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

[partintro]
--
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}

2013-07-31 00:08:16.117  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)
2013-07-31 00:08:16.166  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
2014-03-04 13:09:54.912  INFO 41370 --- [           main] .t.TomcatServletWebServerFactory : Server initialized with port: 8080
2014-03-04 13:09:56.501  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>>,



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

[source,properties,indent=0]
----
	spring.main.lazy-initialization=true
----



[[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 `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 `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
{sc-spring-boot}/ansi/AnsiPropertySource.{sc-ext}[`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 `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]
====
YAML maps `off` to `false`, so be sure to add quotes if you want to disable the banner in
your application, as shown in the following example:

[source,yaml,indent=0]
----
	spring:
		main:
			banner-mode: "off"
----
====

[[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
{dc-spring-boot}/SpringApplication.{dc-ext}[`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
{dc-spring-boot}/builder/SpringApplicationBuilder.{dc-ext}[`SpringApplicationBuilder`
Javadoc] for full details.



[[boot-features-application-events-and-listeners]]
=== Application Events and Listeners
In addition to the usual Spring Framework events, such as
{spring-javadoc}/context/event/ContextRefreshedEvent.{dc-ext}[`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 `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 `ApplicationReadyEvent` is sent after any application and command-line runners have
been called. It indicates that the application is ready to service requests.
. An `ApplicationFailedEvent` is sent if there is an exception on startup.

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.

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 fairly simple:

* 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.

The `CommandLineRunner` interfaces provides access to application arguments as a simple
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
`spring.application.admin.enabled` property. This exposes the
{sc-spring-boot}/admin/SpringApplicationAdminMXBean.{sc-ext}[`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`.

CAUTION: Take care when enabling this feature, as the MBean exposes a method to shutdown
the application.



[[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 properties files, YAML files,
environment variables, and command-line arguments to externalize configuration. 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:

. <<using-boot-devtools-globalsettings,Devtools global settings properties>>
on your home directory (`~/.spring-boot-devtools.properties` when devtools is active).
. {spring-javadoc}/test/context/TestPropertySource.{dc-ext}[`@TestPropertySource`]
annotations on your tests.
. `properties` attribute on your tests. Available on
{dc-spring-boot-test}/context/SpringBootTest.{dc-ext}[`@SpringBootTest`] and the
<<boot-features-testing-spring-boot-applications-testing-autoconfigured-tests,test
annotations for testing a particular slice of your application>>.
. Command line arguments.
. Properties from `SPRING_APPLICATION_JSON` (inline JSON embedded in an environment
variable or system property).
. `ServletConfig` init parameters.
. `ServletContext` init parameters.
. JNDI attributes from `java:comp/env`.
. Java System properties (`System.getProperties()`).
. OS environment variables.
. A `RandomValuePropertySource` that has properties only in `+random.*+`.
. <<boot-features-external-config-profile-specific-properties,Profile-specific
application properties>> outside of your packaged jar
(`application-{profile}.properties` and YAML variants).
. <<boot-features-external-config-profile-specific-properties,Profile-specific
application properties>> packaged inside your jar (`application-{profile}.properties`
and YAML variants).
. Application properties outside of your packaged jar (`application.properties` and YAML
variants).
. Application properties packaged inside your jar (`application.properties` and YAML
variants).
. {spring-javadoc}/context/annotation/PropertySource.{dc-ext}[`@PropertySource`]
annotations on your `@Configuration` classes.
. Default properties (specified by setting `SpringApplication.setDefaultProperties`).

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 `SPRING_APPLICATION_JSON` properties can be supplied on the command line with an
environment variable. For example, you could use the following line in a UN{asterisk}X
shell:

----
$ 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`.
You can also supply the JSON as `spring.application.json` in a System property, as shown
in the following example:

----
$ java -Dspring.application.json='{"name":"test"}' -jar myapp.jar
----

You can also supply the JSON by using a command line argument, as shown in the following
example:

----
$ java -jar myapp.jar --spring.application.json='{"name":"test"}'
----

You can also supply the JSON as a JNDI variable, as follows:
`java:comp/env/spring.application.json`.
====



[[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,properties,indent=0]
----
	my.secret=${random.value}
	my.number=${random.int}
	my.bignumber=${random.long}
	my.uuid=${random.uuid}
	my.number.less.than.ten=${random.int(10)}
	my.number.in.range=${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-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 other 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-property-files]]
=== Application Property Files
`SpringApplication` loads properties from `application.properties` files in the following
locations and adds them to the Spring `Environment`:

. A `/config` subdirectory of the current directory
. The current directory
. A classpath `/config` package
. The classpath root

The list is ordered by precedence (properties defined in locations higher in the list
override those defined in lower locations).

