present and Spring WebFlux is present, an `AnnotationConfigReactiveWebServerApplicationContext` is used
* Otherwise, `AnnotationConfigApplicationContext` is used

This means that if you are using Spring MVC and the new `WebClient` from Spring WebFlux in the same application, Spring MVC will be used by default.
You can override that easily by calling `setWebApplicationType(WebApplicationType)`.

It is also possible to take complete control of the `ApplicationContext` type that is used by calling `setApplicationContextClass(...)`.

TIP: It is often desirable to call `setWebApplicationType(WebApplicationType.NONE)` when using `SpringApplication` within a JUnit test.



[[boot-features-application-arguments]]
=== Accessing Application Arguments
If you need to access the application arguments that were passed to `SpringApplication.run(...)`, you can inject a `org.springframework.boot.ApplicationArguments` bean.
The `ApplicationArguments` interface provides access to both the raw `String[]` arguments as well as parsed `option` and `non-option` arguments, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.boot.*;
	import org.springframework.beans.factory.annotation.*;
	import org.springframework.stereotype.*;

	@Component
	public class MyBean {

		@Autowired
		public MyBean(ApplicationArguments args) {
			boolean debug = args.containsOption("debug");
			List<String> files = args.getNonOptionArgs();
			// if run with "--debug logfile.txt" debug=true, files=["logfile.txt"]
		}

	}
----

TIP: Spring Boot also registers a `CommandLinePropertySource` with the Spring `Environment`.
This lets you also inject single application arguments by using the `@Value` annotation.



[[boot-features-command-line-runner]]
=== Using the ApplicationRunner or CommandLineRunner
If you need to run some specific code once the `SpringApplication` has started, you can implement the `ApplicationRunner` or `CommandLineRunner` interfaces.
Both interfaces work in the same way and offer a single `run` method, which is called just before `SpringApplication.run(...)` completes.

NOTE: This contract is well suited for tasks that should run after application startup but before it starts accepting traffic.


The `CommandLineRunner` interfaces provides access to application arguments as a string array, whereas the `ApplicationRunner` uses the `ApplicationArguments` interface discussed earlier.
The following example shows a `CommandLineRunner` with a `run` method:

[source,java,indent=0]
----
	import org.springframework.boot.*;
	import org.springframework.stereotype.*;

	@Component
	public class MyBean implements CommandLineRunner {

		public void run(String... args) {
			// Do something...
		}

	}
----

If several `CommandLineRunner` or `ApplicationRunner` beans are defined that must be called in a specific order, you can additionally implement the `org.springframework.core.Ordered` interface or use the `org.springframework.core.annotation.Order` annotation.



[[boot-features-application-exit]]
=== Application Exit
Each `SpringApplication` registers a shutdown hook with the JVM to ensure that the `ApplicationContext` closes gracefully on exit.
All the standard Spring lifecycle callbacks (such as the `DisposableBean` interface or the `@PreDestroy` annotation) can be used.

In addition, beans may implement the `org.springframework.boot.ExitCodeGenerator` interface if they wish to return a specific exit code when `SpringApplication.exit()` is called.
This exit code can then be passed to `System.exit()` to return it as a status code, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/ExitCodeApplication.java[tag=example]
----

Also, the `ExitCodeGenerator` interface may be implemented by exceptions.
When such an exception is encountered, Spring Boot returns the exit code provided by the implemented `getExitCode()` method.



[[boot-features-application-admin]]
=== Admin Features
It is possible to enable admin-related features for the application by specifying the configprop:spring.application.admin.enabled[] property.
This exposes the {spring-boot-module-code}/admin/SpringApplicationAdminMXBean.java[`SpringApplicationAdminMXBean`] on the platform `MBeanServer`.
You could use this feature to administer your Spring Boot application remotely.
This feature could also be useful for any service wrapper implementation.

TIP: If you want to know on which HTTP port the application is running, get the property with a key of `local.server.port`.



[[boot-features-application-startup-tracking]]
=== Application Startup tracking
During the application startup, the `SpringApplication` and the `ApplicationContext` perform many tasks related to the application lifecycle,
the beans lifecycle or even processing application events.
With {spring-framework-api}/core/metrics/ApplicationStartup.html[`ApplicationStartup`], Spring Framework  {spring-framework-docs}/core.html#context-functionality-startup[allows you to track the application startup sequence with ``StartupStep``s].
This data can be collected for profiling purposes, or just to have a better understanding of an application startup process.

You can choose an `ApplicationStartup` implementation when setting up the `SpringApplication` instance.
For example, to use the `BufferingApplicationStartup`, you could write:

[source,java,indent=0]
----
	public static void main(String[] args) {
		SpringApplication app = new SpringApplication(MySpringConfiguration.class);
		app.setApplicationStartup(new BufferingApplicationStartup(2048));
		app.run(args);
	}
----

The first available implementation, `FlightRecorderApplicationStartup` is provided by Spring Framework.
It adds Spring-specific startup events to a Java Flight Recorder session and is meant for profiling applications and correlating their Spring context lifecycle with JVM events (such as allocations, GCs, class loading...).
Once configured, you can record data by running the application with the Flight Recorder enabled:

[source,bash,indent=0]
----
	$ java -XX:StartFlightRecording:filename=recording.jfr,duration=10s -jar demo.jar
----

Spring Boot ships with the `BufferingApplicationStartup` variant; this implementation is meant for buffering the startup steps and draining them into an external metrics system.
Applications can ask for the bean of type `BufferingApplicationStartup` in any component.
Additionally, Spring Boot Actuator will {spring-boot-actuator-restapi-docs}/#startup[expose a `startup` endpoint to expose this information as a JSON document].



[[boot-features-external-config]]
== Externalized Configuration
Spring Boot lets you externalize your configuration so that you can work with the same application code in different environments.
You can use a variety of external configuration sources, include Java properties files, YAML files, environment variables, and command-line arguments.

Property values can be injected directly into your beans by using the `@Value` annotation, accessed through Spring's `Environment` abstraction, or be <<boot-features-external-config-typesafe-configuration-properties,bound to structured objects>> through `@ConfigurationProperties`.

Spring Boot uses a very particular `PropertySource` order that is designed to allow sensible overriding of values.
Properties are considered in the following order (with values from lower items overriding earlier ones):

. Default properties (specified by setting `SpringApplication.setDefaultProperties`).
. {spring-framework-api}/context/annotation/PropertySource.html[`@PropertySource`] annotations on your `@Configuration` classes.
  Please note that such property sources are not added to the `Environment` until the application context is being refreshed.
  This is too late to configure certain properties such as `+logging.*+` and `+spring.main.*+` which are read before refresh begins.
. Config data (such as `application.properties` files)
. A `RandomValuePropertySource` that has properties only in `+random.*+`.
. OS environment variables.
. Java System properties (`System.getProperties()`).
. JNDI attributes from `java:comp/env`.
. `ServletContext` init parameters.
. `ServletConfig` init parameters.
. Properties from `SPRING_APPLICATION_JSON` (inline JSON embedded in an environment variable or system property).
. Command line arguments.
. `properties` attribute on your tests.
  Available on {spring-boot-test-module-api}/context/SpringBootTest.html[`@SpringBootTest`] and the <<boot-features-testing-spring-boot-applications-testing-autoconfigured-tests,test annotations for testing a particular slice of your application>>.
. {spring-framework-api}/test/context/TestPropertySource.html[`@TestPropertySource`] annotations on your tests.
. <<using-spring-boot.adoc#using-boot-devtools-globalsettings,Devtools global settings properties>> in the `$HOME/.config/spring-boot` directory when devtools is active.

Config data files are considered in the following order:

. <<boot-features-external-config-files,Application properties>> packaged inside your jar (`application.properties` and YAML variants).
. <<boot-features-external-config-files-profile-specific,Profile-specific application properties>> packaged inside your jar (`application-\{profile}.properties` and YAML variants).
. <<boot-features-external-config-files,Application properties>> outside of your packaged jar (`application.properties` and YAML variants).
. <<boot-features-external-config-files-profile-specific,Profile-specific application properties>> outside of your packaged jar (`application-\{profile}.properties` and YAML variants).

NOTE: It is recommended to stick with one format for your entire application.
If you have configuration files with both `.properties` and `.yml` format in the same location, `.properties` takes precedence.

To provide a concrete example, suppose you develop a `@Component` that uses a `name` property, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.stereotype.*;
	import org.springframework.beans.factory.annotation.*;

	@Component
	public class MyBean {

		@Value("${name}")
		private String name;

		// ...

	}
----

On your application classpath (for example, inside your jar) you can have an `application.properties` file that provides a sensible default property value for `name`.
When running in a new environment, an `application.properties` file can be provided outside of your jar that overrides the `name`.
For one-off testing, you can launch with a specific command line switch (for example, `java -jar app.jar --name="Spring"`).

TIP: The `env` and `configprops` endpoints can be useful in determining why a property has a particular value.
You can use these two endpoints to diagnose unexpected property values.
See the "<<production-ready-features.adoc#production-ready-endpoints, Production ready features>>" section for details.



[[boot-features-external-config-command-line-args]]
=== Accessing Command Line Properties
By default, `SpringApplication` converts any command line option arguments (that is, arguments starting with `--`, such as `--server.port=9000`) to a `property` and adds them to the Spring `Environment`.
As mentioned previously, command line properties always take precedence over file based property sources.

If you do not want command line properties to be added to the `Environment`, you can disable them by using `SpringApplication.setAddCommandLineProperties(false)`.



[[boot-features-external-config-application-json]]
=== JSON Application Properties
Environment variables and system properties often have restrictions that mean some property names cannot be used.
To help with this, Spring Boot allows you to encode a block of properties into a single JSON structure.

When your application starts, any `spring.application.json` or `SPRING_APPLICATION_JSON` properties will be parsed and added to the `Environment`.

For example, the `SPRING_APPLICATION_JSON` property can be supplied on the command line in a UN{asterisk}X shell as an environment variable:

[indent=0]
----
	$ SPRING_APPLICATION_JSON='{"acme":{"name":"test"}}' java -jar myapp.jar
----

In the preceding example, you end up with `acme.name=test` in the Spring `Environment`.

The same JSON can also be provided as a system property:

[indent=0]
----
	$ java -Dspring.application.json='{"acme":{"name":"test"}}' -jar myapp.jar
----

Or you could supply the JSON by using a command line argument:

[indent=0]
----
	$ java -jar myapp.jar --spring.application.json='{"acme":{"name":"test"}}'
----

If you are deploying to a classic Application Server, you could also use a JNDI variable named `java:comp/env/spring.application.json`.

NOTE: Although `null` values from the JSON will be added to the resulting property source, the `PropertySourcesPropertyResolver` treats `null` properties as missing values.
This means that the JSON cannot override properties from lower order property sources with a `null` value.



[[boot-features-external-config-files]]
=== External Application Properties [[boot-features-external-config-application-property-files]]
Spring Boot will automatically find and load `application.properties` and `application.yaml` files from the following locations when your application starts:

. From the classpath
.. The classpath root
.. The classpath `/config` package
. From the current directory
.. The current directory
.. The `/config` subdirectory in the current directory
.. Immediate child directories of the `/config` subdirectory

The list is ordered by precedence (with values from lower items overriding earlier ones).
Documents from the loaded files are added as `PropertySources` to the Spring `Environment`.

If you do not like `application` as the configuration file name, you can switch to another file name by specifying a configprop:spring.config.name[] environment property.
For example, to look for `myproject.properties` and `myproject.yaml` files you can run your application as follows:

[indent=0]
----
	$ java -jar myproject.jar --spring.config.name=myproject
----

You can also refer to an explicit location by using the configprop:spring.config.location[] environment property.
This properties accepts a comma-separated list of one or more locations to check.

The following example shows how to specify two distinct files:

[indent=0]
----
	$ java -jar myproject.jar --spring.config.location=optional:classpath:/default.properties,optional:classpath:/override.properties
----

TIP: Use the prefix `optional:` if the <<boot-features-external-config-optional-prefix,locations are optional>> and you don't mind if they don't exist.

WARNING: `spring.config.name`, `spring.config.location`, and `spring.config.additional-location` are used very early to determine which files have to be loaded.
They must be defined as an environment property (typically an OS environment variable, a system property, or a command-line argument).

If `spring.config.location` contains directories (as opposed to files), they should end in `/`.
At runtime they will be appended with the names generated from `spring.config.name` before being loaded.
Files specified in `spring.config.location` are imported directly.

NOTE: Both directory and file location values are also expanded to check for <<boot-features-external-config-files-profile-specific,profile-specific files>>.
For example, if you have a `spring.config.location` of `classpath:myconfig.properties`, you will also find appropriate `classpath:myconfig-<profile>.properties` files are loaded.

In most situations, each configprop:spring.config.location[] item you add will reference a single file or directory.
Locations are processed in the order that they are defined and later ones can override the values of earlier ones.

[[boot-features-external-config-files-location-groups]]
If you have a complex location setup, and you use profile-specific configuration files, you may need to provide further hints so that Spring Boot knows how they should be grouped.
A location group is a collection of locations that are all considered at the same level.
For example, you might want to group all classpath locations, then all external locations.
Items within a location group should be separated with `;`.
See the example in the "`<<boot-features-external-config-files-profile-specific>>`" section for more details.

Locations configured by using `spring.config.location` replace the default locations.
For example, if `spring.config.location` is configured with the value `optional:classpath:/custom-config/,optional:file:./custom-config/`, the complete set of locations considered is:

. `optional:classpath:custom-config/`
. `optional:file:./custom-config/`

If you prefer to add additional locations, rather than replacing them, you can use `spring.config.additional-location`.
Properties loaded from additional locations can override those in the default locations.
For example, if `spring.config.additional-location` is configured with the value `optional:classpath:/custom-config/,optional:file:./custom-config/`, the complete set of locations considered is:

. `optional:classpath:/;optional:classpath:/config/`
. `optional:file:./;optional:file:./config/;optional:file:./config/*/`
. `optional:classpath:custom-config/`
. `optional:file:./custom-config/`

This search ordering lets you specify default values in one configuration file and then selectively override those values in another.
You can provide default values for your application in `application.properties` (or whatever other basename you choose with `spring.config.name`) in one of the default locations.
These default values can then be overridden at runtime with a different file located in one of the custom locations.

NOTE: If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (for example, configprop:spring.config.name[format=envvar] instead of configprop:spring.config.name[]).
See <<boot-features-external-config-relaxed-binding-from-environment-variables>> for details.

NOTE: If your application runs in a servlet container or application server, then JNDI properties (in `java:comp/env`) or servlet context initialization parameters can be used instead of, or as well as, environment variables or system properties.



[[boot-features-external-config-optional-prefix]]
==== Optional Locations
By default, when a specified config data location does not exist, Spring Boot will throw a `ConfigDataLocationNotFoundException` and your application will not start.

If you want to specify a location, but you don't mind if it doesn't always exist, you can use the `optional:` prefix.
You can use this prefix with the `spring.config.location` and `spring.config.additional-location` properties, as well as with <<boot-features-external-config-files-importing, `spring.config.import`>> declarations.

For example, a `spring.config.import` value of `optional:file:./myconfig.properties` allows your application to start, even if the `myconfig.properties` file is missing.

If you want to ignore all `ConfigDataLocationNotFoundExceptions` and always continue to start your application, you can use the `spring.config.on-not-found` property.
Set the value to `ignore` using `SpringApplication.setDefaultProperties(...)` or with a system/environment variable.



[[boot-features-external-config-files-wildcards]]
==== Wildcard Locations
If a config file location includes the `{asterisk}` character for the last path segment, it is considered a wildcard location.
Wildcards are expanded when the config is loaded so that immediate subdirectories are also checked.
Wildcard locations are particularly useful in an environment such as Kubernetes when there are multiple sources of config properties.

For example, if you have some Redis configuration and some MySQL configuration, you might want to keep those two pieces of configuration separate, while requiring that both those are present in an `application.properties` file.
This might result in two separate `application.properties` files mounted at different locations such as `/config/redis/application.properties` and `/config/mysql/application.properties`.
In such a case, having a wildcard location of `config/*/`, will result in both files being processed.

By default, Spring Boot includes `config/*/` in the default search locations.
It means that all subdirectories of the `/config` directory outside of your jar will be searched.

You can use wildcard locations yourself with the `spring.config.location` and `spring.config.additional-location` properties.

NOTE: A wildcard location must contain only one `{asterisk}` and end with `{asterisk}/` for search locations that are directories or `*/<filename>` for search locations that are files.
Locations with wildcards are sorted alphabetically based on the absolute path of the file names.

TIP: Wildcard locations only work with external directories.
You cannot use a wildcard in a `classpath:` location.



[[boot-features-external-config-files-profile-specific]]
==== Profile Specific Files
As well as `application` property files, Spring Boot will also attempt to load profile-specific files using the naming convention `application-\{profile}`.
For example, if your application activates a profile named `prod` and uses YAML files, then both `application.yml` and `application-prod.yml` will be considered.

Profile-specific properties are loaded from the same locations as standard `application.properties`, with profile-specific files always overriding the non-specific ones.
If several profiles are specified, a last-wins strategy applies.
For example, if profiles `prod,live` are specified by the configprop:spring.profiles.active[] property, values in `application-prod.properties` can be overridden by those in `application-live.properties`.

[NOTE]
====
The last-wins strategy applies at the <<boot-features-external-config-files-location-groups,location group>> level.
A configprop:spring.config.location[] of `classpath:/cfg/,classpath:/ext/` will not have the same override rules as `classpath:/cfg/;classpath:/ext/`.

For example, continuing our `prod,live` example above, we might have the following files:

----
/cfg
  application-live.properties
/ext
  application-live.properties
  application-prod.properties
----

When we have a configprop:spring.config.location[] of `classpath:/cfg/,classpath:/ext/` we process all `/cfg` files before all `/ext` files:

. `/cfg/application-live.properties`
. `/ext/application-prod.properties`
. `/ext/application-live.properties`


When we have `classpath:/cfg/;classpath:/ext/` instead (with a `;` delimiter) we process `/cfg` and `/ext` at the same level:

. `/ext/application-prod.properties`
. `/cfg/application-live.properties`
. `/ext/application-live.properties`
====

The `Environment` has a set of default profiles (by default, `[default]`) that are used if no active profiles are set.
In other words, if no profiles are explicitly activated, then properties from `application-default` are considered.

NOTE: Properties files are only ever loaded once.
If you've already directly <<boot-features-external-config-files-importing,imported>> a profile specific property files then it won't be imported a second time.



[[boot-features-external-config-files-importing]]
==== Importing Additional Data
Application properties may import further config data from other locations using the `spring.config.import` property.
Imports are processed as they are discovered, and are treated as additional documents inserted immediately below the one that declares the import.

For example, you might have the following in your classpath `application.properties` file:

[source,yaml,indent=0,configblocks]
----
	spring:
	  application:
	    name: "myapp"
	  config:
	    import: "optional:file:./dev.properties"
----

This will trigger the import of a `dev.properties` file in current directory (if such a file exists).
Values from the imported `dev.properties` will take precedence over the file that triggered the import.
In the above example, the `dev.properties` could redefine `spring.application.name` to a different value.

An import will only be imported once no matter how many times it is declared.
The order an import is defined inside a single document within the properties/yaml file doesn't matter.
For instance, the two examples below produce the same result:

[source,yaml,indent=0,configblocks]
----
	spring:
	  config:
	    import: my.properties
	my:
	  property: value
----

[source,yaml,indent=0,configblocks]
----
	my:
	  property: value
	spring:
	  config:
	    import: my.properties
----

In both of the above examples, the values from the `my.properties` file will take precedence over the file that triggered its import.

Several locations can be specified under a single `spring.config.import` key.
Locations will be processed in the order that they are defined, with later imports taking precedence.

NOTE: When appropriate, <<boot-features-external-config-files-profile-specific, Profile-specific variants>> are also considered for import.
The example above would import both `my.properties` as well as any `my-<profile>.properties` variants.

[TIP]
====
Spring Boot includes pluggable API that allows various different location addresses to be supported.
By default you can import Java Properties, YAML and "`<<boot-features-external-config-files-configtree, configuration trees>>`".

Third-party jars can offer support for additional technologies (there's no requirement for files to be local).
For example, you can imagine config data being from external stores such as Consul, Apache ZooKeeper or Netflix Archaius.

If you want to support your own locations, see the `ConfigDataLocationResolver` and `ConfigDataLoader` classes in the `org.springframework.boot.context.config` package.
====



[[boot-features-external-config-files-importing-extensionless]]
==== Importing Extensionless Files
Some cloud platforms cannot add a file extension to volume mounted files.
To import these extensionless files, you need to give Spring Boot a hint so that it knows how to load them.
You can do this by putting an extension hint in square brackets.

For example, suppose you have a `/etc/config/myconfig` file that you wish to import as yaml.
You can import it from your `application.properties` using the following:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  config:
	    import: "file:/etc/config/myconfig[.yaml]"
----



[[boot-features-external-config-files-configtree]]
==== Using Configuration Trees
When running applications on a cloud platform (such as Kubernetes) you often need to read config values that the platform supplies.
It's not uncommon to use environment variables for such purposes, but this can have drawbacks, especially if the value is supposed to be kept secret.

As an alternative to environment variables, many cloud platforms now allow you to map configuration into mounted data volumes.
For example, Kubernetes can volume mount both https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/#populate-a-volume-with-data-stored-in-a-configmap[`ConfigMaps`] and https://kubernetes.io/docs/concepts/configuration/secret/#using-secrets-as-files-from-a-pod[`Secrets`].

There are two common volume mount patterns that can be use:

. A single file contains a complete set of properties (usually written as YAML).
. Multiple files are written to a directory tree, with the filename becoming the '`key`' and the contents becoming the '`value`'.

For the first case, you can import the YAML or Properties file directly using `spring.config.import` as described <<boot-features-external-config-files-importing,above>>.
For the second case, you need to use the `configtree:` prefix so that Spring Boot knows it needs to expose all the files as properties.

As an example, let's imagine that Kubernetes has mounted the following volume:

[source,indent=0]
----
	etc/
	  config/
	    myapp/
	      username
	      password
----

The contents of the `username` file would be a config value, and the contents of `password` would be a secret.

To import these properties, you can add the following to your `application.properties` or `application.yaml` file:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  config:
	    import: "optional:configtree:/etc/config/"
----

You can then access or inject `myapp.username` and `myapp.password` properties from the `Environment` in the usual way.

TIP: Configuration tree values can be bound to both string `String` and `byte[]` types depending on the contents expected.

If you have multiple config trees to import from the same parent folder you can use a wildcard shortcut.
Any `configtree:` location that ends with `/*/` will import all immediate children as config trees.

For example, given the following volume:

[source,indent=0]
----
	etc/
	  config/
	    dbconfig/
	      db/
	        username
	        password
	    mqconfig/
	      mq/
	        username
	        password
----

You can use `configtree:/etc/config/*/` as the import location:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  config:
	    import: "optional:configtree:/etc/config/*/"
----

This will add `db.username`, `db.password`, `mq.username` and `mq.password` properties.

NOTE: Directories loaded using a wildcard are sorted alphabetically.
If you need a different order, then you should list each location as a separate import


Configuration trees can also be used for Docker secrets.
When a Docker swarm service is granted access to a secret, the secret gets mounted into the container.
For example, if a secret named `db.password` is mounted at location `/run/secrets/`, you can make `db.password` available to the Spring environment using the following:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  config:
	    import: "optional:configtree:/run/secrets/"
----



[[boot-features-external-config-placeholders-in-properties]]
==== Property Placeholders
The values in `application.properties` and `application.yml` are filtered through the existing `Environment` when they are used, so you can refer back to previously defined values (for example, from System properties).
The standard `$\{name}` property-placeholder syntax can be used anywhere within a value.

For example, the following file will set `app.description` to "`MyApp is a Spring Boot application`":

[source,yaml,indent=0,configblocks]
----
	app:
	  name: "MyApp"
	  description: "${app.name} is a Spring Boot application"
----

TIP: You can also use this technique to create "`short`" variants of existing Spring Boot properties.
See the _<<howto.adoc#howto-use-short-command-line-arguments>>_ how-to for details.



[[boot-features-external-config-files-multi-document]]
==== Working with Multi-Document Files
Spring Boot allows you to split a single physical file into multiple logical documents which are each added independently.
Documents are processed in order, from top to bottom.
Later documents can override the properties defined in earlier ones.

For `application.yml` files, the standard YAML multi-document syntax is used.
Three consecutive hyphens represent the end of one document, and the start of the next.

For example, the following file has two logical documents:

[source,yaml,indent=0]
----
	spring.application.name: MyApp
	---
	spring.config.activate.on-cloud-platform: kubernetes
	spring.application.name: MyCloudApp
----

For `application.properties` files a special `#---` comment is used to mark the document splits:

[source,properties,indent=0]
----
	spring.application.name=MyApp
	#---
	spring.config.activate.on-cloud-platform=kubernetes
	spring.application.name=MyCloudApp
----

NOTE: Property file separators must not have any leading whitespace and must have exactly three hyphen characters.
The lines immediately before and after the separator must not be comments.

TIP: Multi-document property files are often used in conjunction with activation properties such as `spring.config.activate.on-profile`.
See the <<boot-features-external-config-file-activation-properties, next section>> for details.

WARNING: Multi-document property files cannot be loaded by using the `@PropertySource` or `@TestPropertySource` annotations.



[[boot-features-external-config-file-activation-properties]]
==== Activation Properties
It's sometimes useful to only activate a given get of properties when certain conditions are met.
For example, you might have properties that are only relevant when a specific profile is active.

You can conditionally activate a properties document using `spring.config.activate.*`.

The following activation properties are available:

.activation properties
[cols="1,4"]
|===
| Property | Note

| `on-profile`
| A profile expression that must match for the document to be active.

| `on-cloud-platform`
| The `CloudPlatform` that must be detected for the document to be active.
|===

For example, the following specifies that the second document is only active when running on Kubernetes, and only when either the "`prod`" or "`staging`" profiles are active:

[source,yaml,indent=0,configblocks]
----
	myprop:
	  always-set
	---
	spring:
	  config:
	    activate:
	      on-cloud-platform: "kubernetes"
	      on-profile: "prod | staging"
	myotherprop: sometimes-set
----



[[boot-features-encrypting-properties]]
=== Encrypting Properties
Spring Boot does not provide any built in support for encrypting property values, however, it does provide the hook points necessary to modify values contained in the Spring `Environment`.
The `EnvironmentPostProcessor` interface allows you to manipulate the `Environment` before the application starts.
See <<howto.adoc#howto-customize-the-environment-or-application-context>> for details.

If you're looking for a secure way to store credentials and passwords, the https://cloud.spring.io/spring-cloud-vault/[Spring Cloud Vault] project provides support for storing externalized configuration in https://www.vaultproject.io/[HashiCorp Vault].



[[boot-features-external-config-yaml]]
=== Working with YAML
https://yaml.org[YAML] is a superset of JSON and, as such, is a convenient format for specifying hierarchical configuration data.
The `SpringApplication` class automatically supports YAML as an alternative to properties whenever you have the https://bitbucket.org/asomov/snakeyaml[SnakeYAML] library on your classpath.

NOTE: If you use "`Starters`", SnakeYAML is automatically provided by `spring-boot-starter`.



[[boot-features-external-config-yaml-to-properties]]
==== Mapping YAML to Properties
YAML documents need to be converted from their hierarchical format to a flat structure that can be used with the Spring `Environment`.
For example, consider the following YAML document:

[source,yaml,indent=0]
----
	environments:
	  dev:
	    url: https://dev.example.com
	    name: Developer Setup
	  prod:
	    url: https://another.example.com
	    name: My Cool App
----

In order to access these properties from the `Environment`, they would be flattened as follows:

[source,properties,indent=0]
----
	environments.dev.url=https://dev.example.com
	environments.dev.name=Developer Setup
	environments.prod.url=https://another.example.com
	environments.prod.name=My Cool App
----

Likewise, YAML lists also need to be flattened.
They are represented as property keys with `[index]` dereferencers.
For example, consider the following YAML:

[source,yaml,indent=0]
----
	 my:
	  servers:
	  - dev.example.com
	  - another.example.com
----

The preceding example would be transformed into these properties:

[source,properties,indent=0]
----
	my.servers[0]=dev.example.com
	my.servers[1]=another.example.com
----

TIP: Properties that use the `[index]` notation can be bound to Java `List` or `Set` objects using Spring Boot's `Binder` class.
For more details see the "`<<boot-features-external-config-typesafe-configuration-properties>>`" section below.

WARNING: YAML files cannot be loaded by using the `@PropertySource` or `@TestPropertySource` annotations.
So, in the case that you need to load values that way, you need to use a properties file.



[[boot-features-external-config-loading-yaml]]
[[boot-features-external-config-exposing-yaml-to-spring]]
==== Directly Loading YAML
Spring Framework provides two convenient classes that can be used to load YAML documents.
The `YamlPropertiesFactoryBean` loads YAML as `Properties` and the `YamlMapFactoryBean` loads YAML as a `Map`.

You can also use the `YamlPropertySourceLoader` class if you want to load YAML as a Spring `PropertySource`.



[[boot-features-external-config-random-values]]
=== Configuring Random Values
The `RandomValuePropertySource` is useful for injecting random values (for example, into secrets or test cases).
It can produce integers, longs, uuids, or strings, as shown in the following example:

[source,yaml,indent=0,configblocks]
----
	my:
	  secret: "${random.value}"
	  number: "${random.int}"
	  bignumber: "${random.long}"
	  uuid: "${random.uuid}"
	  number-less-than-ten: "${random.int(10)}"
	  number-in-range: "${random.int[1024,65536]}"
----

The `+random.int*+` syntax is `OPEN value (,max) CLOSE` where the `OPEN,CLOSE` are any character and `value,max` are integers.
If `max` is provided, then `value` is the minimum value and `max` is the maximum value (exclusive).



[[boot-features-external-config-typesafe-configuration-properties]]
=== Type-safe Configuration Properties
Using the `@Value("$\{property}")` annotation to inject configuration properties can sometimes be cumbersome, especially if you are working with multiple properties or your data is hierarchical in nature.
Spring Boot provides an alternative method of working with properties that lets strongly typed beans govern and validate the configuration of your application.

TIP: See also the <<boot-features-external-config-vs-value,differences between `@Value` and type-safe configuration properties>>.



[[boot-features-external-config-java-bean-binding]]
==== JavaBean properties binding
It is possible to bind a bean declaring standard JavaBean properties as shown in the following example:

[source,java,indent=0]
----
	package com.example;

	import java.net.InetAddress;
	import java.util.ArrayList;
	import java.util.Collections;
	import java.util.List;

	import org.springframework.boot.context.properties.ConfigurationProperties;

	@ConfigurationProperties("acme")
	public class AcmeProperties {

		private boolean enabled;

		private InetAddress remoteAddress;

		private final Security security = new Security();

		public boolean isEnabled() { ... }

		public void setEnabled(boolean enabled) { ... }

		public InetAddress getRemoteAddress() { ... }

		public void setRemoteAddress(InetAddress remoteAddress) { ... }

		public Security getSecurity() { ... }

		public static class Security {

			private String username;

			private String password;

			private List<String> roles = new ArrayList<>(Collections.singleton("USER"));

			public String getUsername() { ... }

			public void setUsername(String username) { ... }

			public String getPassword() { ... }

			public void setPassword(String password) { ... }

			public List<String> getRoles() { ... }

			public void setRoles(List<String> roles) { ... }

		}
	}
----

The preceding POJO defines the following properties:

* `acme.enabled`, with a value of `false` by default.
* `acme.remote-address`, with a type that can be coerced from `String`.
* `acme.security.username`, with a nested "security" object whose name is determined by the name of the property.
  In particular, the return type is not used at all there and could have been `SecurityProperties`.
* `acme.security.password`.
* `acme.security.roles`, with a collection of `String` that defaults to `USER`.

NOTE: The properties that map to `@ConfigurationProperties` classes available in Spring Boot, which are configured via properties files, YAML files, environment variables etc., are public API but the accessors (getters/setters) of the class itself are not meant to be used directly.

[NOTE]
====
Such arrangement relies on a default empty constructor and getters and setters are usually mandatory, since binding is through standard Java Beans property descriptors, just like in Spring MVC.
A setter may be omitted in the following cases:

* Maps, as long as they are initialized, need a getter but not necessarily a setter, since they can be mutated by the binder.
* Collections and arrays can be accessed either through an index (typically with YAML) or by using a single comma-separated value (properties).
  In the latter case, a setter is mandatory.
  We recommend to always add a setter for such types.
  If you initialize a collection, make sure it is not immutable (as in the preceding example).
* If nested POJO properties are initialized (like the `Security` field in the preceding example), a setter is not required.
  If you want the binder to create the instance on the fly by using its default constructor, you need a setter.

Some people use Project Lombok to add getters and setters automatically.
Make sure that Lombok does not generate any particular constructor for such a type, as it is used automatically by the container to instantiate the object.

Finally, only standard Java Bean properties are considered and binding on static properties is not supported.
====



[[boot-features-external-config-constructor-binding]]
==== Constructor binding
The example in the previous section can be rewritten in an immutable fashion as shown in the following example:

[source,java,indent=0]
----
	package com.example;

	import java.net.InetAddress;
	import java.util.List;

	import org.springframework.boot.context.properties.ConfigurationProperties;
	import org.springframework.boot.context.properties.ConstructorBinding;
	import org.springframework.boot.context.properties.bind.DefaultValue;

	@ConstructorBinding
	@ConfigurationProperties("acme")
	public class AcmeProperties {

		private final boolean enabled;

		private final InetAddress remoteAddress;

		private final Security security;

		public AcmeProperties(boolean enabled, InetAddress remoteAddress, Security security) {
			this.enabled = enabled;
			this.remoteAddress = remoteAddress;
			this.security = security;
		}

		public boolean isEnabled() { ... }

		public InetAddress getRemoteAddress() { ... }

		public Security getSecurity() { ... }

		public static class Security {

			private final String username;

			private final String password;

			private final List<String> roles;

			public Security(String username, String password,
					@DefaultValue("USER") List<String> roles) {
				this.username = username;
				this.password = password;
				this.roles = roles;
			}

			public String getUsername() { ... }

			public String getPassword() { ... }

			public List<String> getRoles() { ... }

		}

	}
----

In this setup, the `@ConstructorBinding` annotation is used to indicate that constructor binding should be used.
This means that the binder will expect to find a constructor with the parameters that you wish to have bound.

Nested members of a `@ConstructorBinding` class (such as `Security` in the example above) will also be bound via their constructor.

Default values can be specified using `@DefaultValue` and the same conversion service will be applied to coerce the `String` value to the target type of a missing property.
By default, if no properties are bound to `Security`, the `AcmeProperties` instance will contain a `null` value for `security`.
If you wish you return a non-null instance of `Security` even when no properties are bound to it, you can use an empty `@DefaultValue` annotation to do so:

[source,java,indent=0]
----
	package com.example;
	import java.net.InetAddress;
	import java.util.List;

	import org.springframework.boot.context.properties.ConfigurationProperties;
	import org.springframework.boot.context.properties.ConstructorBinding;
	import org.springframework.boot.context.properties.bind.DefaultValue;

	@ConstructorBinding
	@ConfigurationProperties("acme")
	public class AcmeProperties {

		private final boolean enabled;

		private final InetAddress remoteAddress;

		private final Security security;

		public AcmeProperties(boolean enabled, InetAddress remoteAddress, @DefaultValue Security security) {
			this.enabled = enabled;
			this.remoteAddress = remoteAddress;
			this.security = security;
		}
	}
----


NOTE: To use constructor binding the class must be enabled using `@EnableConfigurationProperties` or configuration property scanning.
You cannot use constructor binding with beans that are created by the regular Spring mechanisms (e.g. `@Component` beans, beans created via `@Bean` methods or beans loaded using `@Import`)

TIP: If you have more than one constructor for your class you can also use `@ConstructorBinding` directly on the constructor that should be bound.

NOTE: The use of `java.util.Optional` with `@ConfigurationProperties` is not recommended as it is primarily intended for use as a return type.
As such, it is not well-suited to configuration property injection.
For consistency with properties of other types, if you do declare an `Optional` property and it has no value, `null` rather than an empty `Optional` will be bound.



[[boot-features-external-config-enabling]]
==== Enabling @ConfigurationProperties-annotated types
Spring Boot provides infrastructure to bind `@ConfigurationProperties` types and register them as beans.
You can either enable configuration properties on a class-by-class basis or enable configuration property scanning that works in a similar manner to component scanning.

Sometimes, classes annotated with `@ConfigurationProperties` might not be suitable for scanning, for example, if you're developing your own auto-configuration or you want to enable them conditionally.
In these cases, specify the list of types to process using the `@EnableConfigurationProperties` annotation.
This can be done on any `@Configuration` class, as shown in the following example:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	@EnableConfigurationProperties(AcmeProperties.class)
	public class MyConfiguration {
	}
----

To use configuration property scanning, add the `@ConfigurationPropertiesScan` annotation to your application.
Typically, it is added to the main application class that is annotated with `@SpringBootApplication` but it can be added to any `@Configuration` class.
By default, scanning will occur from the package of the class that declares the annotation.
If you want to define specific packages to scan, you can do so as shown in the following example:

[source,java,indent=0]
----
	@SpringBootApplication
	@ConfigurationPropertiesScan({ "com.example.app", "org.acme.another" })
	public class MyApplication {
	}
----

[NOTE]
====
When the `@ConfigurationProperties` bean is registered using configuration property scanning or via `@EnableConfigurationProperties`, the bean has a conventional name: `<prefix>-<fqn>`, where `<prefix>` is the environment key prefix specified in the `@ConfigurationProperties` annotation and `<fqn>` is the fully qualified name of the bean.
If the annotation does not provide any prefix, only the fully qualified name of the bean is used.

The bean name in the example above is `acme-com.example.AcmeProperties`.
====

We recommend that `@ConfigurationProperties` only deal with the environment and, in particular, does not inject other beans from the context.
For corner cases, setter injection can be used or any of the `*Aware` interfaces provided by the framework (such as `EnvironmentAware` if you need access to the `Environment`).
If you still want to inject other beans using the constructor, the configuration properties bean must be annotated with `@Component` and use JavaBean-based property binding.



[[boot-features-external-config-using]]
==== Using @ConfigurationProperties-annotated types
This style of configuration works particularly well with the `SpringApplication` external YAML configuration, as shown in the following example:

[source,yaml,indent=0]
----
	acme:
		remote-address: 192.168.1.1
		security:
			username: admin
			roles:
			  - USER
			  - ADMIN
----

To work with `@ConfigurationProperties` beans, you can inject them in the same way as any other bean, as shown in the following example:

[source,java,indent=0]
----
	@Service
	public class MyService {

		private final AcmeProperties properties;

		@Autowired
		public MyService(AcmeProperties properties) {
			this.properties = properties;
		}

	 	//...

		@PostConstruct
		public void openConnection() {
			Server server = new Server(this.properties.getRemoteAddress());
			// ...
		}

	}
----

TIP: Using `@ConfigurationProperties` also lets you generate metadata files that can be used by IDEs to offer auto-completion for your own keys.
See the <<appendix-configuration-metadata.adoc#configuration-metadata,appendix>> for details.



[[boot-features-external-config-3rd-party-configuration]]
==== Third-party Configuration
As well as using `@ConfigurationProperties` to annotate a class, you can also use it on public `@Bean` methods.
Doing so can be particularly useful when you want to bind properties to third-party components that are outside of your control.

To configure a bean from the `Environment` properties, add `@ConfigurationProperties` to its bean registration, as shown in the following example:

[source,java,indent=0]
----
	@ConfigurationProperties(prefix = "another")
	@Bean
	public AnotherComponent anotherComponent() {
		...
	}
----

Any JavaBean property defined with the `another` prefix is mapped onto that `AnotherComponent` bean in manner similar to the preceding `AcmeProperties` example.



[[boot-features-external-config-relaxed-binding]]
==== Relaxed Binding
Spring Boot uses some relaxed rules for binding `Environment` properties to `@ConfigurationProperties` beans, so there does not need to be an exact match between the `Environment` property name and the bean property name.
Common examples where this is useful include dash-separated environment properties (for example, `context-path` binds to `contextPath`), and capitalized environment properties (for example, `PORT` binds to `port`).

As an example, consider the following `@ConfigurationProperties` class:

[source,java,indent=0]
----
	@ConfigurationProperties(prefix="acme.my-project.person")
	public class OwnerProperties {

		private String firstName;

		public String getFirstName() {
			return this.firstName;
		}

		public void setFirstName(String firstName) {
			this.firstName = firstName;
		}

	}
----

With the preceding code, the following properties names can all be used:

.relaxed binding
[cols="1,4"]
|===
| Property | Note

| `acme.my-project.person.first-name`
| Kebab case, which is recommended for use in `.properties` and `.yml` files.

| `acme.myProject.person.firstName`
| Standard camel case syntax.

| `acme.my_project.person.first_name`
| Underscore notation, which is an alternative format for use in `.properties` and `.yml` files.

| `ACME_MYPROJECT_PERSON_FIRSTNAME`
| Upper case format, which is recommended when using system environment variables.
|===

NOTE: The `prefix` value for the annotation _must_ be in kebab case (lowercase and separated by `-`, such as `acme.my-project.person`).

.relaxed binding rules per property source
[cols="2,4,4"]
|===
| Property Source | Simple | List

| Properties Files
| Camel case, kebab case, or underscore notation
| Standard list syntax using `[ ]` or comma-separated values

| YAML Files
| Camel case, kebab case, or underscore notation
| Standard YAML list syntax or comma-separated values

| Environment Variables
| Upper case format with underscore as the delimiter (see <<boot-features-external-config-relaxed-binding-from-environment-variables>>).
| Numeric values surrounded by underscores (see <<boot-features-external-config-relaxed-binding-from-environment-variables>>)

| System properties
| Camel case, kebab case, or underscore notation
| Standard list syntax using `[ ]` or comma-separated values
|===

TIP: We recommend that, when possible, properties are stored in lower-case kebab format, such as `my.property-name=acme`.