NOTE: You can also <<boot-features-external-config-yaml, use YAML ('.yml') files>> as an
alternative to '.properties'.

If you do not like `application.properties` as the configuration file name, you can
switch to another file name by specifying a `spring.config.name` environment property.
You can also refer to an explicit location by using the `spring.config.location`
environment property (which is a comma-separated list of directory locations or file
paths). The following example shows how to specify a different file name:

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

The following example shows how to specify two locations:

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

WARNING: `spring.config.name` and `spring.config.location` are used very early to
determine which files have to be loaded, so 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 `/` (and, at runtime, be appended with the names generated from `spring.config.name`
before being loaded, including profile-specific file names). Files specified in
`spring.config.location` are used as-is, with no support for profile-specific variants,
and are overridden by any profile-specific properties.

Config locations are searched in reverse order. By default, the configured locations are
`classpath:/,classpath:/config/,file:./,file:./config/`. The resulting search order is
the following:

. `file:./config/`
. `file:./`
. `classpath:/config/`
. `classpath:/`

When custom config locations are configured by using `spring.config.location`, they
replace the default locations. For example, if `spring.config.location` is configured with
the value `classpath:/custom-config/,file:./custom-config/`, the search order becomes the
following:

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

Alternatively, when custom config locations are configured by using
`spring.config.additional-location`, they are used in addition to the default locations.
Additional locations are searched before the default locations. For example, if
additional locations of `classpath:/custom-config/,file:./custom-config/` are configured,
the search order becomes the following:

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

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, `SPRING_CONFIG_NAME` instead of `spring.config.name`).

NOTE: If your application runs in a container, 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-profile-specific-properties]]
=== Profile-specific Properties
In addition to `application.properties` files, profile-specific properties can also be
defined by using the following naming convention: `application-{profile}.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.properties` are loaded.

Profile-specific properties are loaded from the same locations as standard
`application.properties`, with profile-specific files always overriding the non-specific
ones, whether or not the profile-specific files are inside or outside your
packaged jar.

If several profiles are specified, a last-wins strategy applies. For example, profiles
specified by the `spring.profiles.active` property are added after those configured
through the `SpringApplication` API and therefore take precedence.

NOTE: If you have specified any files in `spring.config.location`, profile-specific
variants of those files are not considered. Use directories in
`spring.config.location` if you want to also use profile-specific properties.



[[boot-features-external-config-placeholders-in-properties]]
=== Placeholders in Properties
The values in `application.properties` are filtered through the existing `Environment`
when they are used, so you can refer back to previously defined values (for example, from
System properties).

[source,properties,indent=0]
----
	app.name=MyApp
	app.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-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-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]]
=== Using YAML Instead of Properties
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-loading-yaml]]
==== 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`.

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
----

The preceding example would be transformed into the following properties:

[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
----

YAML lists 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
----

To bind to properties like that by using Spring Boot's `Binder` utilities (which is what
`@ConfigurationProperties` does), you need to have a property in the target bean of type
`java.util.List` (or `Set`) and you either need to provide a setter or initialize it with
a mutable value. For example, the following example binds to the properties shown
previously:

[source,java,indent=0]
----
	@ConfigurationProperties(prefix="my")
	public class Config {

		private List<String> servers = new ArrayList<String>();

		public List<String> getServers() {
			return this.servers;
		}
	}
----



[[boot-features-external-config-exposing-yaml-to-spring]]
==== Exposing YAML as Properties in the Spring Environment
The `YamlPropertySourceLoader` class can be used to expose YAML as a `PropertySource` in
the Spring `Environment`. Doing so lets you use the `@Value` annotation with placeholders
syntax to access YAML properties.



[[boot-features-external-config-multi-profile-yaml]]
==== Multi-profile YAML Documents
You can specify multiple profile-specific YAML documents in a single file by using a
`spring.profiles` key to indicate when the document applies, as shown in the following
example:

[source,yaml,indent=0]
----
	server:
		address: 192.168.1.100
	---
	spring:
		profiles: development
	server:
		address: 127.0.0.1
	---
	spring:
		profiles: production & eu-central
	server:
		address: 192.168.1.120
----

In the preceding example, if the `development` profile is active, the `server.address`
property is `127.0.0.1`. Similarly, if the `production` *and* `eu-central` profiles are
active, the `server.address` property is `192.168.1.120`. If the `development`,
`production` and `eu-central` profiles are *not* enabled, then the value for the property
is `192.168.1.100`.

[NOTE]
====
`spring.profiles` can therefore contain a simple profile name (for example `production`)
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-reference}core.html#beans-definition-profiles-java[reference guide] for more
details.
====

If none are explicitly active when the application context starts, the default profiles
are activated. So, in the following YAML, we set a value for `spring.security.user.password`
that is available *only* in the "default" profile:

[source,yaml,indent=0]
----
	server:
	  port: 8000
	---
	spring:
	  profiles: default
	  security:
	    user:
	      password: weak
----

Whereas, in the following example, the password is always set because it is not attached
to any profile, and it would have to be explicitly reset in all other profiles as
necessary:

[source,yaml,indent=0]
----
	server:
	  port: 8000
	spring:
	  security:
	    user:
	      password: weak
----

Spring profiles designated by using the `spring.profiles` element may optionally be
negated by using the `!` character. If both negated and non-negated profiles are
specified for a single document, at least one non-negated profile must match, and no
negated profiles may match.



[[boot-features-external-config-yaml-shortcomings]]
==== YAML Shortcomings
YAML files cannot be loaded by using the `@PropertySource` annotation. So, in the case
that you need to load values that way, you need to use a properties file.

Using the multi YAML document syntax in profile-specific YAML files can lead to unexpected
behavior. For example, consider the following config in a file called `application-dev.yml`,
with the `dev` profile being active:

[source,yaml,indent=0]
----
	server:
	  port: 8000
	---
	spring:
	  profiles: !test
	  security:
	    user:
	      password: weak
----

In the example above, profile negation and profile expressions will not behave as expected.
We recommend that you don't combine profile-specific YAML files and multiple YAML documents and stick
to using only one of them.



[[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]
====
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.ConfigurationPropertyDefaultValue;

	@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,
					@ConfigurationPropertyDefaultValue("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 one, and only one constructor must be defined with the list of properties
that you wish to bind and not other properties than the ones in the constructor are bound.

Default values can be specified using `@ConfigurationPropertyDefaultValue` and the same
conversion service will be applied to coerce the `String` value to the target type of a
missing property.



[[boot-features-external-config-enabling]]
==== Enabling `@ConfigurationProperties`-annotated types
Spring Boot provides an infrastructure to bind such types and register them as beans
automatically. If your application uses `@SpringBootApplication`, classes annotated with
`@ConfigurationProperties` will automatically be scanned and registered as beans. By default,
scanning will occur from the package of the class that declares this annotation. If you want
to define specific packages to scan, you can do so using an explicit `@ConfigurationPropertiesScan`
directive on your `@SpringBootApplication`-annotated class as shown in the following example:

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

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

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

[NOTE]
====
When the `@ConfigurationProperties` bean is registered using 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. In particular, it is not
possible to inject other beans using the constructor as this would trigger the constructor
binder that only deals with the environment.

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`).

NOTE: Annotating a `@ConfigurationProperties` type with `@Component` will result in two
beans of the same type if the type is also scanned as part of classpath scanning. If you want
to register the bean yourself using `@Component`, consider disabling scanning of
`@ConfigurationProperties`.



[[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]
----
	# application.yml

	acme:
		remote-address: 192.168.1.1
		security:
			username: admin
			roles:
			  - USER
			  - ADMIN

	# additional configuration as required
----

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.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`).

For 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;
		}

	}
----

In the preceding example, 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. `_` should not be used within a
property name
|Numeric values surrounded by underscores, such as `MY_ACME_1_OTHER = my.acme[1].other`

|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`.