[[boot-features-external-config-relaxed-binding-maps]]
===== Binding Maps
When binding to `Map` properties you may need to use a special bracket notation so that the original `key` value is preserved.
If the key is not surrounded by `[]`, any characters that are not alpha-numeric, `-` or `.` are removed.

For example, consider binding the following properties to a `Map<String,String>`:


[source,properties,indent=0,role="primary"]
.Properties
----
	acme.map.[/key1]=value1
	acme.map.[/key2]=value2
	acme.map./key3=value3
----

[source,yaml,indent=0,role="secondary"]
.Yaml
----
	acme:
	  map:
	    "[/key1]": "value1"
	    "[/key2]": "value2"
	    "/key3": "value3"
----

NOTE: For YAML files, the brackets need to be surrounded by quotes for the keys to be parsed properly.

The properties above will bind to a `Map` with `/key1`, `/key2` and `key3` as the keys in the map.
The slash has been removed from `key3` because it wasn't surrounded by square brackets.

You may also occasionally need to use the bracket notation if your `key` contains a `.` and you are binding to non-scalar value.
For example, binding `a.b=c` to `Map<String, Object>` will return a Map with the entry `{"a"={"b"="c"}}` whereas `[a.b]=c` will return a Map with the entry `{"a.b"="c"}`.



[[boot-features-external-config-relaxed-binding-from-environment-variables]]
===== Binding from Environment Variables
Most operating systems impose strict rules around the names that can be used for environment variables.
For example, Linux shell variables can contain only letters (`a` to `z` or `A` to `Z`), numbers (`0` to `9`) or the underscore character (`_`).
By convention, Unix shell variables will also have their names in UPPERCASE.

Spring Boot's relaxed binding rules are, as much as possible, designed to be compatible with these naming restrictions.

To convert a property name in the canonical-form to an environment variable name you can follow these rules:

* Replace dots (`.`) with underscores (`_`).
* Remove any dashes (`-`).
* Convert to uppercase.

For example, the configuration property `spring.main.log-startup-info` would be an environment variable named `SPRING_MAIN_LOGSTARTUPINFO`.

Environment variables can also be used when binding to object lists.
To bind to a `List`, the element number should be surrounded with underscores in the variable name.

For example, the configuration property `my.acme[0].other` would use an environment variable named `MY_ACME_0_OTHER`.



[[boot-features-external-config-complex-type-merge]]
==== Merging Complex Types
When lists are configured in more than one place, overriding works by replacing the entire list.

For example, assume a `MyPojo` object with `name` and `description` attributes that are `null` by default.
The following example exposes a list of `MyPojo` objects from `AcmeProperties`:

[source,java,indent=0]
----
	@ConfigurationProperties("acme")
	public class AcmeProperties {

		private final List<MyPojo> list = new ArrayList<>();

		public List<MyPojo> getList() {
			return this.list;
		}

	}
----

Consider the following configuration:

[source,yaml,indent=0,configblocks]
----
	acme:
	  list:
	  - name: "my name"
	    description: "my description"
	---
	spring:
	  config:
	    activate:
	      on-profile: "dev"
	acme:
	  list:
	  - name: "my another name"
----

If the `dev` profile is not active, `AcmeProperties.list` contains one `MyPojo` entry, as previously defined.
If the `dev` profile is enabled, however, the `list` _still_ contains only one entry (with a name of `my another name` and a description of `null`).
This configuration _does not_ add a second `MyPojo` instance to the list, and it does not merge the items.

When a `List` is specified in multiple profiles, the one with the highest priority (and only that one) is used.
Consider the following example:

[source,yaml,indent=0,configblocks]
----
	acme:
	  list:
	  - name: "my name"
	    description: "my description"
	  - name: "another name"
	    description: "another description"
	---
	spring:
	  config:
	    activate:
	      on-profile: "dev"
	acme:
	  list:
	  - name: "my another name"
----

In the preceding example, if the `dev` profile is active, `AcmeProperties.list` contains _one_ `MyPojo` entry (with a name of `my another name` and a description of `null`).
For YAML, both comma-separated lists and YAML lists can be used for completely overriding the contents of the list.

For `Map` properties, you can bind with property values drawn from multiple sources.
However, for the same property in multiple sources, the one with the highest priority is used.
The following example exposes a `Map<String, MyPojo>` from `AcmeProperties`:

[source,java,indent=0]
----
	@ConfigurationProperties("acme")
	public class AcmeProperties {

		private final Map<String, MyPojo> map = new HashMap<>();

		public Map<String, MyPojo> getMap() {
			return this.map;
		}

	}
----

Consider the following configuration:

[source,yaml,indent=0,configblocks]
----
	acme:
	  map:
	    key1:
	      name: "my name 1"
	      description: "my description 1"
	---
	spring:
	  config:
	    activate:
	      on-profile: "dev"
	acme:
	  map:
	    key1:
	      name: "dev name 1"
	    key2:
	      name: "dev name 2"
	      description: "dev description 2"
----

If the `dev` profile is not active, `AcmeProperties.map` contains one entry with key `key1` (with a name of `my name 1` and a description of `my description 1`).
If the `dev` profile is enabled, however, `map` contains two entries with keys `key1` (with a name of `dev name 1` and a description of `my description 1`) and `key2` (with a name of `dev name 2` and a description of `dev description 2`).

NOTE: The preceding merging rules apply to properties from all property sources, and not just files.



[[boot-features-external-config-conversion]]
==== Properties Conversion
Spring Boot attempts to coerce the external application properties to the right type when it binds to the `@ConfigurationProperties` beans.
If you need custom type conversion, you can provide a `ConversionService` bean (with a bean named `conversionService`) or custom property editors (through a `CustomEditorConfigurer` bean) or custom `Converters` (with bean definitions annotated as `@ConfigurationPropertiesBinding`).

NOTE: As this bean is requested very early during the application lifecycle, make sure to limit the dependencies that your `ConversionService` is using.
Typically, any dependency that you require may not be fully initialized at creation time.
You may want to rename your custom `ConversionService` if it is not required for configuration keys coercion and only rely on custom converters qualified with `@ConfigurationPropertiesBinding`.



[[boot-features-external-config-conversion-duration]]
===== Converting durations
Spring Boot has dedicated support for expressing durations.
If you expose a `java.time.Duration` property, the following formats in application properties are available:

* A regular `long` representation (using milliseconds as the default unit unless a `@DurationUnit` has been specified)
* The standard ISO-8601 format {java-api}/java/time/Duration.html#parse-java.lang.CharSequence-[used by `java.time.Duration`]
* A more readable format where the value and the unit are coupled (e.g. `10s` means 10 seconds)

Consider the following example:

[source,java,indent=0]
----
include::{code-examples}/context/properties/bind/javabean/AppSystemProperties.java[tag=example]
----

To specify a session timeout of 30 seconds, `30`, `PT30S` and `30s` are all equivalent.
A read timeout of 500ms can be specified in any of the following form: `500`, `PT0.5S` and `500ms`.

You can also use any of the supported units.
These are:

* `ns` for nanoseconds
* `us` for microseconds
* `ms` for milliseconds
* `s` for seconds
* `m` for minutes
* `h` for hours
* `d` for days

The default unit is milliseconds and can be overridden using `@DurationUnit` as illustrated in the sample above.

If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/context/properties/bind/constructor/AppSystemProperties.java[tag=example]
----


TIP: If you are upgrading a `Long` property, make sure to define the unit (using `@DurationUnit`) if it isn't milliseconds.
Doing so gives a transparent upgrade path while supporting a much richer format.



[[boot-features-external-config-conversion-period]]
===== Converting periods
In addition to durations, Spring Boot can also work with `java.time.Period` type.
The following formats can be used in application properties:

* An regular `int` representation (using days as the default unit unless a `@PeriodUnit` has been specified)
* The standard ISO-8601 format {java-api}/java/time/Period.html#parse-java.lang.CharSequence-[used by `java.time.Period`]
* A simpler format where the value and the unit pairs are coupled (e.g. `1y3d` means 1 year and 3 days)

The following units are supported with the simple format:

* `y` for years
* `m` for months
* `w` for weeks
* `d` for days

NOTE: The `java.time.Period` type never actually stores the number of weeks, it is a shortcut that means "`7 days`".



[[boot-features-external-config-conversion-datasize]]
===== Converting Data Sizes
Spring Framework has a `DataSize` value type that expresses a size in bytes.
If you expose a `DataSize` property, the following formats in application properties are available:

* A regular `long` representation (using bytes as the default unit unless a `@DataSizeUnit` has been specified)
* A more readable format where the value and the unit are coupled (e.g. `10MB` means 10 megabytes)

Consider the following example:

[source,java,indent=0]
----
include::{code-examples}/context/properties/bind/javabean/AppIoProperties.java[tag=example]
----

To specify a buffer size of 10 megabytes, `10` and `10MB` are equivalent.
A size threshold of 256 bytes can be specified as `256` or `256B`.

You can also use any of the supported units.
These are:

* `B` for bytes
* `KB` for kilobytes
* `MB` for megabytes
* `GB` for gigabytes
* `TB` for terabytes

The default unit is bytes and can be overridden using `@DataSizeUnit` as illustrated in the sample above.

If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/context/properties/bind/constructor/AppIoProperties.java[tag=example]
----

TIP: If you are upgrading a `Long` property, make sure to define the unit (using `@DataSizeUnit`) if it isn't bytes.
Doing so gives a transparent upgrade path while supporting a much richer format.



[[boot-features-external-config-validation]]
==== @ConfigurationProperties Validation
Spring Boot attempts to validate `@ConfigurationProperties` classes whenever they are annotated with Spring's `@Validated` annotation.
You can use JSR-303 `javax.validation` constraint annotations directly on your configuration class.
To do so, ensure that a compliant JSR-303 implementation is on your classpath and then add constraint annotations to your fields, as shown in the following example:

[source,java,indent=0]
----
	@ConfigurationProperties(prefix="acme")
	@Validated
	public class AcmeProperties {

		@NotNull
		private InetAddress remoteAddress;

		// ... getters and setters

	}
----

TIP: You can also trigger validation by annotating the `@Bean` method that creates the configuration properties with `@Validated`.

To ensure that validation is always triggered for nested properties, even when no properties are found, the associated field must be annotated with `@Valid`.
The following example builds on the preceding `AcmeProperties` example:

[source,java,indent=0]
----
	@ConfigurationProperties(prefix="acme")
	@Validated
	public class AcmeProperties {

		@NotNull
		private InetAddress remoteAddress;

		@Valid
		private final Security security = new Security();

		// ... getters and setters

		public static class Security {

			@NotEmpty
			public String username;

			// ... getters and setters

		}

	}
----

You can also add a custom Spring `Validator` by creating a bean definition called `configurationPropertiesValidator`.
The `@Bean` method should be declared `static`.
The configuration properties validator is created very early in the application's lifecycle, and declaring the `@Bean` method as static lets the bean be created without having to instantiate the `@Configuration` class.
Doing so avoids any problems that may be caused by early instantiation.

TIP: The `spring-boot-actuator` module includes an endpoint that exposes all `@ConfigurationProperties` beans.
Point your web browser to `/actuator/configprops` or use the equivalent JMX endpoint.
See the "<<production-ready-features.adoc#production-ready-endpoints, Production ready features>>" section for details.



[[boot-features-external-config-vs-value]]
==== @ConfigurationProperties vs. @Value
The `@Value` annotation is a core container feature, and it does not provide the same features as type-safe configuration properties.
The following table summarizes the features that are supported by `@ConfigurationProperties` and `@Value`:

[cols="4,2,2"]
|===
| Feature |`@ConfigurationProperties` |`@Value`

| <<boot-features-external-config-relaxed-binding,Relaxed binding>>
| Yes
| Limited (see <<boot-features-external-config-vs-value-note,note below>>)

| <<appendix-configuration-metadata.adoc#configuration-metadata,Meta-data support>>
| Yes
| No

| `SpEL` evaluation
| No
| Yes
|===

NOTE: [[boot-features-external-config-vs-value-note]] If you do want to use `@Value`, we recommend that you refer to property names using their canonical form (kebab-case using only lowercase letters).
This will allow Spring Boot to use the same logic as it does when relaxed binding `@ConfigurationProperties`.
For example, `@Value("{demo.item-price}")` will pick up `demo.item-price` and `demo.itemPrice` forms from the `application.properties` file, as well as `DEMO_ITEMPRICE` from the system environment.
If you used `@Value("{demo.itemPrice}")` instead, `demo.item-price` and `DEMO_ITEMPRICE` would not be considered.

If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with `@ConfigurationProperties`.
Doing so will provide you with structured, type-safe object that you can inject into your own beans.

`SpEL` expressions from  <<boot-features-external-config-files,application property files>> are not processed at time of parsing these files and populating the environment.
However, it is possible to write a `SpEL` expression in `@Value`.
If the value of a property from an application property file is a `SpEL` expression, it will be evaluated when consumed via `@Value`.



[[boot-features-profiles]]
== Profiles
Spring Profiles provide a way to segregate parts of your application configuration and make it be available only in certain environments.
Any `@Component`, `@Configuration` or `@ConfigurationProperties` can be marked with `@Profile` to limit when it is loaded, as shown in the following example:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	@Profile("production")
	public class ProductionConfiguration {

		// ...

	}
----

NOTE: If `@ConfigurationProperties` beans are registered via `@EnableConfigurationProperties` instead of automatic scanning, the `@Profile` annotation needs to be specified on the `@Configuration` class that has the `@EnableConfigurationProperties` annotation.
In the case where `@ConfigurationProperties` are scanned, `@Profile` can be specified on the `@ConfigurationProperties` class itself.

You can use a configprop:spring.profiles.active[] `Environment` property to specify which profiles are active.
You can specify the property in any of the ways described earlier in this chapter.
For example, you could include it in your `application.properties`, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  profiles:
	    active: "dev,hsqldb"
----

You could also specify it on the command line by using the following switch: `--spring.profiles.active=dev,hsqldb`.

If no profile is active, a default profile is enabled.
The name of the default profile is `default` and it can be tuned using the configprop:spring.profiles.default[] `Environment` property, as shown in the following example:

[source,properties,indent=0,configprops]
----
	spring.profiles.default=none
----



[[boot-features-adding-active-profiles]]
=== Adding Active Profiles
The configprop:spring.profiles.active[] property follows the same ordering rules as other properties: The highest `PropertySource` wins.
This means that you can specify active profiles in `application.properties` and then *replace* them by using the command line switch.

Sometimes, it is useful to have properties that *add* to the active profiles rather than replace them.
The `SpringApplication` entry point has a Java API for setting additional profiles (that is, on top of those activated by the configprop:spring.profiles.active[] property).
See the `setAdditionalProfiles()` method in {spring-boot-module-api}/SpringApplication.html[SpringApplication].
Profile groups, which are described in the <<boot-features-profiles-groups,next section>> can also be used to add active profiles if a given profile is active.



[[boot-features-profiles-groups]]
=== Profile Groups
Occasionally the profiles that you define and use in your application are too fine-grained and become cumbersome to use.
For example, you might have `proddb` and `prodmq` profiles that you use to enable database and messaging features independently.

To help with this, Spring Boot lets you define profile groups.
A profile group allows you to define a logical name for a related group of profiles.

For example, we can create a `production` group that consists of our `proddb` and `prodmq` profiles.

[source,yaml,indent=0,configblocks]
----
	spring:
	  profiles:
	    group:
	      production:
	      - "proddb"
	      - "prodmq"
----

Our application can now be started using `--spring.profiles.active=production` to active the `production`, `proddb` and `prodmq` profiles in one hit.



[[boot-features-programmatically-setting-profiles]]
=== Programmatically Setting Profiles
You can programmatically set active profiles by calling `SpringApplication.setAdditionalProfiles(...)` before your application runs.
It is also possible to activate profiles by using Spring's `ConfigurableEnvironment` interface.



[[boot-features-profile-specific-configuration]]
=== Profile-specific Configuration Files
Profile-specific variants of both `application.properties` (or `application.yml`) and files referenced through `@ConfigurationProperties` are considered as files and loaded.
See "<<boot-features-external-config-files-profile-specific>>" for details.



[[boot-features-logging]]
== Logging
Spring Boot uses https://commons.apache.org/logging[Commons Logging] for all internal logging but leaves the underlying log implementation open.
Default configurations are provided for {java-api}/java/util/logging/package-summary.html[Java Util Logging], https://logging.apache.org/log4j/2.x/[Log4J2], and https://logback.qos.ch/[Logback].
In each case, loggers are pre-configured to use console output with optional file output also available.

By default, if you use the "`Starters`", Logback is used for logging.
Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J, or SLF4J all work correctly.

TIP: There are a lot of logging frameworks available for Java.
Do not worry if the above list seems confusing.
Generally, you do not need to change your logging dependencies and the Spring Boot defaults work just fine.

TIP: When you deploy your application to a servlet container or application server, logging performed via the Java Util Logging API is not routed into your application's logs.
This prevents logging performed by the container or other applications that have been deployed to it from appearing in your application's logs.



[[boot-features-logging-format]]
=== Log Format
The default log output from Spring Boot resembles the following example:

[indent=0]
----
2019-03-05 10:57:51.112  INFO 45469 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/7.0.52
2019-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1358 ms
2019-03-05 10:57:51.698  INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]
2019-03-05 10:57:51.702  INFO 45469 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
----

The following items are output:

* Date and Time: Millisecond precision and easily sortable.
* Log Level: `ERROR`, `WARN`, `INFO`, `DEBUG`, or `TRACE`.
* Process ID.
* A `---` separator to distinguish the start of actual log messages.
* Thread name: Enclosed in square brackets (may be truncated for console output).
* Logger name: This is usually the source class name (often abbreviated).
* The log message.

NOTE: Logback does not have a `FATAL` level.
It is mapped to `ERROR`.



[[boot-features-logging-console-output]]
=== Console Output
The default log configuration echoes messages to the console as they are written.
By default, `ERROR`-level, `WARN`-level, and `INFO`-level messages are logged.
You can also enable a "`debug`" mode by starting your application with a `--debug` flag.

[indent=0]
----
	$ java -jar myapp.jar --debug
----

NOTE: You can also specify `debug=true` in your `application.properties`.

When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate, and Spring Boot) are configured to output more information.
Enabling the debug mode does _not_ configure your application to log all messages with `DEBUG` level.

Alternatively, you can enable a "`trace`" mode by starting your application with a `--trace` flag (or `trace=true` in your `application.properties`).
Doing so enables trace logging for a selection of core loggers (embedded container, Hibernate schema generation, and the whole Spring portfolio).



[[boot-features-logging-color-coded-output]]
==== Color-coded Output
If your terminal supports ANSI, color output is used to aid readability.
You can set `spring.output.ansi.enabled` to a {spring-boot-module-api}/ansi/AnsiOutput.Enabled.html[supported value] to override the auto-detection.

Color coding is configured by using the `%clr` conversion word.
In its simplest form, the converter colors the output according to the log level, as shown in the following example:

[source,indent=0]
----
%clr(%5p)
----

The following table describes the mapping of log levels to colors:

|===
| Level | Color

| `FATAL`
| Red

| `ERROR`
| Red

| `WARN`
| Yellow

| `INFO`
| Green

| `DEBUG`
| Green

| `TRACE`
| Green
|===

Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion.
For example, to make the text yellow, use the following setting:

[source,indent=0]
----
%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}
----

The following colors and styles are supported:

* `blue`
* `cyan`
* `faint`
* `green`
* `magenta`
* `red`
* `yellow`



[[boot-features-logging-file-output]]
=== File Output
By default, Spring Boot logs only to the console and does not write log files.
If you want to write log files in addition to the console output, you need to set a configprop:logging.file.name[] or configprop:logging.file.path[] property (for example, in your `application.properties`).

The following table shows how the `logging.*` properties can be used together:

.Logging properties
[cols="1,1,1,4"]
|===
| configprop:logging.file.name[] | configprop:logging.file.path[] | Example | Description

| _(none)_
| _(none)_
|
| Console only logging.

| Specific file
| _(none)_
| `my.log`
| Writes to the specified log file.
  Names can be an exact location or relative to the current directory.

| _(none)_
| Specific directory
| `/var/log`
| Writes `spring.log` to the specified directory.
  Names can be an exact location or relative to the current directory.
|===

Log files rotate when they reach 10 MB and, as with console output, `ERROR`-level, `WARN`-level, and `INFO`-level messages are logged by default.

TIP: Logging properties are independent of the actual logging infrastructure.
As a result, specific configuration keys (such as `logback.configurationFile` for Logback) are not managed by spring Boot.



[[boot-features-logging-file-rotation]]
=== File Rotation
If you are using the Logback, it's possible to fine-tune log rotation settings using your `application.properties` or `application.yaml` file.
For all other logging system, you'll need to configure rotation settings directly yourself (for example, if you use Log4J2 then you could add a `log4j.xml` file).

The following rotation policy properties are supported:

|===
| Name | Description

| configprop:logging.logback.rollingpolicy.file-name-pattern[]
| The filename pattern used to create log archives.

| configprop:logging.logback.rollingpolicy.clean-history-on-start[]
| If log archive cleanup should occur when the application starts.

| configprop:logging.logback.rollingpolicy.max-file-size[]
| The maximum size of log file before it's archived.

| configprop:logging.logback.rollingpolicy.total-size-cap[]
| The maximum amount of size log archives can take before being deleted.

| configprop:logging.logback.rollingpolicy.max-history[]
| The number of days to keep log archives (defaults to 7)
|===



[[boot-features-custom-log-levels]]
=== Log Levels
All the supported logging systems can have the logger levels set in the Spring `Environment` (for example, in `application.properties`) by using `+logging.level.<logger-name>=<level>+` where `level` is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, or OFF.
The `root` logger can be configured by using `logging.level.root`.

The following example shows potential logging settings in `application.properties`:

[source,properties,indent=0,subs="verbatim,quotes,attributes",configprops,role="primary"]
.Properties
----
	logging.level.root=warn
	logging.level.org.springframework.web=debug
	logging.level.org.hibernate=error
----

[source,properties,indent=0,subs="verbatim,quotes,attributes",role="secondary"]
.Yaml
----
	logging:
	  level:
	    root: "warn"
	    org.springframework.web: "debug"
	    org.hibernate: "error"
----

It's also possible to set logging levels using environment variables.
For example, `LOGGING_LEVEL_ORG_SPRINGFRAMEWORK_WEB=DEBUG` will set `org.springframework.web` to `DEBUG`.

NOTE: The above approach will only work for package level logging.
Since relaxed binding always converts environment variables to lowercase, it's not possible to configure logging for an individual class in this way.
If you need to configure logging for a class, you can use <<boot-features-external-config-application-json, the `SPRING_APPLICATION_JSON`>> variable.



[[boot-features-custom-log-groups]]
=== Log Groups
It's often useful to be able to group related loggers together so that they can all be configured at the same time.
For example, you might commonly change the logging levels for _all_ Tomcat related loggers, but you can't easily remember top level packages.

To help with this, Spring Boot allows you to define logging groups in your Spring `Environment`.
For example, here's how you could define a "`tomcat`" group by adding it to your `application.properties`:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	logging:
	  group:
	    tomcat: "org.apache.catalina,org.apache.coyote,org.apache.tomcat"
----

Once defined, you can change the level for all the loggers in the group with a single line:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	logging:
	  level:
	    tomcat: "trace"
----

Spring Boot includes the following pre-defined logging groups that can be used out-of-the-box:

[cols="1,4"]
|===
| Name | Loggers

| web
| `org.springframework.core.codec`, `org.springframework.http`, `org.springframework.web`, `org.springframework.boot.actuate.endpoint.web`, `org.springframework.boot.web.servlet.ServletContextInitializerBeans`

| sql
| `org.springframework.jdbc.core`, `org.hibernate.SQL`, `org.jooq.tools.LoggerListener`
|===



[[boot-features-log-shutdown-hook]]
=== Using a Log Shutdown Hook
In order to release logging resources it is usually a good idea to stop the logging system when your application terminates.
Unfortunately, there's no single way to do this that will work with all application types.
If your application has complex context hierarchies or is deployed as a war file, you'll need to investigate the options provided directly by the underlying logging system.
For example, Logback offers http://logback.qos.ch/manual/loggingSeparation.html[context selectors] which allow each Logger to be created in its own context.

For simple "single jar" applications deployed in their own JVM, you can use the `logging.register-shutdown-hook` property.
Setting `logging.register-shutdown-hook` to `true` will register a shutdown hook that will trigger log system cleanup when the JVM exits.

You can set the property in your `application.properties` or `application.yaml` file:

[source,yaml,indent=0,configprops,configblocks]
----
	logging:
	  register-shutdown-hook: true
----



[[boot-features-custom-log-configuration]]
=== Custom Log Configuration
The various logging systems can be activated by including the appropriate libraries on the classpath and can be further customized by providing a suitable configuration file in the root of the classpath or in a location specified by the following Spring `Environment` property: configprop:logging.config[].

You can force Spring Boot to use a particular logging system by using the `org.springframework.boot.logging.LoggingSystem` system property.
The value should be the fully qualified class name of a `LoggingSystem` implementation.
You can also disable Spring Boot's logging configuration entirely by using a value of `none`.

NOTE: Since logging is initialized *before* the `ApplicationContext` is created, it is not possible to control logging from `@PropertySources` in Spring `@Configuration` files.
The only way to change the logging system or disable it entirely is via System properties.

Depending on your logging system, the following files are loaded:

|===
| Logging System | Customization

| Logback
| `logback-spring.xml`, `logback-spring.groovy`, `logback.xml`, or `logback.groovy`

| Log4j2
| `log4j2-spring.xml` or `log4j2.xml`

| JDK (Java Util Logging)
| `logging.properties`
|===

NOTE: When possible, we recommend that you use the `-spring` variants for your logging configuration (for example, `logback-spring.xml` rather than `logback.xml`).
If you use standard configuration locations, Spring cannot completely control log initialization.

WARNING: There are known classloading issues with Java Util Logging that cause problems when running from an 'executable jar'.
We recommend that you avoid it when running from an 'executable jar' if at all possible.

To help with the customization, some other properties are transferred from the Spring `Environment` to System properties, as described in the following table:

|===
| Spring Environment | System Property | Comments

| configprop:logging.exception-conversion-word[]
| `LOG_EXCEPTION_CONVERSION_WORD`
| The conversion word used when logging exceptions.

| configprop:logging.file.name[]
| `LOG_FILE`
| If defined, it is used in the default log configuration.

| configprop:logging.file.path[]
| `LOG_PATH`
| If defined, it is used in the default log configuration.

| configprop:logging.pattern.console[]
| `CONSOLE_LOG_PATTERN`
| The log pattern to use on the console (stdout).

| configprop:logging.pattern.dateformat[]
| `LOG_DATEFORMAT_PATTERN`
| Appender pattern for log date format.

| configprop:logging.charset.console[]
| `CONSOLE_LOG_CHARSET`
| The charset to use for console logging.

| configprop:logging.pattern.file[]
| `FILE_LOG_PATTERN`
| The log pattern to use in a file (if `LOG_FILE` is enabled).

| configprop:logging.charset.file[]
| `FILE_LOG_CHARSET`
| The charset to use for file logging (if `LOG_FILE` is enabled).

| configprop:logging.pattern.level[]
| `LOG_LEVEL_PATTERN`
| The format to use when rendering the log level (default `%5p`).

| `PID`
| `PID`
| The current process ID (discovered if possible and when not already defined as an OS environment variable).
|===

If you're using Logback, the following properties are also transferred:

|===
| Spring Environment | System Property | Comments

| configprop:logging.logback.rollingpolicy.file-name-pattern[]
| `LOGBACK_ROLLINGPOLICY_FILE_NAME_PATTERN`
| Pattern for rolled-over log file names (default `$\{LOG_FILE}.%d\{yyyy-MM-dd}.%i.gz`).

| configprop:logging.logback.rollingpolicy.clean-history-on-start[]
| `LOGBACK_ROLLINGPOLICY_CLEAN_HISTORY_ON_START`
| Whether to clean the archive log files on startup.

| configprop:logging.logback.rollingpolicy.max-file-size[]
| `LOGBACK_ROLLINGPOLICY_MAX_FILE_SIZE`
| Maximum log file size.

| configprop:logging.logback.rollingpolicy.total-size-cap[]
| `LOGBACK_ROLLINGPOLICY_TOTAL_SIZE_CAP`
| Total size of log backups to be kept.

| configprop:logging.logback.rollingpolicy.max-history[]
| `LOGBACK_ROLLINGPOLICY_MAX_HISTORY`
| Maximum number of archive log files to keep.
|===


All the supported logging systems can consult System properties when parsing their configuration files.
See the default configurations in `spring-boot.jar` for examples:

* {spring-boot-code}/spring-boot-project/spring-boot/src/main/resources/org/springframework/boot/logging/logback/defaults.xml[Logback]
* {spring-boot-code}/spring-boot-project/spring-boot/src/main/resources/org/springframework/boot/logging/log4j2/log4j2.xml[Log4j 2]
* {spring-boot-code}/spring-boot-project/spring-boot/src/main/resources/org/springframework/boot/logging/java/logging-file.properties[Java Util logging]

[TIP]
====
If you want to use a placeholder in a logging property, you should use <<boot-features-external-config-placeholders-in-properties,Spring Boot's syntax>> and not the syntax of the underlying framework.
Notably, if you use Logback, you should use `:` as the delimiter between a property name and its default value and not use `:-`.
====

[TIP]
====
You can add MDC and other ad-hoc content to log lines by overriding only the `LOG_LEVEL_PATTERN` (or `logging.pattern.level` with Logback).
For example, if you use `logging.pattern.level=user:%X\{user} %5p`, then the default log format contains an MDC entry for "user", if it exists, as shown in the following example.

[indent=0]
----
	2019-08-30 12:30:04.031 user:someone INFO 22174 --- [  nio-8080-exec-0] demo.Controller
	Handling authenticated request
----
====



[[boot-features-logback-extensions]]
=== Logback Extensions
Spring Boot includes a number of extensions to Logback that can help with advanced configuration.
You can use these extensions in your `logback-spring.xml` configuration file.

NOTE: Because the standard `logback.xml` configuration file is loaded too early, you cannot use extensions in it.
You need to either use `logback-spring.xml` or define a configprop:logging.config[] property.

WARNING: The extensions cannot be used with Logback's https://logback.qos.ch/manual/configuration.html#autoScan[configuration scanning].
If you attempt to do so, making changes to the configuration file results in an error similar to one of the following being logged:

[indent=0]
----
	ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]]
	ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]
----



[[boot-features-logback-extensions-profile-specific]]
==== Profile-specific Configuration
The `<springProfile>` tag lets you optionally include or exclude sections of configuration based on the active Spring profiles.
Profile sections are supported anywhere within the `<configuration>` element.
Use the `name` attribute to specify which profile accepts the configuration.
The `<springProfile>` tag can contain a profile name (for example `staging`) or a profile expression.
A profile expression allows for more complicated profile logic to be expressed, for example `production & (eu-central | eu-west)`.
Check the {spring-framework-docs}/core.html#beans-definition-profiles-java[reference guide] for more details.
The following listing shows three sample profiles:

[source,xml,indent=0]
----
	<springProfile name="staging">
		<!-- configuration to be enabled when the "staging" profile is active -->
	</springProfile>

	<springProfile name="dev | staging">
		<!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
	</springProfile>

	<springProfile name="!production">
		<!-- configuration to be enabled when the "production" profile is not active -->
	</springProfile>
----



[[boot-features-logback-environment-properties]]
==== Environment Properties
The `<springProperty>` tag lets you expose properties from the Spring `Environment` for use within Logback.
Doing so can be useful if you want to access values from your `application.properties` file in your Logback configuration.
The tag works in a similar way to Logback's standard `<property>` tag.
However, rather than specifying a direct `value`, you specify the `source` of the property (from the `Environment`).
If you need to store the property somewhere other than in `local` scope, you can use the `scope` attribute.
If you need a fallback value (in case the property is not set in the `Environment`), you can use the `defaultValue` attribute.
The following example shows how to expose properties for use within Logback:

[source,xml,indent=0]
----
	<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
			defaultValue="localhost"/>
	<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
		<remoteHost>${fluentHost}</remoteHost>
		...
	</appender>
----

NOTE: The `source` must be specified in kebab case (such as `my.property-name`).
However, properties can be added to the `Environment` by using the relaxed rules.



[[boot-features-internationalization]]
== Internationalization
Spring Boot supports localized messages so that your application can cater to users of different language preferences.
By default, Spring Boot looks for the presence of a `messages` resource bundle at the root of the classpath.

NOTE: The auto-configuration applies when the default properties file for the configured resource bundle is available (i.e. `messages.properties` by default).
If your resource bundle contains only language-specific properties files, you are required to add the default.
If no properties file is found that matches any of the configured base names, there will be no auto-configured `MessageSource`.

The basename of the resource bundle as well as several other attributes can be configured using the `spring.messages` namespace, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  messages:
	    basename: "messages,config.i18n.messages"
	    fallback-to-system-locale: false
----

TIP: `spring.messages.basename` supports comma-separated list of locations, either a package qualifier or a resource resolved from the classpath root.

See {spring-boot-autoconfigure-module-code}/context/MessageSourceProperties.java[`MessageSourceProperties`] for more supported options.



[[boot-features-json]]
== JSON
Spring Boot provides integration with three JSON mapping libraries:

- Gson
- Jackson
- JSON-B

Jackson is the preferred and default library.



[[boot-features-json-jackson]]
=== Jackson
Auto-configuration for Jackson is provided and Jackson is part of `spring-boot-starter-json`.
When Jackson is on the classpath an `ObjectMapper` bean is automatically configured.
Several configuration properties are provided for <<howto.adoc#howto-customize-the-jackson-objectmapper,customizing the configuration of the `ObjectMapper`>>.



[[boot-features-json-gson]]
=== Gson
Auto-configuration for Gson is provided.
When Gson is on the classpath a `Gson` bean is automatically configured.
Several `+spring.gson.*+` configuration properties are provided for customizing the configuration.
To take more control, one or more `GsonBuilderCustomizer` beans can be used.



[[boot-features-json-json-b]]
=== JSON-B
Auto-configuration for JSON-B is provided.
When the JSON-B API and an implementation are on the classpath a `Jsonb` bean will be automatically configured.
The preferred JSON-B implementation is Apache Johnzon for which dependency management is provided.



[[boot-features-developing-web-applications]]
== Developing Web Applications
Spring Boot is well suited for web application development.
You can create a self-contained HTTP server by using embedded Tomcat, Jetty, Undertow, or Netty.
Most web applications use the `spring-boot-starter-web` module to get up and running quickly.
You can also choose to build reactive web applications by using the `spring-boot-starter-webflux` module.

If you have not yet developed a Spring Boot web application, you can follow the "Hello World!" example in the _<<getting-started.adoc#getting-started-first-application, Getting started>>_ section.



[[boot-features-spring-mvc]]
=== The "`Spring Web MVC Framework`"
The {spring-framework-docs}/web.html#mvc[Spring Web MVC framework] (often referred to as "`Spring MVC`") is a rich "`model view controller`" web framework.
Spring MVC lets you create special `@Controller` or `@RestController` beans to handle incoming HTTP requests.
Methods in your controller are mapped to HTTP by using `@RequestMapping` annotations.

The following code shows a typical `@RestController` that serves JSON data:

[source,java,indent=0]
----
	@RestController
	@RequestMapping(value="/users")
	public class MyRestController {

		@RequestMapping(value="/{user}", method=RequestMethod.GET)
		public User getUser(@PathVariable Long user) {
			// ...
		}

		@RequestMapping(value="/{user}/customers", method=RequestMethod.GET)
		List<Customer> getUserCustomers(@PathVariable Long user) {
			// ...
		}

		@RequestMapping(value="/{user}", method=RequestMethod.DELETE)
		public User deleteUser(@PathVariable Long user) {
			// ...
		}

	}
----

Spring MVC is part of the core Spring Framework, and detailed information is available in the  {spring-framework-docs}/web.html#mvc[reference documentation].
There are also several guides that cover Spring MVC available at https://spring.io/guides.



[[boot-features-spring-mvc-auto-configuration]]
==== Spring MVC Auto-configuration
Spring Boot provides auto-configuration for Spring MVC that works well with most applications.

The auto-configuration adds the following features on top of Spring's defaults:

* Inclusion of `ContentNegotiatingViewResolver` and `BeanNameViewResolver` beans.
* Support for serving static resources, including support for WebJars (covered <<boot-features-spring-mvc-static-content,later in this document>>)).
* Automatic registration of `Converter`, `GenericConverter`, and `Formatter` beans.
* Support for `HttpMessageConverters` (covered <<boot-features-spring-mvc-message-converters,later in this document>>).
* Automatic registration of `MessageCodesResolver` (covered <<boot-features-spring-message-codes,later in this document>>).
* Static `index.html` support.
* Automatic use of a `ConfigurableWebBindingInitializer` bean (covered <<boot-features-spring-mvc-web-binding-initializer,later in this document>>).

If you want to keep those Spring Boot MVC customizations and make more {spring-framework-docs}/web.html#mvc[MVC customizations] (interceptors, formatters, view controllers, and other features), you can add your own `@Configuration` class of type `WebMvcConfigurer` but *without* `@EnableWebMvc`.

If you want to provide custom instances of `RequestMappingHandlerMapping`, `RequestMappingHandlerAdapter`, or `ExceptionHandlerExceptionResolver`, and still keep the Spring Boot MVC customizations, you can declare a bean of type `WebMvcRegistrations` and use it to provide custom instances of those components.

If you want to take complete control of Spring MVC, you can add your own `@Configuration` annotated with `@EnableWebMvc`, or alternatively add your own `@Configuration`-annotated `DelegatingWebMvcConfiguration` as described in the Javadoc of `@EnableWebMvc`.

[NOTE]
====
Spring MVC uses a different `ConversionService` to the one used to convert values from your `application.properties` or `application.yaml` file.
It means that `Period`, `Duration` and `DataSize` converters are not available and that `@DurationUnit` and `@DataSizeUnit` annotations will be ignored.

If you want to customize the `ConversionService` used by Spring MVC, you can provide a `WebMvcConfigurer` bean with an `addFormatters` method.
From this method you can register any converter that you like, or you can delegate to the static methods available on `ApplicationConversionService`.
====



[[boot-features-spring-mvc-message-converters]]
==== HttpMessageConverters
Spring MVC uses the `HttpMessageConverter` interface to convert HTTP requests and responses.
Sensible defaults are included out of the box.
For example, objects can be automatically converted to JSON (by using the Jackson library) or XML (by using the Jackson XML extension, if available, or by using JAXB if the Jackson XML extension is not available).
By default, strings are encoded in `UTF-8`.

If you need to add or customize converters, you can use Spring Boot's `HttpMessageConverters` class, as shown in the following listing:

[source,java,indent=0]
----
	import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
	import org.springframework.context.annotation.*;
	import org.springframework.http.converter.*;

	@Configuration(proxyBeanMethods = false)
	public class MyConfiguration {

		@Bean
		public HttpMessageConverters customConverters() {
			HttpMessageConverter<?> additional = ...
			HttpMessageConverter<?> another = ...
			return new HttpMessageConverters(additional, another);
		}

	}
----

Any `HttpMessageConverter` bean that is present in the context is added to the list of converters.
You can also override default converters in the same way.



[[boot-features-json-components]]
==== Custom JSON Serializers and Deserializers
If you use Jackson to serialize and deserialize JSON data, you might want to write your own `JsonSerializer` and `JsonDeserializer` classes.
Custom serializers are usually https://github.com/FasterXML/jackson-docs/wiki/JacksonHowToCustomSerializers[registered with Jackson through a module], but Spring Boot provides an alternative `@JsonComponent` annotation that makes it easier to directly register Spring Beans.

You can use the `@JsonComponent` annotation directly on `JsonSerializer`, `JsonDeserializer` or `KeyDeserializer` implementations.
You can also use it on classes that contain serializers/deserializers as inner classes, as shown in the following example:

[source,java,indent=0]
----
	import java.io.*;
	import com.fasterxml.jackson.core.*;
	import com.fasterxml.jackson.databind.*;
	import org.springframework.boot.jackson.*;

	@JsonComponent
	public class Example {

		public static class Serializer extends JsonSerializer<SomeObject> {
			// ...
		}

		public static class Deserializer extends JsonDeserializer<SomeObject> {
			// ...
		}

	}
----

All `@JsonComponent` beans in the `ApplicationContext` are automatically registered with Jackson.
Because `@JsonComponent` is meta-annotated with `@Component`, the usual component-scanning rules apply.

Spring Boot also provides {spring-boot-module-code}/jackson/JsonObjectSerializer.java[`JsonObjectSerializer`] and {spring-boot-module-code}/jackson/JsonObjectDeserializer.java[`JsonObjectDeserializer`] base classes that provide useful alternatives to the standard Jackson versions when serializing objects.
See {spring-boot-module-api}/jackson/JsonObjectSerializer.html[`JsonObjectSerializer`] and {spring-boot-module-api}/jackson/JsonObjectDeserializer.html[`JsonObjectDeserializer`] in the Javadoc for details.



[[boot-features-spring-message-codes]]
==== MessageCodesResolver
Spring MVC has a strategy for generating error codes for rendering error messages from binding errors: `MessageCodesResolver`.
If you set the configprop:spring.mvc.message-codes-resolver-format[] property `PREFIX_ERROR_CODE` or `POSTFIX_ERROR_CODE`, Spring Boot creates one for you (see the enumeration in {spring-framework-api}/validation/DefaultMessageCodesResolver.Format.html[`DefaultMessageCodesResolver.Format`]).



[[boot-features-spring-mvc-static-content]]
==== Static Content
By default, Spring Boot serves static content from a directory called `/static` (or `/public` or `/resources` or `/META-INF/resources`) in the classpath or from the root of the `ServletContext`.
It uses the `ResourceHttpRequestHandler` from Spring MVC so that you can modify that behavior by adding your own `WebMvcConfigurer` and overriding the `addResourceHandlers` method.

In a stand-alone web application, the default servlet from the container is also enabled and acts as a fallback, serving content from the root of the `ServletContext` if Spring decides not to handle it.
Most of the time, this does not happen (unless you modify the default MVC configuration), because Spring can always handle requests through the `DispatcherServlet`.

By default, resources are mapped on `+/**+`, but you can tune that with the configprop:spring.mvc.static-path-pattern[] property.
For instance, relocating all resources to `/resources/**` can be achieved as follows:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	spring:
	  mvc:
	    static-path-pattern: "/resources/**"
----

You can also customize the static resource locations by using the configprop:spring.web.resources.static-locations[] property (replacing the default values with a list of directory locations).
The root Servlet context path, `"/"`, is automatically added as a location as well.

In addition to the "`standard`" static resource locations mentioned earlier, a special case is made for https://www.webjars.org/[Webjars content].
Any resources with a path in `+/webjars/**+` are served from jar files if they are packaged in the Webjars format.

TIP: Do not use the `src/main/webapp` directory if your application is packaged as a jar.
Although this directory is a common standard, it works *only* with war packaging, and it is silently ignored by most build tools if you generate a jar.

Spring Boot also supports the advanced resource handling features provided by Spring MVC, allowing use cases such as cache-busting static resources or using version agnostic URLs for Webjars.

To use version agnostic URLs for Webjars, add the `webjars-locator-core` dependency.
Then declare your Webjar.
Using jQuery as an example, adding `"/webjars/jquery/jquery.min.js"` results in `"/webjars/jquery/x.y.z/jquery.min.js"` where `x.y.z` is the Webjar version.

NOTE: If you use JBoss, you need to declare the `webjars-locator-jboss-vfs` dependency instead of the `webjars-locator-core`.
Otherwise, all Webjars resolve as a `404`.

To use cache busting, the following configuration configures a cache busting solution for all static resources, effectively adding a content hash, such as `<link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>`, in URLs:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	spring:
	  web:
	    resources:
	      chain:
	        strategy:
	          content:
	            enabled: true
	            paths: "/**"
----

NOTE: Links to resources are rewritten in templates at runtime, thanks to a `ResourceUrlEncodingFilter` that is auto-configured for Thymeleaf and FreeMarker.
You should manually declare this filter when using JSPs.
Other template engines are currently not automatically supported but can be with custom template macros/helpers and the use of the {spring-framework-api}/web/servlet/resource/ResourceUrlProvider.html[`ResourceUrlProvider`].

When loading resources dynamically with, for example, a JavaScript module loader, renaming files is not an option.
That is why other strategies are also supported and can be combined.
A "fixed" strategy adds a static version string in the URL without changing the file name, as shown in the following example:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	spring:
	  web:
	    resources:
	      chain:
	        strategy:
	          content:
	            enabled: true
	            paths: "/**"
	          fixed:
	            enabled: true
	            paths: "/js/lib/"
	            version: "v12"
----

With this configuration, JavaScript modules located under `"/js/lib/"` use a fixed versioning strategy (`"/v12/js/lib/mymodule.js"`), while other resources still use the content one (`<link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>`).

See {spring-boot-autoconfigure-module-code}/web/ResourceProperties.java[`ResourceProperties`] for more supported options.

[TIP]
====
This feature has been thoroughly described in a dedicated https://spring.io/blog/2014/07/24/spring-framework-4-1-handling-static-web-resources[blog post] and in Spring Framework's {spring-framework-docs}/web.html#mvc-config-static-resources[reference documentation].
====



[[boot-features-spring-mvc-welcome-page]]
==== Welcome Page
Spring Boot supports both static and templated welcome pages.
It first looks for an `index.html` file in the configured static content locations.
If one is not found, it then looks for an `index` template.
If either is found, it is automatically used as the welcome page of the application.



[[boot-features-spring-mvc-pathmatch]]
==== Path Matching and Content Negotiation
Spring MVC can map incoming HTTP requests to handlers by looking at the request path and matching it to the mappings defined in your application (for example, `@GetMapping` annotations on Controller methods).

Spring Boot chooses to disable suffix pattern matching by default, which means that requests like `"GET /projects/spring-boot.json"` won't be matched to `@GetMapping("/projects/spring-boot")` mappings.
This is considered as a {spring-framework-docs}/web.html#mvc-ann-requestmapping-suffix-pattern-match[best practice for Spring MVC applications].
This feature was mainly useful in the past for HTTP clients which did not send proper "Accept" request headers; we needed to make sure to send the correct Content Type to the client.
Nowadays, Content Negotiation is much more reliable.

There are other ways to deal with HTTP clients that don't consistently send proper "Accept" request headers.
Instead of using suffix matching, we can use a query parameter to ensure that requests like `"GET /projects/spring-boot?format=json"` will be mapped to `@GetMapping("/projects/spring-boot")`:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configblocks]
----
	spring:
	  mvc:
	    contentnegotiation:
	      favor-parameter: true
----

Or if you prefer to use a different parameter name:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring:
	  mvc:
	    contentnegotiation:
	      favor-parameter: true
	      parameter-name: "myparam"
----

Most standard media types are supported out-of-the-box, but you can also define new ones:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configblocks]
----
	spring:
	  mvc:
	    contentnegotiation:
	      media-types:
	        markdown: "text/markdown"
----



Suffix pattern matching is deprecated and will be removed in a future release.
If you understand the caveats and would still like your application to use suffix pattern matching, the following configuration is required:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configblocks]
----
	spring:
	  mvc:
	    contentnegotiation:
	      favor-path-extension: true
	    pathmatch:
	      use-suffix-pattern: true
----

Alternatively, rather than open all suffix patterns, it's more secure to only support registered suffix patterns:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configblocks]
----
	spring:
	  mvc:
	    contentnegotiation:
	      favor-path-extension: true
	    pathmatch:
	      use-registered-suffix-pattern: true
----

As of Spring Framework 5.3, Spring MVC supports several implementation strategies for matching request paths to Controller handlers.
It was previously only supporting the `AntPathMatcher` strategy, but it now also offers `PathPatternParser`.
Spring Boot now provides a configuration property to choose and opt in the new strategy:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	spring:
	  mvc:
	    pathmatch:
	      matching-strategy: "path-pattern-parser"
----

For more details on why you should consider this new implementation, please check out the
https://spring.io/blog/2020/06/30/url-matching-with-pathpattern-in-spring-mvc[dedicated blog post].

NOTE: `PathPatternParser` is an optimized implementation but restricts usage of
{spring-framework-docs}/web.html#mvc-ann-requestmapping-uri-templates[some path patterns variants]
and is incompatible with suffix pattern matching (configprop:spring.mvc.pathmatch.use-suffix-pattern[deprecated],
configprop:spring.mvc.pathmatch.use-registered-suffix-pattern[deprecated]) or mapping the `DispatcherServlet`
with a Servlet prefix (configprop:spring.mvc.servlet.path[]).



[[boot-features-spring-mvc-web-binding-initializer]]
==== ConfigurableWebBindingInitializer
Spring MVC uses a `WebBindingInitializer` to initialize a `WebDataBinder` for a particular request.
If you create your own `ConfigurableWebBindingInitializer` `@Bean`, Spring Boot automatically configures Spring MVC to use it.



[[boot-features-spring-mvc-template-engines]]
==== Template Engines
As well as REST web services, you can also use Spring MVC to serve dynamic HTML content.
Spring MVC supports a variety of templating technologies, including Thymeleaf, FreeMarker, and JSPs.
Also, many other templating engines include their own Spring MVC integrations.

Spring Boot includes auto-configuration support for the following templating engines:

 * https://freemarker.apache.org/docs/[FreeMarker]
 * https://docs.groovy-lang.org/docs/next/html/documentation/template-engines.html#_the_markuptemplateengine[Groovy]
 * https://www.thymeleaf.org[Thymeleaf]
 * https://mustache.github.io/[Mustache]

TIP: If possible, JSPs should be avoided.
There are several <<boot-features-jsp-limitations, known limitations>> when using them with embedded servlet containers.

When you use one of these templating engines with the default configuration, your templates are picked up automatically from `src/main/resources/templates`.

TIP: Depending on how you run your application, your IDE may order the classpath differently.
Running your application in the IDE from its main method results in a different ordering than when you run your application by using Maven or Gradle or from its packaged jar.
This can cause Spring Boot to fail to find the expected template.
If you have this problem, you can reorder the classpath in the IDE to place the module's classes and resources first.



[[boot-features-error-handling]]
==== Error Handling
By default, Spring Boot provides an `/error` mapping that handles all errors in a sensible way, and it is registered as a "`global`" error page in the servlet container.
For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message.
For browser clients, there is a "`whitelabel`" error view that renders the same data in HTML format (to customize it, add a `View` that resolves to `error`).

There are a number of `server.error` properties that can be set if you want to customize the default error handling behavior.
See the <<appendix-application-properties.adoc#common-application-properties-server, "`Server Properties`">> section of the Appendix.

To replace the default behavior completely, you can implement `ErrorController` and register a bean definition of that type or add a bean of type `ErrorAttributes` to use the existing mechanism but replace the contents.

TIP: The `BasicErrorController` can be used as a base class for a custom `ErrorController`.
This is particularly useful if you want to add a handler for a new content type (the default is to handle `text/html` specifically and provide a fallback for everything else).
To do so, extend `BasicErrorController`, add a public method with a `@RequestMapping` that has a `produces` attribute, and create a bean of your new type.

You can also define a class annotated with `@ControllerAdvice` to customize the JSON document to return for a particular controller and/or exception type, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@ControllerAdvice(basePackageClasses = AcmeController.class)
	public class AcmeControllerAdvice extends ResponseEntityExceptionHandler {

		@ExceptionHandler(YourException.class)
		@ResponseBody
		ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {
			HttpStatus status = getStatus(request);
			return new ResponseEntity<>(new CustomErrorType(status.value(), ex.getMessage()), status);
		}

		private HttpStatus getStatus(HttpServletRequest request) {
			Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
			if (statusCode == null) {
				return HttpStatus.INTERNAL_SERVER_ERROR;
			}
			return HttpStatus.valueOf(statusCode);
		}

	}
----

In the preceding example, if `YourException` is thrown by a controller defined in the same package as `AcmeController`, a JSON representation of the `CustomErrorType` POJO is used instead of the `ErrorAttributes` representation.



[[boot-features-error-handling-custom-error-pages]]
===== Custom Error Pages
If you want to display a custom HTML error page for a given status code, you can add a file to an `/error` directory.
Error pages can either be static HTML (that is, added under any of the static resource directories) or be built by using templates.
The name of the file should be the exact status code or a series mask.

For example, to map `404` to a static HTML file, your directory structure would be as follows:

[source,indent=0,subs="verbatim,quotes,attributes"]
----
	src/
	 +- main/
	     +- java/
	     |   + <source code>
	     +- resources/
	         +- public/
	             +- error/
	             |   +- 404.html
	             +- <other public assets>
----

To map all `5xx` errors by using a FreeMarker template, your directory structure would be as follows:

[source,indent=0,subs="verbatim,quotes,attributes"]
----
	src/
	 +- main/
	     +- java/
	     |   + <source code>
	     +- resources/
	         +- templates/
	             +- error/
	             |   +- 5xx.ftlh
	             +- <other templates>
----

For more complex mappings, you can also add beans that implement the `ErrorViewResolver` interface, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	public class MyErrorViewResolver implements ErrorViewResolver {

		@Override
		public ModelAndView resolveErrorView(HttpServletRequest request,
				HttpStatus status, Map<String, Object> model) {
			// Use the request or status to optionally return a ModelAndView
			return ...
		}

	}
----


You can also use regular Spring MVC features such as {spring-framework-docs}/web.html#mvc-exceptionhandlers[`@ExceptionHandler` methods] and {spring-framework-docs}/web.html#mvc-ann-controller-advice[`@ControllerAdvice`].
The `ErrorController` then picks up any unhandled exceptions.



[[boot-features-error-handling-mapping-error-pages-without-mvc]]
===== Mapping Error Pages outside of Spring MVC
For applications that do not use Spring MVC, you can use the `ErrorPageRegistrar` interface to directly register `ErrorPages`.
This abstraction works directly with the underlying embedded servlet container and works even if you do not have a Spring MVC `DispatcherServlet`.

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Bean
	public ErrorPageRegistrar errorPageRegistrar(){
		return new MyErrorPageRegistrar();
	}

	// ...

	private static class MyErrorPageRegistrar implements ErrorPageRegistrar {

		@Override
		public void registerErrorPages(ErrorPageRegistry registry) {
			registry.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
		}

	}
----

NOTE: If you register an `ErrorPage` with a path that ends up being handled by a `Filter` (as is common with some non-Spring web frameworks, like Jersey and Wicket), then the `Filter` has to be explicitly registered as an `ERROR` dispatcher, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Bean
	public FilterRegistrationBean myFilter() {
		FilterRegistrationBean registration = new FilterRegistrationBean();
		registration.setFilter(new MyFilter());
		...
		registration.setDispatcherTypes(EnumSet.allOf(DispatcherType.class));
		return registration;
	}
----

Note that the default `FilterRegistrationBean` does not include the `ERROR` dispatcher type.



[[boot-features-error-handling-war-deployment]]
===== Error handling in a war deployment
When deployed to a servlet container, Spring Boot uses its error page filter to forward a request with an error status to the appropriate error page.
This is necessary as the Servlet specification does not provide an API for registering error pages.
Depending on the container that you are deploying your war file to and the technologies that your application uses, some additional configuration may be required.

The error page filter can only forward the request to the correct error page if the response has not already been committed.
By default, WebSphere Application Server 8.0 and later commits the response upon successful completion of a servlet's service method.
You should disable this behavior by setting `com.ibm.ws.webcontainer.invokeFlushAfterService` to `false`.

If you are using Spring Security and want to access the principal in an error page, you must configure Spring Security's filter to be invoked on error dispatches.
To do so, set the `spring.security.filter.dispatcher-types` property to `async, error, forward, request`.



[[boot-features-spring-hateoas]]
==== Spring HATEOAS
If you develop a RESTful API that makes use of hypermedia, Spring Boot provides auto-configuration for Spring HATEOAS that works well with most applications.
The auto-configuration replaces the need to use `@EnableHypermediaSupport` and registers a number of beans to ease building hypermedia-based applications, including a `LinkDiscoverers` (for client side support) and an `ObjectMapper` configured to correctly marshal responses into the desired representation.
The `ObjectMapper` is customized by setting the various `spring.jackson.*` properties or, if one exists, by a `Jackson2ObjectMapperBuilder` bean.

You can take control of Spring HATEOAS's configuration by using `@EnableHypermediaSupport`.
Note that doing so disables the `ObjectMapper` customization described earlier.

WARNING: `spring-boot-starter-hateoas` is specific to Spring MVC and should not be combined with Spring WebFlux.
In order to use Spring HATEOAS with Spring WebFlux, you can add a direct dependency on `org.springframework.hateoas:spring-hateoas` along with `spring-boot-starter-webflux`.



[[boot-features-cors]]
==== CORS Support
https://en.wikipedia.org/wiki/Cross-origin_resource_sharing[Cross-origin resource sharing] (CORS) is a https://www.w3.org/TR/cors/[W3C specification] implemented by https://caniuse.com/#feat=cors[most browsers] that lets you specify in a flexible way what kind of cross-domain requests are authorized., instead of using some less secure and less powerful approaches such as IFRAME or JSONP.

As of version 4.2, Spring MVC {spring-framework-docs}/web.html#mvc-cors[supports CORS].
Using {spring-framework-docs}/web.html#mvc-cors-controller[controller method CORS configuration] with {spring-framework-api}/web/bind/annotation/CrossOrigin.html[`@CrossOrigin`] annotations in your Spring Boot application does not require any specific configuration.
{spring-framework-docs}/web.html#mvc-cors-global[Global CORS configuration] can be defined by registering a `WebMvcConfigurer` bean with a customized `addCorsMappings(CorsRegistry)` method, as shown in the following example:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	public class MyConfiguration {

		@Bean
		public WebMvcConfigurer corsConfigurer() {
			return new WebMvcConfigurer() {
				@Override
				public void addCorsMappings(CorsRegistry registry) {
					registry.addMapping("/api/**");
				}
			};
		}
	}
----



[[boot-features-webflux]]
=== The "`Spring WebFlux Framework`"
Spring WebFlux is the new reactive web framework introduced in Spring Framework 5.0.
Unlike Spring MVC, it does not require the Servlet API, is fully asynchronous and non-blocking, and implements the https://www.reactive-streams.org/[Reactive Streams] specification through https://projectreactor.io/[the Reactor project].

Spring WebFlux comes in two flavors: functional and annotation-based.
The annotation-based one is quite close to the Spring MVC model, as shown in the following example:

[source,java,indent=0]
----
	@RestController
	@RequestMapping("/users")
	public class MyRestController {

		@GetMapping("/{user}")
		public Mono<User> getUser(@PathVariable Long user) {
			// ...
		}

		@GetMapping("/{user}/customers")
		public Flux<Customer> getUserCustomers(@PathVariable Long user) {
			// ...
		}

		@DeleteMapping("/{user}")
		public Mono<User> deleteUser(@PathVariable Long user) {
			// ...
		}

	}
----

"`WebFlux.fn`", the functional variant, separates the routing configuration from the actual handling of the requests, as shown in the following example:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	public class RoutingConfiguration {

		@Bean
		public RouterFunction<ServerResponse> monoRouterFunction(UserHandler userHandler) {
			return route(GET("/{user}").and(accept(APPLICATION_JSON)), userHandler::getUser)
					.andRoute(GET("/{user}/customers").and(accept(APPLICATION_JSON)), userHandler::getUserCustomers)
					.andRoute(DELETE("/{user}").and(accept(APPLICATION_JSON)), userHandler::deleteUser);
		}

	}

	@Component
	public class UserHandler {

		public Mono<ServerResponse> getUser(ServerRequest request) {
			// ...
		}

		public Mono<ServerResponse> getUserCustomers(ServerRequest request) {
			// ...
		}

		public Mono<ServerResponse> deleteUser(ServerRequest request) {
			// ...
		}
	}
----

WebFlux is part of the Spring Framework and detailed information is available in its {spring-framework-docs}/web-reactive.html#webflux-fn[reference documentation].

TIP: You can define as many `RouterFunction` beans as you like to modularize the definition of the router.
Beans can be ordered if you need to apply a precedence.

To get started, add the `spring-boot-starter-webflux` module to your application.

NOTE: Adding both `spring-boot-starter-web` and `spring-boot-starter-webflux` modules in your application results in Spring Boot auto-configuring Spring MVC, not WebFlux.
This behavior has been chosen because many Spring developers add `spring-boot-starter-webflux` to their Spring MVC application to use the reactive `WebClient`.
You can still enforce your choice by setting the chosen application type to `SpringApplication.setWebApplicationType(WebApplicationType.REACTIVE)`.



[[boot-features-webflux-auto-configuration]]
==== Spring WebFlux Auto-configuration
Spring Boot provides auto-configuration for Spring WebFlux that works well with most applications.

The auto-configuration adds the following features on top of Spring's defaults:

* Configuring codecs for `HttpMessageReader` and `HttpMessageWriter` instances (described <<boot-features-webflux-httpcodecs,later in this document>>).
* Support for serving static resources, including support for WebJars (described <<boot-features-spring-mvc-static-content,later in this document>>).

If you want to keep Spring Boot WebFlux features and you want to add additional {spring-framework-docs}/web-reactive.html#webflux-config[WebFlux configuration], you can add your own `@Configuration` class of type `WebFluxConfigurer` but *without* `@EnableWebFlux`.

If you want to take complete control of Spring WebFlux, you can add your own `@Configuration` annotated with `@EnableWebFlux`.



[[boot-features-webflux-httpcodecs]]
==== HTTP Codecs with HttpMessageReaders and HttpMessageWriters
Spring WebFlux uses the `HttpMessageReader` and `HttpMessageWriter` interfaces to convert HTTP requests and responses.
They are configured with `CodecConfigurer` to have sensible defaults by looking at the libraries available in your classpath.

Spring Boot provides dedicated configuration properties for codecs, `+spring.codec.*+`.
It also applies further customization by using `CodecCustomizer` instances.
For example, `+spring.jackson.*+` configuration keys are applied to the Jackson codec.

If you need to add or customize codecs, you can create a custom `CodecCustomizer` component, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.boot.web.codec.CodecCustomizer;

	@Configuration(proxyBeanMethods = false)
	public class MyConfiguration {

		@Bean
		public CodecCustomizer myCodecCustomizer() {
			return codecConfigurer -> {
				// ...
			};
		}

	}
----

You can also leverage <<boot-features-json-components,Boot's custom JSON serializers and deserializers>>.



[[boot-features-webflux-static-content]]
==== Static Content
By default, Spring Boot serves static content from a directory called `/static` (or `/public` or `/resources` or `/META-INF/resources`) in the classpath.
It uses the `ResourceWebHandler` from Spring WebFlux so that you can modify that behavior by adding your own `WebFluxConfigurer` and overriding the `addResourceHandlers` method.

By default, resources are mapped on `+/**+`, but you can tune that by setting the configprop:spring.webflux.static-path-pattern[] property.
For instance, relocating all resources to `/resources/**` can be achieved as follows:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	spring:
	  webflux:
	    static-path-pattern: "/resources/**"
----

You can also customize the static resource locations by using `spring.web.resources.static-locations`.
Doing so replaces the default values with a list of directory locations.
If you do so, the default welcome page detection switches to your custom locations.
So, if there is an `index.html` in any of your locations on startup, it is the home page of the application.

In addition to the "`standard`" static resource locations listed earlier, a special case is made for https://www.webjars.org/[Webjars content].
Any resources with a path in `+/webjars/**+` are served from jar files if they are packaged in the Webjars format.

TIP: Spring WebFlux applications do not strictly depend on the Servlet API, so they cannot be deployed as war files and do not use the `src/main/webapp` directory.



[[boot-features-webflux-welcome-page]]
==== Welcome Page
Spring Boot supports both static and templated welcome pages.
It first looks for an `index.html` file in the configured static content locations.
If one is not found, it then looks for an `index` template.
If either is found, it is automatically used as the welcome page of the application.



[[boot-features-webflux-template-engines]]
==== Template Engines
As well as REST web services, you can also use Spring WebFlux to serve dynamic HTML content.
Spring WebFlux supports a variety of templating technologies, including Thymeleaf, FreeMarker, and Mustache.

Spring Boot includes auto-configuration support for the following templating engines:

 * https://freemarker.apache.org/docs/[FreeMarker]
 * https://www.thymeleaf.org[Thymeleaf]
 * https://mustache.github.io/[Mustache]

When you use one of these templating engines with the default configuration, your templates are picked up automatically from `src/main/resources/templates`.



[[boot-features-webflux-error-handling]]
==== Error Handling
Spring Boot provides a `WebExceptionHandler` that handles all errors in a sensible way.
Its position in the processing order is immediately before the handlers provided by WebFlux, which are considered last.
For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message.
For browser clients, there is a "`whitelabel`" error handler that renders the same data in HTML format.
You can also provide your own HTML templates to display errors (see the <<boot-features-webflux-error-handling-custom-error-pages,next section>>).

The first step to customizing this feature often involves using the existing mechanism but replacing or augmenting the error contents.
For that, you can add a bean of type `ErrorAttributes`.

To change the error handling behavior, you can implement `ErrorWebExceptionHandler` and register a bean definition of that type.
Because a `WebExceptionHandler` is quite low-level, Spring Boot also provides a convenient `AbstractErrorWebExceptionHandler` to let you handle errors in a WebFlux functional way, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	public class CustomErrorWebExceptionHandler extends AbstractErrorWebExceptionHandler {

		// Define constructor here

		@Override
		protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {

			return RouterFunctions
					.route(aPredicate, aHandler)
					.andRoute(anotherPredicate, anotherHandler);
		}

	}
----

For a more complete picture, you can also subclass `DefaultErrorWebExceptionHandler` directly and override specific methods.



[[boot-features-webflux-error-handling-custom-error-pages]]
===== Custom Error Pages
If you want to display a custom HTML error page for a given status code, you can add a file to an `/error` directory.
Error pages can either be static HTML (that is, added under any of the static resource directories) or built with templates.
The name of the file should be the exact status code or a series mask.

For example, to map `404` to a static HTML file, your directory structure would be as follows:

[source,indent=0,subs="verbatim,quotes,attributes"]
----
	src/
	 +- main/
	     +- java/
	     |   + <source code>
	     +- resources/
	         +- public/
	             +- error/
	             |   +- 404.html
	             +- <other public assets>
----

To map all `5xx` errors by using a Mustache template, your directory structure would be as follows:

[source,indent=0,subs="verbatim,quotes,attributes"]
----
	src/
	 +- main/
	     +- java/
	     |   + <source code>
	     +- resources/
	         +- templates/
	             +- error/
	             |   +- 5xx.mustache
	             +- <other templates>
----



[[boot-features-webflux-web-filters]]
==== Web Filters
Spring WebFlux provides a `WebFilter` interface that can be implemented to filter HTTP request-response exchanges.
`WebFilter` beans found in the application context will be automatically used to filter each exchange.

Where the order of the filters is important they can implement `Ordered` or be annotated with `@Order`.
Spring Boot auto-configuration may configure web filters for you.
When it does so, the orders shown in the following table will be used:

|===
| Web Filter | Order

| `MetricsWebFilter`
| `Ordered.HIGHEST_PRECEDENCE + 1`

| `WebFilterChainProxy` (Spring Security)
| `-100`

| `HttpTraceWebFilter`
| `Ordered.LOWEST_PRECEDENCE - 10`
|===



[[boot-features-jersey]]
=== JAX-RS and Jersey
If you prefer the JAX-RS programming model for REST endpoints, you can use one of the available implementations instead of Spring MVC.
https://jersey.github.io/[Jersey] and https://cxf.apache.org/[Apache CXF] work quite well out of the box.
CXF requires you to register its `Servlet` or `Filter` as a `@Bean` in your application context.
Jersey has some native Spring support, so we also provide auto-configuration support for it in Spring Boot, together with a starter.

To get started with Jersey, include the `spring-boot-starter-jersey` as a dependency and then you need one `@Bean` of type `ResourceConfig` in which you register all the endpoints, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Component
	public class JerseyConfig extends ResourceConfig {

		public JerseyConfig() {
			register(Endpoint.class);
		}

	}
----

WARNING: Jersey's support for scanning executable archives is rather limited.
For example, it cannot scan for endpoints in a package found in a <<deployment.adoc#deployment-install, fully executable jar file>> or in `WEB-INF/classes` when running an executable war file.
To avoid this limitation, the `packages` method should not be used, and endpoints should be registered individually by using the `register` method, as shown in the preceding example.

For more advanced customizations, you can also register an arbitrary number of beans that implement `ResourceConfigCustomizer`.

All the registered endpoints should be `@Components` with HTTP resource annotations (`@GET` and others), as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Component
	@Path("/hello")
	public class Endpoint {

		@GET
		public String message() {
			return "Hello";
		}

	}
----

Since the `Endpoint` is a Spring `@Component`, its lifecycle is managed by Spring and you can use the `@Autowired` annotation to inject dependencies and use the `@Value` annotation to inject external configuration.
By default, the Jersey servlet is registered and mapped to `/*`.
You can change the mapping by adding `@ApplicationPath` to your `ResourceConfig`.

By default, Jersey is set up as a Servlet in a `@Bean` of type `ServletRegistrationBean` named `jerseyServletRegistration`.
By default, the servlet is initialized lazily, but you can customize that behavior by setting `spring.jersey.servlet.load-on-startup`.
You can disable or override that bean by creating one of your own with the same name.
You can also use a filter instead of a servlet by setting `spring.jersey.type=filter` (in which case, the `@Bean` to replace or override is `jerseyFilterRegistration`).
The filter has an `@Order`, which you can set with `spring.jersey.filter.order`.
When using Jersey as a filter, a Servlet that will handle any requests that are not intercepted by Jersey must be present.
If your application does not contain such a servlet, you may want to enable the default servlet by setting configprop:server.servlet.register-default-servlet[] to `true`.
Both the servlet and the filter registrations can be given init parameters by using `spring.jersey.init.*` to specify a map of properties.



[[boot-features-embedded-container]]
=== Embedded Servlet Container Support
Spring Boot includes support for embedded https://tomcat.apache.org/[Tomcat], https://www.eclipse.org/jetty/[Jetty], and https://github.com/undertow-io/undertow[Undertow] servers.
Most developers use the appropriate "`Starter`" to obtain a fully configured instance.
By default, the embedded server listens for HTTP requests on port `8080`.



[[boot-features-embedded-container-servlets-filters-listeners]]
==== Servlets, Filters, and listeners
When using an embedded servlet container, you can register servlets, filters, and all the listeners (such as `HttpSessionListener`) from the Servlet spec, either by using Spring beans or by scanning for Servlet components.



[[boot-features-embedded-container-servlets-filters-listeners-beans]]
===== Registering Servlets, Filters, and Listeners as Spring Beans
Any `Servlet`, `Filter`, or servlet `*Listener` instance that is a Spring bean is registered with the embedded container.
This can be particularly convenient if you want to refer to a value from your `application.properties` during configuration.

By default, if the context contains only a single Servlet, it is mapped to `/`.
In the case of multiple servlet beans, the bean name is used as a path prefix.
Filters map to `+/*+`.

If convention-based mapping is not flexible enough, you can use the `ServletRegistrationBean`, `FilterRegistrationBean`, and `ServletListenerRegistrationBean` classes for complete control.

It is usually safe to leave Filter beans unordered.
If a specific order is required, you should annotate the `Filter` with `@Order` or make it implement `Ordered`.
You cannot configure the order of a `Filter` by annotating its bean method with `@Order`.
If you cannot change the `Filter` class to add `@Order` or implement `Ordered`, you must define a `FilterRegistrationBean` for the `Filter` and set the registration bean's order using the `setOrder(int)` method.
Avoid configuring a Filter that reads the request body at `Ordered.HIGHEST_PRECEDENCE`, since it might go against the character encoding configuration of your application.
If a Servlet filter wraps the request, it should be configured with an order that is less than or equal to `OrderedFilter.REQUEST_WRAPPER_FILTER_MAX_ORDER`.

TIP: To see the order of every `Filter` in your application, enable debug level logging for the `web` <<boot-features-custom-log-groups,logging group>> (`logging.level.web=debug`).
Details of the registered filters, including their order and URL patterns, will then be logged at startup.

WARNING: Take care when registering `Filter` beans since they are initialized very early in the application lifecycle.
If you need to register a `Filter` that interacts with other beans, consider using a {spring-boot-module-api}/web/servlet/DelegatingFilterProxyRegistrationBean.html[`DelegatingFilterProxyRegistrationBean`] instead.



[[boot-features-embedded-container-context-initializer]]
==== Servlet Context Initialization
Embedded servlet containers do not directly execute the Servlet 3.0+ `javax.servlet.ServletContainerInitializer` interface or Spring's `org.springframework.web.WebApplicationInitializer` interface.
This is an intentional design decision intended to reduce the risk that third party libraries designed to run inside a war may break Spring Boot applications.

If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the `org.springframework.boot.web.servlet.ServletContextInitializer` interface.
The single `onStartup` method provides access to the `ServletContext` and, if necessary, can easily be used as an adapter to an existing `WebApplicationInitializer`.



[[boot-features-embedded-container-servlets-filters-listeners-scanning]]
===== Scanning for Servlets, Filters, and listeners
When using an embedded container, automatic registration of classes annotated with `@WebServlet`, `@WebFilter`, and `@WebListener` can be enabled by using `@ServletComponentScan`.

TIP: `@ServletComponentScan` has no effect in a standalone container, where the container's built-in discovery mechanisms are used instead.



[[boot-features-embedded-container-application-context]]
==== The ServletWebServerApplicationContext
Under the hood, Spring Boot uses a different type of `ApplicationContext` for embedded servlet container support.
The `ServletWebServerApplicationContext` is a special type of `WebApplicationContext` that bootstraps itself by searching for a single `ServletWebServerFactory` bean.
Usually a `TomcatServletWebServerFactory`, `JettyServletWebServerFactory`, or `UndertowServletWebServerFactory` has been auto-configured.

NOTE: You usually do not need to be aware of these implementation classes.
Most applications are auto-configured, and the appropriate `ApplicationContext` and `ServletWebServerFactory` are created on your behalf.



[[boot-features-customizing-embedded-containers]]
==== Customizing Embedded Servlet Containers
Common servlet container settings can be configured by using Spring `Environment` properties.
Usually, you would define the properties in your `application.properties` or `application.yaml` file.

Common server settings include:

* Network settings: Listen port for incoming HTTP requests (`server.port`), interface address to bind to `server.address`, and so on.
* Session settings: Whether the session is persistent (`server.servlet.session.persistent`), session timeout (`server.servlet.session.timeout`), location of session data (`server.servlet.session.store-dir`), and session-cookie configuration (`server.servlet.session.cookie.*`).
* Error management: Location of the error page (`server.error.path`) and so on.
* <<howto.adoc#howto-configure-ssl,SSL>>
* <<howto.adoc#how-to-enable-http-response-compression,HTTP compression>>

Spring Boot tries as much as possible to expose common settings, but this is not always possible.
For those cases, dedicated namespaces offer server-specific customizations (see `server.tomcat` and `server.undertow`).
For instance, <<howto.adoc#howto-configure-accesslogs,access logs>> can be configured with specific features of the embedded servlet container.

TIP: See the {spring-boot-autoconfigure-module-code}/web/ServerProperties.java[`ServerProperties`] class for a complete list.



[[boot-features-programmatic-embedded-container-customization]]
===== Programmatic Customization
If you need to programmatically configure your embedded servlet container, you can register a Spring bean that implements the `WebServerFactoryCustomizer` interface.
`WebServerFactoryCustomizer` provides access to the `ConfigurableServletWebServerFactory`, which includes numerous customization setter methods.
The following example shows programmatically setting the port:

[source,java,indent=0]
----
	import org.springframework.boot.web.server.WebServerFactoryCustomizer;
	import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
	import org.springframework.stereotype.Component;

	@Component
	public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

		@Override
		public void customize(ConfigurableServletWebServerFactory server) {
			server.setPort(9000);
		}

	}
----

`TomcatServletWebServerFactory`, `JettyServletWebServerFactory` and `UndertowServletWebServerFactory` are dedicated variants of `ConfigurableServletWebServerFactory` that have additional customization setter methods for Tomcat, Jetty and Undertow respectively.
The following example shows how to customize `TomcatServletWebServerFactory` that provides access to Tomcat-specific configuration options:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
include::{code-examples}/context/embedded/TomcatServerCustomizerExample.java[tag=configuration]
----



[[boot-features-customizing-configurableservletwebserverfactory-directly]]
===== Customizing ConfigurableServletWebServerFactory Directly
For more advanced use cases that require you to extend from `ServletWebServerFactory`, you can expose a bean of such type yourself.

Setters are provided for many configuration options.
Several protected method "`hooks`" are also provided should you need to do something more exotic.
See the {spring-boot-module-api}/web/servlet/server/ConfigurableServletWebServerFactory.html[source code documentation] for details.

NOTE: Auto-configured customizers are still applied on your custom factory, so use that option carefully.



[[boot-features-jsp-limitations]]
==== JSP Limitations
When running a Spring Boot application that uses an embedded servlet container (and is packaged as an executable archive), there are some limitations in the JSP support.

* With Jetty and Tomcat, it should work if you use war packaging.
  An executable war will work when launched with `java -jar`, and will also be deployable to any standard container.
  JSPs are not supported when using an executable jar.

* Undertow does not support JSPs.

* Creating a custom `error.jsp` page does not override the default view for <<boot-features-error-handling,error handling>>.
  <<boot-features-error-handling-custom-error-pages,Custom error pages>> should be used instead.



[[boot-features-reactive-server]]
=== Embedded Reactive Server Support
Spring Boot includes support for the following embedded reactive web servers: Reactor Netty, Tomcat, Jetty, and Undertow.
Most developers use the appropriate “Starter” to obtain a fully configured instance.
By default, the embedded server listens for HTTP requests on port 8080.



[[boot-features-reactive-server-resources]]
=== Reactive Server Resources Configuration
When auto-configuring a Reactor Netty or Jetty server, Spring Boot will create specific beans that will provide HTTP resources to the server instance: `ReactorResourceFactory` or `JettyResourceFactory`.

By default, those resources will be also shared with the Reactor Netty and Jetty clients for optimal performances, given:

* the same technology is used for server and client
* the client instance is built using the `WebClient.Builder` bean auto-configured by Spring Boot

Developers can override the resource configuration for Jetty and Reactor Netty by providing a custom `ReactorResourceFactory` or `JettyResourceFactory` bean - this will be applied to both clients and servers.

You can learn more about the resource configuration on the client side in the <<boot-features-webclient-runtime, WebClient Runtime section>>.



[[boot-features-graceful-shutdown]]
== Graceful shutdown
Graceful shutdown is supported with all four embedded web servers (Jetty, Reactor Netty, Tomcat, and Undertow) and with both reactive and Servlet-based web applications.
It occurs as part of closing the application context and is performed in the earliest phase of stopping `SmartLifecycle` beans.
This stop processing uses a timeout which provides a grace period during which existing requests will be allowed to complete but no new requests will be permitted.
The exact way in which new requests are not permitted varies depending on the web server that is being used.
Jetty, Reactor Netty, and Tomcat will stop accepting requests at the network layer.
Undertow will accept requests but respond immediately with a service unavailable (503) response.

NOTE: Graceful shutdown with Tomcat requires Tomcat 9.0.33 or later.

To enable graceful shutdown, configure the configprop:server.shutdown[] property, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
server:
  shutdown: "graceful"
----

To configure the timeout period, configure the configprop:spring.lifecycle.timeout-per-shutdown-phase[] property, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
spring:
  lifecycle:
    timeout-per-shutdown-phase: "20s"
----

IMPORTANT: Using graceful shutdown with your IDE may not work properly if it does not send a proper `SIGTERM` signal.
Refer to the documentation of your IDE for more details.



[[boot-features-rsocket]]
== RSocket
https://rsocket.io[RSocket] is a binary protocol for use on byte stream transports.
It enables symmetric interaction models via async message passing over a single connection.


The `spring-messaging` module of the Spring Framework provides support for RSocket requesters and responders, both on the client and on the server side.
See the {spring-framework-docs}/web-reactive.html#rsocket-spring[RSocket section] of the Spring Framework reference for more details, including an overview of the RSocket protocol.



[[boot-features-rsocket-strategies-auto-configuration]]
=== RSocket Strategies Auto-configuration
Spring Boot auto-configures an `RSocketStrategies` bean that provides all the required infrastructure for encoding and decoding RSocket payloads.
By default, the auto-configuration will try to configure the following (in order):

. https://cbor.io/[CBOR] codecs with Jackson
. JSON codecs with Jackson

The `spring-boot-starter-rsocket` starter provides both dependencies.
Check out the <<boot-features-json-jackson,Jackson support section>> to know more about customization possibilities.

Developers can customize the `RSocketStrategies` component by creating beans that implement the `RSocketStrategiesCustomizer` interface.
Note that their `@Order` is important, as it determines the order of codecs.



[[boot-features-rsocket-server-auto-configuration]]
=== RSocket server Auto-configuration
Spring Boot provides RSocket server auto-configuration.
The required dependencies are provided by the `spring-boot-starter-rsocket`.

Spring Boot allows exposing RSocket over WebSocket from a WebFlux server, or standing up an independent RSocket server.
This depends on the type of application and its configuration.

For WebFlux application (i.e. of type `WebApplicationType.REACTIVE`), the RSocket server will be plugged into the Web Server only if the following properties match:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	spring:
	  rsocket:
	    server:
	      mapping-path: "/rsocket"
	      transport: "websocket"
----

WARNING: Plugging RSocket into a web server is only supported with Reactor Netty, as RSocket itself is built with that library.

Alternatively, an RSocket TCP or websocket server is started as an independent, embedded server.
Besides the dependency requirements, the only required configuration is to define a port for that server:

[source,yaml,indent=0,subs="verbatim,quotes,attributes",configprops,configblocks]
----
	spring:
	  rsocket:
	    server:
	      port: 9898
----



[[boot-features-rsocket-messaging]]
=== Spring Messaging RSocket support
Spring Boot will auto-configure the Spring Messaging infrastructure for RSocket.

This means that Spring Boot will create a `RSocketMessageHandler` bean that will handle RSocket requests to your application.



[[boot-features-rsocket-requester]]
=== Calling RSocket Services with RSocketRequester
Once the `RSocket` channel is established between server and client, any party can send or receive requests to the other.

As a server, you can get injected with an `RSocketRequester` instance on any handler method of an RSocket `@Controller`.
As a client, you need to configure and establish an RSocket connection first.
Spring Boot auto-configures an `RSocketRequester.Builder` for such cases with the expected codecs.

The `RSocketRequester.Builder` instance is a prototype bean, meaning each injection point will provide you with a new instance .
This is done on purpose since this builder is stateful and you shouldn't create requesters with different setups using the same instance.