When binding to `Map` properties, if the `key` contains anything other than lowercase
alpha-numeric characters or `-`, you need to use the bracket notation so that the original
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`:

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

----

The properties above will bind to a `Map` with `/key1`, `/key2` and `key3` as the keys in the map.


[[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]
----
	acme:
	  list:
	    - name: my name
	      description: my description
	---
	spring:
	  profiles: 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]
----
	acme:
	  list:
	    - name: my name
	      description: my description
	    - name: another name
	      description: another description
	---
	spring:
	  profiles: 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]
----
	acme:
	  map:
	    key1:
	      name: my name 1
	      description: my description 1
	---
	spring:
	  profiles: 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
YAML 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-javadoc}/java/time/Duration.html#parse-java.lang.CharSequence-[used by
`java.util.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/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.

TIP: If you are upgrading from a previous version that is simply using `Long` to express
the duration, make sure to define the unit (using `@DurationUnit`) if it isn't
milliseconds alongside the switch to `Duration`. Doing so gives a transparent upgrade path
while supporting a much richer format.



[[boot-features-external-config-conversion-datasize]]
===== Converting Data Sizes
Spring Framework has a `DataSize` value type that allows to express 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/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.

TIP: If you are upgrading from a previous version that is simply using `Long` to express
the size, make sure to define the unit (using `@DataSizeUnit`) if it isn't bytes alongside
the switch to `DataSize`. 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`.

Although nested properties will also be validated when bound, it's good practice to
also annotate the associated field as `@Valid`. This ensure that validation is triggered
even if no nested properties are found. 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. There is a
{github-code}/spring-boot-samples/spring-boot-sample-property-validation[property
validation sample] that shows how to set things up.

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
| No

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

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

If you define a set of configuration keys for your own components, we recommend you
group them in a POJO annotated with `@ConfigurationProperties`. You should also be aware
that, since `@Value` does not support relaxed binding, it is not a good candidate if you
need to provide the value by using environment variables.

Finally, while you can write a `SpEL` expression in `@Value`, such expressions are not
processed from <<boot-features-external-config-application-property-files,application
property files>>.



[[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` or `@Configuration`
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 {

		// ...

	}
----

You can use a `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,properties,indent=0]
----
	spring.profiles.active=dev,hsqldb
----

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



[[boot-features-adding-active-profiles]]
=== Adding Active Profiles
The `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 profile-specific properties that *add* to the active
profiles rather than replace them. The `spring.profiles.include` property can be used to
unconditionally add active profiles. The `SpringApplication` entry point also has a Java
API for setting additional profiles (that is, on top of those activated by the
`spring.profiles.active` property). See the `setAdditionalProfiles()` method in
{dc-spring-boot}/SpringApplication.html[SpringApplication].

For example, when an application with the following properties is run by using the
switch, `--spring.profiles.active=prod`, the `proddb` and `prodmq` profiles are also
activated:

[source,yaml,indent=0]
----
	---
	my.property: fromyamlfile
	---
	spring.profiles: prod
	spring.profiles.include:
	  - proddb
	  - prodmq
----

NOTE: Remember that the `spring.profiles` property can be defined in a YAML document to
determine when this particular document is included in the configuration. See
<<howto-change-configuration-depending-on-the-environment>> for more details.



[[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-profile-specific-properties>>" 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-javadoc}/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.



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

[indent=0]
----
2014-03-05 10:57:51.112  INFO 45469 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/7.0.52
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1358 ms
2014-03-05 10:57:51.698  INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]
2014-03-05 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
{dc-spring-boot}/ansi/AnsiOutput.Enabled.{dc-ext}[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
`logging.file.name` or `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"]
|===
|`logging.file.name` |`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. Size limits can be changed
using the `logging.file.max-size` property. Previously rotated files are archived
indefinitely unless the `logging.file.max-history` property has been set. The total size
of log archives can be capped using `logging.file.total-size-cap`. When the total size of
log archives exceeds that threshold, backups will be deleted. To force log archive cleanup
on application startup, use the `logging.file.clean-history-on-start` property.

NOTE: The logging system is initialized early in the application lifecycle. Consequently,
logging properties are not found in property files loaded through `@PropertySource`
annotations.