The following code shows a typical example:

[source,java,indent=0]
----
	@Service
	public class MyService {

		private final Mono<RSocketRequester> rsocketRequester;

		public MyService(RSocketRequester.Builder rsocketRequesterBuilder) {
			this.rsocketRequester = rsocketRequesterBuilder
					.connectTcp("example.org", 9898).cache();
		}

		public Mono<User> someRSocketCall(String name) {
			return this.rsocketRequester.flatMap(req ->
			            req.route("user").data(name).retrieveMono(User.class));
		}

	}
----



[[boot-features-security]]
== Security
If {spring-security}[Spring Security] is on the classpath, then web applications are secured by default.
Spring Boot relies on Spring Security’s content-negotiation strategy to determine whether to use `httpBasic` or `formLogin`.
To add method-level security to a web application, you can also add `@EnableGlobalMethodSecurity` with your desired settings.
Additional information can be found in the {spring-security-docs}#jc-method[Spring Security Reference Guide].

The default `UserDetailsService` has a single user.
The user name is `user`, and the password is random and is printed at INFO level when the application starts, as shown in the following example:

[indent=0]
----
	Using generated security password: 78fa095d-3f4c-48b1-ad50-e24c31d5cf35
----

NOTE: If you fine-tune your logging configuration, ensure that the `org.springframework.boot.autoconfigure.security` category is set to log `INFO`-level messages.
Otherwise, the default password is not printed.

You can change the username and password by providing a `spring.security.user.name` and `spring.security.user.password`.

The basic features you get by default in a web application are:

* A `UserDetailsService` (or `ReactiveUserDetailsService` in case of a WebFlux application) bean with in-memory store and a single user with a generated password (see {spring-boot-module-api}/autoconfigure/security/SecurityProperties.User.html[`SecurityProperties.User`] for the properties of the user).
* Form-based login or HTTP Basic security (depending on the `Accept` header in the request) for the entire application (including actuator endpoints if actuator is on the classpath).
* A `DefaultAuthenticationEventPublisher` for publishing authentication events.

You can provide a different `AuthenticationEventPublisher` by adding a bean for it.



[[boot-features-security-mvc]]
=== MVC Security
The default security configuration is implemented in `SecurityAutoConfiguration` and `UserDetailsServiceAutoConfiguration`.
`SecurityAutoConfiguration` imports `SpringBootWebSecurityConfiguration` for web security and `UserDetailsServiceAutoConfiguration` configures authentication, which is also relevant in non-web applications.
To switch off the default web application security configuration completely or to combine multiple Spring Security components such as OAuth2 Client and Resource Server, add a bean of type `SecurityFilterChain` (doing so does not disable the `UserDetailsService` configuration or Actuator's security).

To also switch off the `UserDetailsService` configuration, you can add a bean of type `UserDetailsService`, `AuthenticationProvider`, or `AuthenticationManager`.

Access rules can be overridden by adding a custom `SecurityFilterChain` or `WebSecurityConfigurerAdapter` bean.
Spring Boot provides convenience methods that can be used to override access rules for actuator endpoints and static resources.
`EndpointRequest` can be used to create a `RequestMatcher` that is based on the configprop:management.endpoints.web.base-path[] property.
`PathRequest` can be used to create a `RequestMatcher` for resources in commonly used locations.



[[boot-features-security-webflux]]
=== WebFlux Security
Similar to Spring MVC applications, you can secure your WebFlux applications by adding the `spring-boot-starter-security` dependency.
The default security configuration is implemented in `ReactiveSecurityAutoConfiguration` and `UserDetailsServiceAutoConfiguration`.
`ReactiveSecurityAutoConfiguration` imports `WebFluxSecurityConfiguration` for web security and `UserDetailsServiceAutoConfiguration` configures authentication, which is also relevant in non-web applications.
To switch off the default web application security configuration completely, you can add a bean of type `WebFilterChainProxy` (doing so does not disable the `UserDetailsService` configuration or Actuator's security).

To also switch off the `UserDetailsService` configuration, you can add a bean of type `ReactiveUserDetailsService` or `ReactiveAuthenticationManager`.

Access rules and the use of multiple Spring Security components such as OAuth 2 Client and Resource Server can be configured by adding a custom `SecurityWebFilterChain` bean.
Spring Boot provides convenience methods that can be used to override access rules for actuator endpoints and static resources.
`EndpointRequest` can be used to create a `ServerWebExchangeMatcher` that is based on the configprop:management.endpoints.web.base-path[] property.

`PathRequest` can be used to create a `ServerWebExchangeMatcher` for resources in commonly used locations.

For example, you can customize your security configuration by adding something like:

[source,java,indent=0]
----
include::{code-examples}/web/security/CustomWebFluxSecurityExample.java[tag=configuration]
----



[[boot-features-security-oauth2]]
=== OAuth2
https://oauth.net/2/[OAuth2] is a widely used authorization framework that is supported by Spring.



[[boot-features-security-oauth2-client]]
==== Client
If you have `spring-security-oauth2-client` on your classpath, you can take advantage of some auto-configuration to set up an OAuth2/Open ID Connect clients.
This configuration makes use of the properties under `OAuth2ClientProperties`.
The same properties are applicable to both servlet and reactive applications.

You can register multiple OAuth2 clients and providers under the `spring.security.oauth2.client` prefix, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  security:
	    oauth2:
	      client:
	        registration:
	          my-client-1:
	            client-id: "abcd"
	            client-secret: "password"
	            client-name: "Client for user scope"
	            provider: "my-oauth-provider"
	            scope: "user"
	            redirect-uri: "https://my-redirect-uri.com"
	            client-authentication-method: "basic"
	            authorization-grant-type: "authorization-code"

	          my-client-2:
	            client-id: "abcd"
	            client-secret: "password"
	            client-name: "Client for email scope"
	            provider: "my-oauth-provider"
	            scope: "email"
	            redirect-uri: "https://my-redirect-uri.com"
	            client-authentication-method: "basic"
	            authorization-grant-type: "authorization_code"

	        provider:
	          my-oauth-provider:
	            authorization-uri: "https://my-auth-server/oauth/authorize"
	            token-uri: "https://my-auth-server/oauth/token"
	            user-info-uri: "https://my-auth-server/userinfo"
	            user-info-authentication-method: "header"
	            jwk-set-uri: "https://my-auth-server/token_keys"
	            user-name-attribute: "name"
----

For OpenID Connect providers that support https://openid.net/specs/openid-connect-discovery-1_0.html[OpenID Connect discovery], the configuration can be further simplified.
The provider needs to be configured with an `issuer-uri` which is the URI that the it asserts as its Issuer Identifier.
For example, if the `issuer-uri` provided is "https://example.com", then an `OpenID Provider Configuration Request` will be made to "https://example.com/.well-known/openid-configuration".
The result is expected to be an `OpenID Provider Configuration Response`.
The following example shows how an OpenID Connect Provider can be configured with the `issuer-uri`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  security:
	    oauth2:
	      client:
	        provider:
	          oidc-provider:
	            issuer-uri: "https://dev-123456.oktapreview.com/oauth2/default/"
----

By default, Spring Security's `OAuth2LoginAuthenticationFilter` only processes URLs matching `/login/oauth2/code/*`.
If you want to customize the `redirect-uri` to use a different pattern, you need to provide configuration to process that custom pattern.
For example, for servlet applications, you can add your own `SecurityFilterChain` that resembles the following:

[source,java,indent=0]
----
    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .anyRequest().authenticated()
                .and()
            .oauth2Login()
                .redirectionEndpoint()
                    .baseUri("/custom-callback");
        return http.build();
    }
----

TIP: Spring Boot auto-configures an `InMemoryOAuth2AuthorizedClientService` which is used by Spring Security for the management of client registrations.
The `InMemoryOAuth2AuthorizedClientService` has limited capabilities and we recommend using it only for development environments.
For production environments, consider using a `JdbcOAuth2AuthorizedClientService` or creating your own implementation of `OAuth2AuthorizedClientService`.



[[boot-features-security-oauth2-common-providers]]
===== OAuth2 client registration for common providers
For common OAuth2 and OpenID providers, including Google, Github, Facebook, and Okta, we provide a set of provider defaults (`google`, `github`, `facebook`, and `okta`, respectively).

If you do not need to customize these providers, you can set the `provider` attribute to the one for which you need to infer defaults.
Also, if the key for the client registration matches a default supported provider, Spring Boot infers that as well.

In other words, the two configurations in the following example use the Google provider:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  security:
	    oauth2:
	      client:
	        registration:
	          my-client:
	            client-id: "abcd"
	            client-secret: "password"
	            provider: "google"
	          google:
	            client-id: "abcd"
	            client-secret: "password"
----



[[boot-features-security-oauth2-server]]
==== Resource Server
If you have `spring-security-oauth2-resource-server` on your classpath, Spring Boot can set up an OAuth2 Resource Server.
For JWT configuration, a JWK Set URI or OIDC Issuer URI needs to be specified, as shown in the following examples:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  security:
	    oauth2:
	      resourceserver:
	        jwt:
	          jwk-set-uri: "https://example.com/oauth2/default/v1/keys"
----

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  security:
	    oauth2:
	      resourceserver:
	        jwt:
	          issuer-uri: "https://dev-123456.oktapreview.com/oauth2/default/"
----

NOTE: If the authorization server does not support a JWK Set URI, you can configure the resource server with the Public Key used for verifying the signature of the JWT.
This can be done using the configprop:spring.security.oauth2.resourceserver.jwt.public-key-location[] property, where the value needs to point to a file containing the public key in the PEM-encoded x509 format.

The same properties are applicable for both servlet and reactive applications.

Alternatively, you can define your own `JwtDecoder` bean for servlet applications or a `ReactiveJwtDecoder` for reactive applications.

In cases where opaque tokens are used instead of JWTs, you can configure the following properties to validate tokens via introspection:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  security:
	    oauth2:
	      resourceserver:
	        opaquetoken:
	          introspection-uri: "https://example.com/check-token"
	          client-id: "my-client-id"
	          client-secret: "my-client-secret"
----

Again, the same properties are applicable for both servlet and reactive applications.

Alternatively, you can define your own `OpaqueTokenIntrospector` bean for servlet applications or a `ReactiveOpaqueTokenIntrospector` for reactive applications.



[[boot-features-security-authorization-server]]
==== Authorization Server
Currently, Spring Security does not provide support for implementing an OAuth 2.0 Authorization Server.
However, this functionality is available from the {spring-security-oauth2}[Spring Security OAuth] project, which will eventually be superseded by Spring Security completely.
Until then, you can use the `spring-security-oauth2-autoconfigure` module to easily set up an OAuth 2.0 authorization server; see its https://docs.spring.io/spring-security-oauth2-boot/[documentation] for instructions.



[[boot-features-security-saml]]
=== SAML 2.0



[[boot-features-security-saml2-relying-party]]
==== Relying Party
If you have `spring-security-saml2-service-provider` on your classpath, you can take advantage of some auto-configuration to set up a SAML 2.0 Relying Party.
This configuration makes use of the properties under `Saml2RelyingPartyProperties`.

A relying party registration represents a paired configuration between an Identity Provider, IDP, and a Service Provider, SP.
You can register multiple relying parties under the `spring.security.saml2.relyingparty` prefix, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  security:
	    saml2:
	      relyingparty:
	        registration:
	          my-relying-party1:
	            signing:
                  credentials:
                  - private-key-location: "path-to-private-key"
                    certificate-location: "path-to-certificate"
	            decryption:
	              credentials:
	              - private-key-location: "path-to-private-key"
                    certificate-location: "path-to-certificate"
	            identityprovider:
	              verification:
	                credentials:
	                - certificate-location: "path-to-verification-cert"
	              entity-id: "remote-idp-entity-id1"
	              sso-url: "https://remoteidp1.sso.url"
	          my-relying-party2:
	            signing:
	              credentials:
	              - private-key-location: "path-to-private-key"
                    certificate-location: "path-to-certificate"
                decryption:
	              credentials:
	              - private-key-location: "path-to-private-key"
                    certificate-location: "path-to-certificate"
                identityprovider:
                  verification:
                    credentials:
                    - certificate-location: "path-to-other-verification-cert"
                  entity-id: "remote-idp-entity-id2"
                  sso-url: "https://remoteidp2.sso.url"
----



[[boot-features-security-actuator]]
=== Actuator Security
For security purposes, all actuators other than `/health` and `/info` are disabled by default.
The configprop:management.endpoints.web.exposure.include[] property can be used to enable the actuators.

If Spring Security is on the classpath and no other `WebSecurityConfigurerAdapter` or `SecurityFilterChain` bean is present, all actuators other than `/health` and `/info` are secured by Spring Boot auto-configuration.
If you define a custom `WebSecurityConfigurerAdapter` or `SecurityFilterChain` bean, Spring Boot auto-configuration will back off and you will be in full control of actuator access rules.

NOTE: Before setting the `management.endpoints.web.exposure.include`, ensure that the exposed actuators do not contain sensitive information and/or are secured by placing them behind a firewall or by something like Spring Security.



[[boot-features-security-csrf]]
==== Cross Site Request Forgery Protection
Since Spring Boot relies on Spring Security's defaults, CSRF protection is turned on by default.
This means that the actuator endpoints that require a `POST` (shutdown and loggers endpoints), `PUT` or `DELETE` will get a 403 forbidden error when the default security configuration is in use.

NOTE: We recommend disabling CSRF protection completely only if you are creating a service that is used by non-browser clients.

Additional information about CSRF protection can be found in the {spring-security-docs}#csrf[Spring Security Reference Guide].



[[boot-features-sql]]
== Working with SQL Databases
The {spring-framework}[Spring Framework] provides extensive support for working with SQL databases, from direct JDBC access using `JdbcTemplate` to complete "`object relational mapping`" technologies such as Hibernate.
{spring-data}[Spring Data] provides an additional level of functionality: creating `Repository` implementations directly from interfaces and using conventions to generate queries from your method names.



[[boot-features-configure-datasource]]
=== Configure a DataSource
Java's `javax.sql.DataSource` interface provides a standard method of working with database connections.
Traditionally, a 'DataSource' uses a `URL` along with some credentials to establish a database connection.

TIP: See <<howto.adoc#howto-configure-a-datasource,the "`How-to`" section>> for more advanced examples, typically to take full control over the configuration of the DataSource.



[[boot-features-embedded-database-support]]
==== Embedded Database Support
It is often convenient to develop applications by using an in-memory embedded database.
Obviously, in-memory databases do not provide persistent storage.
You need to populate your database when your application starts and be prepared to throw away data when your application ends.

TIP: The "`How-to`" section includes a <<howto.adoc#howto-database-initialization, section on how to initialize a database>>.

Spring Boot can auto-configure embedded https://www.h2database.com[H2], http://hsqldb.org/[HSQL], and https://db.apache.org/derby/[Derby] databases.
You need not provide any connection URLs.
You need only include a build dependency to the embedded database that you want to use.

[NOTE]
====
If you are using this feature in your tests, you may notice that the same database is reused by your whole test suite regardless of the number of application contexts that you use.
If you want to make sure that each context has a separate embedded database, you should set `spring.datasource.generate-unique-name` to `true`.
====

For example, the typical POM dependencies would be as follows:

[source,xml,indent=0]
----
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-data-jpa</artifactId>
	</dependency>
	<dependency>
		<groupId>org.hsqldb</groupId>
		<artifactId>hsqldb</artifactId>
		<scope>runtime</scope>
	</dependency>
----

NOTE: You need a dependency on `spring-jdbc` for an embedded database to be auto-configured.
In this example, it is pulled in transitively through `spring-boot-starter-data-jpa`.

TIP: If, for whatever reason, you do configure the connection URL for an embedded database, take care to ensure that the database's automatic shutdown is disabled.
If you use H2, you should use `DB_CLOSE_ON_EXIT=FALSE` to do so.
If you use HSQLDB, you should ensure that `shutdown=true` is not used.
Disabling the database's automatic shutdown lets Spring Boot control when the database is closed, thereby ensuring that it happens once access to the database is no longer needed.



[[boot-features-connect-to-production-database]]
==== Connection to a Production Database
Production database connections can also be auto-configured by using a pooling `DataSource`.



[[boot-features-connect-to-production-database-configuration]]
==== DataSource Configuration
DataSource configuration is controlled by external configuration properties in `+spring.datasource.*+`.
For example, you might declare the following section in `application.properties`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  datasource:
	    url: "jdbc:mysql://localhost/test"
	    username: "dbuser"
	    password: "dbpass"
----

NOTE: You should at least specify the URL by setting the configprop:spring.datasource.url[] property.
Otherwise, Spring Boot tries to auto-configure an embedded database.

TIP: Spring Boot can deduce the JDBC driver class for most databases from the URL.
If you need to specify a specific class, you can use the configprop:spring.datasource.driver-class-name[] property.

NOTE: For a pooling `DataSource` to be created, we need to be able to verify that a valid `Driver` class is available, so we check for that before doing anything.
In other words, if you set `spring.datasource.driver-class-name=com.mysql.jdbc.Driver`, then that class has to be loadable.

See {spring-boot-autoconfigure-module-code}/jdbc/DataSourceProperties.java[`DataSourceProperties`] for more of the supported options.
These are the standard options that work regardless of <<boot-features-connect-to-production-database-connection-pool, the actual implementation>>.
It is also possible to fine-tune implementation-specific settings by using their respective prefix (`+spring.datasource.hikari.*+`, `+spring.datasource.tomcat.*+`, `+spring.datasource.dbcp2.*+`, and `+spring.datasource.oracleucp.*+`).
Refer to the documentation of the connection pool implementation you are using for more details.

For instance, if you use the {tomcat-docs}/jdbc-pool.html#Common_Attributes[Tomcat connection pool], you could customize many additional settings, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  datasource:
	    tomcat:
	      max-wait: 10000
	      max-active: 50
	      test-on-borrow: true
----

This will set the pool to wait 10000 ms before throwing an exception if no connection is available, limit the maximum number of connections to 50 and validate the connection before borrowing it from the pool.



[[boot-features-connect-to-production-database-connection-pool]]
==== Supported Connection Pools
Spring Boot uses the following algorithm for choosing a specific implementation:

. We prefer https://github.com/brettwooldridge/HikariCP[HikariCP] for its performance and concurrency.
If HikariCP is available, we always choose it.
. Otherwise, if the Tomcat pooling `DataSource` is available, we use it.
. Otherwise, if https://commons.apache.org/proper/commons-dbcp/[Commons DBCP2] is available, we use it.
. If none of HikariCP, Tomcat, and DBCP2 are available and if Oracle UCP is available, we use it.

NOTE: If you use the `spring-boot-starter-jdbc` or `spring-boot-starter-data-jpa` "`starters`", you automatically get a dependency to `HikariCP`.

You can bypass that algorithm completely and specify the connection pool to use by setting the configprop:spring.datasource.type[] property.
This is especially important if you run your application in a Tomcat container, as `tomcat-jdbc` is provided by default.

Additional connection pools can always be configured manually, using `DataSourceBuilder`.
If you define your own `DataSource` bean, auto-configuration does not occur.
The following connection pools are supported by `DataSourceBuilder`:

* HikariCP
* Tomcat pooling `Datasource`
* Commons DBCP2
* Oracle UCP & `OracleDataSource`
* Spring Framework's `SimpleDriverDataSource`
* H2 `JdbcDataSource`
* PostgreSQL `PGSimpleDataSource`



[[boot-features-connecting-to-a-jndi-datasource]]
==== Connection to a JNDI DataSource
If you deploy your Spring Boot application to an Application Server, you might want to configure and manage your DataSource by using your Application Server's built-in features and access it by using JNDI.

The configprop:spring.datasource.jndi-name[] property can be used as an alternative to the configprop:spring.datasource.url[], configprop:spring.datasource.username[], and configprop:spring.datasource.password[] properties to access the `DataSource` from a specific JNDI location.
For example, the following section in `application.properties` shows how you can access a JBoss AS defined `DataSource`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  datasource:
	    jndi-name: "java:jboss/datasources/customers"
----



[[boot-features-using-jdbc-template]]
=== Using JdbcTemplate
Spring's `JdbcTemplate` and `NamedParameterJdbcTemplate` classes are auto-configured, and you can `@Autowire` them directly into your own beans, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.jdbc.core.JdbcTemplate;
	import org.springframework.stereotype.Component;

	@Component
	public class MyBean {

		private final JdbcTemplate jdbcTemplate;

		@Autowired
		public MyBean(JdbcTemplate jdbcTemplate) {
			this.jdbcTemplate = jdbcTemplate;
		}

		// ...

	}
----

You can customize some properties of the template by using the `spring.jdbc.template.*` properties, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  jdbc:
	    template:
	      max-rows: 500
----

NOTE: The `NamedParameterJdbcTemplate` reuses the same `JdbcTemplate` instance behind the scenes.
If more than one `JdbcTemplate` is defined and no primary candidate exists, the `NamedParameterJdbcTemplate` is not auto-configured.



[[boot-features-jpa-and-spring-data]]
=== JPA and Spring Data JPA
The Java Persistence API is a standard technology that lets you "`map`" objects to relational databases.
The `spring-boot-starter-data-jpa` POM provides a quick way to get started.
It provides the following key dependencies:

* Hibernate: One of the most popular JPA implementations.
* Spring Data JPA: Helps you to implement JPA-based repositories.
* Spring ORM: Core ORM support from the Spring Framework.

TIP: We do not go into too many details of JPA or {spring-data}[Spring Data] here.
You can follow the https://spring.io/guides/gs/accessing-data-jpa/["`Accessing Data with JPA`"] guide from https://spring.io and read the {spring-data-jpa}[Spring Data JPA] and https://hibernate.org/orm/documentation/[Hibernate] reference documentation.



[[boot-features-entity-classes]]
==== Entity Classes
Traditionally, JPA "`Entity`" classes are specified in a `persistence.xml` file.
With Spring Boot, this file is not necessary and "`Entity Scanning`" is used instead.
By default, all packages below your main configuration class (the one annotated with `@EnableAutoConfiguration` or `@SpringBootApplication`) are searched.

Any classes annotated with `@Entity`, `@Embeddable`, or `@MappedSuperclass` are considered.
A typical entity class resembles the following example:

[source,java,indent=0]
----
	package com.example.myapp.domain;

	import java.io.Serializable;
	import javax.persistence.*;

	@Entity
	public class City implements Serializable {

		@Id
		@GeneratedValue
		private Long id;

		@Column(nullable = false)
		private String name;

		@Column(nullable = false)
		private String state;

		// ... additional members, often include @OneToMany mappings

		protected City() {
			// no-args constructor required by JPA spec
			// this one is protected since it shouldn't be used directly
		}

		public City(String name, String state) {
			this.name = name;
			this.state = state;
		}

		public String getName() {
			return this.name;
		}

		public String getState() {
			return this.state;
		}

		// ... etc

	}
----

TIP: You can customize entity scanning locations by using the `@EntityScan` annotation.
See the "`<<howto.adoc#howto-separate-entity-definitions-from-spring-configuration>>`" how-to.



[[boot-features-spring-data-jpa-repositories]]
==== Spring Data JPA Repositories
{spring-data-jpa}[Spring Data JPA] repositories are interfaces that you can define to access data.
JPA queries are created automatically from your method names.
For example, a `CityRepository` interface might declare a `findAllByState(String state)` method to find all the cities in a given state.

For more complex queries, you can annotate your method with Spring Data's {spring-data-jpa-api}/repository/Query.html[`Query`] annotation.

Spring Data repositories usually extend from the {spring-data-commons-api}/repository/Repository.html[`Repository`] or {spring-data-commons-api}/repository/CrudRepository.html[`CrudRepository`] interfaces.
If you use auto-configuration, repositories are searched from the package containing your main configuration class (the one annotated with `@EnableAutoConfiguration` or `@SpringBootApplication`) down.

The following example shows a typical Spring Data repository interface definition:

[source,java,indent=0]
----
	package com.example.myapp.domain;

	import org.springframework.data.domain.*;
	import org.springframework.data.repository.*;

	public interface CityRepository extends Repository<City, Long> {

		Page<City> findAll(Pageable pageable);

		City findByNameAndStateAllIgnoringCase(String name, String state);

	}
----

Spring Data JPA repositories support three different modes of bootstrapping: default, deferred, and lazy.
To enable deferred or lazy bootstrapping, set the configprop:spring.data.jpa.repositories.bootstrap-mode[] property to `deferred` or `lazy` respectively.
When using deferred or lazy bootstrapping, the auto-configured `EntityManagerFactoryBuilder` will use the context's `AsyncTaskExecutor`, if any, as the bootstrap executor.
If more than one exists, the one named `applicationTaskExecutor` will be used.

[NOTE]
====
When using deferred or lazy bootstrapping, make sure to defer any access to the JPA infrastructure after the application context bootstrap phase.
You can use `SmartInitializingSingleton` to invoke any initialization that requires the JPA infrastructure.
For JPA components (such as converters) that are created as Spring beans, use `ObjectProvider` to delay the resolution of dependencies, if any.
====

TIP: We have barely scratched the surface of Spring Data JPA.
For complete details, see the {spring-data-jpa-docs}[Spring Data JPA reference documentation].



[[boot-features-creating-and-dropping-jpa-databases]]
==== Creating and Dropping JPA Databases
By default, JPA databases are automatically created *only* if you use an embedded database (H2, HSQL, or Derby).
You can explicitly configure JPA settings by using `+spring.jpa.*+` properties.
For example, to create and drop tables you can add the following line to your `application.properties`:

[indent=0]
----
	spring.jpa.hibernate.ddl-auto=create-drop
----

NOTE: Hibernate's own internal property name for this (if you happen to remember it better) is `hibernate.hbm2ddl.auto`.
You can set it, along with other Hibernate native properties, by using `+spring.jpa.properties.*+` (the prefix is stripped before adding them to the entity manager).
The following line shows an example of setting JPA properties for Hibernate:

[indent=0]
----
	spring.jpa.properties.hibernate.globally_quoted_identifiers=true
----

The line in the preceding example passes a value of `true` for the `hibernate.globally_quoted_identifiers` property to the Hibernate entity manager.

By default, the DDL execution (or validation) is deferred until the `ApplicationContext` has started.
There is also a `spring.jpa.generate-ddl` flag, but it is not used if Hibernate auto-configuration is active, because the `ddl-auto` settings are more fine-grained.



[[boot-features-jpa-in-web-environment]]
==== Open EntityManager in View
If you are running a web application, Spring Boot by default registers {spring-framework-api}/orm/jpa/support/OpenEntityManagerInViewInterceptor.html[`OpenEntityManagerInViewInterceptor`] to apply the "`Open EntityManager in View`" pattern, to allow for lazy loading in web views.
If you do not want this behavior, you should set `spring.jpa.open-in-view` to `false` in your `application.properties`.



[[boot-features-data-jdbc]]
=== Spring Data JDBC
Spring Data includes repository support for JDBC and will automatically generate SQL for the methods on `CrudRepository`.
For more advanced queries, a `@Query` annotation is provided.

Spring Boot will auto-configure Spring Data's JDBC repositories when the necessary dependencies are on the classpath.
They can be added to your project with a single dependency on `spring-boot-starter-data-jdbc`.
If necessary, you can take control of Spring Data JDBC's configuration by adding the `@EnableJdbcRepositories` annotation or a `JdbcConfiguration` subclass to your application.

TIP: For complete details of Spring Data JDBC, please refer to the {spring-data-jdbc-docs}[reference documentation].



[[boot-features-sql-h2-console]]
=== Using H2's Web Console
The https://www.h2database.com[H2 database] provides a https://www.h2database.com/html/quickstart.html#h2_console[browser-based console] that Spring Boot can auto-configure for you.
The console is auto-configured when the following conditions are met:

* You are developing a servlet-based web application.
* `com.h2database:h2` is on the classpath.
* You are using <<using-spring-boot.adoc#using-boot-devtools,Spring Boot's developer tools>>.

TIP: If you are not using Spring Boot's developer tools but would still like to make use of H2's console, you can configure the configprop:spring.h2.console.enabled[] property with a value of `true`.

NOTE: The H2 console is only intended for use during development, so you should take care to ensure that `spring.h2.console.enabled` is not set to `true` in production.



[[boot-features-sql-h2-console-custom-path]]
==== Changing the H2 Console's Path
By default, the console is available at `/h2-console`.
You can customize the console's path by using the configprop:spring.h2.console.path[] property.



[[boot-features-jooq]]
=== Using jOOQ
jOOQ Object Oriented Querying (https://www.jooq.org/[jOOQ]) is a popular product from https://www.datageekery.com/[Data Geekery] which generates Java code from your database and lets you build type-safe SQL queries through its fluent API.
Both the commercial and open source editions can be used with Spring Boot.



[[boot-features-jooq-codegen]]
==== Code Generation
In order to use jOOQ type-safe queries, you need to generate Java classes from your database schema.
You can follow the instructions in the {jooq-docs}/#jooq-in-7-steps-step3[jOOQ user manual].
If you use the `jooq-codegen-maven` plugin and you also use the `spring-boot-starter-parent` "`parent POM`", you can safely omit the plugin's `<version>` tag.
You can also use Spring Boot-defined version variables (such as `h2.version`) to declare the plugin's database dependency.
The following listing shows an example:

[source,xml,indent=0]
----
	<plugin>
		<groupId>org.jooq</groupId>
		<artifactId>jooq-codegen-maven</artifactId>
		<executions>
			...
		</executions>
		<dependencies>
			<dependency>
				<groupId>com.h2database</groupId>
				<artifactId>h2</artifactId>
				<version>${h2.version}</version>
			</dependency>
		</dependencies>
		<configuration>
			<jdbc>
				<driver>org.h2.Driver</driver>
				<url>jdbc:h2:~/yourdatabase</url>
			</jdbc>
			<generator>
				...
			</generator>
		</configuration>
	</plugin>
----



[[boot-features-jooq-dslcontext]]
==== Using DSLContext
The fluent API offered by jOOQ is initiated through the `org.jooq.DSLContext` interface.
Spring Boot auto-configures a `DSLContext` as a Spring Bean and connects it to your application `DataSource`.
To use the `DSLContext`, you can `@Autowire` it, as shown in the following example:

[source,java,indent=0]
----
	@Component
	public class JooqExample implements CommandLineRunner {

		private final DSLContext create;

		@Autowired
		public JooqExample(DSLContext dslContext) {
			this.create = dslContext;
		}

	}
----

TIP: The jOOQ manual tends to use a variable named `create` to hold the `DSLContext`.

You can then use the `DSLContext` to construct your queries, as shown in the following example:

[source,java,indent=0]
----
	public List<GregorianCalendar> authorsBornAfter1980() {
		return this.create.selectFrom(AUTHOR)
			.where(AUTHOR.DATE_OF_BIRTH.greaterThan(new GregorianCalendar(1980, 0, 1)))
			.fetch(AUTHOR.DATE_OF_BIRTH);
	}
----



[[boot-features-jooq-sqldialect]]
==== jOOQ SQL Dialect
Unless the configprop:spring.jooq.sql-dialect[] property has been configured, Spring Boot determines the SQL dialect to use for your datasource.
If Spring Boot could not detect the dialect, it uses `DEFAULT`.

NOTE: Spring Boot can only auto-configure dialects supported by the open source version of jOOQ.



[[boot-features-jooq-customizing]]
==== Customizing jOOQ
More advanced customizations can be achieved by defining your own `@Bean` definitions, which is used when the jOOQ `Configuration` is created.
You can define beans for the following jOOQ Types:

* `ConnectionProvider`
* `ExecutorProvider`
* `TransactionProvider`
* `RecordMapperProvider`
* `RecordUnmapperProvider`
* `Settings`
* `RecordListenerProvider`
* `ExecuteListenerProvider`
* `VisitListenerProvider`
* `TransactionListenerProvider`

You can also create your own `org.jooq.Configuration` `@Bean` if you want to take complete control of the jOOQ configuration.



[[boot-features-r2dbc]]
=== Using R2DBC
The Reactive Relational Database Connectivity (https://r2dbc.io[R2DBC]) project brings reactive programming APIs to relational databases.
R2DBC's `io.r2dbc.spi.Connection` provides a standard method of working with non-blocking database connections.
Connections are provided via a `ConnectionFactory`, similar to a `DataSource` with jdbc.

`ConnectionFactory` configuration is controlled by external configuration properties in `+spring.r2dbc.*+`.
For example, you might declare the following section in `application.properties`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  r2dbc:
	    url: "r2dbc:postgresql://localhost/test"
	    username: "dbuser"
	    password: "dbpass"
----

TIP: You do not need to specify a driver class name, since Spring Boot obtains the driver from R2DBC's Connection Factory discovery.

NOTE: At least the url should be provided.
Information specified in the URL takes precedence over individual properties, i.e. `name`, `username`, `password` and pooling options.

TIP: The "`How-to`" section includes a <<howto.adoc#howto-initialize-a-database-using-r2dbc, section on how to initialize a database>>.

To customize the connections created by a `ConnectionFactory`, i.e., set specific parameters that you do not want (or cannot) configure in your central database configuration, you can use a `ConnectionFactoryOptionsBuilderCustomizer` `@Bean`.
The following example shows how to manually override the database port while the rest of the options is taken from the application configuration:

[source,java,indent=0]
----
	@Bean
	public ConnectionFactoryOptionsBuilderCustomizer connectionFactoryPortCustomizer() {
		return (builder) -> builder.option(PORT, 5432);
	}
----

The following examples show how to set some PostgreSQL connection options:

[source,java,indent=0]
----
	@Bean
	public ConnectionFactoryOptionsBuilderCustomizer postgresCustomizer() {
		Map<String, String> options = new HashMap<>();
		options.put("lock_timeout", "30s");
		options.put("statement_timeout", "60s");
		return (builder) -> builder.option(OPTIONS, options);
	}
----

When a `ConnectionFactory` bean is available, the regular JDBC `DataSource` auto-configuration backs off.
If you want to retain the JDBC `DataSource` auto-configuration, and are comfortable with the risk of using the blocking JDBC API in a reactive application, add `@Import(DataSourceAutoConfiguration.class)` on a `@Configuration` class in your application to re-enable it.



[[boot-features-r2dbc-embedded-database]]
==== Embedded Database Support
Similarly to <<boot-features-embedded-database-support,the JDBC support>>, Spring Boot can automatically configure an embedded database for reactive usage.
You need not provide any connection URLs.
You need only include a build dependency to the embedded database that you want to use, as shown in the following example:

[source,xml,indent=0]
----
	<dependency>
		<groupId>io.r2dbc</groupId>
		<artifactId>r2dbc-h2</artifactId>
		<scope>runtime</scope>
	</dependency>
----

[NOTE]
====
If you are using this feature in your tests, you may notice that the same database is reused by your whole test suite regardless of the number of application contexts that you use.
If you want to make sure that each context has a separate embedded database, you should set `spring.r2dbc.generate-unique-name` to `true`.
====



[[boot-features-r2dbc-using-database-client]]
==== Using DatabaseClient
A `DatabaseClient` bean is auto-configured, and you can `@Autowire` it directly into your own beans, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.data.r2dbc.function.DatabaseClient;
	import org.springframework.stereotype.Component;

	@Component
	public class MyBean {

		private final DatabaseClient databaseClient;

		@Autowired
		public MyBean(DatabaseClient databaseClient) {
			this.databaseClient = databaseClient;
		}

		// ...

	}
----



[[boot-features-spring-data-r2dbc-repositories]]
==== Spring Data R2DBC Repositories
https://spring.io/projects/spring-data-r2dbc[Spring Data R2DBC] repositories are interfaces that you can define to access data.
Queries are created automatically from your method names.
For example, a `CityRepository` interface might declare a `findAllByState(String state)` method to find all the cities in a given state.

For more complex queries, you can annotate your method with Spring Data's {spring-data-r2dbc-api}/repository/Query.html[`Query`] annotation.

Spring Data repositories usually extend from the {spring-data-commons-api}/repository/Repository.html[`Repository`] or {spring-data-commons-api}/repository/CrudRepository.html[`CrudRepository`] interfaces.
If you use auto-configuration, repositories are searched from the package containing your main configuration class (the one annotated with `@EnableAutoConfiguration` or `@SpringBootApplication`) down.

The following example shows a typical Spring Data repository interface definition:

[source,java,indent=0]
----
	package com.example.myapp.domain;

	import org.springframework.data.domain.*;
	import org.springframework.data.repository.*;
	import reactor.core.publisher.Mono;

	public interface CityRepository extends Repository<City, Long> {

		Mono<City> findByNameAndStateAllIgnoringCase(String name, String state);

	}
----

TIP: We have barely scratched the surface of Spring Data R2DBC. For complete details, see the {spring-data-r2dbc-docs}[Spring Data R2DBC reference documentation].



[[boot-features-nosql]]
== Working with NoSQL Technologies
Spring Data provides additional projects that help you access a variety of NoSQL technologies, including:

* {spring-data-mongodb}[MongoDB]
* {spring-data-neo4j}[Neo4J]
* {spring-data-elasticsearch}[Elasticsearch]
* {spring-data-solr}[Solr]
* {spring-data-redis}[Redis]
* {spring-data-gemfire}[GemFire] or {spring-data-geode}[Geode]
* {spring-data-cassandra}[Cassandra]
* {spring-data-couchbase}[Couchbase]
* {spring-data-ldap}[LDAP]

Spring Boot provides auto-configuration for Redis, MongoDB, Neo4j, Elasticsearch, Solr Cassandra, Couchbase, and LDAP.
You can make use of the other projects, but you must configure them yourself.
Refer to the appropriate reference documentation at {spring-data}.



[[boot-features-redis]]
=== Redis
https://redis.io/[Redis] is a cache, message broker, and richly-featured key-value store.
Spring Boot offers basic auto-configuration for the https://github.com/lettuce-io/lettuce-core/[Lettuce] and https://github.com/xetorthio/jedis/[Jedis] client libraries and the abstractions on top of them provided by https://github.com/spring-projects/spring-data-redis[Spring Data Redis].

There is a `spring-boot-starter-data-redis` "`Starter`" for collecting the dependencies in a convenient way.
By default, it uses https://github.com/lettuce-io/lettuce-core/[Lettuce].
That starter handles both traditional and reactive applications.

TIP: We also provide a `spring-boot-starter-data-redis-reactive` "`Starter`" for consistency with the other stores with reactive support.



[[boot-features-connecting-to-redis]]
==== Connecting to Redis
You can inject an auto-configured `RedisConnectionFactory`, `StringRedisTemplate`, or vanilla `RedisTemplate` instance as you would any other Spring Bean.
By default, the instance tries to connect to a Redis server at `localhost:6379`.
The following listing shows an example of such a bean:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		private StringRedisTemplate template;

		@Autowired
		public MyBean(StringRedisTemplate template) {
			this.template = template;
		}

		// ...

	}
----

TIP: You can also register an arbitrary number of beans that implement `LettuceClientConfigurationBuilderCustomizer` for more advanced customizations.
If you use Jedis, `JedisClientConfigurationBuilderCustomizer` is also available.

If you add your own `@Bean` of any of the auto-configured types, it replaces the default (except in the case of `RedisTemplate`, when the exclusion is based on the bean name, `redisTemplate`, not its type).

A pooled connection factory is auto-configured if `commons-pool2` is on the classpath and at least one `Pool` option of {spring-boot-autoconfigure-module-code}/data/redis/RedisProperties.java[`RedisProperties`] is set.


[[boot-features-mongodb]]
=== MongoDB
https://www.mongodb.com/[MongoDB] is an open-source NoSQL document database that uses a JSON-like schema instead of traditional table-based relational data.
Spring Boot offers several conveniences for working with MongoDB, including the `spring-boot-starter-data-mongodb` and `spring-boot-starter-data-mongodb-reactive` "`Starters`".



[[boot-features-connecting-to-mongodb]]
==== Connecting to a MongoDB Database
To access MongoDB databases, you can inject an auto-configured `org.springframework.data.mongodb.MongoDatabaseFactory`.
By default, the instance tries to connect to a MongoDB server at `mongodb://localhost/test`.
The following example shows how to connect to a MongoDB database:

[source,java,indent=0]
----
	import org.springframework.data.mongodb.MongoDatabaseFactory;
	import com.mongodb.client.MongoDatabase;

	@Component
	public class MyBean {

		private final MongoDatabaseFactory mongo;

		@Autowired
		public MyBean(MongoDatabaseFactory mongo) {
			this.mongo = mongo;
		}

		// ...

		public void example() {
			MongoDatabase db = mongo.getMongoDatabase();
			// ...
		}

	}
----

If you have defined your own `MongoClient`, it will be used to auto-configure a suitable `MongoDatabaseFactory`.

The auto-configured `MongoClient` is created using a `MongoClientSettings` bean.
If you have defined your own `MongoClientSettings`, it will be used without modification and the `spring.data.mongodb` properties will be ignored.
Otherwise a `MongoClientSettings` will be auto-configured and will have the `spring.data.mongodb` properties applied to it.
In either case, you can declare one or more `MongoClientSettingsBuilderCustomizer` beans to fine-tune the `MongoClientSettings` configuration.
Each will be called in order with the `MongoClientSettings.Builder` that is used to build the `MongoClientSettings`.

You can set the configprop:spring.data.mongodb.uri[] property to change the URL and configure additional settings such as the _replica set_, as shown in the following example:

[source,properties,indent=0,configprops]
----
	spring.data.mongodb.uri=mongodb://user:secret@mongo1.example.com:12345,mongo2.example.com:23456/test
----

Alternatively, you can specify connection details using discrete properties.
For example, you might declare the following settings in your `application.properties`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  data:
	    mongodb:
	      host: "mongoserver.example.com"
	      port: 27017
	      database: "test"
	      username: "user"
	      password: "secret"
----

TIP: If `spring.data.mongodb.port` is not specified, the default of `27017` is used.
You could delete this line from the example shown earlier.

TIP: If you do not use Spring Data MongoDB, you can inject a `MongoClient` bean instead of using `MongoDatabaseFactory`.
If you want to take complete control of establishing the MongoDB connection, you can also declare your own `MongoDatabaseFactory` or `MongoClient` bean.