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-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"]
----
	logging.level.root=WARN
	logging.level.org.springframework.web=DEBUG
	logging.level.org.hibernate=ERROR
----



[[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,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	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,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	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`

|sql
|`org.springframework.jdbc.core`, `org.hibernate.SQL`

|===



[[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: `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

|`logging.exception-conversion-word`
|`LOG_EXCEPTION_CONVERSION_WORD`
|The conversion word used when logging exceptions.

|`logging.file.clean-history-on-start`
|`LOG_FILE_CLEAN_HISTORY_ON_START`
|Whether to clean the archive log files on startup (if LOG_FILE enabled). (Only supported
with the default Logback setup.)

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

|`logging.file.max-size`
|`LOG_FILE_MAX_SIZE`
|Maximum log file size (if LOG_FILE enabled). (Only supported with the default Logback
setup.)

|`logging.file.max-history`
|`LOG_FILE_MAX_HISTORY`
|Maximum number of archive log files to keep (if LOG_FILE enabled). (Only supported with
the default Logback setup.)

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

|`logging.file.total-size-cap`
|`LOG_FILE_TOTAL_SIZE_CAP`
|Total size of log backups to be kept (if LOG_FILE enabled). (Only supported with the
default Logback setup.)

|`logging.pattern.console`
|`CONSOLE_LOG_PATTERN`
|The log pattern to use on the console (stdout). (Only supported with the default Logback
setup.)

|`logging.pattern.dateformat`
|`LOG_DATEFORMAT_PATTERN`
|Appender pattern for log date format. (Only supported with the default Logback setup.)

|`logging.pattern.file`
|`FILE_LOG_PATTERN`
|The log pattern to use in a file (if `LOG_FILE` is enabled). (Only supported with the
default Logback setup.)

|`logging.pattern.level`
|`LOG_LEVEL_PATTERN`
|The format to use when rendering the log level (default `%5p`). (Only supported with the
default Logback setup.)

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

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

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

----
2015-09-30 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
`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:

----
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]]
----



==== 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 simple 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-reference}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>
----



==== 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.

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,properties,indent=0]
----
	spring.messages.basename=messages,config.i18n.messages
	spring.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 {sc-spring-boot-autoconfigure}/context/MessageSourceProperties.{sc-ext}[
`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-reference}web.html#mvc[Spring Web MVC framework] (often referred to as simply
"`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-reference}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.
* Custom `Favicon` support (covered <<boot-features-spring-mvc-favicon,later in this
document>>).
* Automatic use of a `ConfigurableWebBindingInitializer` bean (covered
<<boot-features-spring-mvc-web-binding-initializer,later in this document>>).

If you want to keep Spring Boot MVC features and you want to add additional
{spring-reference}web.html#mvc[MVC configuration] (interceptors, formatters, view
controllers, and other features), you can add your own `@Configuration` class of type
`WebMvcConfigurer` but *without* `@EnableWebMvc`. If you wish to provide custom
instances of `RequestMappingHandlerMapping`, `RequestMappingHandlerAdapter`, or
`ExceptionHandlerExceptionResolver`, you can declare a `WebMvcRegistrationsAdapter`
instance to provide such components.

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


[[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` or
`JsonDeserializer` 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
{sc-spring-boot}/jackson/JsonObjectSerializer.{sc-ext}[`JsonObjectSerializer`] and
{sc-spring-boot}/jackson/JsonObjectDeserializer.{sc-ext}[`JsonObjectDeserializer`] base
classes that provide useful alternatives to the standard Jackson versions when
serializing objects. See
{dc-spring-boot}/jackson/JsonObjectSerializer.{dc-ext}[`JsonObjectSerializer`]
and {dc-spring-boot}/jackson/JsonObjectDeserializer.{dc-ext}[`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
`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-javadoc}/validation/DefaultMessageCodesResolver.Format.{dc-ext}[`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
`spring.mvc.static-path-pattern` property. For instance, relocating all resources to
`/resources/**` can be achieved as follows:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.mvc.static-path-pattern=/resources/**
----

You can also customize the static resource locations by using the
`spring.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,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.resources.chain.strategy.content.enabled=true
	spring.resources.chain.strategy.content.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-javadoc}/web/servlet/resource/ResourceUrlProvider.{dc-ext}[`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,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.resources.chain.strategy.content.enabled=true
	spring.resources.chain.strategy.content.paths=/**
	spring.resources.chain.strategy.fixed.enabled=true
	spring.resources.chain.strategy.fixed.paths=/js/lib/
	spring.resources.chain.strategy.fixed.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 {sc-spring-boot-autoconfigure}/web/ResourceProperties.{sc-ext}[`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-reference}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-favicon]]
==== Custom Favicon
Spring Boot looks for a `favicon.ico` in the configured static content locations and the
root of the classpath (in that order). If such a file is present, it is automatically
used as the favicon 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-reference}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,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.mvc.contentnegotiation.favor-parameter=true

	# We can change the parameter name, which is "format" by default:
	# spring.mvc.contentnegotiation.parameter-name=myparam

	# We can also register additional file extensions/media types with:
	spring.mvc.contentnegotiation.media-types.markdown=text/markdown
----

If you understand the caveats and would still like your application to use
suffix pattern matching, the following configuration is required:

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

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

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

	# You can also register additional file extensions/media types with:
	# spring.mvc.contentnegotiation.media-types.adoc=text/asciidoc
----



[[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]
 * http://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, IntelliJ IDEA orders 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 templates on the
classpath. If you have this problem, you can reorder the classpath in the IDE to place
the module's classes and resources first. Alternatively, you can configure the template
prefix to search every `templates` directory on the classpath, as follows:
`classpath*:/templates/`.



[[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`). 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` folder. Error pages can either be static HTML (that is, added under
any of the static resource folders) 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 folder 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 folder structure would be as
follows:

[source,indent=0,subs="verbatim,quotes,attributes"]
----
	src/
	 +- main/
	     +- java/
	     |   + <source code>
	     +- resources/
	         +- templates/
	             +- error/
	             |   +- 5xx.ftl
	             +- <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-reference}web.html#mvc-exceptionhandlers[`@ExceptionHandler` methods] and
{spring-reference}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-websphere]]
CAUTION: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. The request can only
be forwarded 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`.



[[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.



[[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-reference}web.html#cors[supports CORS].
Using {spring-reference}web.html#controller-method-cors-configuration[controller method
CORS configuration] with
{spring-javadoc}/web/bind/annotation/CrossOrigin.{dc-ext}[`@CrossOrigin`]
annotations in your Spring Boot application does not require any specific configuration.
{spring-reference}web.html#global-cors-configuration[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-reference}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-reference}web.html#web-reactive[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 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
`spring.webflux.static-path-pattern` property. For instance, relocating all resources to
`/resources/**` can be achieved as follows:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.webflux.static-path-pattern=/resources/**
----

You can also customize the static resource locations by using
`spring.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-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` folder. Error pages can either be static HTML (that is, added under
any of the static resource folders) 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 folder 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 folder 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`. Both the servlet and
the filter registrations can be given init parameters by using `spring.jersey.init.*` to
specify a map of properties.

There is a {github-code}/spring-boot-samples/spring-boot-sample-jersey[Jersey sample] so
that you can see how to set things up.



[[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.

Spring Boot ships with many auto-configurations that may define Filter beans. Here are a
few examples of Filters and their respective order (lower order value means higher
precedence):

|===
| Servlet Filter | Order

|`OrderedCharacterEncodingFilter`
|`Ordered.HIGHEST_PRECEDENCE`

|`WebMvcMetricsFilter`
|`Ordered.HIGHEST_PRECEDENCE + 1`

|`ErrorPageFilter`
|`Ordered.HIGHEST_PRECEDENCE + 1`

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

It is usually safe to leave Filter beans unordered.

If a specific order is required, you should 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`.



[[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`
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.persistence`),
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
{sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[`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);
		}

	}
----

NOTE: `TomcatServletWebServerFactory`, `JettyServletWebServerFactory` and `UndertowServletWebServerFactory`
are dedicated variants of `ConfigurableServletWebServerFactory` that have additional customization setter methods
for Tomcat, Jetty and Undertow respectively.

[[boot-features-customizing-configurableservletwebserverfactory-directly]]
===== Customizing ConfigurableServletWebServerFactory Directly
If the preceding customization techniques are too limited, you can register the
`TomcatServletWebServerFactory`, `JettyServletWebServerFactory`, or
`UndertowServletWebServerFactory` bean yourself.