NOTE: If you are using the reactive driver, Netty is required for SSL.
The auto-configuration configures this factory automatically if Netty is available and the factory to use hasn't been customized already.



[[boot-features-mongo-template]]
==== MongoTemplate
{spring-data-mongodb}[Spring Data MongoDB] provides a {spring-data-mongodb-api}/core/MongoTemplate.html[`MongoTemplate`] class that is very similar in its design to Spring's `JdbcTemplate`.
As with `JdbcTemplate`, Spring Boot auto-configures a bean for you to inject the template, as follows:

[source,java,indent=0]
----
	import org.springframework.data.mongodb.core.MongoTemplate;
	import org.springframework.stereotype.Component;

	@Component
	public class MyBean {

		private final MongoTemplate mongoTemplate;

		public MyBean(MongoTemplate mongoTemplate) {
			this.mongoTemplate = mongoTemplate;
		}

		// ...

	}
----

See the {spring-data-mongodb-api}/core/MongoOperations.html[`MongoOperations` Javadoc] for complete details.



[[boot-features-spring-data-mongo-repositories]]
[[boot-features-spring-data-mongodb-repositories]]
==== Spring Data MongoDB Repositories
Spring Data includes repository support for MongoDB.
As with the JPA repositories discussed earlier, the basic principle is that queries are constructed automatically, based on method names.

In fact, both Spring Data JPA and Spring Data MongoDB share the same common infrastructure.
You could take the JPA example from earlier and, assuming that `City` is now a MongoDB data class rather than a JPA `@Entity`, it works in the same way, as shown in the following example:

[source,java,indent=0]
----
	package com.example.myapp.domain;

	import org.springframework.data.domain.*;
	import org.springframework.data.repository.*;

	public interface CityRepository extends Repository<City, Long> {

		Page<City> findAll(Pageable pageable);

		City findByNameAndStateAllIgnoringCase(String name, String state);

	}
----

TIP: You can customize document scanning locations by using the `@EntityScan` annotation.

TIP: For complete details of Spring Data MongoDB, including its rich object mapping technologies, refer to its {spring-data-mongodb}[reference documentation].



[[boot-features-mongo-embedded]]
==== Embedded Mongo
Spring Boot offers auto-configuration for https://github.com/flapdoodle-oss/de.flapdoodle.embed.mongo[Embedded Mongo].
To use it in your Spring Boot application, add a dependency on `de.flapdoodle.embed:de.flapdoodle.embed.mongo`.

The port that Mongo listens on can be configured by setting the configprop:spring.data.mongodb.port[] property.
To use a randomly allocated free port, use a value of 0.
The `MongoClient` created by `MongoAutoConfiguration` is automatically configured to use the randomly allocated port.

NOTE: If you do not configure a custom port, the embedded support uses a random port (rather than 27017) by default.

If you have SLF4J on the classpath, the output produced by Mongo is automatically routed to a logger named `org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongo`.

You can declare your own `IMongodConfig` and `IRuntimeConfig` beans to take control of the Mongo instance's configuration and logging routing.
The download configuration can be customized by declaring a `DownloadConfigBuilderCustomizer` bean.



[[boot-features-neo4j]]
=== Neo4j
https://neo4j.com/[Neo4j] is an open-source NoSQL graph database that uses a rich data model of nodes connected by first class relationships, which is better suited for connected big data than traditional RDBMS approaches.
Spring Boot offers several conveniences for working with Neo4j, including the `spring-boot-starter-data-neo4j` "`Starter`".



[[boot-features-connecting-to-neo4j]]
==== Connecting to a Neo4j Database
To access a Neo4j server, you can inject an auto-configured `org.neo4j.driver.Driver`.
By default, the instance tries to connect to a Neo4j server at `localhost:7687` using the Bolt protocol.
The following example shows how to inject a Neo4j `Driver` that gives you access, amongst other things, to a `Session`:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		private final Driver driver;

		@Autowired
		public MyBean(Driver driver) {
			this.driver = driver;
		}

		// ...

	}
----

You can configure various aspects of the driver using `spring.neo4j.*` properties.
The following example shows how to configure the uri and credentials to use:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  neo4j:
	    uri: "bolt://my-server:7687"
	    authentication:
	      username: "neo4j"
	      password: "secret"
----

The auto-configured `Driver` is created using `ConfigBuilder`.
To fine-tune its configuration, declare one or more `ConfigBuilderCustomizer` beans.
Each will be called in order with the `ConfigBuilder` that is used to build the `Driver`.



[[boot-features-spring-data-neo4j-repositories]]
==== Spring Data Neo4j Repositories
Spring Data includes repository support for Neo4j.
For complete details of Spring Data Neo4j, refer to the {spring-data-neo4j-docs}[reference documentation].

Spring Data Neo4j shares the common infrastructure with Spring Data JPA as many other Spring Data modules do.
You could take the JPA example from earlier and define `City` as Spring Data Neo4j `@Node` rather than JPA `@Entity` and the repository abstraction works in the same way, as shown in the following example:

[source,java,indent=0]
----
	package com.example.myapp.domain;

	import java.util.Optional;

	import org.springframework.data.neo4j.repository.*;

	public interface CityRepository extends Neo4jRepository<City, Long> {

		Optional<City> findOneByNameAndState(String name, String state);

	}
----

The `spring-boot-starter-data-neo4j` "`Starter`" enables the repository support as well as transaction management.
Spring Boot supports both classic and reactive Neo4j repositories, using the `Neo4jTemplate` or `ReactiveNeo4jTemplate` beans.
When Project Reactor is available on the classpath, the reactive style is also auto-configured.

You can customize the locations to look for repositories and entities by using `@EnableNeo4jRepositories` and `@EntityScan` respectively on a `@Configuration`-bean.

[NOTE]
====
In an application using the reactive style, a `ReactiveTransactionManager` is not auto-configured.
To enable transaction management, the following bean must be defined in your configuration:

[source,java,indent=0]
----
include::{code-examples}/neo4j/Neo4jReactiveTransactionManagerExample.java[tag=configuration]
----
====



[[boot-features-solr]]
=== Solr
https://lucene.apache.org/solr/[Apache Solr] is a search engine.
Spring Boot offers basic auto-configuration for the Solr 5 client library and the abstractions on top of it provided by https://github.com/spring-projects/spring-data-solr[Spring Data Solr].
There is a `spring-boot-starter-data-solr` "`Starter`" for collecting the dependencies in a convenient way.

NOTE: As of Spring Boot 2.3, support for Spring Data Solr has been deprecated and will be removed in a future release.



[[boot-features-connecting-to-solr]]
==== Connecting to Solr
You can inject an auto-configured `SolrClient` instance as you would any other Spring bean.
By default, the instance tries to connect to a server at `http://localhost:8983/solr`.
The following example shows how to inject a Solr bean:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		private SolrClient solr;

		@Autowired
		public MyBean(SolrClient solr) {
			this.solr = solr;
		}

		// ...

	}
----

If you add your own `@Bean` of type `SolrClient`, it replaces the default.



[[boot-features-spring-data-solr-repositories]]
==== Spring Data Solr Repositories
Spring Data includes repository support for Apache Solr.
As with the JPA repositories discussed earlier, the basic principle is that queries are automatically constructed for you based on method names.

In fact, both Spring Data JPA and Spring Data Solr share the same common infrastructure.
You could take the JPA example from earlier and, assuming that `City` is now a `@SolrDocument` class rather than a JPA `@Entity`, it works in the same way.

IP: For complete details of Spring Data Solr, refer to the {spring-data-solr-docs}[reference documentation].



[[boot-features-elasticsearch]]
=== Elasticsearch
https://www.elastic.co/products/elasticsearch[Elasticsearch] is an open source, distributed, RESTful search and analytics engine.
Spring Boot offers basic auto-configuration for Elasticsearch.

Spring Boot supports several clients:

* The official Java "Low Level" and "High Level" REST clients
* The `ReactiveElasticsearchClient` provided by Spring Data Elasticsearch

Spring Boot provides a dedicated "`Starter`", `spring-boot-starter-data-elasticsearch`.



[[boot-features-connecting-to-elasticsearch-rest]]
==== Connecting to Elasticsearch using REST clients
Elasticsearch ships https://www.elastic.co/guide/en/elasticsearch/client/java-rest/current/index.html[two different REST clients] that you can use to query a cluster: the "Low Level" client and the "High Level" client.
Spring Boot provides support for the "High Level" client, which ships with `org.elasticsearch.client:elasticsearch-rest-high-level-client`.

If you have this dependency on the classpath, Spring Boot will auto-configure and register a `RestHighLevelClient` bean that by default targets `http://localhost:9200`.
You can further tune how `RestHighLevelClient` is configured, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  elasticsearch:
	    rest:
	      uris: "https://search.example.com:9200"
	      read-timeout: "10s"
	      username: "user"
	      password: "secret"
----

You can also register an arbitrary number of beans that implement `RestClientBuilderCustomizer` for more advanced customizations.
To take full control over the registration, define a `RestClientBuilder` bean.

TIP: If your application needs access to a "Low Level" `RestClient`, you can get it by calling `client.getLowLevelClient()` on the auto-configured `RestHighLevelClient`.



[[boot-features-connecting-to-elasticsearch-reactive-rest]]
==== Connecting to Elasticsearch using Reactive REST clients
{spring-data-elasticsearch}[Spring Data Elasticsearch] ships `ReactiveElasticsearchClient` for querying Elasticsearch instances in a reactive fashion.
It is built on top of WebFlux's `WebClient`, so both `spring-boot-starter-elasticsearch` and `spring-boot-starter-webflux` dependencies are useful to enable this support.

By default, Spring Boot will auto-configure and register a `ReactiveElasticsearchClient`
bean that targets `http://localhost:9200`.
You can further tune how it is configured, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  data:
	    elasticsearch:
	      client:
	        reactive:
	          endpoints: "search.example.com:9200"
	          use-ssl: true
	          socket-timeout: "10s"
	          username: "user"
	          password: "secret"
----

If the configuration properties are not enough and you'd like to fully control the client
configuration, you can register a custom `ClientConfiguration` bean.



[[boot-features-connecting-to-elasticsearch-spring-data]]
==== Connecting to Elasticsearch by Using Spring Data
To connect to Elasticsearch, a `RestHighLevelClient` bean must be defined,
auto-configured by Spring Boot or manually provided by the application (see previous sections).
With this configuration in place, an
`ElasticsearchRestTemplate` can be injected like any other Spring bean,
as shown in the following example:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		private final ElasticsearchRestTemplate template;

		public MyBean(ElasticsearchRestTemplate template) {
			this.template = template;
		}

		// ...

	}
----

In the presence of `spring-data-elasticsearch` and the required dependencies for using a `WebClient` (typically `spring-boot-starter-webflux`), Spring Boot can also auto-configure a <<boot-features-connecting-to-elasticsearch-reactive-rest,ReactiveElasticsearchClient>> and a `ReactiveElasticsearchTemplate` as beans.
They are the reactive equivalent of the other REST clients.



[[boot-features-spring-data-elasticsearch-repositories]]
==== Spring Data Elasticsearch Repositories
Spring Data includes repository support for Elasticsearch.
As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data Elasticsearch share the same common infrastructure.
You could take the JPA example from earlier and, assuming that `City` is now an Elasticsearch `@Document` class rather than a JPA `@Entity`, it works in the same way.

TIP: For complete details of Spring Data Elasticsearch, refer to the {spring-data-elasticsearch-docs}[reference documentation].

Spring Boot supports both classic and reactive Elasticsearch repositories, using the `ElasticsearchRestTemplate` or `ReactiveElasticsearchTemplate` beans.
Most likely those beans are auto-configured by Spring Boot given the required dependencies are present.

If you wish to use your own template for backing the Elasticsearch repositories, you can add your own `ElasticsearchRestTemplate` or `ElasticsearchOperations` `@Bean`, as long as it is named `"elasticsearchTemplate"`.
Same applies to `ReactiveElasticsearchTemplate` and `ReactiveElasticsearchOperations`, with the bean name `"reactiveElasticsearchTemplate"`.

You can choose to disable the repositories support with the following property:

[source,yaml,indent=0,configprops,configblocks]
----
    spring:
      data:
        elasticsearch:
          repositories:
            enabled: false
----



[[boot-features-cassandra]]
=== Cassandra
https://cassandra.apache.org/[Cassandra] is an open source, distributed database management system designed to handle large amounts of data across many commodity servers.
Spring Boot offers auto-configuration for Cassandra and the abstractions on top of it provided by https://github.com/spring-projects/spring-data-cassandra[Spring Data Cassandra].
There is a `spring-boot-starter-data-cassandra` "`Starter`" for collecting the dependencies in a convenient way.



[[boot-features-connecting-to-cassandra]]
==== Connecting to Cassandra
You can inject an auto-configured `CassandraTemplate` or a Cassandra `CqlSession` instance as you would with any other Spring Bean.
The `spring.data.cassandra.*` properties can be used to customize the connection.
Generally, you provide `keyspace-name` and `contact-points` as well the local datacenter name, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  data:
	    cassandra:
	      keyspace-name: "mykeyspace"
	      contact-points: "cassandrahost1:9042,cassandrahost2:9042"
	      local-datacenter: "datacenter1"
----

If the port is the same for all your contact points you can use a shortcut and only specify the host names, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  data:
	    cassandra:
	      keyspace-name: "mykeyspace"
	      contact-points: "cassandrahost1,cassandrahost2"
	      local-datacenter: "datacenter1"
----

TIP: Those two examples are identical as the port default to `9042`.
If you need to configure the port, use `spring.data.cassandra.port`.

[NOTE]
====
The Cassandra driver has its own configuration infrastructure that loads an `application.conf` at the root of the classpath.

Spring Boot does not look for such a file and rather provides a number of configuration properties via the `spring.data.cassandra.*` namespace.
For more advanced driver customizations, you can register an arbitrary number of beans that implement `DriverConfigLoaderBuilderCustomizer`.
The `CqlSession` can be customized with a bean of type `CqlSessionBuilderCustomizer`.
====

NOTE: If you're using `CqlSessionBuilder` to create multiple `CqlSession` beans, keep in mind the builder is mutable so make sure to inject a fresh copy for each session.

The following code listing shows how to inject a Cassandra bean:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		private final CassandraTemplate template;

		public MyBean(CassandraTemplate template) {
			this.template = template;
		}

		// ...

	}
----

If you add your own `@Bean` of type `CassandraTemplate`, it replaces the default.



[[boot-features-spring-data-cassandra-repositories]]
==== Spring Data Cassandra Repositories
Spring Data includes basic repository support for Cassandra.
Currently, this is more limited than the JPA repositories discussed earlier and needs to annotate finder methods with `@Query`.

TIP: For complete details of Spring Data Cassandra, refer to the https://docs.spring.io/spring-data/cassandra/docs/[reference documentation].



[[boot-features-couchbase]]
=== Couchbase
https://www.couchbase.com/[Couchbase] is an open-source, distributed, multi-model NoSQL document-oriented database that is optimized for interactive applications.
Spring Boot offers auto-configuration for Couchbase and the abstractions on top of it provided by https://github.com/spring-projects/spring-data-couchbase[Spring Data Couchbase].
There are `spring-boot-starter-data-couchbase` and `spring-boot-starter-data-couchbase-reactive` "`Starters`" for collecting the dependencies in a convenient way.



[[boot-features-connecting-to-couchbase]]
==== Connecting to Couchbase
You can get a `Cluster` by adding the Couchbase SDK and some configuration.
The `spring.couchbase.*` properties can be used to customize the connection.
Generally, you provide the https://github.com/couchbaselabs/sdk-rfcs/blob/master/rfc/0011-connection-string.md[connection string], username, and password, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  couchbase:
	    connection-string: "couchbase://192.168.1.123"
	    username: "user"
	    password: "secret"
----

It is also possible to customize some of the `ClusterEnvironment` settings.
For instance, the following configuration changes the timeout to use to open a new `Bucket` and enables SSL support:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  couchbase:
	    env:
	      timeouts:
	        connect: "3s"
	      ssl:
	        key-store: "/location/of/keystore.jks"
	        key-store-password: "secret"
----

TIP: Check the `spring.couchbase.env.*` properties for more details.
To take more control, one or more `ClusterEnvironmentBuilderCustomizer` beans can be used.



[[boot-features-spring-data-couchbase-repositories]]
==== Spring Data Couchbase Repositories
Spring Data includes repository support for Couchbase.
For complete details of Spring Data Couchbase, refer to the {spring-data-couchbase-docs}[reference documentation].

You can inject an auto-configured `CouchbaseTemplate` instance as you would with any other Spring Bean, provided a `CouchbaseClientFactory` bean is available.
This happens when a `Cluster` is available, as described above, and a bucket name has been specified:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  data:
	    couchbase:
	      bucket-name: "my-bucket"
----

The following examples shows how to inject a `CouchbaseTemplate` bean:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		private final CouchbaseTemplate template;

		@Autowired
		public MyBean(CouchbaseTemplate template) {
			this.template = template;
		}

		// ...

	}
----

There are a few beans that you can define in your own configuration to override those provided by the auto-configuration:

* A `CouchbaseMappingContext` `@Bean` with a name of `couchbaseMappingContext`.
* A `CustomConversions` `@Bean` with a name of `couchbaseCustomConversions`.
* A `CouchbaseTemplate` `@Bean` with a name of `couchbaseTemplate`.

To avoid hard-coding those names in your own config, you can reuse `BeanNames` provided by Spring Data Couchbase.
For instance, you can customize the converters to use, as follows:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	public class SomeConfiguration {

		@Bean(BeanNames.COUCHBASE_CUSTOM_CONVERSIONS)
		public CustomConversions myCustomConversions() {
			return new CustomConversions(...);
		}

		// ...

	}
----



[[boot-features-ldap]]
=== LDAP
https://en.wikipedia.org/wiki/Lightweight_Directory_Access_Protocol[LDAP] (Lightweight Directory Access Protocol) is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an IP network.
Spring Boot offers auto-configuration for any compliant LDAP server as well as support for the embedded in-memory LDAP server from https://ldap.com/unboundid-ldap-sdk-for-java/[UnboundID].

LDAP abstractions are provided by https://github.com/spring-projects/spring-data-ldap[Spring Data LDAP].
There is a `spring-boot-starter-data-ldap` "`Starter`" for collecting the dependencies in a convenient way.



[[boot-features-ldap-connecting]]
==== Connecting to an LDAP Server
To connect to an LDAP server, make sure you declare a dependency on the `spring-boot-starter-data-ldap` "`Starter`" or `spring-ldap-core` and then declare the URLs of your server in your application.properties, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  ldap:
	    urls: "ldap://myserver:1235"
	    username: "admin"
	    password: "secret"
----

If you need to customize connection settings, you can use the `spring.ldap.base` and `spring.ldap.base-environment` properties.

An `LdapContextSource` is auto-configured based on these settings.
If a `DirContextAuthenticationStrategy` bean is available, it is associated to the auto-configured `LdapContextSource`.
If you need to customize it, for instance to use a `PooledContextSource`, you can still inject the auto-configured `LdapContextSource`.
Make sure to flag your customized `ContextSource` as `@Primary` so that the auto-configured `LdapTemplate` uses it.



[[boot-features-ldap-spring-data-repositories]]
==== Spring Data LDAP Repositories
Spring Data includes repository support for LDAP.
For complete details of Spring Data LDAP, refer to the https://docs.spring.io/spring-data/ldap/docs/1.0.x/reference/html/[reference documentation].

You can also inject an auto-configured `LdapTemplate` instance as you would with any other Spring Bean, as shown in the following example:


[source,java,indent=0]
----
	@Component
	public class MyBean {

		private final LdapTemplate template;

		@Autowired
		public MyBean(LdapTemplate template) {
			this.template = template;
		}

		// ...

	}
----



[[boot-features-ldap-embedded]]
==== Embedded In-memory LDAP Server
For testing purposes, Spring Boot supports auto-configuration of an in-memory LDAP server from https://ldap.com/unboundid-ldap-sdk-for-java/[UnboundID].
To configure the server, add a dependency to `com.unboundid:unboundid-ldapsdk` and declare a configprop:spring.ldap.embedded.base-dn[] property, as follows:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  ldap:
	    embedded:
	      base-dn: "dc=spring,dc=io"
----

[NOTE]
====
It is possible to define multiple base-dn values, however, since distinguished names usually contain commas, they must be defined using the correct notation.

In yaml files, you can use the yaml list notation. In properties files, you must include the index as part of the property name:

[source,yaml,indent=0,configprops,configblocks]
----
	spring.ldap.embedded.base-dn:
	  - dc=spring,dc=io
	  - dc=pivotal,dc=io
----
====

By default, the server starts on a random port and triggers the regular LDAP support.
There is no need to specify a configprop:spring.ldap.urls[] property.

If there is a `schema.ldif` file on your classpath, it is used to initialize the server.
If you want to load the initialization script from a different resource, you can also use the configprop:spring.ldap.embedded.ldif[] property.

By default, a standard schema is used to validate `LDIF` files.
You can turn off validation altogether by setting the configprop:spring.ldap.embedded.validation.enabled[] property.
If you have custom attributes, you can use configprop:spring.ldap.embedded.validation.schema[] to define your custom attribute types or object classes.



[[boot-features-influxdb]]
=== InfluxDB
https://www.influxdata.com/[InfluxDB] is an open-source time series database optimized for fast, high-availability storage and retrieval of time series data in fields such as operations monitoring, application metrics, Internet-of-Things sensor data, and real-time analytics.



[[boot-features-connecting-to-influxdb]]
==== Connecting to InfluxDB
Spring Boot auto-configures an `InfluxDB` instance, provided the `influxdb-java` client is on the classpath and the URL of the database is set, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  influx:
	    url: "https://172.0.0.1:8086"
----

If the connection to InfluxDB requires a user and password, you can set the `spring.influx.user` and `spring.influx.password` properties accordingly.

InfluxDB relies on OkHttp.
If you need to tune the http client `InfluxDB` uses behind the scenes, you can register an `InfluxDbOkHttpClientBuilderProvider` bean.



[[boot-features-caching]]
== Caching
The Spring Framework provides support for transparently adding caching to an application.
At its core, the abstraction applies caching to methods, thus reducing the number of executions based on the information available in the cache.
The caching logic is applied transparently, without any interference to the invoker.
Spring Boot auto-configures the cache infrastructure as long as caching support is enabled via the `@EnableCaching` annotation.

NOTE: Check the {spring-framework-docs}/integration.html#cache[relevant section] of the Spring Framework reference for more details.

In a nutshell, to add caching to an operation of your service add the relevant annotation to its method, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.cache.annotation.Cacheable;
	import org.springframework.stereotype.Component;

	@Component
	public class MathService {

		@Cacheable("piDecimals")
		public int computePiDecimal(int i) {
			// ...
		}

	}
----

This example demonstrates the use of caching on a potentially costly operation.
Before invoking `computePiDecimal`, the abstraction looks for an entry in the `piDecimals` cache that matches the `i` argument.
If an entry is found, the content in the cache is immediately returned to the caller, and the method is not invoked.
Otherwise, the method is invoked, and the cache is updated before returning the value.

CAUTION: You can also use the standard JSR-107 (JCache) annotations (such as `@CacheResult`) transparently.
However, we strongly advise you to not mix and match the Spring Cache and JCache annotations.

If you do not add any specific cache library, Spring Boot auto-configures a <<boot-features-caching-provider-simple,simple provider>> that uses concurrent maps in memory.
When a cache is required (such as `piDecimals` in the preceding example), this provider creates it for you.
The simple provider is not really recommended for production usage, but it is great for getting started and making sure that you understand the features.
When you have made up your mind about the cache provider to use, please make sure to read its documentation to figure out how to configure the caches that your application uses.
Nearly all providers require you to explicitly configure every cache that you use in the application.
Some offer a way to customize the default caches defined by the configprop:spring.cache.cache-names[] property.

TIP: It is also possible to transparently {spring-framework-docs}/integration.html#cache-annotations-put[update] or {spring-framework-docs}/integration.html#cache-annotations-evict[evict] data from the cache.



[[boot-features-caching-provider]]
=== Supported Cache Providers
The cache abstraction does not provide an actual store and relies on abstraction materialized by the `org.springframework.cache.Cache` and `org.springframework.cache.CacheManager` interfaces.

If you have not defined a bean of type `CacheManager` or a `CacheResolver` named `cacheResolver` (see {spring-framework-api}/cache/annotation/CachingConfigurer.html[`CachingConfigurer`]), Spring Boot tries to detect the following providers (in the indicated order):

. <<boot-features-caching-provider-generic,Generic>>
. <<boot-features-caching-provider-jcache,JCache (JSR-107)>> (EhCache 3, Hazelcast, Infinispan, and others)
. <<boot-features-caching-provider-ehcache2,EhCache 2.x>>
. <<boot-features-caching-provider-hazelcast,Hazelcast>>
. <<boot-features-caching-provider-infinispan,Infinispan>>
. <<boot-features-caching-provider-couchbase,Couchbase>>
. <<boot-features-caching-provider-redis,Redis>>
. <<boot-features-caching-provider-caffeine,Caffeine>>
. <<boot-features-caching-provider-simple,Simple>>

TIP: It is also possible to _force_ a particular cache provider by setting the configprop:spring.cache.type[] property.
Use this property if you need to <<boot-features-caching-provider-none,disable caching altogether>> in certain environment (such as tests).

TIP: Use the `spring-boot-starter-cache` "`Starter`" to quickly add basic caching dependencies.
The starter brings in `spring-context-support`.
If you add dependencies manually, you must include `spring-context-support` in order to use the JCache, EhCache 2.x, or Caffeine support.

If the `CacheManager` is auto-configured by Spring Boot, you can further tune its configuration before it is fully initialized by exposing a bean that implements the `CacheManagerCustomizer` interface.
The following example sets a flag to say that `null` values should be passed down to the underlying map:

[source,java,indent=0]
----
	@Bean
	public CacheManagerCustomizer<ConcurrentMapCacheManager> cacheManagerCustomizer() {
		return new CacheManagerCustomizer<ConcurrentMapCacheManager>() {

			@Override
			public void customize(ConcurrentMapCacheManager cacheManager) {
				cacheManager.setAllowNullValues(false);
			}

		};
	}
----

NOTE: In the preceding example, an auto-configured `ConcurrentMapCacheManager` is expected.
If that is not the case (either you provided your own config or a different cache provider was auto-configured), the customizer is not invoked at all.
You can have as many customizers as you want, and you can also order them by using `@Order` or `Ordered`.



[[boot-features-caching-provider-generic]]
==== Generic
Generic caching is used if the context defines _at least_ one `org.springframework.cache.Cache` bean.
A `CacheManager` wrapping all beans of that type is created.



[[boot-features-caching-provider-jcache]]
==== JCache (JSR-107)
https://jcp.org/en/jsr/detail?id=107[JCache] is bootstrapped through the presence of a `javax.cache.spi.CachingProvider` on the classpath (that is, a JSR-107 compliant caching library exists on the classpath), and the `JCacheCacheManager` is provided by the `spring-boot-starter-cache` "`Starter`".
Various compliant libraries are available, and Spring Boot provides dependency management for Ehcache 3, Hazelcast, and Infinispan.
Any other compliant library can be added as well.

It might happen that more than one provider is present, in which case the provider must be explicitly specified.
Even if the JSR-107 standard does not enforce a standardized way to define the location of the configuration file, Spring Boot does its best to accommodate setting a cache with implementation details, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
    # Only necessary if more than one provider is present
	spring:
	  cache:
	    jcache:
	      provider: "com.acme.MyCachingProvider"
	      config: "classpath:acme.xml"
----

NOTE: When a cache library offers both a native implementation and JSR-107 support, Spring Boot prefers the JSR-107 support, so that the same features are available if you switch to a different JSR-107 implementation.

TIP: Spring Boot has <<boot-features-hazelcast,general support for Hazelcast>>.
If a single `HazelcastInstance` is available, it is automatically reused for the `CacheManager` as well, unless the configprop:spring.cache.jcache.config[] property is specified.

There are two ways to customize the underlying `javax.cache.cacheManager`:

* Caches can be created on startup by setting the configprop:spring.cache.cache-names[] property.
  If a custom `javax.cache.configuration.Configuration` bean is defined, it is used to customize them.
* `org.springframework.boot.autoconfigure.cache.JCacheManagerCustomizer` beans are invoked with the reference of the `CacheManager` for full customization.

TIP: If a standard `javax.cache.CacheManager` bean is defined, it is wrapped automatically in an `org.springframework.cache.CacheManager` implementation that the abstraction expects.
No further customization is applied to it.



[[boot-features-caching-provider-ehcache2]]
==== EhCache 2.x
https://www.ehcache.org/[EhCache] 2.x is used if a file named `ehcache.xml` can be found at the root of the classpath.
If EhCache 2.x is found, the `EhCacheCacheManager` provided by the `spring-boot-starter-cache` "`Starter`" is used to bootstrap the cache manager.
An alternate configuration file can be provided as well, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  cache:
	    ehcache:
	      config: "classpath:config/another-config.xml"
----



[[boot-features-caching-provider-hazelcast]]
==== Hazelcast
Spring Boot has <<boot-features-hazelcast,general support for Hazelcast>>.
If a `HazelcastInstance` has been auto-configured, it is automatically wrapped in a `CacheManager`.



[[boot-features-caching-provider-infinispan]]
==== Infinispan
https://infinispan.org/[Infinispan] has no default configuration file location, so it must be specified explicitly.
Otherwise, the default bootstrap is used.

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  cache:
	    infinispan:
	      config: "infinispan.xml"
----

Caches can be created on startup by setting the configprop:spring.cache.cache-names[] property.
If a custom `ConfigurationBuilder` bean is defined, it is used to customize the caches.

NOTE: The support of Infinispan in Spring Boot is restricted to the embedded mode and is quite basic.
If you want more options, you should use the official Infinispan Spring Boot starter instead.
See https://github.com/infinispan/infinispan-spring-boot[Infinispan's documentation] for more details.



[[boot-features-caching-provider-couchbase]]
==== Couchbase
If Spring Data Couchbase is available and Couchbase is <<boot-features-couchbase,configured>>, a `CouchbaseCacheManager` is auto-configured.
It is possible to create additional caches on startup by setting the configprop:spring.cache.cache-names[] property and cache defaults can be configured by using `spring.cache.couchbase.*` properties.
For instance, the following configuration creates `cache1` and `cache2` caches with an entry _expiration_ of 10 minutes:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  cache:
	    cache-names: "cache1,cache2"
        couchbase:
          expiration: "10m"
----

If you need more control over the configuration, consider registering a `CouchbaseCacheManagerBuilderCustomizer` bean.
The following example shows a customizer that configures a specific entry expiration for `cache1` and `cache2`:

[source,java,indent=0]
----
include::{code-examples}/cache/CouchbaseCacheManagerCustomizationExample.java[tag=configuration]
----



[[boot-features-caching-provider-redis]]
==== Redis
If https://redis.io/[Redis] is available and configured, a `RedisCacheManager` is auto-configured.
It is possible to create additional caches on startup by setting the configprop:spring.cache.cache-names[] property and cache defaults can be configured by using `spring.cache.redis.*` properties.
For instance, the following configuration creates `cache1` and `cache2` caches with a _time to live_ of 10 minutes:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  cache:
	    cache-names: "cache1,cache2"
	    redis:
	      time-to-live: "10m"
----

NOTE: By default, a key prefix is added so that, if two separate caches use the same key, Redis does not have overlapping keys and cannot return invalid values.
We strongly recommend keeping this setting enabled if you create your own `RedisCacheManager`.

TIP: You can take full control of the default configuration by adding a `RedisCacheConfiguration` `@Bean` of your own.
This can be useful if you're looking for customizing the default serialization strategy.

If you need more control over the configuration, consider registering a `RedisCacheManagerBuilderCustomizer` bean.
The following example shows a customizer that configures a specific time to live for `cache1` and `cache2`:

[source,java,indent=0]
----
include::{code-examples}/cache/RedisCacheManagerCustomizationExample.java[tag=configuration]
----



[[boot-features-caching-provider-caffeine]]
==== Caffeine
https://github.com/ben-manes/caffeine[Caffeine] is a Java 8 rewrite of Guava's cache that supersedes support for Guava.
If Caffeine is present, a `CaffeineCacheManager` (provided by the `spring-boot-starter-cache` "`Starter`") is auto-configured.
Caches can be created on startup by setting the configprop:spring.cache.cache-names[] property and can be customized by one of the following (in the indicated order):

. A cache spec defined by `spring.cache.caffeine.spec`
. A `com.github.benmanes.caffeine.cache.CaffeineSpec` bean is defined
. A `com.github.benmanes.caffeine.cache.Caffeine` bean is defined

For instance, the following configuration creates `cache1` and `cache2` caches with a maximum size of 500 and a _time to live_ of 10 minutes

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  cache:
	    cache-names: "cache1,cache2"
	    caffeine:
	      spec: "maximumSize=500,expireAfterAccess=600s"
----

If a `com.github.benmanes.caffeine.cache.CacheLoader` bean is defined, it is automatically associated to the `CaffeineCacheManager`.
Since the `CacheLoader` is going to be associated with _all_ caches managed by the cache manager, it must be defined as `CacheLoader<Object, Object>`.
The auto-configuration ignores any other generic type.



[[boot-features-caching-provider-simple]]
==== Simple
If none of the other providers can be found, a simple implementation using a `ConcurrentHashMap` as the cache store is configured.
This is the default if no caching library is present in your application.
By default, caches are created as needed, but you can restrict the list of available caches by setting the `cache-names` property.
For instance, if you want only `cache1` and `cache2` caches, set the `cache-names` property as follows:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  cache:
	    cache-names: "cache1,cache2"
----

If you do so and your application uses a cache not listed, then it fails at runtime when the cache is needed, but not on startup.
This is similar to the way the "real" cache providers behave if you use an undeclared cache.



[[boot-features-caching-provider-none]]
==== None
When `@EnableCaching` is present in your configuration, a suitable cache configuration is expected as well.
If you need to disable caching altogether in certain environments, force the cache type to `none` to use a no-op implementation, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  cache:
	    type: "none"
----



[[boot-features-messaging]]
== Messaging
The Spring Framework provides extensive support for integrating with messaging systems, from simplified use of the JMS API using `JmsTemplate` to a complete infrastructure to receive messages asynchronously.
Spring AMQP provides a similar feature set for the Advanced Message Queuing Protocol.
Spring Boot also provides auto-configuration options for `RabbitTemplate` and RabbitMQ.
Spring WebSocket natively includes support for STOMP messaging, and Spring Boot has support for that through starters and a small amount of auto-configuration.
Spring Boot also has support for Apache Kafka.



[[boot-features-jms]]
=== JMS
The `javax.jms.ConnectionFactory` interface provides a standard method of creating a `javax.jms.Connection` for interacting with a JMS broker.
Although Spring needs a `ConnectionFactory` to work with JMS, you generally need not use it directly yourself and can instead rely on higher level messaging abstractions.
(See the {spring-framework-docs}/integration.html#jms[relevant section] of the Spring Framework reference documentation for details.)
Spring Boot also auto-configures the necessary infrastructure to send and receive messages.



[[boot-features-activemq]]
==== ActiveMQ Support
When https://activemq.apache.org/[ActiveMQ] is available on the classpath, Spring Boot can also configure a `ConnectionFactory`.
If the broker is present, an embedded broker is automatically started and configured (provided no broker URL is specified through configuration).

NOTE: If you use `spring-boot-starter-activemq`, the necessary dependencies to connect or embed an ActiveMQ instance are provided, as is the Spring infrastructure to integrate with JMS.

ActiveMQ configuration is controlled by external configuration properties in `+spring.activemq.*+`.
For example, you might declare the following section in `application.properties`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  activemq:
	    broker-url: "tcp://192.168.1.210:9876"
	    user: "admin"
	    password: "secret"
----

By default, a `CachingConnectionFactory` wraps the native `ConnectionFactory` with sensible settings that you can control by external configuration properties in `+spring.jms.*+`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  jms:
	    cache:
	      session-cache-size: 5
----

If you'd rather use native pooling, you can do so by adding a dependency to `org.messaginghub:pooled-jms` and configuring the `JmsPoolConnectionFactory` accordingly, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  activemq:
	    pool:
	      enabled: true
	      max-connections: 50
----

TIP: See {spring-boot-autoconfigure-module-code}/jms/activemq/ActiveMQProperties.java[`ActiveMQProperties`] for more of the supported options.
You can also register an arbitrary number of beans that implement `ActiveMQConnectionFactoryCustomizer` for more advanced customizations.

By default, ActiveMQ creates a destination if it does not yet exist so that destinations are resolved against their provided names.



[[boot-features-artemis]]
==== ActiveMQ Artemis Support
Spring Boot can auto-configure a `ConnectionFactory` when it detects that https://activemq.apache.org/components/artemis/[ActiveMQ Artemis] is available on the classpath.
If the broker is present, an embedded broker is automatically started and configured (unless the mode property has been explicitly set).
The supported modes are `embedded` (to make explicit that an embedded broker is required and that an error should occur if the broker is not available on the classpath) and `native` (to connect to a broker using the `netty` transport protocol).
When the latter is configured, Spring Boot configures a `ConnectionFactory` that connects to a broker running on the local machine with the default settings.

NOTE: If you use `spring-boot-starter-artemis`, the necessary dependencies to connect to an existing ActiveMQ Artemis instance are provided, as well as the Spring infrastructure to integrate with JMS.
Adding `org.apache.activemq:artemis-jms-server` to your application lets you use embedded mode.

ActiveMQ Artemis configuration is controlled by external configuration properties in `+spring.artemis.*+`.
For example, you might declare the following section in `application.properties`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  artemis:
	    mode: native
	    host: "192.168.1.210"
	    port: 9876
	    user: "admin"
	    password: "secret"
----

When embedding the broker, you can choose if you want to enable persistence and list the destinations that should be made available.
These can be specified as a comma-separated list to create them with the default options, or you can define bean(s) of type `org.apache.activemq.artemis.jms.server.config.JMSQueueConfiguration` or `org.apache.activemq.artemis.jms.server.config.TopicConfiguration`, for advanced queue and topic configurations, respectively.

By default, a `CachingConnectionFactory` wraps the native `ConnectionFactory` with sensible settings that you can control by external configuration properties in `+spring.jms.*+`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  jms:
	    cache:
	      session-cache-size: 5
----

If you'd rather use native pooling, you can do so by adding a dependency to `org.messaginghub:pooled-jms` and configuring the `JmsPoolConnectionFactory` accordingly, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  artemis:
	    pool:
	      enabled: true
	      max-connections: 50
----

See {spring-boot-autoconfigure-module-code}/jms/artemis/ArtemisProperties.java[`ArtemisProperties`] for more supported options.

No JNDI lookup is involved, and destinations are resolved against their names, using either the `name` attribute in the Artemis configuration or the names provided through configuration.



[[boot-features-jms-jndi]]
==== Using a JNDI ConnectionFactory
If you are running your application in an application server, Spring Boot tries to locate a JMS `ConnectionFactory` by using JNDI.
By default, the `java:/JmsXA` and `java:/XAConnectionFactory` location are checked.
You can use the configprop:spring.jms.jndi-name[] property if you need to specify an alternative location, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  jms:
	    jndi-name: "java:/MyConnectionFactory"
----



[[boot-features-using-jms-sending]]
==== Sending a Message
Spring's `JmsTemplate` is auto-configured, and you can autowire it directly into your own beans, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.jms.core.JmsTemplate;
	import org.springframework.stereotype.Component;

	@Component
	public class MyBean {

		private final JmsTemplate jmsTemplate;

		@Autowired
		public MyBean(JmsTemplate jmsTemplate) {
			this.jmsTemplate = jmsTemplate;
		}

		// ...

	}
----

NOTE: {spring-framework-api}/jms/core/JmsMessagingTemplate.html[`JmsMessagingTemplate`] can be injected in a similar manner.
If a `DestinationResolver` or a `MessageConverter` bean is defined, it is associated automatically to the auto-configured `JmsTemplate`.



[[boot-features-using-jms-receiving]]
==== Receiving a Message
When the JMS infrastructure is present, any bean can be annotated with `@JmsListener` to create a listener endpoint.
If no `JmsListenerContainerFactory` has been defined, a default one is configured automatically.
If a `DestinationResolver` or a `MessageConverter` beans is defined, it is associated automatically to the default factory.

By default, the default factory is transactional.
If you run in an infrastructure where a `JtaTransactionManager` is present, it is associated to the listener container by default.
If not, the `sessionTransacted` flag is enabled.
In that latter scenario, you can associate your local data store transaction to the processing of an incoming message by adding `@Transactional` on your listener method (or a delegate thereof).
This ensures that the incoming message is acknowledged, once the local transaction has completed.
This also includes sending response messages that have been performed on the same JMS session.

The following component creates a listener endpoint on the `someQueue` destination:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		@JmsListener(destination = "someQueue")
		public void processMessage(String content) {
			// ...
		}

	}
----

TIP: See {spring-framework-api}/jms/annotation/EnableJms.html[the Javadoc of `@EnableJms`] for more details.

If you need to create more `JmsListenerContainerFactory` instances or if you want to override the default, Spring Boot provides a `DefaultJmsListenerContainerFactoryConfigurer` that you can use to initialize a `DefaultJmsListenerContainerFactory` with the same settings as the one that is auto-configured.

For instance, the following example exposes another factory that uses a specific `MessageConverter`:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	static class JmsConfiguration {

		@Bean
		public DefaultJmsListenerContainerFactory myFactory(
				DefaultJmsListenerContainerFactoryConfigurer configurer) {
			DefaultJmsListenerContainerFactory factory =
					new DefaultJmsListenerContainerFactory();
			configurer.configure(factory, connectionFactory());
			factory.setMessageConverter(myMessageConverter());
			return factory;
		}

	}
----

Then you can use the factory in any `@JmsListener`-annotated method as follows:

[source,java,indent=0]
[subs="verbatim,quotes"]
----
	@Component
	public class MyBean {

		@JmsListener(destination = "someQueue", **containerFactory="myFactory"**)
		public void processMessage(String content) {
			// ...
		}

	}
----



[[boot-features-amqp]]
=== AMQP
The Advanced Message Queuing Protocol (AMQP) is a platform-neutral, wire-level protocol for message-oriented middleware.
The Spring AMQP project applies core Spring concepts to the development of AMQP-based messaging solutions.
Spring Boot offers several conveniences for working with AMQP through RabbitMQ, including the `spring-boot-starter-amqp` "`Starter`".



[[boot-features-rabbitmq]]
==== RabbitMQ support
https://www.rabbitmq.com/[RabbitMQ] is a lightweight, reliable, scalable, and portable message broker based on the AMQP protocol.
Spring uses `RabbitMQ` to communicate through the AMQP protocol.

RabbitMQ configuration is controlled by external configuration properties in `+spring.rabbitmq.*+`.
For example, you might declare the following section in `application.properties`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  rabbitmq:
	    host: "localhost"
	    port: 5672
	    username: "admin"
	    password: "secret"
----

Alternatively, you could configure the same connection using the `addresses` attribute:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  rabbitmq:
	    addresses: "amqp://admin:secret@localhost"
----

NOTE: When specifying addresses that way, the `host` and `port` properties are ignored.
If the address uses the `amqps` protocol, SSL support is enabled automatically.

If a `ConnectionNameStrategy` bean exists in the context, it will be automatically used to name connections created by the auto-configured `ConnectionFactory`.
See {spring-boot-autoconfigure-module-code}/amqp/RabbitProperties.java[`RabbitProperties`] for more of the supported options.

TIP: See https://spring.io/blog/2010/06/14/understanding-amqp-the-protocol-used-by-rabbitmq/[Understanding AMQP, the protocol used by RabbitMQ] for more details.



[[boot-features-using-amqp-sending]]
==== Sending a Message
Spring's `AmqpTemplate` and `AmqpAdmin` are auto-configured, and you can autowire them directly into your own beans, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.amqp.core.AmqpAdmin;
	import org.springframework.amqp.core.AmqpTemplate;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.stereotype.Component;

	@Component
	public class MyBean {

		private final AmqpAdmin amqpAdmin;
		private final AmqpTemplate amqpTemplate;

		@Autowired
		public MyBean(AmqpAdmin amqpAdmin, AmqpTemplate amqpTemplate) {
			this.amqpAdmin = amqpAdmin;
			this.amqpTemplate = amqpTemplate;
		}

		// ...

	}
----

NOTE: {spring-amqp-api}/rabbit/core/RabbitMessagingTemplate.html[`RabbitMessagingTemplate`] can be injected in a similar manner.
If a `MessageConverter` bean is defined, it is associated automatically to the auto-configured `AmqpTemplate`.

If necessary, any `org.springframework.amqp.core.Queue` that is defined as a bean is automatically used to declare a corresponding queue on the RabbitMQ instance.

To retry operations, you can enable retries on the `AmqpTemplate` (for example, in the event that the broker connection is lost):

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  rabbitmq:
	    template:
	      retry:
	        enabled: true
	        initial-interval: "2s"
----

Retries are disabled by default.
You can also customize the `RetryTemplate` programmatically by declaring a `RabbitRetryTemplateCustomizer` bean.

If you need to create more `RabbitTemplate` instances or if you want to override the default, Spring Boot provides a `RabbitTemplateConfigurer` bean that you can use to initialize a `RabbitTemplate` with the same settings as the factories used by the auto-configuration.



[[boot-features-using-amqp-receiving]]
==== Receiving a Message
When the Rabbit infrastructure is present, any bean can be annotated with `@RabbitListener` to create a listener endpoint.
If no `RabbitListenerContainerFactory` has been defined, a default `SimpleRabbitListenerContainerFactory` is automatically configured and you can switch to a direct container using the configprop:spring.rabbitmq.listener.type[] property.
If a `MessageConverter` or a `MessageRecoverer` bean is defined, it is automatically associated with the default factory.

The following sample component creates a listener endpoint on the `someQueue` queue:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		@RabbitListener(queues = "someQueue")
		public void processMessage(String content) {
			// ...
		}

	}
----

TIP: See {spring-amqp-api}/rabbit/annotation/EnableRabbit.html[the Javadoc of `@EnableRabbit`] for more details.

If you need to create more `RabbitListenerContainerFactory` instances or if you want to override the default, Spring Boot provides a `SimpleRabbitListenerContainerFactoryConfigurer` and a `DirectRabbitListenerContainerFactoryConfigurer` that you can use to initialize a `SimpleRabbitListenerContainerFactory` and a `DirectRabbitListenerContainerFactory` with the same settings as the factories used by the auto-configuration.

TIP: It does not matter which container type you chose.
Those two beans are exposed by the auto-configuration.

For instance, the following configuration class exposes another factory that uses a specific `MessageConverter`:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	static class RabbitConfiguration {

		@Bean
		public SimpleRabbitListenerContainerFactory myFactory(
				SimpleRabbitListenerContainerFactoryConfigurer configurer) {
			SimpleRabbitListenerContainerFactory factory =
					new SimpleRabbitListenerContainerFactory();
			configurer.configure(factory, connectionFactory);
			factory.setMessageConverter(myMessageConverter());
			return factory;
		}

	}
----

Then you can use the factory in any `@RabbitListener`-annotated method, as follows:

[source,java,indent=0]
[subs="verbatim,quotes"]
----
	@Component
	public class MyBean {

		@RabbitListener(queues = "someQueue", **containerFactory="myFactory"**)
		public void processMessage(String content) {
			// ...
		}

	}
----

You can enable retries to handle situations where your listener throws an exception.
By default, `RejectAndDontRequeueRecoverer` is used, but you can define a `MessageRecoverer` of your own.
When retries are exhausted, the message is rejected and either dropped or routed to a dead-letter exchange if the broker is configured to do so.
By default, retries are disabled.
You can also customize the `RetryTemplate` programmatically by declaring a `RabbitRetryTemplateCustomizer` bean.

IMPORTANT: By default, if retries are disabled and the listener throws an exception, the delivery is retried indefinitely.
You can modify this behavior in two ways: Set the `defaultRequeueRejected` property to `false` so that zero re-deliveries are attempted or throw an `AmqpRejectAndDontRequeueException` to signal the message should be rejected.
The latter is the mechanism used when retries are enabled and the maximum number of delivery attempts is reached.



[[boot-features-kafka]]
=== Apache Kafka Support
https://kafka.apache.org/[Apache Kafka] is supported by providing auto-configuration of the `spring-kafka` project.

Kafka configuration is controlled by external configuration properties in `spring.kafka.*`.
For example, you might declare the following section in `application.properties`:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  kafka:
	    bootstrap-servers: "localhost:9092"
	    consumer:
	      group-id: "myGroup"
----

TIP: To create a topic on startup, add a bean of type `NewTopic`.
If the topic already exists, the bean is ignored.

See {spring-boot-autoconfigure-module-code}/kafka/KafkaProperties.java[`KafkaProperties`] for more supported options.



[[boot-features-kafka-sending-a-message]]
==== Sending a Message
Spring's `KafkaTemplate` is auto-configured, and you can autowire it directly in your own beans, as shown in the following example:

[source,java,indent=0]
----
@Component
public class MyBean {

	private final KafkaTemplate kafkaTemplate;

	@Autowired
	public MyBean(KafkaTemplate kafkaTemplate) {
		this.kafkaTemplate = kafkaTemplate;
	}

	// ...

}
----

NOTE: If the property configprop:spring.kafka.producer.transaction-id-prefix[] is defined, a `KafkaTransactionManager` is automatically configured.
Also, if a `RecordMessageConverter` bean is defined, it is automatically associated to the auto-configured `KafkaTemplate`.



[[boot-features-kafka-receiving-a-message]]
==== Receiving a Message
When the Apache Kafka infrastructure is present, any bean can be annotated with `@KafkaListener` to create a listener endpoint.
If no `KafkaListenerContainerFactory` has been defined, a default one is automatically configured with keys defined in `spring.kafka.listener.*`.

The following component creates a listener endpoint on the `someTopic` topic:

[source,java,indent=0]
----
	@Component
	public class MyBean {

		@KafkaListener(topics = "someTopic")
		public void processMessage(String content) {
			// ...
		}

	}
----

If a `KafkaTransactionManager` bean is defined, it is automatically associated to the container factory.
Similarly, if a `RecordFilterStrategy`, `ErrorHandler`, `AfterRollbackProcessor` or `ConsumerAwareRebalanceListener` bean is defined, it is automatically associated to the default factory.

Depending on the listener type, a `RecordMessageConverter` or `BatchMessageConverter` bean is associated to the default factory.
If only a `RecordMessageConverter` bean is present for a batch listener, it is wrapped in a `BatchMessageConverter`.

TIP: A custom `ChainedKafkaTransactionManager` must be marked `@Primary` as it usually references the auto-configured `KafkaTransactionManager` bean.



[[boot-features-kafka-streams]]
==== Kafka Streams
Spring for Apache Kafka provides a factory bean to create a `StreamsBuilder` object and manage the lifecycle of its streams.
Spring Boot auto-configures the required `KafkaStreamsConfiguration` bean as long as `kafka-streams` is on the classpath and Kafka Streams is enabled via the `@EnableKafkaStreams` annotation.

Enabling Kafka Streams means that the application id and bootstrap servers must be set.
The former can be configured using `spring.kafka.streams.application-id`, defaulting to `spring.application.name` if not set.
The latter can be set globally or specifically overridden only for streams.

Several additional properties are available using dedicated properties; other arbitrary Kafka properties can be set using the `spring.kafka.streams.properties` namespace.
See also <<boot-features-kafka-extra-props>> for more information.

To use the factory bean, wire `StreamsBuilder` into your `@Bean` as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/kafka/KafkaStreamsBeanExample.java[tag=configuration]
----

By default, the streams managed by the `StreamBuilder` object it creates are started automatically.
You can customize this behaviour using the configprop:spring.kafka.streams.auto-startup[] property.



[[boot-features-kafka-extra-props]]
==== Additional Kafka Properties
The properties supported by auto configuration are shown in <<appendix-application-properties.adoc#common-application-properties>>.
Note that, for the most part, these properties (hyphenated or camelCase) map directly to the Apache Kafka dotted properties.
Refer to the Apache Kafka documentation for details.

The first few of these properties apply to all components (producers, consumers, admins, and streams) but can be specified at the component level if you wish to use different values.
Apache Kafka designates properties with an importance of HIGH, MEDIUM, or LOW.
Spring Boot auto-configuration supports all HIGH importance properties, some selected MEDIUM and LOW properties, and any properties that do not have a default value.

Only a subset of the properties supported by Kafka are available directly through the `KafkaProperties` class.
If you wish to configure the producer or consumer with additional properties that are not directly supported, use the following properties:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  kafka:
	    properties:
	      "[prop.one]": "first"
	    admin:
	      properties:
	        "[prop.two]": "second"
	    consumer:
	      properties:
	        "[prop.three]": "third"
	    producer:
	      properties:
	        "[prop.four]": "fourth"
	    streams:
	      properties:
	        "[prop.five]": "fifth"
----

This sets the common `prop.one` Kafka property to `first` (applies to producers, consumers and admins), the `prop.two` admin property to `second`, the `prop.three` consumer property to `third`, the `prop.four` producer property to `fourth` and the `prop.five` streams property to `fifth`.

You can also configure the Spring Kafka `JsonDeserializer` as follows:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  kafka:
	    consumer:
	      value-deserializer: "org.springframework.kafka.support.serializer.JsonDeserializer"
	      properties:
	        "[spring.json.value.default.type]": "com.example.Invoice"
	        "[spring.json.trusted.packages]": "com.example,org.acme"
----

Similarly, you can disable the `JsonSerializer` default behavior of sending type information in headers:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  kafka:
	    producer:
	      value-serializer: "org.springframework.kafka.support.serializer.JsonSerializer"
	      properties:
	        "[spring.json.add.type.headers]": false
----

IMPORTANT: Properties set in this way override any configuration item that Spring Boot explicitly supports.



[[boot-features-embedded-kafka]]
==== Testing with Embedded Kafka
Spring for Apache Kafka provides a convenient way to test projects with an embedded Apache Kafka broker.
To use this feature, annotate a test class with `@EmbeddedKafka` from the `spring-kafka-test` module.
For more information, please see the Spring for Apache Kafka {spring-kafka-docs}#embedded-kafka-annotation[reference manual].

To make Spring Boot auto-configuration work with the aforementioned embedded Apache Kafka broker, you need to remap a system property for embedded broker addresses (populated by the `EmbeddedKafkaBroker`) into the Spring Boot configuration property for Apache Kafka.
There are several ways to do that:

* Provide a system property to map embedded broker addresses into configprop:spring.kafka.bootstrap-servers[] in the test class:

[source,java,indent=0]
----
	static {
	    System.setProperty(EmbeddedKafkaBroker.BROKER_LIST_PROPERTY, "spring.kafka.bootstrap-servers");
	}
----

* Configure a property name on the `@EmbeddedKafka` annotation:

[source,java,indent=0]
----
	@EmbeddedKafka(topics = "someTopic",
	        bootstrapServersProperty = "spring.kafka.bootstrap-servers")
----

* Use a placeholder in configuration properties:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  kafka:
	    bootstrap-servers: "${spring.embedded.kafka.brokers}"
----



[[boot-features-resttemplate]]
== Calling REST Services with RestTemplate
If you need to call remote REST services from your application, you can use the Spring Framework's {spring-framework-api}/web/client/RestTemplate.html[`RestTemplate`] class.
Since `RestTemplate` instances often need to be customized before being used, Spring Boot does not provide any single auto-configured `RestTemplate` bean.
It does, however, auto-configure a `RestTemplateBuilder`, which can be used to create `RestTemplate` instances when needed.
The auto-configured `RestTemplateBuilder` ensures that sensible `HttpMessageConverters` are applied to `RestTemplate` instances.

The following code shows a typical example:

[source,java,indent=0]
----
	@Service
	public class MyService {

		private final RestTemplate restTemplate;

		public MyService(RestTemplateBuilder restTemplateBuilder) {
			this.restTemplate = restTemplateBuilder.build();
		}

		public Details someRestCall(String name) {
			return this.restTemplate.getForObject("/{name}/details", Details.class, name);
		}

	}
----

TIP: `RestTemplateBuilder` includes a number of useful methods that can be used to quickly configure a `RestTemplate`.
For example, to add BASIC auth support, you can use `builder.basicAuthentication("user", "password").build()`.



[[boot-features-resttemplate-customization]]
=== RestTemplate Customization
There are three main approaches to `RestTemplate` customization, depending on how broadly you want the customizations to apply.

To make the scope of any customizations as narrow as possible, inject the auto-configured `RestTemplateBuilder` and then call its methods as required.
Each method call returns a new `RestTemplateBuilder` instance, so the customizations only affect this use of the builder.

To make an application-wide, additive customization, use a `RestTemplateCustomizer` bean.
All such beans are automatically registered with the auto-configured `RestTemplateBuilder` and are applied to any templates that are built with it.

The following example shows a customizer that configures the use of a proxy for all hosts except `192.168.0.5`:

[source,java,indent=0]
----
include::{code-examples}/web/client/RestTemplateProxyCustomizationExample.java[tag=customizer]
----

Finally, you can also create your own `RestTemplateBuilder` bean.
To prevent switching off the auto-configuration of a `RestTemplateBuilder` and prevent any `RestTemplateCustomizer` beans from being used, make sure to configure your custom instance with a `RestTemplateBuilderConfigurer`.
The following example exposes a `RestTemplateBuilder` with what Spring Boot would auto-configure, except that custom connect and read timeouts are also specified:

[source,java,indent=0]
----
include::{code-examples}/web/client/RestTemplateBuilderCustomizationExample.java[tag=customizer]
----

The most extreme (and rarely used) option is to create your own `RestTemplateBuilder` bean without using a configurer.
Doing so switches off the auto-configuration of a `RestTemplateBuilder` and prevents any `RestTemplateCustomizer` beans from being used.



[[boot-features-webclient]]
== Calling REST Services with WebClient
If you have Spring WebFlux on your classpath, you can also choose to use `WebClient` to call remote REST services.
Compared to `RestTemplate`, this client has a more functional feel and is fully reactive.
You can learn more about the `WebClient` in the dedicated {spring-framework-docs}/web-reactive.html#webflux-client[section in the Spring Framework docs].

Spring Boot creates and pre-configures a `WebClient.Builder` for you; it is strongly advised to inject it in your components and use it to create `WebClient` instances.
Spring Boot is configuring that builder to share HTTP resources, reflect codecs setup in the same fashion as the server ones (see <<boot-features-webflux-httpcodecs,WebFlux HTTP codecs auto-configuration>>), and more.

The following code shows a typical example:

[source,java,indent=0]
----
	@Service
	public class MyService {

		private final WebClient webClient;

		public MyService(WebClient.Builder webClientBuilder) {
			this.webClient = webClientBuilder.baseUrl("https://example.org").build();
		}

		public Mono<Details> someRestCall(String name) {
			return this.webClient.get().uri("/{name}/details", name)
							.retrieve().bodyToMono(Details.class);
		}

	}
----



[[boot-features-webclient-runtime]]
=== WebClient Runtime
Spring Boot will auto-detect which `ClientHttpConnector` to use to drive `WebClient`, depending on the libraries available on the application classpath.
For now, Reactor Netty and Jetty RS client are supported.

The `spring-boot-starter-webflux` starter depends on `io.projectreactor.netty:reactor-netty` by default, which brings both server and client implementations.
If you choose to use Jetty as a reactive server instead, you should add a dependency on the Jetty Reactive HTTP client library, `org.eclipse.jetty:jetty-reactive-httpclient`.
Using the same technology for server and client has it advantages, as it will automatically share HTTP resources between client and server.

Developers can override the resource configuration for Jetty and Reactor Netty by providing a custom `ReactorResourceFactory` or `JettyResourceFactory` bean - this will be applied to both clients and servers.

If you wish to override that choice for the client, you can define your own `ClientHttpConnector` bean and have full control over the client configuration.

You can learn more about the {spring-framework-docs}/web-reactive.html#webflux-client-builder[`WebClient` configuration options in the Spring Framework reference documentation].



[[boot-features-webclient-customization]]
=== WebClient Customization
There are three main approaches to `WebClient` customization, depending on how broadly you want the customizations to apply.

To make the scope of any customizations as narrow as possible, inject the auto-configured `WebClient.Builder` and then call its methods as required.
`WebClient.Builder` instances are stateful: Any change on the builder is reflected in all clients subsequently created with it.
If you want to create several clients with the same builder, you can also consider cloning the builder with `WebClient.Builder other = builder.clone();`.

To make an application-wide, additive customization to all `WebClient.Builder` instances, you can declare `WebClientCustomizer` beans and change the `WebClient.Builder` locally at the point of injection.

Finally, you can fall back to the original API and use `WebClient.create()`.
In that case, no auto-configuration or `WebClientCustomizer` is applied.



[[boot-features-validation]]
== Validation
The method validation feature supported by Bean Validation 1.1 is automatically enabled as long as a JSR-303 implementation (such as Hibernate validator) is on the classpath.
This lets bean methods be annotated with `javax.validation` constraints on their parameters and/or on their return value.
Target classes with such annotated methods need to be annotated with the `@Validated` annotation at the type level for their methods to be searched for inline constraint annotations.

For instance, the following service triggers the validation of the first argument, making sure its size is between 8 and 10:

[source,java,indent=0]
----
	@Service
	@Validated
	public class MyBean {

		public Archive findByCodeAndAuthor(@Size(min = 8, max = 10) String code,
				Author author) {
			...
		}

	}
----



[[boot-features-email]]
== Sending Email
The Spring Framework provides an abstraction for sending email by using the `JavaMailSender` interface, and Spring Boot provides auto-configuration for it as well as a starter module.

TIP: See the {spring-framework-docs}/integration.html#mail[reference documentation] for a detailed explanation of how you can use `JavaMailSender`.

If `spring.mail.host` and the relevant libraries (as defined by `spring-boot-starter-mail`) are available, a default `JavaMailSender` is created if none exists.
The sender can be further customized by configuration items from the `spring.mail` namespace.
See {spring-boot-autoconfigure-module-code}/mail/MailProperties.java[`MailProperties`] for more details.

In particular, certain default timeout values are infinite, and you may want to change that to avoid having a thread blocked by an unresponsive mail server, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  mail:
	    properties:
	      "[mail.smtp.connectiontimeout]": 5000
	      "[mail.smtp.timeout]": 3000
	      "[mail.smtp.writetimeout]": 5000
----

It is also possible to configure a `JavaMailSender` with an existing `Session` from JNDI:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  mail:
	    jndi-name: "mail/Session"
----

When a `jndi-name` is set, it takes precedence over all other Session-related settings.



[[boot-features-jta]]
== Distributed Transactions with JTA
Spring Boot supports distributed JTA transactions across multiple XA resources by using an https://www.atomikos.com/[Atomikos] embedded transaction manager.
Deprecated support for using a https://github.com/bitronix/btm[Bitronix] embedded transaction manager is also provided but it will be removed in a future release.
JTA transactions are also supported when deploying to a suitable Java EE Application Server.

When a JTA environment is detected, Spring's `JtaTransactionManager` is used to manage transactions.
Auto-configured JMS, DataSource, and JPA beans are upgraded to support XA transactions.
You can use standard Spring idioms, such as `@Transactional`, to participate in a distributed transaction.
If you are within a JTA environment and still want to use local transactions, you can set the configprop:spring.jta.enabled[] property to `false` to disable the JTA auto-configuration.



[[boot-features-jta-atomikos]]
=== Using an Atomikos Transaction Manager
https://www.atomikos.com/[Atomikos] is a popular open source transaction manager which can be embedded into your Spring Boot application.
You can use the `spring-boot-starter-jta-atomikos` starter to pull in the appropriate Atomikos libraries.
Spring Boot auto-configures Atomikos and ensures that appropriate `depends-on` settings are applied to your Spring beans for correct startup and shutdown ordering.

By default, Atomikos transaction logs are written to a `transaction-logs` directory in your application's home directory (the directory in which your application jar file resides).
You can customize the location of this directory by setting a configprop:spring.jta.log-dir[] property in your `application.properties` file.
Properties starting with `spring.jta.atomikos.properties` can also be used to customize the Atomikos `UserTransactionServiceImp`.
See the {spring-boot-module-api}/jta/atomikos/AtomikosProperties.html[`AtomikosProperties` Javadoc] for complete details.

NOTE: To ensure that multiple transaction managers can safely coordinate the same resource managers, each Atomikos instance must be configured with a unique ID.
By default, this ID is the IP address of the machine on which Atomikos is running.
To ensure uniqueness in production, you should configure the configprop:spring.jta.transaction-manager-id[] property with a different value for each instance of your application.



[[boot-features-jta-bitronix]]
=== Using a Bitronix Transaction Manager
NOTE: As of Spring Boot 2.3, support for Bitronix has been deprecated and will be removed in a future release.

You can use the `spring-boot-starter-jta-bitronix` starter to add the appropriate Bitronix dependencies to your project.
As with Atomikos, Spring Boot automatically configures Bitronix and post-processes your beans to ensure that startup and shutdown ordering is correct.

By default, Bitronix transaction log files (`part1.btm` and `part2.btm`) are written to a `transaction-logs` directory in your application home directory.
You can customize the location of this directory by setting the configprop:spring.jta.log-dir[] property.
Properties starting with `spring.jta.bitronix.properties` are also bound to the `bitronix.tm.Configuration` bean, allowing for complete customization.
See the https://github.com/bitronix/btm/wiki/Transaction-manager-configuration[Bitronix documentation] for details.

NOTE: To ensure that multiple transaction managers can safely coordinate the same resource managers, each Bitronix instance must be configured with a unique ID.
By default, this ID is the IP address of the machine on which Bitronix is running.
To ensure uniqueness in production, you should configure the configprop:spring.jta.transaction-manager-id[] property with a different value for each instance of your application.



[[boot-features-jta-javaee]]
=== Using a Java EE Managed Transaction Manager
If you package your Spring Boot application as a `war` or `ear` file and deploy it to a Java EE application server, you can use your application server's built-in transaction manager.
Spring Boot tries to auto-configure a transaction manager by looking at common JNDI locations (`java:comp/UserTransaction`, `java:comp/TransactionManager`, and so on).
If you use a transaction service provided by your application server, you generally also want to ensure that all resources are managed by the server and exposed over JNDI.
Spring Boot tries to auto-configure JMS by looking for a `ConnectionFactory` at the JNDI path (`java:/JmsXA` or `java:/XAConnectionFactory`), and you can use the <<boot-features-connecting-to-a-jndi-datasource, configprop:spring.datasource.jndi-name[] property>> to configure your `DataSource`.



[[boot-features-jta-mixed-jms]]
=== Mixing XA and Non-XA JMS Connections
When using JTA, the primary JMS `ConnectionFactory` bean is XA-aware and participates in distributed transactions.
In some situations, you might want to process certain JMS messages by using a non-XA `ConnectionFactory`.
For example, your JMS processing logic might take longer than the XA timeout.

If you want to use a non-XA `ConnectionFactory`, you can inject the `nonXaJmsConnectionFactory` bean rather than the `@Primary` `jmsConnectionFactory` bean.
For consistency, the `jmsConnectionFactory` bean is also provided by using the bean alias `xaJmsConnectionFactory`.

The following example shows how to inject `ConnectionFactory` instances:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	// Inject the primary (XA aware) ConnectionFactory
	@Autowired
	private ConnectionFactory defaultConnectionFactory;

	// Inject the XA aware ConnectionFactory (uses the alias and injects the same as above)
	@Autowired
	@Qualifier("xaJmsConnectionFactory")
	private ConnectionFactory xaConnectionFactory;

	// Inject the non-XA aware ConnectionFactory
	@Autowired
	@Qualifier("nonXaJmsConnectionFactory")
	private ConnectionFactory nonXaConnectionFactory;
----



[[boot-features-jta-supporting-alternative-embedded]]
=== Supporting an Alternative Embedded Transaction Manager
The {spring-boot-module-code}/jms/XAConnectionFactoryWrapper.java[`XAConnectionFactoryWrapper`] and {spring-boot-module-code}/jdbc/XADataSourceWrapper.java[`XADataSourceWrapper`] interfaces can be used to support alternative embedded transaction managers.
The interfaces are responsible for wrapping `XAConnectionFactory` and `XADataSource` beans and exposing them as regular `ConnectionFactory` and `DataSource` beans, which transparently enroll in the distributed transaction.
DataSource and JMS auto-configuration use JTA variants, provided you have a `JtaTransactionManager` bean and appropriate XA wrapper beans registered within your `ApplicationContext`.

The {spring-boot-module-code}/jta/atomikos/AtomikosXAConnectionFactoryWrapper.java[AtomikosXAConnectionFactoryWrapper] and {spring-boot-module-code}/jta/atomikos/AtomikosXADataSourceWrapper.java[AtomikosXADataSourceWrapper] provide good examples of how to write XA wrappers.



[[boot-features-hazelcast]]
== Hazelcast
If https://hazelcast.com/[Hazelcast] is on the classpath and a suitable configuration is found, Spring Boot auto-configures a `HazelcastInstance` that you can inject in your application.

Spring Boot first attempts to create a client by checking the following configuration options:

* The presence of a `com.hazelcast.client.config.ClientConfig` bean.
* A configuration file defined by the configprop:spring.hazelcast.config[] property.
* The presence of the `hazelcast.client.config` system property.
* A `hazelcast-client.xml` in the working directory or at the root of the classpath.
* A `hazelcast-client.yaml` in the working directory or at the root of the classpath.

NOTE: Spring Boot supports both Hazelcast 4 and Hazelcast 3.
If you downgrade to Hazelcast 3, `hazelcast-client` should be added to the classpath to configure a client.

If a client can't be created, Spring Boot attempts to configure an embedded server.
If you define a `com.hazelcast.config.Config` bean, Spring Boot uses that.
If your configuration defines an instance name, Spring Boot tries to locate an existing instance rather than creating a new one.

You could also specify the Hazelcast configuration file to use through configuration, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  hazelcast:
	    config: "classpath:config/my-hazelcast.xml"
----

Otherwise, Spring Boot tries to find the Hazelcast configuration from the default locations: `hazelcast.xml` in the working directory or at the root of the classpath, or a `.yaml` counterpart in the same locations.
We also check if the `hazelcast.config` system property is set.
See the https://docs.hazelcast.org/docs/latest/manual/html-single/[Hazelcast documentation] for more details.

NOTE: Spring Boot also has <<boot-features-caching-provider-hazelcast,explicit caching support for Hazelcast>>.
If caching is enabled, the `HazelcastInstance` is automatically wrapped in a `CacheManager` implementation.



[[boot-features-quartz]]
== Quartz Scheduler
Spring Boot offers several conveniences for working with the https://www.quartz-scheduler.org/[Quartz scheduler], including the `spring-boot-starter-quartz` "`Starter`".
If Quartz is available, a `Scheduler` is auto-configured (through the `SchedulerFactoryBean` abstraction).

Beans of the following types are automatically picked up and associated with the `Scheduler`:

* `JobDetail`: defines a particular Job.
  `JobDetail` instances can be built with the `JobBuilder` API.
* `Calendar`.
* `Trigger`: defines when a particular job is triggered.

By default, an in-memory `JobStore` is used.
However, it is possible to configure a JDBC-based store if a `DataSource` bean is available in your application and if the configprop:spring.quartz.job-store-type[] property is configured accordingly, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  quartz:
	    job-store-type: "jdbc"
----

When the JDBC store is used, the schema can be initialized on startup, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  quartz:
	    jdbc:
	      initialize-schema: "always"
----

WARNING: By default, the database is detected and initialized by using the standard scripts provided with the Quartz library.
These scripts drop existing tables, deleting all triggers on every restart.
It is also possible to provide a custom script by setting the configprop:spring.quartz.jdbc.schema[] property.

To have Quartz use a `DataSource` other than the application's main `DataSource`, declare a `DataSource` bean, annotating its `@Bean` method with `@QuartzDataSource`.
Doing so ensures that the Quartz-specific `DataSource` is used by both the `SchedulerFactoryBean` and for schema initialization.
Similarly, to have Quartz use a `TransactionManager` other than the application's main `TransactionManager` declare a `TransactionManager` bean, annotating its `@Bean` method with `@QuartzTransactionManager`.

By default, jobs created by configuration will not overwrite already registered jobs that have been read from a persistent job store.
To enable overwriting existing job definitions set the configprop:spring.quartz.overwrite-existing-jobs[] property.

Quartz Scheduler configuration can be customized using `spring.quartz` properties and `SchedulerFactoryBeanCustomizer` beans, which allow programmatic `SchedulerFactoryBean` customization.
Advanced Quartz configuration properties can be customized using `spring.quartz.properties.*`.

NOTE: In particular, an `Executor` bean is not associated with the scheduler as Quartz offers a way to configure the scheduler via `spring.quartz.properties`.
If you need to customize the task executor, consider implementing `SchedulerFactoryBeanCustomizer`.

Jobs can define setters to inject data map properties.
Regular beans can also be injected in a similar manner, as shown in the following example:

[source,java,indent=0]
----
	public class SampleJob extends QuartzJobBean {

		private MyService myService;

		private String name;

		// Inject "MyService" bean
		public void setMyService(MyService myService) { ... }

		// Inject the "name" job data property
		public void setName(String name) { ... }

		@Override
		protected void executeInternal(JobExecutionContext context)
				throws JobExecutionException {
			...
		}

	}
----



[[boot-features-task-execution-scheduling]]
== Task Execution and Scheduling
In the absence of an `Executor` bean in the context, Spring Boot auto-configures a `ThreadPoolTaskExecutor` with sensible defaults that can be automatically associated to asynchronous task execution (`@EnableAsync`) and Spring MVC asynchronous request processing.

[TIP]
====
If you have defined a custom `Executor` in the context, regular task execution (i.e. `@EnableAsync`) will use it transparently but the Spring MVC support will not be configured as it requires an `AsyncTaskExecutor` implementation (named `applicationTaskExecutor`).
Depending on your target arrangement, you could change your `Executor` into a `ThreadPoolTaskExecutor` or define both a `ThreadPoolTaskExecutor` and an `AsyncConfigurer` wrapping your custom `Executor`.

The auto-configured `TaskExecutorBuilder` allows you to easily create instances that reproduce what the auto-configuration does by default.
====

The thread pool uses 8 core threads that can grow and shrink according to the load.
Those default settings can be fine-tuned using the `spring.task.execution` namespace as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  task:
	    execution:
	      pool:
	        max-size: 16
	        queue-capacity: 100
	        keep-alive: "10s"
----

This changes the thread pool to use a bounded queue so that when the queue is full (100 tasks), the thread pool increases to maximum 16 threads.
Shrinking of the pool is more aggressive as threads are reclaimed when they are idle for 10 seconds (rather than 60 seconds by default).

A `ThreadPoolTaskScheduler` can also be auto-configured if need to be associated to scheduled task execution (`@EnableScheduling`).
The thread pool uses one thread by default and those settings can be fine-tuned using the `spring.task.scheduling` namespace.

Both a `TaskExecutorBuilder` bean and a `TaskSchedulerBuilder` bean are made available in the context if a custom executor or scheduler needs to be created.



[[boot-features-integration]]
== Spring Integration
Spring Boot offers several conveniences for working with {spring-integration}[Spring Integration], including the `spring-boot-starter-integration` "`Starter`".
Spring Integration provides abstractions over messaging and also other transports such as HTTP, TCP, and others.
If Spring Integration is available on your classpath, it is initialized through the `@EnableIntegration` annotation.

Spring Boot also configures some features that are triggered by the presence of additional Spring Integration modules.
If `spring-integration-jmx` is also on the classpath, message processing statistics are published over JMX.
If `spring-integration-jdbc` is available, the default database schema can be created on startup, as shown in the following line:

[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  integration:
	    jdbc:
	      initialize-schema: "always"
----

If `spring-integration-rsocket` is available, developers can configure an RSocket server using `"spring.rsocket.server.*"` properties and let it use `IntegrationRSocketEndpoint` or `RSocketOutboundGateway` components to handle incoming RSocket messages.
This infrastructure can handle Spring Integration RSocket channel adapters and `@MessageMapping` handlers (given `"spring.integration.rsocket.server.message-mapping-enabled"` is configured).

Spring Boot can also auto-configure an `ClientRSocketConnector` using configuration properties:

[source,yaml,indent=0,configprops,configblocks]
----
	# Connecting to a RSocket server over TCP
	spring:
	  integration:
	    rsocket:
	      client:
	        host: "example.org"
	        port: 9898
----

[source,yaml,indent=0,configprops,configblocks]
----
	# Connecting to a RSocket Server over WebSocket
	spring:
	  integration:
	    rsocket:
	      client:
	        uri: "ws://example.org"
----

See the {spring-boot-autoconfigure-module-code}/integration/IntegrationAutoConfiguration.java[`IntegrationAutoConfiguration`] and {spring-boot-autoconfigure-module-code}/integration/IntegrationProperties.java[`IntegrationProperties`] classes for more details.

By default, if a Micrometer `meterRegistry` bean is present, Spring Integration metrics will be managed by Micrometer.
If you wish to use legacy Spring Integration metrics, add a `DefaultMetricsFactory` bean to the application context.



[[boot-features-session]]
== Spring Session
Spring Boot provides {spring-session}[Spring Session] auto-configuration for a wide range of data stores.
When building a Servlet web application, the following stores can be auto-configured:

* JDBC
* Redis
* Hazelcast
* MongoDB

The Servlet auto-configuration replaces the need to use `@Enable*HttpSession`.

When building a reactive web application, the following stores can be auto-configured:

* Redis
* MongoDB

The reactive auto-configuration replaces the need to use `@Enable*WebSession`.

If a single Spring Session module is present on the classpath, Spring Boot uses that store implementation automatically.
If you have more than one implementation, you must choose the {spring-boot-autoconfigure-module-code}/session/StoreType.java[`StoreType`] that you wish to use to store the sessions.
For instance, to use JDBC as the back-end store, you can configure your application as follows:

[source,yaml,indent=0,configprops,configblocks]
----
    spring:
      session:
        store-type: "jdbc"
----

TIP: You can disable Spring Session by setting the `store-type` to `none`.

Each store has specific additional settings.
For instance, it is possible to customize the name of the table for the JDBC store, as shown in the following example:

[source,yaml,indent=0,configprops,configblocks]
----
    spring:
      session:
        jdbc:
          table-name: "SESSIONS"
----

For setting the timeout of the session you can use the configprop:spring.session.timeout[] property.
If that property is not set with a Servlet web application, the auto-configuration falls back to the value of configprop:server.servlet.session.timeout[].


You can take control over Spring Session's configuration using `@Enable*HttpSession` (Servlet) or `@Enable*WebSession` (Reactive).
This will cause the auto-configuration to back off.
Spring Session can then be configured using the annotation's attributes rather than the previously described configuration properties.



[[boot-features-jmx]]
== Monitoring and Management over JMX
Java Management Extensions (JMX) provide a standard mechanism to monitor and manage applications.
Spring Boot exposes the most suitable `MBeanServer` as a bean with an ID of `mbeanServer`.
Any of your beans that are annotated with Spring JMX annotations (`@ManagedResource`, `@ManagedAttribute`, or `@ManagedOperation`) are exposed to it.

If your platform provides a standard `MBeanServer`, Spring Boot will use that and default to the VM `MBeanServer` if necessary.
If all that fails, a new `MBeanServer` will be created.

See the {spring-boot-autoconfigure-module-code}/jmx/JmxAutoConfiguration.java[`JmxAutoConfiguration`] class for more details.



[[boot-features-testing]]
== Testing
Spring Boot provides a number of utilities and annotations to help when testing your application.
Test support is provided by two modules: `spring-boot-test` contains core items, and `spring-boot-test-autoconfigure` supports auto-configuration for tests.

Most developers use the `spring-boot-starter-test` "`Starter`", which imports both Spring Boot test modules as well as JUnit Jupiter, AssertJ, Hamcrest, and a number of other useful libraries.

[TIP]
====
If you have tests that use JUnit 4, JUnit 5's vintage engine can be used to run them.
To use the vintage engine, add a dependency on `junit-vintage-engine`, as shown in the following example:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>org.junit.vintage</groupId>
		<artifactId>junit-vintage-engine</artifactId>
		<scope>test</scope>
		<exclusions>
			<exclusion>
				<groupId>org.hamcrest</groupId>
				<artifactId>hamcrest-core</artifactId>
			</exclusion>
		</exclusions>
	</dependency>
----
====

`hamcrest-core` is excluded in favor of `org.hamcrest:hamcrest` that is part of `spring-boot-starter-test`.



[[boot-features-test-scope-dependencies]]
=== Test Scope Dependencies
The `spring-boot-starter-test` "`Starter`" (in the `test` `scope`) contains the following provided libraries:

* https://junit.org/junit5/[JUnit 5]: The de-facto standard for unit testing Java applications.
* {spring-framework-docs}/testing.html#integration-testing[Spring Test] & Spring Boot Test: Utilities and integration test support for Spring Boot applications.
* https://assertj.github.io/doc/[AssertJ]: A fluent assertion library.
* https://github.com/hamcrest/JavaHamcrest[Hamcrest]: A library of matcher objects (also known as constraints or predicates).
* https://site.mockito.org/[Mockito]: A Java mocking framework.
* https://github.com/skyscreamer/JSONassert[JSONassert]: An assertion library for JSON.
* https://github.com/jayway/JsonPath[JsonPath]: XPath for JSON.

We generally find these common libraries to be useful when writing tests.
If these libraries do not suit your needs, you can add additional test dependencies of your own.



[[boot-features-testing-spring-applications]]
=== Testing Spring Applications
One of the major advantages of dependency injection is that it should make your code easier to unit test.
You can instantiate objects by using the `new` operator without even involving Spring.
You can also use _mock objects_ instead of real dependencies.

Often, you need to move beyond unit testing and start integration testing (with a Spring `ApplicationContext`).
It is useful to be able to perform integration testing without requiring deployment of your application or needing to connect to other infrastructure.

The Spring Framework includes a dedicated test module for such integration testing.
You can declare a dependency directly to `org.springframework:spring-test` or use the `spring-boot-starter-test` "`Starter`" to pull it in transitively.

If you have not used the `spring-test` module before, you should start by reading the {spring-framework-docs}/testing.html#testing[relevant section] of the Spring Framework reference documentation.



[[boot-features-testing-spring-boot-applications]]
=== Testing Spring Boot Applications
A Spring Boot application is a Spring `ApplicationContext`, so nothing very special has to be done to test it beyond what you would normally do with a vanilla Spring context.

NOTE: External properties, logging, and other features of Spring Boot are installed in the context by default only if you use `SpringApplication` to create it.

Spring Boot provides a `@SpringBootTest` annotation, which can be used as an alternative to the standard `spring-test` `@ContextConfiguration` annotation when you need Spring Boot features.
The annotation works by <<boot-features-testing-spring-boot-applications-detecting-config,creating the `ApplicationContext` used in your tests through `SpringApplication`>>.
In addition to `@SpringBootTest` a number of other annotations are also provided for <<boot-features-testing-spring-boot-applications-testing-autoconfigured-tests,testing more specific slices>> of an application.

TIP: If you are using JUnit 4, don't forget to also add `@RunWith(SpringRunner.class)` to your test, otherwise the annotations will be ignored.
If you are using JUnit 5, there's no need to add the equivalent `@ExtendWith(SpringExtension.class)` as `@SpringBootTest` and the other `@…Test` annotations are already annotated with it.

By default, `@SpringBootTest` will not start a server.
You can use the `webEnvironment` attribute of `@SpringBootTest` to further refine how your tests run:

* `MOCK`(Default) : Loads a web `ApplicationContext` and provides a mock web environment.
  Embedded servers are not started when using this annotation.
	If a web environment is not available on your classpath, this mode transparently falls back to creating a regular non-web `ApplicationContext`.
	It can be used in conjunction with <<boot-features-testing-spring-boot-applications-testing-with-mock-environment, `@AutoConfigureMockMvc` or `@AutoConfigureWebTestClient`>> for mock-based testing of your web application.
* `RANDOM_PORT`: Loads a `WebServerApplicationContext` and provides a real web environment.
  Embedded servers are started and listen on a random port.
* `DEFINED_PORT`: Loads a `WebServerApplicationContext` and provides a real web environment.
  Embedded servers are started and listen on a defined port (from your `application.properties`) or on the default port of `8080`.
* `NONE`: Loads an `ApplicationContext` by using `SpringApplication` but does not provide _any_ web environment (mock or otherwise).

NOTE: If your test is `@Transactional`, it rolls back the transaction at the end of each test method by default.
However, as using this arrangement with either `RANDOM_PORT` or `DEFINED_PORT` implicitly provides a real servlet environment, the HTTP client and server run in separate threads and, thus, in separate transactions.
Any transaction initiated on the server does not roll back in this case.

NOTE: `@SpringBootTest` with `webEnvironment = WebEnvironment.RANDOM_PORT` will also start the management server on a separate random port if your application uses a different port for the management server.



[[boot-features-testing-spring-boot-applications-detecting-web-app-type]]
==== Detecting Web Application Type
If Spring MVC is available, a regular MVC-based application context is configured.
If you have only Spring WebFlux, we'll detect that and configure a WebFlux-based application context instead.

If both are present, Spring MVC takes precedence.
If you want to test a reactive web application in this scenario, you must set the configprop:spring.main.web-application-type[] property:

[source,java,indent=0]
----
	@SpringBootTest(properties = "spring.main.web-application-type=reactive")
	class MyWebFluxTests { ... }
----



[[boot-features-testing-spring-boot-applications-detecting-config]]
==== Detecting Test Configuration
If you are familiar with the Spring Test Framework, you may be used to using `@ContextConfiguration(classes=...)` in order to specify which Spring `@Configuration` to load.
Alternatively, you might have often used nested `@Configuration` classes within your test.

When testing Spring Boot applications, this is often not required.
Spring Boot's `@*Test` annotations search for your primary configuration automatically whenever you do not explicitly define one.

The search algorithm works up from the package that contains the test until it finds a class annotated with `@SpringBootApplication` or `@SpringBootConfiguration`.
As long as you <<using-spring-boot.adoc#using-boot-structuring-your-code, structured your code>> in a sensible way, your main configuration is usually found.

[NOTE]
====
If you use a <<boot-features-testing-spring-boot-applications-testing-autoconfigured-tests, test annotation to test a more specific slice of your application>>, you should avoid adding configuration settings that are specific to a particular area on the <<boot-features-testing-spring-boot-applications-testing-user-configuration, main method's application class>>.

The underlying component scan configuration of `@SpringBootApplication` defines exclude filters that are used to make sure slicing works as expected.
If you are using an explicit `@ComponentScan` directive on your `@SpringBootApplication`-annotated class, be aware that those filters will be disabled.
If you are using slicing, you should define them again.
====

If you want to customize the primary configuration, you can use a nested `@TestConfiguration` class.
Unlike a nested `@Configuration` class, which would be used instead of your application's primary configuration, a nested `@TestConfiguration` class is used in addition to your application's primary configuration.

NOTE: Spring's test framework caches application contexts between tests.
Therefore, as long as your tests share the same configuration (no matter how it is discovered), the potentially time-consuming process of loading the context happens only once.



[[boot-features-testing-spring-boot-applications-excluding-config]]
==== Excluding Test Configuration
If your application uses component scanning (for example, if you use `@SpringBootApplication` or `@ComponentScan`), you may find top-level configuration classes that you created only for specific tests accidentally get picked up everywhere.

As we <<boot-features-testing-spring-boot-applications-detecting-config,have seen earlier>>, `@TestConfiguration` can be used on an inner class of a test to customize the primary configuration.
When placed on a top-level class, `@TestConfiguration` indicates that classes in `src/test/java` should not be picked up by scanning.
You can then import that class explicitly where it is required, as shown in the following example:

[source,java,indent=0]
----
	@SpringBootTest
	@Import(MyTestsConfiguration.class)
	class MyTests {

		@Test
		void exampleTest() {
			...
		}

	}
----

NOTE: If you directly use `@ComponentScan` (that is, not through `@SpringBootApplication`) you need to register the `TypeExcludeFilter` with it.
See {spring-boot-module-api}/context/TypeExcludeFilter.html[the Javadoc] for details.



[[boot-features-testing-spring-boot-application-arguments]]
==== Using Application Arguments
If your application expects <<boot-features-application-arguments,arguments>>, you can
have `@SpringBootTest` inject them using the `args` attribute.

[source,java,indent=0]
----
include::{code-examples}/test/context/ApplicationArgumentsExampleTests.java[tag=example]
----



[[boot-features-testing-spring-boot-applications-testing-with-mock-environment]]
==== Testing with a mock environment
By default, `@SpringBootTest` does not start the server.
If you have web endpoints that you want to test against this mock environment, you can additionally configure {spring-framework-docs}/testing.html#spring-mvc-test-framework[`MockMvc`] as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/web/MockMvcExampleTests.java[tag=test-mock-mvc]
----

TIP: If you want to focus only on the web layer and not start a complete `ApplicationContext`, consider <<boot-features-testing-spring-boot-applications-testing-autoconfigured-mvc-tests,using `@WebMvcTest` instead>>.

Alternatively, you can configure a {spring-framework-docs}/testing.html#webtestclient-tests[`WebTestClient`] as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/web/MockWebTestClientExampleTests.java[tag=test-mock-web-test-client]
----

[TIP]
====
Testing within a mocked environment is usually faster than running with a full Servlet container.
However, since mocking occurs at the Spring MVC layer, code that relies on lower-level Servlet container behavior cannot be directly tested with MockMvc.

For example, Spring Boot's error handling is based on the "`error page`" support provided by the Servlet container.
This means that, whilst you can test your MVC layer throws and handles exceptions as expected, you cannot directly test that a specific <<boot-features-error-handling-custom-error-pages, custom error page>> is rendered.
If you need to test these lower-level concerns, you can start a fully running server as described in the next section.
====



[[boot-features-testing-spring-boot-applications-testing-with-running-server]]
==== Testing with a running server
If you need to start a full running server, we recommend that you use random ports.
If you use `@SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT)`, an available port is picked at random each time your test runs.

The `@LocalServerPort` annotation can be used to <<howto.adoc#howto-discover-the-http-port-at-runtime,inject the actual port used>> into your test.
For convenience, tests that need to make REST calls to the started server can additionally `@Autowire` a {spring-framework-docs}/testing.html#webtestclient-tests[`WebTestClient`], which resolves relative links to the running server and comes with a dedicated API for verifying responses, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/web/RandomPortWebTestClientExampleTests.java[tag=test-random-port]
----

This setup requires `spring-webflux` on the classpath.
If you can't or won't add webflux, Spring Boot also provides a `TestRestTemplate` facility:

[source,java,indent=0]
----
include::{code-examples}/test/web/RandomPortTestRestTemplateExampleTests.java[tag=test-random-port]
----



[[boot-features-testing-spring-boot-applications-customizing-web-test-client]]
==== Customizing WebTestClient
To customize the `WebTestClient` bean, configure a `WebTestClientBuilderCustomizer` bean.
Any such beans are called with the `WebTestClient.Builder` that is used to create the `WebTestClient`.



[[boot-features-testing-spring-boot-applications-jmx]]
==== Using JMX
As the test context framework caches context, JMX is disabled by default to prevent identical components to register on the same domain.
If such test needs access to an `MBeanServer`, consider marking it dirty as well:

[source,java,indent=0]
----
include::{test-examples}/jmx/SampleJmxTests.java[tag=test]
----



[[boot-features-testing-spring-boot-applications-metrics]]
==== Using Metrics
Regardless of your classpath, meter registries, except the in-memory backed, are not auto-configured when using `@SpringBootTest`.

If you need to export metrics to a different backend as part of an integration test, annotate it with `@AutoConfigureMetrics`.



[[boot-features-testing-spring-boot-applications-mocking-beans]]
==== Mocking and Spying Beans
When running tests, it is sometimes necessary to mock certain components within your application context.
For example, you may have a facade over some remote service that is unavailable during development.
Mocking can also be useful when you want to simulate failures that might be hard to trigger in a real environment.

Spring Boot includes a `@MockBean` annotation that can be used to define a Mockito mock for a bean inside your `ApplicationContext`.
You can use the annotation to add new beans or replace a single existing bean definition.
The annotation can be used directly on test classes, on fields within your test, or on `@Configuration` classes and fields.
When used on a field, the instance of the created mock is also injected.
Mock beans are automatically reset after each test method.

[NOTE]
====
If your test uses one of Spring Boot's test annotations (such as `@SpringBootTest`), this feature is automatically enabled.
To use this feature with a different arrangement, listeners must be explicitly added, as shown in the following example:

[source,java,indent=0]
----
	@TestExecutionListeners({ MockitoTestExecutionListener.class, ResetMocksTestExecutionListener.class })
----

====

The following example replaces an existing `RemoteService` bean with a mock implementation:

[source,java,indent=0]
----
	import org.junit.jupiter.api.Test;
	import org.springframework.beans.factory.annotation.*;
	import org.springframework.boot.test.context.*;
	import org.springframework.boot.test.mock.mockito.*;

	import static org.assertj.core.api.Assertions.*;
	import static org.mockito.BDDMockito.*;

	@SpringBootTest
	class MyTests {

		@MockBean
		private RemoteService remoteService;

		@Autowired
		private Reverser reverser;

		@Test
		void exampleTest() {
			// RemoteService has been injected into the reverser bean
			given(this.remoteService.someCall()).willReturn("mock");
			String reverse = reverser.reverseSomeCall();
			assertThat(reverse).isEqualTo("kcom");
		}

	}
----

NOTE: `@MockBean` cannot be used to mock the behavior of a bean that's exercised during application context refresh.
By the time the test is executed, the application context refresh has completed and it is too late to configure the mocked behavior.
We recommend using a `@Bean` method to create and configure the mock in this situation.

Additionally, you can use `@SpyBean` to wrap any existing bean with a Mockito `spy`.
See the {spring-boot-test-module-api}/mock/mockito/SpyBean.html[Javadoc] for full details.

NOTE: CGLib proxies, such as those created for scoped beans, declare the proxied methods as `final`.
This stops Mockito from functioning correctly as it cannot mock or spy on `final` methods in its default configuration.
If you want to mock or spy on such a bean, configure Mockito to use its inline mock maker by adding `org.mockito:mockito-inline` to your application's test dependencies.
This allows Mockito to mock and spy on `final` methods.

NOTE: While Spring's test framework caches application contexts between tests and reuses a context for tests sharing the same configuration, the use of `@MockBean` or `@SpyBean` influences the cache key, which will most likely increase the number of contexts.

TIP: If you are using `@SpyBean` to spy on a bean with `@Cacheable` methods that refer to parameters by name, your application must be compiled with `-parameters`.
This ensures that the parameter names are available to the caching infrastructure once the bean has been spied upon.

TIP: When you are using `@SpyBean` to spy on a bean that is proxied by Spring, you may need to remove Spring's proxy in some situations, for example when setting expectations using `given` or `when`.
Use `AopTestUtils.getTargetObject(yourProxiedSpy)` to do so.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-tests]]
==== Auto-configured Tests
Spring Boot's auto-configuration system works well for applications but can sometimes be a little too much for tests.
It often helps to load only the parts of the configuration that are required to test a "`slice`" of your application.
For example, you might want to test that Spring MVC controllers are mapping URLs correctly, and you do not want to involve database calls in those tests, or you might want to test JPA entities, and you are not interested in the web layer when those tests run.

The `spring-boot-test-autoconfigure` module includes a number of annotations that can be used to automatically configure such "`slices`".
Each of them works in a similar way, providing a `@...Test` annotation that loads the `ApplicationContext` and one or more `@AutoConfigure...` annotations that can be used to customize auto-configuration settings.

NOTE: Each slice restricts component scan to appropriate components and loads a very restricted set of auto-configuration classes.
If you need to exclude one of them, most `@...Test` annotations provide an `excludeAutoConfiguration` attribute.
Alternatively, you can use `@ImportAutoConfiguration#exclude`.

NOTE: Including multiple "`slices`" by using several `@...Test` annotations in one test is not supported.
If you need multiple "`slices`", pick one of the `@...Test` annotations and include the `@AutoConfigure...` annotations of the other "`slices`" by hand.

TIP: It is also possible to use the `@AutoConfigure...` annotations with the standard `@SpringBootTest` annotation.
You can use this combination if you are not interested in "`slicing`" your application but you want some of the auto-configured test beans.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-json-tests]]
==== Auto-configured JSON Tests
To test that object JSON serialization and deserialization is working as expected, you can use the `@JsonTest` annotation.
`@JsonTest` auto-configures the available supported JSON mapper, which can be one of the following libraries:

* Jackson `ObjectMapper`, any `@JsonComponent` beans and any Jackson ``Module``s
* `Gson`
* `Jsonb`

TIP: A list of the auto-configurations that are enabled by `@JsonTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

If you need to configure elements of the auto-configuration, you can use the `@AutoConfigureJsonTesters` annotation.

Spring Boot includes AssertJ-based helpers that work with the JSONAssert and JsonPath libraries to check that JSON appears as expected.
The `JacksonTester`, `GsonTester`, `JsonbTester`, and `BasicJsonTester` classes can be used for Jackson, Gson, Jsonb, and Strings respectively.
Any helper fields on the test class can be `@Autowired` when using `@JsonTest`.
The following example shows a test class for Jackson:

[source,java,indent=0]
----
	import org.junit.jupiter.api.Test;
	import org.springframework.beans.factory.annotation.*;
	import org.springframework.boot.test.autoconfigure.json.*;
	import org.springframework.boot.test.context.*;
	import org.springframework.boot.test.json.*;

	import static org.assertj.core.api.Assertions.*;

	@JsonTest
	class MyJsonTests {

		@Autowired
		private JacksonTester<VehicleDetails> json;

		@Test
		void testSerialize() throws Exception {
			VehicleDetails details = new VehicleDetails("Honda", "Civic");
			// Assert against a `.json` file in the same package as the test
			assertThat(this.json.write(details)).isEqualToJson("expected.json");
			// Or use JSON path based assertions
			assertThat(this.json.write(details)).hasJsonPathStringValue("@.make");
			assertThat(this.json.write(details)).extractingJsonPathStringValue("@.make")
					.isEqualTo("Honda");
		}

		@Test
		void testDeserialize() throws Exception {
			String content = "{\"make\":\"Ford\",\"model\":\"Focus\"}";
			assertThat(this.json.parse(content))
					.isEqualTo(new VehicleDetails("Ford", "Focus"));
			assertThat(this.json.parseObject(content).getMake()).isEqualTo("Ford");
		}

	}
----

NOTE: JSON helper classes can also be used directly in standard unit tests.
To do so, call the `initFields` method of the helper in your `@Before` method if you do not use `@JsonTest`.

If you're using Spring Boot's AssertJ-based helpers to assert on a number value at a given JSON path, you might not be able to use `isEqualTo` depending on the type.
Instead, you can use AssertJ's `satisfies` to assert that the value matches the given condition.
For instance, the following example asserts that the actual number is a float value close to `0.15` within an offset of `0.01`.

[source,java,indent=0]
----
assertThat(json.write(message))
    .extractingJsonPathNumberValue("@.test.numberValue")
    .satisfies((number) -> assertThat(number.floatValue()).isCloseTo(0.15f, within(0.01f)));
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-mvc-tests]]
==== Auto-configured Spring MVC Tests
To test whether Spring MVC controllers are working as expected, use the `@WebMvcTest` annotation.
`@WebMvcTest` auto-configures the Spring MVC infrastructure and limits scanned beans to `@Controller`, `@ControllerAdvice`, `@JsonComponent`, `Converter`, `GenericConverter`, `Filter`, `HandlerInterceptor`, `WebMvcConfigurer`, and `HandlerMethodArgumentResolver`.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@WebMvcTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.

TIP: A list of the auto-configuration settings that are enabled by `@WebMvcTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

TIP: If you need to register extra components, such as the Jackson `Module`, you can import additional configuration classes by using `@Import` on your test.

Often, `@WebMvcTest` is limited to a single controller and is used in combination with `@MockBean` to provide mock implementations for required collaborators.

`@WebMvcTest` also auto-configures `MockMvc`.
Mock MVC offers a powerful way to quickly test MVC controllers without needing to start a full HTTP server.

TIP: You can also auto-configure `MockMvc` in a non-`@WebMvcTest` (such as `@SpringBootTest`) by annotating it with `@AutoConfigureMockMvc`.
The following example uses `MockMvc`:

[source,java,indent=0]
----
	import org.junit.jupiter.api.*;
	import org.springframework.beans.factory.annotation.*;
	import org.springframework.boot.test.autoconfigure.web.servlet.*;
	import org.springframework.boot.test.mock.mockito.*;

	import static org.assertj.core.api.Assertions.*;
	import static org.mockito.BDDMockito.*;
	import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
	import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

	@WebMvcTest(UserVehicleController.class)
	class MyControllerTests {

		@Autowired
		private MockMvc mvc;

		@MockBean
		private UserVehicleService userVehicleService;

		@Test
		void testExample() throws Exception {
			given(this.userVehicleService.getVehicleDetails("sboot"))
					.willReturn(new VehicleDetails("Honda", "Civic"));
			this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
					.andExpect(status().isOk()).andExpect(content().string("Honda Civic"));
		}

	}
----

TIP: If you need to configure elements of the auto-configuration (for example, when servlet filters should be applied) you can use attributes in the `@AutoConfigureMockMvc` annotation.

If you use HtmlUnit and Selenium, auto-configuration also provides an HtmlUnit `WebClient` bean and/or a Selenium `WebDriver` bean.
The following example uses HtmlUnit:

[source,java,indent=0]
----
	import com.gargoylesoftware.htmlunit.*;
	import org.junit.jupiter.api.*;
	import org.springframework.beans.factory.annotation.*;
	import org.springframework.boot.test.autoconfigure.web.servlet.*;
	import org.springframework.boot.test.mock.mockito.*;

	import static org.assertj.core.api.Assertions.*;
	import static org.mockito.BDDMockito.*;

	@WebMvcTest(UserVehicleController.class)
	class MyHtmlUnitTests {

		@Autowired
		private WebClient webClient;

		@MockBean
		private UserVehicleService userVehicleService;

		@Test
		void testExample() throws Exception {
			given(this.userVehicleService.getVehicleDetails("sboot"))
					.willReturn(new VehicleDetails("Honda", "Civic"));
			HtmlPage page = this.webClient.getPage("/sboot/vehicle.html");
			assertThat(page.getBody().getTextContent()).isEqualTo("Honda Civic");
		}

	}
----

NOTE: By default, Spring Boot puts `WebDriver` beans in a special "`scope`" to ensure that the driver exits after each test and that a new instance is injected.
If you do not want this behavior, you can add `@Scope("singleton")` to your `WebDriver` `@Bean` definition.

WARNING: The `webDriver` scope created by Spring Boot will replace any user defined scope of the same name.
If you define your own `webDriver` scope you may find it stops working when you use `@WebMvcTest`.

If you have Spring Security on the classpath, `@WebMvcTest` will also scan `WebSecurityConfigurer` beans.
Instead of disabling security completely for such tests, you can use Spring Security's test support.
More details on how to use Spring Security's `MockMvc` support can be found in this _<<howto.adoc#howto-use-test-with-spring-security>>_ how-to section.

TIP: Sometimes writing Spring MVC tests is not enough; Spring Boot can help you run <<boot-features-testing-spring-boot-applications-testing-with-running-server, full end-to-end tests with an actual server>>.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-webflux-tests]]
==== Auto-configured Spring WebFlux Tests
To test that {spring-framework-docs}/web-reactive.html[Spring WebFlux] controllers are working as expected, you can use the `@WebFluxTest` annotation.
`@WebFluxTest` auto-configures the Spring WebFlux infrastructure and limits scanned beans to `@Controller`, `@ControllerAdvice`, `@JsonComponent`, `Converter`, `GenericConverter`, `WebFilter`, and `WebFluxConfigurer`.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@WebFluxTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.

TIP: A list of the auto-configurations that are enabled by `@WebFluxTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

TIP: If you need to register extra components, such as Jackson `Module`, you can import additional configuration classes using `@Import` on your test.

Often, `@WebFluxTest` is limited to a single controller and used in combination with the `@MockBean` annotation to provide mock implementations for required collaborators.

`@WebFluxTest` also auto-configures {spring-framework-docs}/testing.html#webtestclient[`WebTestClient`], which offers a powerful way to quickly test WebFlux controllers without needing to start a full HTTP server.

TIP: You can also auto-configure `WebTestClient` in a non-`@WebFluxTest` (such as `@SpringBootTest`) by annotating it with `@AutoConfigureWebTestClient`.
The following example shows a class that uses both `@WebFluxTest` and a `WebTestClient`:

[source,java,indent=0]
----
	import org.junit.jupiter.api.Test;

	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
	import org.springframework.http.MediaType;
	import org.springframework.test.web.reactive.server.WebTestClient;

	@WebFluxTest(UserVehicleController.class)
	class MyControllerTests {

		@Autowired
		private WebTestClient webClient;

		@MockBean
		private UserVehicleService userVehicleService;

		@Test
		void testExample() throws Exception {
			given(this.userVehicleService.getVehicleDetails("sboot"))
					.willReturn(new VehicleDetails("Honda", "Civic"));
			this.webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN)
					.exchange()
					.expectStatus().isOk()
					.expectBody(String.class).isEqualTo("Honda Civic");
		}

	}
----

TIP: This setup is only supported by WebFlux applications as using `WebTestClient` in a mocked web application only works with WebFlux at the moment.

NOTE: `@WebFluxTest` cannot detect routes registered via the functional web framework.
For testing `RouterFunction` beans in the context, consider importing your `RouterFunction` yourself via `@Import` or using `@SpringBootTest`.

NOTE: `@WebFluxTest` cannot detect custom security configuration registered via a `@Bean` of type `SecurityWebFilterChain`.
To include that in your test, you will need to import the configuration that registers the bean via `@Import` or use `@SpringBootTest`.

TIP: Sometimes writing Spring WebFlux tests is not enough; Spring Boot can help you run <<boot-features-testing-spring-boot-applications-testing-with-running-server, full end-to-end tests with an actual server>>.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-cassandra-test]]
==== Auto-configured Data Cassandra Tests
You can use `@DataCassandraTest` to test Cassandra applications.
By default, it configures a `CassandraTemplate`, scans for `@Table` classes, and configures Spring Data Cassandra repositories.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@DataCassandraTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.
(For more about using Cassandra with Spring Boot, see "<<boot-features-cassandra>>", earlier in this chapter.)

TIP: A list of the auto-configuration settings that are enabled by `@DataCassandraTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

The following example shows a typical setup for using Cassandra tests in Spring Boot:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.cassandra.DataCassandraTest;

	@DataCassandraTest
	class ExampleDataCassandraTests {

		@Autowired
		private YourRepository repository;

		//
	}
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-jpa-test]]
==== Auto-configured Data JPA Tests
You can use the `@DataJpaTest` annotation to test JPA applications.
By default, it scans for `@Entity` classes and configures Spring Data JPA repositories.
If an embedded database is available on the classpath, it configures one as well.
SQL queries are logged by default by setting the `spring.jpa.show-sql` property to `true`.
This can be disabled using the `showSql()` attribute of the annotation.

Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@DataJpaTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.

TIP: A list of the auto-configuration settings that are enabled by `@DataJpaTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

By default, data JPA tests are transactional and roll back at the end of each test.
See the {spring-framework-docs}/testing.html#testcontext-tx-enabling-transactions[relevant section] in the Spring Framework Reference Documentation for more details.
If that is not what you want, you can disable transaction management for a test or for the whole class as follows:

[source,java,indent=0]
----
	import org.junit.jupiter.api.Test;
	import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
	import org.springframework.transaction.annotation.Propagation;
	import org.springframework.transaction.annotation.Transactional;

	@DataJpaTest
	@Transactional(propagation = Propagation.NOT_SUPPORTED)
	class ExampleNonTransactionalTests {

	}
----

Data JPA tests may also inject a {spring-boot-test-autoconfigure-module-code}/orm/jpa/TestEntityManager.java[`TestEntityManager`] bean, which provides an alternative to the standard JPA `EntityManager` that is specifically designed for tests.

TIP: `TestEntityManager` can also be auto-configured to any of your Spring-based test class by adding `@AutoConfigureTestEntityManager`.
When doing so, make sure that your test is running in a transaction, for instance by adding  `@Transactional` on your test class or method.


A `JdbcTemplate` is also available if you need that.
The following example shows the `@DataJpaTest` annotation in use:

[source,java,indent=0]
----
	import org.junit.jupiter.api.Test;
	import org.springframework.boot.test.autoconfigure.orm.jpa.*;

	import static org.assertj.core.api.Assertions.*;

	@DataJpaTest
	class ExampleRepositoryTests {

		@Autowired
		private TestEntityManager entityManager;

		@Autowired
		private UserRepository repository;

		@Test
		void testExample() throws Exception {
			this.entityManager.persist(new User("sboot", "1234"));
			User user = this.repository.findByUsername("sboot");
			assertThat(user.getUsername()).isEqualTo("sboot");
			assertThat(user.getVin()).isEqualTo("1234");
		}

	}
----

In-memory embedded databases generally work well for tests, since they are fast and do not require any installation.
If, however, you prefer to run tests against a real database you can use the `@AutoConfigureTestDatabase` annotation, as shown in the following example:

[source,java,indent=0]
----
	@DataJpaTest
	@AutoConfigureTestDatabase(replace=Replace.NONE)
	class ExampleRepositoryTests {

		// ...

	}
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-jdbc-test]]
==== Auto-configured JDBC Tests
`@JdbcTest` is similar to `@DataJpaTest` but is for tests that only require a `DataSource` and do not use Spring Data JDBC.
By default, it configures an in-memory embedded database and a `JdbcTemplate`.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@JdbcTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.

TIP: A list of the auto-configurations that are enabled by `@JdbcTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

By default, JDBC tests are transactional and roll back at the end of each test.
See the {spring-framework-docs}/testing.html#testcontext-tx-enabling-transactions[relevant section] in the Spring Framework Reference Documentation for more details.
If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:

[source,java,indent=0]
----
	import org.junit.jupiter.api.Test;
	import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;
	import org.springframework.transaction.annotation.Propagation;
	import org.springframework.transaction.annotation.Transactional;

	@JdbcTest
	@Transactional(propagation = Propagation.NOT_SUPPORTED)
	class ExampleNonTransactionalTests {

	}
----

If you prefer your test to run against a real database, you can use the `@AutoConfigureTestDatabase` annotation in the same way as for `DataJpaTest`.
(See "<<boot-features-testing-spring-boot-applications-testing-autoconfigured-jpa-test>>".)



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-data-jdbc-test]]
==== Auto-configured Data JDBC Tests
`@DataJdbcTest` is similar to `@JdbcTest` but is for tests that use Spring Data JDBC repositories.
By default, it configures an in-memory embedded database, a `JdbcTemplate`, and Spring Data JDBC repositories.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@DataJdbcTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.

TIP: A list of the auto-configurations that are enabled by `@DataJdbcTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

By default, Data JDBC tests are transactional and roll back at the end of each test.
See the {spring-framework-docs}/testing.html#testcontext-tx-enabling-transactions[relevant section] in the Spring Framework Reference Documentation for more details.
If that is not what you want, you can disable transaction management for a test or for the whole test class as <<boot-features-testing-spring-boot-applications-testing-autoconfigured-jdbc-test,shown in the JDBC example>>.

If you prefer your test to run against a real database, you can use the `@AutoConfigureTestDatabase` annotation in the same way as for `DataJpaTest`.
(See "<<boot-features-testing-spring-boot-applications-testing-autoconfigured-jpa-test>>".)



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-jooq-test]]
==== Auto-configured jOOQ Tests
You can use `@JooqTest` in a similar fashion as `@JdbcTest` but for jOOQ-related tests.
As jOOQ relies heavily on a Java-based schema that corresponds with the database schema, the existing `DataSource` is used.
If you want to replace it with an in-memory database, you can use `@AutoConfigureTestDatabase` to override those settings.
(For more about using jOOQ with Spring Boot, see "<<boot-features-jooq>>", earlier in this chapter.)
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@JooqTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.

TIP: A list of the auto-configurations that are enabled by `@JooqTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

`@JooqTest` configures a `DSLContext`.
The following example shows the `@JooqTest` annotation in use:

[source,java,indent=0]
----
	import org.jooq.DSLContext;
	import org.junit.jupiter.api.Test;
	import org.springframework.boot.test.autoconfigure.jooq.JooqTest;

	@JooqTest
	class ExampleJooqTests {

		@Autowired
		private DSLContext dslContext;
	}
----

JOOQ tests are transactional and roll back at the end of each test by default.
If that is not what you want, you can disable transaction management for a test or for the whole test class as <<boot-features-testing-spring-boot-applications-testing-autoconfigured-jdbc-test,shown in the JDBC example>>.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-mongo-test]]
==== Auto-configured Data MongoDB Tests
You can use `@DataMongoTest` to test MongoDB applications.
By default, it configures an in-memory embedded MongoDB (if available), configures a `MongoTemplate`, scans for `@Document` classes, and configures Spring Data MongoDB repositories.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@DataMongoTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.
(For more about using MongoDB with Spring Boot, see "<<boot-features-mongodb>>", earlier in this chapter.)

TIP: A list of the auto-configuration settings that are enabled by `@DataMongoTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

The following class shows the `@DataMongoTest` annotation in use:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
	import org.springframework.data.mongodb.core.MongoTemplate;

	@DataMongoTest
	class ExampleDataMongoTests {

		@Autowired
		private MongoTemplate mongoTemplate;

		//
	}
----

In-memory embedded MongoDB generally works well for tests, since it is fast and does not require any developer installation.
If, however, you prefer to run tests against a real MongoDB server, you should exclude the embedded MongoDB auto-configuration, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration;
	import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;

	@DataMongoTest(excludeAutoConfiguration = EmbeddedMongoAutoConfiguration.class)
	class ExampleDataMongoNonEmbeddedTests {

	}
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-neo4j-test]]
==== Auto-configured Data Neo4j Tests
You can use `@DataNeo4jTest` to test Neo4j applications.
By default, it scans for `@Node` classes, and configures Spring Data Neo4j repositories.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@DataNeo4jTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.
(For more about using Neo4J with Spring Boot, see "<<boot-features-neo4j>>", earlier in this chapter.)

TIP: A list of the auto-configuration settings that are enabled by `@DataNeo4jTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

The following example shows a typical setup for using Neo4J tests in Spring Boot:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;

	@DataNeo4jTest
	class ExampleDataNeo4jTests {

		@Autowired
		private YourRepository repository;

		//
	}
----

By default, Data Neo4j tests are transactional and roll back at the end of each test.
See the {spring-framework-docs}/testing.html#testcontext-tx-enabling-transactions[relevant section] in the Spring Framework Reference Documentation for more details.
If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:

[source,java,indent=0]
----
	import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
	import org.springframework.transaction.annotation.Propagation;
	import org.springframework.transaction.annotation.Transactional;

	@DataNeo4jTest
	@Transactional(propagation = Propagation.NOT_SUPPORTED)
	class ExampleNonTransactionalTests {

	}
----

NOTE: Transactional tests are not supported with reactive access.
If you are using this style, you must configure `@DataNeo4jTest` tests as described above.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-redis-test]]
==== Auto-configured Data Redis Tests
You can use `@DataRedisTest` to test Redis applications.
By default, it scans for `@RedisHash` classes and configures Spring Data Redis repositories.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@DataRedisTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.
(For more about using Redis with Spring Boot, see "<<boot-features-redis>>", earlier in this chapter.)

TIP: A list of the auto-configuration settings that are enabled by `@DataRedisTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

The following example shows the `@DataRedisTest` annotation in use:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.redis.DataRedisTest;

	@DataRedisTest
	class ExampleDataRedisTests {

		@Autowired
		private YourRepository repository;

		//
	}
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-ldap-test]]
==== Auto-configured Data LDAP Tests
You can use `@DataLdapTest` to test LDAP applications.
By default, it configures an in-memory embedded LDAP (if available), configures an `LdapTemplate`, scans for `@Entry` classes, and configures Spring Data LDAP repositories.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@DataLdapTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.
(For more about using LDAP with Spring Boot, see "<<boot-features-ldap>>", earlier in this chapter.)

TIP: A list of the auto-configuration settings that are enabled by `@DataLdapTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

The following example shows the `@DataLdapTest` annotation in use:

[source,java,indent=0]
----
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
	import org.springframework.ldap.core.LdapTemplate;

	@DataLdapTest
	class ExampleDataLdapTests {

		@Autowired
		private LdapTemplate ldapTemplate;

		//
	}
----

In-memory embedded LDAP generally works well for tests, since it is fast and does not require any developer installation.
If, however, you prefer to run tests against a real LDAP server, you should exclude the embedded LDAP auto-configuration, as shown in the following example:

[source,java,indent=0]
----
	import org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration;
	import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;

	@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
	class ExampleDataLdapNonEmbeddedTests {

	}
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-rest-client]]
==== Auto-configured REST Clients
You can use the `@RestClientTest` annotation to test REST clients.
By default, it auto-configures Jackson, GSON, and Jsonb support, configures a `RestTemplateBuilder`, and adds support for `MockRestServiceServer`.
Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@RestClientTest` annotation is used.
`@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.

TIP: A list of the auto-configuration settings that are enabled by `@RestClientTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

The specific beans that you want to test should be specified by using the `value` or `components` attribute of `@RestClientTest`, as shown in the following example:

[source,java,indent=0]
----
	@RestClientTest(RemoteVehicleDetailsService.class)
	class ExampleRestClientTest {

		@Autowired
		private RemoteVehicleDetailsService service;

		@Autowired
		private MockRestServiceServer server;

		@Test
		void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails()
				throws Exception {
			this.server.expect(requestTo("/greet/details"))
					.andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
			String greeting = this.service.callRestService();
			assertThat(greeting).isEqualTo("hello");
		}

	}
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-rest-docs]]
==== Auto-configured Spring REST Docs Tests
You can use the `@AutoConfigureRestDocs` annotation to use {spring-restdocs}[Spring REST Docs] in your tests with Mock MVC, REST Assured, or WebTestClient.
It removes the need for the JUnit extension in Spring REST Docs.

`@AutoConfigureRestDocs` can be used to override the default output directory (`target/generated-snippets` if you are using Maven or `build/generated-snippets` if you are using Gradle).
It can also be used to configure the host, scheme, and port that appears in any documented URIs.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-rest-docs-mock-mvc]]
===== Auto-configured Spring REST Docs Tests with Mock MVC
`@AutoConfigureRestDocs` customizes the `MockMvc` bean to use Spring REST Docs when testing Servlet-based web applications.
You can inject it by using `@Autowired` and use it in your tests as you normally would when using Mock MVC and Spring REST Docs, as shown in the following example:

[source,java,indent=0]
----
	import org.junit.jupiter.api.Test;

	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
	import org.springframework.http.MediaType;
	import org.springframework.test.web.servlet.MockMvc;

	import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
	import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
	import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

	@WebMvcTest(UserController.class)
	@AutoConfigureRestDocs
	class UserDocumentationTests {

		@Autowired
		private MockMvc mvc;

		@Test
		void listUsers() throws Exception {
			this.mvc.perform(get("/users").accept(MediaType.TEXT_PLAIN))
					.andExpect(status().isOk())
					.andDo(document("list-users"));
		}

	}
----

If you require more control over Spring REST Docs configuration than offered by the attributes of `@AutoConfigureRestDocs`, you can use a `RestDocsMockMvcConfigurationCustomizer` bean, as shown in the following example:

[source,java,indent=0]
----
	@TestConfiguration
	static class CustomizationConfiguration
			implements RestDocsMockMvcConfigurationCustomizer {

		@Override
		public void customize(MockMvcRestDocumentationConfigurer configurer) {
			configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
		}

	}
----

If you want to make use of Spring REST Docs support for a parameterized output directory, you can create a `RestDocumentationResultHandler` bean.
The auto-configuration calls `alwaysDo` with this result handler, thereby causing each `MockMvc` call to automatically generate the default snippets.
The following example shows a `RestDocumentationResultHandler` being defined:

[source,java,indent=0]
----
	@TestConfiguration(proxyBeanMethods = false)
	static class ResultHandlerConfiguration {

		@Bean
		public RestDocumentationResultHandler restDocumentation() {
			return MockMvcRestDocumentation.document("{method-name}");
		}

	}
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-rest-docs-web-test-client]]
===== Auto-configured Spring REST Docs Tests with WebTestClient
`@AutoConfigureRestDocs` can also be used with `WebTestClient` when testing reactive web applications.
You can inject it by using `@Autowired` and use it in your tests as you normally would when using `@WebFluxTest` and Spring REST Docs, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/autoconfigure/restdocs/webclient/UsersDocumentationTests.java[tag=source]
----

If you require more control over Spring REST Docs configuration than offered by the attributes of `@AutoConfigureRestDocs`, you can use a `RestDocsWebTestClientConfigurationCustomizer` bean, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/autoconfigure/restdocs/webclient/AdvancedConfigurationExample.java[tag=configuration]
----

If you want to make use of Spring REST Docs support for a parameterized output directory, you can use a `WebTestClientBuilderCustomizer` to configure a consumer for every entity exchange result.
The following example shows such a `WebTestClientBuilderCustomizer` being defined:

[source,java,indent=0]
----
include::{code-examples}/test/autoconfigure/restdocs/webclient/ParameterizedOutputConfigurationExample.java[tag=configuration]
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-rest-docs-rest-assured]]
===== Auto-configured Spring REST Docs Tests with REST Assured
`@AutoConfigureRestDocs` makes a `RequestSpecification` bean, preconfigured to use Spring REST Docs, available to your tests.
You can inject it by using `@Autowired` and use it in your tests as you normally would when using REST Assured and Spring REST Docs, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/autoconfigure/restdocs/restassured/UserDocumentationTests.java[tag=source]
----

If you require more control over Spring REST Docs configuration than offered by the attributes of `@AutoConfigureRestDocs`, a `RestDocsRestAssuredConfigurationCustomizer` bean can be used, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/autoconfigure/restdocs/restassured/AdvancedConfigurationExample.java[tag=configuration]
----



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-webservices]]
==== Auto-configured Spring Web Services Tests
You can use `@WebServiceClientTest` to test applications that use call web services using the Spring Web Services project.
By default, it configures a mock `WebServiceServer` bean and automatically customizes your `WebServiceTemplateBuilder`.
(For more about using Web Services with Spring Boot, see "<<boot-features-webservices>>", earlier in this chapter.)


TIP: A list of the auto-configuration settings that are enabled by `@WebServiceClientTest` can be <<appendix-test-auto-configuration.adoc#test-auto-configuration,found in the appendix>>.

The following example shows the `@WebServiceClientTest` annotation in use:

[source,java,indent=0]
----
	@WebServiceClientTest(ExampleWebServiceClient.class)
	class WebServiceClientIntegrationTests {

		@Autowired
		private MockWebServiceServer server;

		@Autowired
		private ExampleWebServiceClient client;

		@Test
		void mockServerCall() {
			this.server.expect(payload(new StringSource("<request/>"))).andRespond(
					withPayload(new StringSource("<response><status>200</status></response>")));
			assertThat(this.client.test()).extracting(Response::getStatus).isEqualTo(200);
		}

	}
----



[[boot-features-testing-spring-boot-applications-testing-auto-configured-additional-auto-config]]
==== Additional Auto-configuration and Slicing
Each slice provides one or more `@AutoConfigure...` annotations that namely defines the auto-configurations that should be included as part of a slice.
Additional auto-configurations can be added on a test-by-test basis by creating a custom `@AutoConfigure...` annotation or by adding `@ImportAutoConfiguration` to the test as shown in the following example:

[source,java,indent=0]
----
	@JdbcTest
	@ImportAutoConfiguration(IntegrationAutoConfiguration.class)
	class ExampleJdbcTests {

	}
----

NOTE: Make sure to not use the regular `@Import` annotation to import auto-configurations as they are handled in a specific way by Spring Boot.

Alternatively, additional auto-configurations can be added for any use of a slice annotation by registering them in `META-INF/spring.factories` as shown in the following example:

[indent=0]
----
	org.springframework.boot.test.autoconfigure.jdbc.JdbcTest=com.example.IntegrationAutoConfiguration
----

TIP: A slice or `@AutoConfigure...` annotation can be customized this way as long as it is meta-annotated with `@ImportAutoConfiguration`.



[[boot-features-testing-spring-boot-applications-testing-user-configuration]]
==== User Configuration and Slicing
If you <<using-spring-boot.adoc#using-boot-structuring-your-code, structure your code>> in a sensible way, your `@SpringBootApplication` class is <<boot-features-testing-spring-boot-applications-detecting-config, used by default>> as the configuration of your tests.

It then becomes important not to litter the application's main class with configuration settings that are specific to a particular area of its functionality.

Assume that you are using Spring Batch and you rely on the auto-configuration for it.
You could define your `@SpringBootApplication` as follows:

[source,java,indent=0]
----
	@SpringBootApplication
	@EnableBatchProcessing
	public class SampleApplication { ... }
----

Because this class is the source configuration for the test, any slice test actually tries to start Spring Batch, which is definitely not what you want to do.
A recommended approach is to move that area-specific configuration to a separate `@Configuration` class at the same level as your application, as shown in the following example:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	@EnableBatchProcessing
	public class BatchConfiguration { ... }
----

NOTE: Depending on the complexity of your application, you may either have a single `@Configuration` class for your customizations or one class per domain area.
The latter approach lets you enable it in one of your tests, if necessary, with the `@Import` annotation.

Test slices exclude `@Configuration` classes from scanning.
For example, for a `@WebMvcTest`, the following configuration will not include the given `WebMvcConfigurer` bean in the application context loaded by the test slice:

[source,java,indent=0]
----
	@Configuration
	public class WebConfiguration {
		@Bean
		public WebMvcConfigurer testConfigurer() {
			return new WebMvcConfigurer() {
				...
			};
		}
	}
----

The configuration below will, however, cause the custom `WebMvcConfigurer` to be loaded by the test slice.

[source,java,indent=0]
----
	@Component
	public class TestWebMvcConfigurer implements WebMvcConfigurer {
		...
	}
----

Another source of confusion is classpath scanning.
Assume that, while you structured your code in a sensible way, you need to scan an additional package.
Your application may resemble the following code:

[source,java,indent=0]
----
	@SpringBootApplication
	@ComponentScan({ "com.example.app", "org.acme.another" })
	public class SampleApplication { ... }
----

Doing so effectively overrides the default component scan directive with the side effect of scanning those two packages regardless of the slice that you chose.
For instance, a `@DataJpaTest` seems to suddenly scan components and user configurations of your application.
Again, moving the custom directive to a separate class is a good way to fix this issue.

TIP: If this is not an option for you, you can create a `@SpringBootConfiguration` somewhere in the hierarchy of your test so that it is used instead.
Alternatively, you can specify a source for your test, which disables the behavior of finding a default one.



[[boot-features-testing-spring-boot-applications-with-spock]]
==== Using Spock to Test Spring Boot Applications
If you wish to use Spock to test a Spring Boot application, you should add a dependency on Spock's `spock-spring` module to your application's build.
`spock-spring` integrates Spring's test framework into Spock.
It is recommended that you use Spock 1.2 or later to benefit from a number of improvements to Spock's Spring Framework and Spring Boot integration.
See https://spockframework.org/spock/docs/1.2/modules.html#_spring_module[the documentation for Spock's Spring module] for further details.



[[boot-features-test-utilities]]
=== Test Utilities
A few test utility classes that are generally useful when testing your application are packaged as part of `spring-boot`.



[[boot-features-configfileapplicationcontextinitializer-test-utility]]
==== ConfigFileApplicationContextInitializer
`ConfigFileApplicationContextInitializer` is an `ApplicationContextInitializer` that you can apply to your tests to load Spring Boot `application.properties` files.
You can use it when you do not need the full set of features provided by `@SpringBootTest`, as shown in the following example:

[source,java,indent=0]
----
	@ContextConfiguration(classes = Config.class,
		initializers = ConfigFileApplicationContextInitializer.class)
----

NOTE: Using `ConfigFileApplicationContextInitializer` alone does not provide support for `@Value("${...}")` injection.
Its only job is to ensure that `application.properties` files are loaded into Spring's `Environment`.
For `@Value` support, you need to either additionally configure a `PropertySourcesPlaceholderConfigurer` or use `@SpringBootTest`, which auto-configures one for you.



[[boot-features-test-property-values]]
==== TestPropertyValues
`TestPropertyValues` lets you quickly add properties to a `ConfigurableEnvironment` or `ConfigurableApplicationContext`.
You can call it with `key=value` strings, as follows:

[source,java,indent=0]
----
	TestPropertyValues.of("org=Spring", "name=Boot").applyTo(env);
----



[[boot-features-output-capture-test-utility]]
==== OutputCapture
`OutputCapture` is a JUnit `Extension` that you can use to capture `System.out` and `System.err` output.
To use add `@ExtendWith(OutputCaptureExtension.class)` and inject `CapturedOutput` as an argument to your test class constructor or test method as follows:

[source,java,indent=0]
----
include::{test-examples}/test/system/OutputCaptureTests.java[tag=test]
----



[[boot-features-rest-templates-test-utility]]
==== TestRestTemplate
`TestRestTemplate` is a convenience alternative to Spring's `RestTemplate` that is useful in integration tests.
You can get a vanilla template or one that sends Basic HTTP authentication (with a username and password).
In either case, the template is fault tolerant.
This means that it behaves in a test-friendly way by not throwing exceptions on 4xx and 5xx errors.
Instead, such errors can be detected via the returned `ResponseEntity` and its status code.

TIP: Spring Framework 5.0 provides a new `WebTestClient` that works for <<boot-features-testing-spring-boot-applications-testing-autoconfigured-webflux-tests, WebFlux integration tests>> and both <<boot-features-testing-spring-boot-applications-testing-with-running-server, WebFlux and MVC end-to-end testing>>.
It provides a fluent API for assertions, unlike `TestRestTemplate`.

It is recommended, but not mandatory, to use the Apache HTTP Client (version 4.3.2 or better).
If you have that on your classpath, the `TestRestTemplate` responds by configuring the client appropriately.
If you do use Apache's HTTP client, some additional test-friendly features are enabled:

* Redirects are not followed (so you can assert the response location).
* Cookies are ignored (so the template is stateless).

`TestRestTemplate` can be instantiated directly in your integration tests, as shown in the following example:

[source,java,indent=0]
----
	public class MyTest {

		private TestRestTemplate template = new TestRestTemplate();

		@Test
		public void testRequest() throws Exception {
			HttpHeaders headers = this.template.getForEntity(
					"https://myhost.example.com/example", String.class).getHeaders();
			assertThat(headers.getLocation()).hasHost("other.example.com");
		}

	}
----

Alternatively, if you use the `@SpringBootTest` annotation with `WebEnvironment.RANDOM_PORT` or `WebEnvironment.DEFINED_PORT`, you can inject a fully configured `TestRestTemplate` and start using it.
If necessary, additional customizations can be applied through the `RestTemplateBuilder` bean.
Any URLs that do not specify a host and port automatically connect to the embedded server, as shown in the following example:

[source,java,indent=0]
----
include::{test-examples}/web/client/SampleWebClientTests.java[tag=test]
----



[[boot-features-websockets]]
== WebSockets
Spring Boot provides WebSockets auto-configuration for embedded Tomcat, Jetty, and Undertow.
If you deploy a war file to a standalone container, Spring Boot assumes that the container is responsible for the configuration of its WebSocket support.

Spring Framework provides {spring-framework-docs}/web.html#websocket[rich WebSocket support] for MVC web applications that can be easily accessed through the `spring-boot-starter-websocket` module.

WebSocket support is also available for {spring-framework-docs}/web-reactive.html#webflux-websocket[reactive web applications] and requires to include the WebSocket API alongside `spring-boot-starter-webflux`:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>javax.websocket</groupId>
		<artifactId>javax.websocket-api</artifactId>
	</dependency>
----



[[boot-features-webservices]]
== Web Services
Spring Boot provides Web Services auto-configuration so that all you must do is define your `Endpoints`.

The {spring-webservices-docs}[Spring Web Services features] can be easily accessed with the `spring-boot-starter-webservices` module.

`SimpleWsdl11Definition` and `SimpleXsdSchema` beans can be automatically created for your WSDLs and XSDs respectively.
To do so, configure their location, as shown in the following example:


[source,yaml,indent=0,configprops,configblocks]
----
	spring:
	  webservices:
	    wsdl-locations: "classpath:/wsdl"
----



[[boot-features-webservices-template]]
=== Calling Web Services with WebServiceTemplate
If you need to call remote Web services from your application, you can use the {spring-webservices-docs}#client-web-service-template[`WebServiceTemplate`] class.
Since `WebServiceTemplate` instances often need to be customized before being used, Spring Boot does not provide any single auto-configured `WebServiceTemplate` bean.
It does, however, auto-configure a `WebServiceTemplateBuilder`, which can be used to create `WebServiceTemplate` instances when needed.

The following code shows a typical example:

[source,java,indent=0]
----
	@Service
	public class MyService {

		private final WebServiceTemplate webServiceTemplate;

		public MyService(WebServiceTemplateBuilder webServiceTemplateBuilder) {
			this.webServiceTemplate = webServiceTemplateBuilder.build();
		}

		public DetailsResp someWsCall(DetailsReq detailsReq) {
			 return (DetailsResp) this.webServiceTemplate.marshalSendAndReceive(detailsReq, new SoapActionCallback(ACTION));
		}

	}
----

By default, `WebServiceTemplateBuilder` detects a suitable HTTP-based `WebServiceMessageSender` using the available HTTP client libraries on the classpath.
You can also customize read and connection timeouts as follows:

[source,java,indent=0]
----
	@Bean
	public WebServiceTemplate webServiceTemplate(WebServiceTemplateBuilder builder) {
		return builder.messageSenders(new HttpWebServiceMessageSenderBuilder()
				.setConnectTimeout(5000).setReadTimeout(2000).build()).build();
	}
----



[[boot-features-developing-auto-configuration]]
== Creating Your Own Auto-configuration
If you work in a company that develops shared libraries, or if you work on an open-source or commercial library, you might want to develop your own auto-configuration.
Auto-configuration classes can be bundled in external jars and still be picked-up by Spring Boot.

Auto-configuration can be associated to a "`starter`" that provides the auto-configuration code as well as the typical libraries that you would use with it.
We first cover what you need to know to build your own auto-configuration and then we move on to the <<boot-features-custom-starter,typical steps required to create a custom starter>>.

TIP: A https://github.com/snicoll-demos/spring-boot-master-auto-configuration[demo project] is available to showcase how you can create a starter step-by-step.



[[boot-features-understanding-auto-configured-beans]]
=== Understanding Auto-configured Beans
Under the hood, auto-configuration is implemented with standard `@Configuration` classes.
Additional `@Conditional` annotations are used to constrain when the auto-configuration should apply.
Usually, auto-configuration classes use `@ConditionalOnClass` and `@ConditionalOnMissingBean` annotations.
This ensures that auto-configuration applies only when relevant classes are found and when you have not declared your own `@Configuration`.

You can browse the source code of {spring-boot-autoconfigure-module-code}[`spring-boot-autoconfigure`] to see the `@Configuration` classes that Spring provides (see the {spring-boot-code}/spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring.factories[`META-INF/spring.factories`] file).



[[boot-features-locating-auto-configuration-candidates]]
=== Locating Auto-configuration Candidates
Spring Boot checks for the presence of a `META-INF/spring.factories` file within your published jar.
The file should list your configuration classes under the `EnableAutoConfiguration` key, as shown in the following example:

[indent=0]
----
	org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
	com.mycorp.libx.autoconfigure.LibXAutoConfiguration,\
	com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration
----

NOTE: Auto-configurations must be loaded that way _only_.
Make sure that they are defined in a specific package space and that they are never the target of component scanning.
Furthermore, auto-configuration classes should not enable component scanning to find additional components.
Specific ``@Import``s should be used instead.

You can use the {spring-boot-autoconfigure-module-code}/AutoConfigureAfter.java[`@AutoConfigureAfter`] or {spring-boot-autoconfigure-module-code}/AutoConfigureBefore.java[`@AutoConfigureBefore`] annotations if your configuration needs to be applied in a specific order.
For example, if you provide web-specific configuration, your class may need to be applied after `WebMvcAutoConfiguration`.

If you want to order certain auto-configurations that should not have any direct knowledge of each other, you can also use `@AutoConfigureOrder`.
That annotation has the same semantic as the regular `@Order` annotation but provides a dedicated order for auto-configuration classes.

As with standard `@Configuration` classes, the order in which auto-configuration classes are applied only affects the order in which their beans are defined.
The order in which those beans are subsequently created is unaffected and is determined by each bean's dependencies and any `@DependsOn` relationships.



[[boot-features-condition-annotations]]
=== Condition Annotations
You almost always want to include one or more `@Conditional` annotations on your auto-configuration class.
The `@ConditionalOnMissingBean` annotation is one common example that is used to allow developers to override auto-configuration if they are not happy with your defaults.

Spring Boot includes a number of `@Conditional` annotations that you can reuse in your own code by annotating `@Configuration` classes or individual `@Bean` methods.
These annotations include:

* <<boot-features-class-conditions>>
* <<boot-features-bean-conditions>>
* <<boot-features-property-conditions>>
* <<boot-features-resource-conditions>>
* <<boot-features-web-application-conditions>>
* <<boot-features-spel-conditions>>



[[boot-features-class-conditions]]
==== Class Conditions
The `@ConditionalOnClass` and `@ConditionalOnMissingClass` annotations let `@Configuration` classes be included based on the presence or absence of specific classes.
Due to the fact that annotation metadata is parsed by using https://asm.ow2.io/[ASM], you can use the `value` attribute to refer to the real class, even though that class might not actually appear on the running application classpath.
You can also use the `name` attribute if you prefer to specify the class name by using a `String` value.

This mechanism does not apply the same way to `@Bean` methods where typically the return type is the target of the condition: before the condition on the method applies, the JVM will have loaded the class and potentially processed method references which will fail if the class is not present.

To handle this scenario, a separate `@Configuration` class can be used to isolate the condition, as shown in the following example:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	// Some conditions
	public class MyAutoConfiguration {

		// Auto-configured beans

		@Configuration(proxyBeanMethods = false)
		@ConditionalOnClass(EmbeddedAcmeService.class)
		static class EmbeddedConfiguration {

			@Bean
			@ConditionalOnMissingBean
			public EmbeddedAcmeService embeddedAcmeService() { ... }

		}

	}
----

TIP: If you use `@ConditionalOnClass` or `@ConditionalOnMissingClass` as a part of a meta-annotation to compose your own composed annotations, you must use `name` as referring to the class in such a case is not handled.



[[boot-features-bean-conditions]]
==== Bean Conditions
The `@ConditionalOnBean` and `@ConditionalOnMissingBean` annotations let a bean be included based on the presence or absence of specific beans.
You can use the `value` attribute to specify beans by type or `name` to specify beans by name.
The `search` attribute lets you limit the `ApplicationContext` hierarchy that should be considered when searching for beans.

When placed on a `@Bean` method, the target type defaults to the return type of the method, as shown in the following example:

[source,java,indent=0]
----
	@Configuration(proxyBeanMethods = false)
	public class MyAutoConfiguration {

		@Bean
		@ConditionalOnMissingBean
		public MyService myService() { ... }

	}
----

In the preceding example, the `myService` bean is going to be created if no bean of type `MyService` is already contained in the `ApplicationContext`.

TIP: You need to be very careful about the order in which bean definitions are added, as these conditions are evaluated based on what has been processed so far.
For this reason, we recommend using only `@ConditionalOnBean` and `@ConditionalOnMissingBean` annotations on auto-configuration classes (since these are guaranteed to load after any user-defined bean definitions have been added).

NOTE: `@ConditionalOnBean` and `@ConditionalOnMissingBean` do not prevent `@Configuration` classes from being created.
The only difference between using these conditions at the class level and marking each contained `@Bean` method with the annotation is that the former prevents registration of the `@Configuration` class as a bean if the condition does not match.

TIP: When declaring a `@Bean` method, provide as much type information as possible in the method's return type.
For example, if your bean's concrete class implements an interface the bean method's return type should be the concrete class and not the interface.
Providing as much type information as possible in `@Bean` methods is particularly important when using bean conditions as their evaluation can only rely upon to type information that's available in the method signature.



[[boot-features-property-conditions]]
==== Property Conditions
The `@ConditionalOnProperty` annotation lets configuration be included based on a Spring Environment property.
Use the `prefix` and `name` attributes to specify the property that should be checked.
By default, any property that exists and is not equal to `false` is matched.
You can also create more advanced checks by using the `havingValue` and `matchIfMissing` attributes.



[[boot-features-resource-conditions]]
==== Resource Conditions
The `@ConditionalOnResource` annotation lets configuration be included only when a specific resource is present.
Resources can be specified by using the usual Spring conventions, as shown in the following example: `file:/home/user/test.dat`.



[[boot-features-web-application-conditions]]
==== Web Application Conditions
The `@ConditionalOnWebApplication` and `@ConditionalOnNotWebApplication` annotations let configuration be included depending on whether the application is a "`web application`".
A servlet-based web application is any application that uses a Spring `WebApplicationContext`, defines a `session` scope, or has a `ConfigurableWebEnvironment`.
A reactive web application is any application that uses a `ReactiveWebApplicationContext`, or has a `ConfigurableReactiveWebEnvironment`.

The `@ConditionalOnWarDeployment` annotation lets configuration be included depending on whether the application is a traditional WAR application that is deployed to a container.
This condition will not match for applications that are run with an embedded server.



[[boot-features-spel-conditions]]
==== SpEL Expression Conditions
The `@ConditionalOnExpression` annotation lets configuration be included based on the result of a {spring-framework-docs}/core.html#expressions[SpEL expression].



[[boot-features-test-autoconfig]]
=== Testing your Auto-configuration
An auto-configuration can be affected by many factors: user configuration (`@Bean` definition and `Environment` customization), condition evaluation (presence of a particular library), and others.
Concretely, each test should create a well defined `ApplicationContext` that represents a combination of those customizations.
`ApplicationContextRunner` provides a great way to achieve that.

`ApplicationContextRunner` is usually defined as a field of the test class to gather the base, common configuration.
The following example makes sure that `UserServiceAutoConfiguration` is always invoked:

[source,java,indent=0]
----
include::{test-examples}/autoconfigure/UserServiceAutoConfigurationTests.java[tag=runner]
----

TIP: If multiple auto-configurations have to be defined, there is no need to order their declarations as they are invoked in the exact same order as when running the application.

Each test can use the runner to represent a particular use case.
For instance, the sample below invokes a user configuration (`UserConfiguration`) and checks that the auto-configuration backs off properly.
Invoking `run` provides a callback context that can be used with `AssertJ`.

[source,java,indent=0]
----
include::{test-examples}/autoconfigure/UserServiceAutoConfigurationTests.java[tag=test-user-config]
----

It is also possible to easily customize the `Environment`, as shown in the following example:

[source,java,indent=0]
----
include::{test-examples}/autoconfigure/UserServiceAutoConfigurationTests.java[tag=test-env]
----

The runner can also be used to display the `ConditionEvaluationReport`.
The report can be printed at `INFO` or `DEBUG` level.
The following example shows how to use the `ConditionEvaluationReportLoggingListener` to print the report in auto-configuration tests.

[source,java,indent=0]
----
	@Test
	void autoConfigTest() {
		ConditionEvaluationReportLoggingListener initializer = new ConditionEvaluationReportLoggingListener(
				LogLevel.INFO);
		ApplicationContextRunner contextRunner = new ApplicationContextRunner()
				.withInitializer(initializer).run((context) -> {
						// Do something...
				});
	}
----



[[boot-features-test-autoconfig-simulating-web-context]]
==== Simulating a Web Context
If you need to test an auto-configuration that only operates in a Servlet or Reactive web application context, use the `WebApplicationContextRunner` or `ReactiveWebApplicationContextRunner` respectively.



[[boot-features-test-autoconfig-overriding-classpath]]
==== Overriding the Classpath
It is also possible to test what happens when a particular class and/or package is not present at runtime.
Spring Boot ships with a `FilteredClassLoader` that can easily be used by the runner.
In the following example, we assert that if `UserService` is not present, the auto-configuration is properly disabled:

[source,java,indent=0]
----
include::{test-examples}/autoconfigure/UserServiceAutoConfigurationTests.java[tag=test-classloader]
----



[[boot-features-custom-starter]]
=== Creating Your Own Starter
A typical Spring Boot starter contains code to auto-configure and customize the infrastructure of a given technology, let's call that "acme".
To make it easily extensible, a number of configuration keys in a dedicated namespace can be exposed to the environment.
Finally, a single "starter" dependency is provided to help users get started as easily as possible.

Concretely, a custom starter can contain the following:

* The `autoconfigure` module that contains the auto-configuration code for "acme".
* The `starter` module that provides a dependency to the `autoconfigure` module as well as "acme" and any additional dependencies that are typically useful.
In a nutshell, adding the starter should provide everything needed to start using that library.

This separation in two modules is in no way necessary.
If "acme" has several flavours, options or optional features, then it is better to separate the auto-configuration as you can clearly express the fact some features are optional.
Besides, you have the ability to craft a starter that provides an opinion about those optional dependencies.
At the same time, others can rely only on the `autoconfigure` module and craft their own starter with different opinions.

If the auto-configuration is relatively straightforward and does not have optional feature, merging the two modules in the starter is definitely an option.



[[boot-features-custom-starter-naming]]
==== Naming
You should make sure to provide a proper namespace for your starter.
Do not start your module names with `spring-boot`, even if you use a different Maven `groupId`.
We may offer official support for the thing you auto-configure in the future.

As a rule of thumb, you should name a combined module after the starter.
For example, assume that you are creating a starter for "acme" and that you name the auto-configure module `acme-spring-boot` and the starter `acme-spring-boot-starter`.
If you only have one module that combines the two, name it `acme-spring-boot-starter`.



[[boot-features-custom-starter-configuration-keys]]
==== Configuration keys
If your starter provides configuration keys, use a unique namespace for them.
In particular, do not include your keys in the namespaces that Spring Boot uses (such as `server`, `management`, `spring`, and so on).
If you use the same namespace, we may modify these namespaces in the future in ways that break your modules.
As a rule of thumb, prefix all your keys with a namespace that you own (e.g. `acme`).

Make sure that configuration keys are documented by adding field javadoc for each property, as shown in the following example:

[source,java,indent=0]
----
	@ConfigurationProperties("acme")
	public class AcmeProperties {

		/**
		 * Whether to check the location of acme resources.
		 */
		private boolean checkLocation = true;

		/**
		 * Timeout for establishing a connection to the acme server.
		 */
		private Duration loginTimeout = Duration.ofSeconds(3);

		// getters & setters

	}
----

NOTE: You should only use plain text with `@ConfigurationProperties` field Javadoc, since they are not processed before being added to the JSON.

Here are some rules we follow internally to make sure descriptions are consistent:

* Do not start the description by "The" or "A".
* For `boolean` types, start the description with "Whether" or "Enable".
* For collection-based types, start the description with "Comma-separated list"
* Use `java.time.Duration` rather than `long` and describe the default unit if it differs from milliseconds, e.g. "If a duration suffix is not specified, seconds will be used".
* Do not provide the default value in the description unless it has to be determined at runtime.

Make sure to <<appendix-configuration-metadata.adoc#configuration-metadata-annotation-processor,trigger meta-data generation>> so that IDE assistance is available for your keys as well.
You may want to review the generated metadata (`META-INF/spring-configuration-metadata.json`) to make sure your keys are properly documented.
Using your own starter in a compatible IDE is also a good idea to validate that quality of the metadata.



[[boot-features-custom-starter-module-autoconfigure]]
==== The "`autoconfigure`" Module
The `autoconfigure` module contains everything that is necessary to get started with the library.
It may also contain configuration key definitions (such as `@ConfigurationProperties`) and any callback interface that can be used to further customize how the components are initialized.

TIP: You should mark the dependencies to the library as optional so that you can include the `autoconfigure` module in your projects more easily.
If you do it that way, the library is not provided and, by default, Spring Boot backs off.

Spring Boot uses an annotation processor to collect the conditions on auto-configurations in a metadata file (`META-INF/spring-autoconfigure-metadata.properties`).
If that file is present, it is used to eagerly filter auto-configurations that do not match, which will improve startup time.
It is recommended to add the following dependency in a module that contains auto-configurations:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-autoconfigure-processor</artifactId>
		<optional>true</optional>
	</dependency>
----

If you have defined auto-configurations directly in your application, make sure to configure the `spring-boot-maven-plugin` to prevent the `repackage` goal from adding the dependency into the fat jar:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<project>
		<build>
			<plugins>
				<plugin>
					<groupId>org.springframework.boot</groupId>
					<artifactId>spring-boot-maven-plugin</artifactId>
					<configuration>
						<excludes>
							<exclude>
								<groupId>org.springframework.boot</groupId>
								<artifactId>spring-boot-autoconfigure-processor</artifactId>
							</exclude>
						</excludes>
					</configuration>
				</plugin>
			</plugins>
		</build>
	</project>
----

With Gradle 4.5 and earlier, the dependency should be declared in the `compileOnly` configuration, as shown in the following example:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	dependencies {
		compileOnly "org.springframework.boot:spring-boot-autoconfigure-processor"
	}
----

With Gradle 4.6 and later, the dependency should be declared in the `annotationProcessor` configuration, as shown in the following example:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	dependencies {
		annotationProcessor "org.springframework.boot:spring-boot-autoconfigure-processor"
	}
----



[[boot-features-custom-starter-module-starter]]
==== Starter Module
The starter is really an empty jar.
Its only purpose is to provide the necessary dependencies to work with the library.
You can think of it as an opinionated view of what is required to get started.

Do not make assumptions about the project in which your starter is added.
If the library you are auto-configuring typically requires other starters, mention them as well.
Providing a proper set of _default_ dependencies may be hard if the number of optional dependencies is high, as you should avoid including dependencies that are unnecessary for a typical usage of the library.
In other words, you should not include optional dependencies.

NOTE: Either way, your starter must reference the core Spring Boot starter (`spring-boot-starter`) directly or indirectly (i.e. no need to add it if your starter relies on another starter).
If a project is created with only your custom starter, Spring Boot's core features will be honoured by the presence of the core starter.



[[boot-features-kotlin]]
== Kotlin support
https://kotlinlang.org[Kotlin] is a statically-typed language targeting the JVM (and other platforms) which allows writing concise and elegant code while providing {kotlin-docs}java-interop.html[interoperability] with existing libraries written in Java.

Spring Boot provides Kotlin support by leveraging the support in other Spring projects such as Spring Framework, Spring Data, and Reactor.
See the {spring-framework-docs}/languages.html#kotlin[Spring Framework Kotlin support documentation] for more information.

The easiest way to start with Spring Boot and Kotlin is to follow https://spring.io/guides/tutorials/spring-boot-kotlin/[this comprehensive tutorial].
You can create new Kotlin projects via https://start.spring.io/#!language=kotlin[start.spring.io].
Feel free to join the #spring channel of https://slack.kotlinlang.org/[Kotlin Slack] or ask a question with the `spring` and `kotlin` tags on https://stackoverflow.com/questions/tagged/spring+kotlin[Stack Overflow] if you need support.



[[boot-features-kotlin-requirements]]
=== Requirements
Spring Boot requires at least Kotlin 1.3.x and manages a suitable Kotlin version via dependency management.
To use Kotlin, `org.jetbrains.kotlin:kotlin-stdlib` and `org.jetbrains.kotlin:kotlin-reflect` must be present on the classpath.
The `kotlin-stdlib` variants `kotlin-stdlib-jdk7` and `kotlin-stdlib-jdk8` can also be used.

Since https://discuss.kotlinlang.org/t/classes-final-by-default/166[Kotlin classes are final by default], you are likely to want to configure {kotlin-docs}compiler-plugins.html#spring-support[kotlin-spring] plugin in order to automatically open Spring-annotated classes so that they can be proxied.

https://github.com/FasterXML/jackson-module-kotlin[Jackson's Kotlin module] is required for serializing / deserializing JSON data in Kotlin.
It is automatically registered when found on the classpath.
A warning message is logged if Jackson and Kotlin are present but the Jackson Kotlin module is not.

TIP: These dependencies and plugins are provided by default if one bootstraps a Kotlin project on https://start.spring.io/#!language=kotlin[start.spring.io].



[[boot-features-kotlin-null-safety]]
=== Null-safety
One of Kotlin's key features is {kotlin-docs}null-safety.html[null-safety].
It deals with `null` values at compile time rather than deferring the problem to runtime and encountering a `NullPointerException`.
This helps to eliminate a common source of bugs without paying the cost of wrappers like `Optional`.
Kotlin also allows using functional constructs with nullable values as described in this https://www.baeldung.com/kotlin-null-safety[comprehensive guide to null-safety in Kotlin].

Although Java does not allow one to express null-safety in its type system, Spring Framework, Spring Data, and Reactor now provide null-safety of their API via tooling-friendly annotations.
By default, types from Java APIs used in Kotlin are recognized as {kotlin-docs}java-interop.html#null-safety-and-platform-types[platform types] for which null-checks are relaxed.
{kotlin-docs}java-interop.html#jsr-305-support[Kotlin's support for JSR 305 annotations] combined with nullability annotations provide null-safety for the related Spring API in Kotlin.

The JSR 305 checks can be configured by adding the `-Xjsr305` compiler flag with the following options: `-Xjsr305={strict|warn|ignore}`.
The default behavior is the same as `-Xjsr305=warn`.
The `strict` value is required to have null-safety taken in account in Kotlin types inferred from Spring API but should be used with the knowledge that Spring API nullability declaration could evolve even between minor releases and more checks may be added in the future).

WARNING: Generic type arguments, varargs and array elements nullability are not yet supported.
See https://jira.spring.io/browse/SPR-15942[SPR-15942] for up-to-date information.
Also be aware that Spring Boot's own API is {github-issues}10712[not yet annotated].



[[boot-features-kotlin-api]]
=== Kotlin API



[[boot-features-kotlin-api-runapplication]]
==== runApplication
Spring Boot provides an idiomatic way to run an application with `runApplication<MyApplication>(*args)` as shown in the following example:

[source,kotlin,indent=0]
----
	import org.springframework.boot.autoconfigure.SpringBootApplication
	import org.springframework.boot.runApplication

	@SpringBootApplication
	class MyApplication

	fun main(args: Array<String>) {
		runApplication<MyApplication>(*args)
	}
----

This is a drop-in replacement for `SpringApplication.run(MyApplication::class.java, *args)`.
It also allows customization of the application as shown in the following example:

[source,kotlin,indent=0]
----
	runApplication<MyApplication>(*args) {
		setBannerMode(OFF)
	}
----



[[boot-features-kotlin-api-extensions]]
==== Extensions
Kotlin {kotlin-docs}extensions.html[extensions] provide the ability to extend existing classes with additional functionality.
The Spring Boot Kotlin API makes use of these extensions to add new Kotlin specific conveniences to existing APIs.

`TestRestTemplate` extensions, similar to those provided by Spring Framework for `RestOperations` in Spring Framework, are provided.
Among other things, the extensions make it possible to take advantage of Kotlin reified type parameters.



[[boot-features-kotlin-dependency-management]]
=== Dependency management
In order to avoid mixing different versions of Kotlin dependencies on the classpath, Spring Boot imports the Kotlin BOM.

With Maven, the Kotlin version can be customized via the `kotlin.version` property and plugin management is provided for `kotlin-maven-plugin`.
With Gradle, the Spring Boot plugin automatically aligns the `kotlin.version` with the version of the Kotlin plugin.

Spring Boot also manages the version of Coroutines dependencies by importing the Kotlin Coroutines BOM.
The version can be customized via the `kotlin-coroutines.version` property.

TIP: `org.jetbrains.kotlinx:kotlinx-coroutines-reactor` dependency is provided by default if one bootstraps a Kotlin project with at least one reactive dependency on https://start.spring.io/#!language=kotlin[start.spring.io].



[[boot-features-kotlin-configuration-properties]]
=== @ConfigurationProperties
`@ConfigurationProperties` when used in combination with <<boot-features-external-config-constructor-binding,`@ConstructorBinding`>> supports classes with immutable `val` properties as shown in the following example:

[source,kotlin,indent=0]
----
@ConstructorBinding
@ConfigurationProperties("example.kotlin")
data class KotlinExampleProperties(
		val name: String,
		val description: String,
		val myService: MyService) {

	data class MyService(
			val apiToken: String,
			val uri: URI
	)
}
----

TIP: To generate <<appendix-configuration-metadata.adoc#configuration-metadata-annotation-processor,your own metadata>> using the annotation processor, {kotlin-docs}kapt.html[`kapt` should be configured] with the `spring-boot-configuration-processor` dependency.
Note that some features (such as detecting the default value or deprecated items) are not working due to limitations in the model kapt provides.



[[boot-features-kotlin-testing]]
=== Testing
While it is possible to use JUnit 4 to test Kotlin code, JUnit 5 is provided by default and is recommended.
JUnit 5 enables a test class to be instantiated once and reused for all of the class's tests.
This makes it possible to use `@BeforeAll` and `@AfterAll` annotations on non-static methods, which is a good fit for Kotlin.

To mock Kotlin classes, https://mockk.io/[MockK] is recommended.
If you need the `Mockk` equivalent of the Mockito specific <<boot-features-testing-spring-boot-applications-mocking-beans,`@MockBean` and `@SpyBean` annotations>>, you can use https://github.com/Ninja-Squad/springmockk[SpringMockK] which provides similar `@MockkBean` and `@SpykBean` annotations.



[[boot-features-kotlin-resources]]
=== Resources



[[boot-features-kotlin-resources-further-reading]]
==== Further reading
* {kotlin-docs}[Kotlin language reference]
* https://kotlinlang.slack.com/[Kotlin Slack] (with a dedicated #spring channel)
* https://stackoverflow.com/questions/tagged/spring+kotlin[Stackoverflow with `spring` and `kotlin` tags]
* https://try.kotlinlang.org/[Try Kotlin in your browser]
* https://blog.jetbrains.com/kotlin/[Kotlin blog]
* https://kotlin.link/[Awesome Kotlin]
* https://spring.io/guides/tutorials/spring-boot-kotlin/[Tutorial: building web applications with Spring Boot and Kotlin]
* https://spring.io/blog/2016/02/15/developing-spring-boot-applications-with-kotlin[Developing Spring Boot applications with Kotlin]
* https://spring.io/blog/2016/03/20/a-geospatial-messenger-with-kotlin-spring-boot-and-postgresql[A Geospatial Messenger with Kotlin, Spring Boot and PostgreSQL]
* https://spring.io/blog/2017/01/04/introducing-kotlin-support-in-spring-framework-5-0[Introducing Kotlin support in Spring Framework 5.0]
* https://spring.io/blog/2017/08/01/spring-framework-5-kotlin-apis-the-functional-way[Spring Framework 5 Kotlin APIs, the functional way]



[[boot-features-kotlin-resources-examples]]
==== Examples
* https://github.com/sdeleuze/spring-boot-kotlin-demo[spring-boot-kotlin-demo]: regular Spring Boot + Spring Data JPA project
* https://github.com/mixitconf/mixit[mixit]: Spring Boot 2 + WebFlux + Reactive Spring Data MongoDB
* https://github.com/sdeleuze/spring-kotlin-fullstack[spring-kotlin-fullstack]: WebFlux Kotlin fullstack example with Kotlin2js for frontend instead of JavaScript or TypeScript
* https://github.com/spring-petclinic/spring-petclinic-kotlin[spring-petclinic-kotlin]: Kotlin version of the Spring PetClinic Sample Application
* https://github.com/sdeleuze/spring-kotlin-deepdive[spring-kotlin-deepdive]: a step by step migration for Boot 1.0 + Java to Boot 2.0 + Kotlin
* https://github.com/sdeleuze/spring-boot-coroutines-demo[spring-boot-coroutines-demo]: Coroutines sample project



[[boot-features-container-images]]
== Container Images
It is easily possible to package a Spring Boot fat jar as a docker image.
However, there are various downsides to copying and running the fat jar as is in the docker image.
There’s always a certain amount of overhead when running a fat jar without unpacking it, and in a containerized environment this can be noticeable.
The other issue is that putting your application's code and all its dependencies in one layer in the Docker image is sub-optimal.
Since you probably recompile your code more often than you upgrade the version of Spring Boot you use, it’s often better to separate things a bit more.
If you put jar files in the layer before your application classes, Docker often only needs to change the very bottom layer and can pick others up from its cache.



[[boot-layering-docker-images]]
=== Layering Docker Images
To make it easier to create optimized Docker images, Spring Boot supports adding a layer index file to the jar.
It provides a list of layers and the parts of the jar that should be contained within them.
The list of layers in the index is ordered based on the order in which the layers should be added to the Docker/OCI image.
Out-of-the-box, the following layers are supported:

* `dependencies` (for regular released dependencies)
* `spring-boot-loader` (for everything under `org/springframework/boot/loader`)
* `snapshot-dependencies` (for snapshot dependencies)
* `application` (for application classes and resources)

The following shows an example of a `layers.idx` file:

[source,yaml,indent=0]
----
	- "dependencies":
	  - BOOT-INF/lib/library1.jar
	  - BOOT-INF/lib/library2.jar
	- "spring-boot-loader":
	  - org/springframework/boot/loader/JarLauncher.class
	  - org/springframework/boot/loader/jar/JarEntry.class
	- "snapshot-dependencies":
	  - BOOT-INF/lib/library3-SNAPSHOT.jar
	- "application":
	  - META-INF/MANIFEST.MF
	  - BOOT-INF/classes/a/b/C.class
----

This layering is designed to separate code based on how likely it is to change between application builds.
Library code is less likely to change between builds, so it is placed in its own layers to allow tooling to re-use the layers from cache.
Application code is more likely to change between builds so it is isolated in a separate layer.

For Maven, refer to the {spring-boot-maven-plugin-docs}#repackage-layers[packaging layered jars section] for more details on adding a layer index to the jar.
For Gradle, refer to the {spring-boot-gradle-plugin-docs}#packaging-layered-jars[packaging layered jars section] of the Gradle plugin documentation.



[[boot-features-container-images-building]]
=== Building Container Images
Spring Boot applications can be containerized <<boot-features-container-images-docker,using Dockerfiles>>, or by <<boot-features-container-images-buildpacks,using Cloud Native Buildpacks to create docker compatible container images that you can run anywhere>>.



[[boot-features-container-images-docker]]
==== Dockerfiles
While it is possible to convert a Spring Boot fat jar into a docker image with just a few lines in the Dockerfile, we will use the <<boot-layering-docker-images,layering feature>> to create an optimized docker image.
When you create a jar containing the layers index file, the `spring-boot-jarmode-layertools` jar will be added as a dependency to your jar.
With this jar on the classpath, you can launch your application in a special mode which allows the bootstrap code to run something entirely different from your application, for example, something that extracts the layers.

CAUTION: The `layertools` mode can not be used with a <<deployment.adoc#deployment-install, fully executable Spring Boot archive>> that includes a launch script.
Disable launch script configuration when building a jar file that is intended to be used with `layertools`.

Here’s how you can launch your jar with a `layertools` jar mode:

[source]
----
$ java -Djarmode=layertools -jar my-app.jar
----

This will provide the following output:

[source]
----
Usage:
  java -Djarmode=layertools -jar my-app.jar

Available commands:
  list     List layers from the jar that can be extracted
  extract  Extracts layers from the jar for image creation
  help     Help about any command
----

The `extract` command can be used to easily split the application into layers to be added to the dockerfile.
Here's an example of a Dockerfile using `jarmode`.

[source]
----
FROM adoptopenjdk:11-jre-hotspot as builder
WORKDIR application
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} application.jar
RUN java -Djarmode=layertools -jar application.jar extract

FROM adoptopenjdk:11-jre-hotspot
WORKDIR application
COPY --from=builder application/dependencies/ ./
COPY --from=builder application/spring-boot-loader/ ./
COPY --from=builder application/snapshot-dependencies/ ./
COPY --from=builder application/application/ ./
ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]
----

Assuming the above `Dockerfile` is in the current directory, your docker image can be built with `docker build .`, or optionally specifying the path to your application jar, as shown in the following example:

[indent=0]
----
	docker build --build-arg JAR_FILE=path/to/myapp.jar .
----

This is a multi-stage dockerfile.
The builder stage extracts the directories that are needed later.
Each of the `COPY` commands relates to the layers extracted by the jarmode.

Of course, a Dockerfile can be written without using the jarmode.
You can use some combination of `unzip` and `mv` to move things to the right layer but jarmode simplifies that.



[[boot-features-container-images-buildpacks]]
==== Cloud Native Buildpacks
Dockerfiles are just one way to build docker images.
Another way to build docker images is directly from your Maven or Gradle plugin, using buildpacks.
If you’ve ever used an application platform such as Cloud Foundry or Heroku then you’ve probably used a buildpack.
Buildpacks are the part of the platform that takes your application and converts it into something that the platform can actually run.
For example, Cloud Foundry’s Java buildpack will notice that you’re pushing a `.jar` file and automatically add a relevant JRE.

With Cloud Native Buildpacks, you can create Docker compatible images that you can run anywhere.
Spring Boot includes buildpack support directly for both Maven and Gradle.
This means you can just type a single command and quickly get a sensible image into your locally running Docker daemon.

Refer to the individual plugin documentation on how to use buildpacks with {spring-boot-maven-plugin-docs}#build-image[Maven] and {spring-boot-gradle-plugin-docs}#build-image[Gradle].

NOTE: The https://github.com/paketo-buildpacks/spring-boot[Paketo Spring Boot buildpack] has also been updated to support the `layers.idx` file so any customization that is applied to it will be reflected in the image created by the buildpack.

NOTE: In order to achieve reproducible builds and container image caching, Buildpacks can manipulate the application resources metadata (such as the file "last modified" information).
You should ensure that your application does not rely on that metadata at runtime.
Spring Boot can use that information when serving static resources, but this can be disabled with configprop:spring.web.resources.cache.use-last-modified[]



[[boot-features-whats-next]]
== What to Read Next
If you want to learn more about any of the classes discussed in this section, you can check out the {spring-boot-api}/[Spring Boot API documentation] or you can browse the {spring-boot-code}[source code directly].
If you have specific questions, take a look at the <<howto.adoc#howto, how-to>> section.

If you are comfortable with Spring Boot's core features, you can continue on and read about <<production-ready-features.adoc#production-ready, production-ready features>>.