[source,java,indent=0]
----
	@Bean
	public ConfigurableServletWebServerFactory webServerFactory() {
		TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
		factory.setPort(9000);
		factory.setSessionTimeout(10, TimeUnit.MINUTES);
		factory.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND, "/notfound.html"));
		return factory;
	}
----

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


[[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.

There is a {github-code}/spring-boot-samples/spring-boot-sample-web-jsp[JSP sample] so
that you can see how to set things up.

[[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-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-reference}#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
{dc-spring-boot}/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, you can add a bean of type `WebSecurityConfigurerAdapter` (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`.
There are several secure applications in the {github-code}/spring-boot-samples/[Spring
Boot samples] to get you started with common use cases.

Access rules can be overridden by adding a custom `WebSecurityConfigurerAdapter`. 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 `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 can be configured by adding a custom `SecurityWebFilterChain`. 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 `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 make it easy 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,properties,indent=0]
----
	spring.security.oauth2.client.registration.my-client-1.client-id=abcd
	spring.security.oauth2.client.registration.my-client-1.client-secret=password
	spring.security.oauth2.client.registration.my-client-1.client-name=Client for user scope
	spring.security.oauth2.client.registration.my-client-1.provider=my-oauth-provider
	spring.security.oauth2.client.registration.my-client-1.scope=user
	spring.security.oauth2.client.registration.my-client-1.redirect-uri-template=https://my-redirect-uri.com
	spring.security.oauth2.client.registration.my-client-1.client-authentication-method=basic
	spring.security.oauth2.client.registration.my-client-1.authorization-grant-type=authorization_code

	spring.security.oauth2.client.registration.my-client-2.client-id=abcd
	spring.security.oauth2.client.registration.my-client-2.client-secret=password
	spring.security.oauth2.client.registration.my-client-2.client-name=Client for email scope
	spring.security.oauth2.client.registration.my-client-2.provider=my-oauth-provider
	spring.security.oauth2.client.registration.my-client-2.scope=email
	spring.security.oauth2.client.registration.my-client-2.redirect-uri-template=https://my-redirect-uri.com
	spring.security.oauth2.client.registration.my-client-2.client-authentication-method=basic
	spring.security.oauth2.client.registration.my-client-2.authorization-grant-type=authorization_code

	spring.security.oauth2.client.provider.my-oauth-provider.authorization-uri=https://my-auth-server/oauth/authorize
	spring.security.oauth2.client.provider.my-oauth-provider.token-uri=https://my-auth-server/oauth/token
	spring.security.oauth2.client.provider.my-oauth-provider.user-info-uri=https://my-auth-server/userinfo
	spring.security.oauth2.client.provider.my-oauth-provider.user-info-authentication-method=header
	spring.security.oauth2.client.provider.my-oauth-provider.jwk-set-uri=https://my-auth-server/token_keys
	spring.security.oauth2.client.provider.my-oauth-provider.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,properties,indent=0]
----
	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 `WebSecurityConfigurerAdapter` that resembles the
following:

[source,java,indent=0]
----
public class OAuth2LoginSecurityConfig extends WebSecurityConfigurerAdapter {

	@Override
	protected void configure(HttpSecurity http) throws Exception {
		http
			.authorizeRequests()
				.anyRequest().authenticated()
				.and()
			.oauth2Login()
				.redirectionEndpoint()
					.baseUri("/custom-callback");
	}
}
----



[[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,properties,indent=0]
----
	spring.security.oauth2.client.registration.my-client.client-id=abcd
	spring.security.oauth2.client.registration.my-client.client-secret=password
	spring.security.oauth2.client.registration.my-client.provider=google

	spring.security.oauth2.client.registration.google.client-id=abcd
	spring.security.oauth2.client.registration.google.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 as long as a JWK Set URI or OIDC Issuer URI is specified,
as shown in the following examples:

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

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

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.



==== Authorization Server
Currently, Spring Security does not provide support for implementing an OAuth 2.0
Authorization Server. However, this functionality is available from
the https://projects.spring.io/spring-security-oauth/[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-actuator]]
=== Actuator Security
For security purposes, all actuators other than `/health` and `/info` are disabled by
default. The `management.endpoints.web.exposure.include` property can be used to enable
the actuators.

If Spring Security is on the classpath and no other WebSecurityConfigurerAdapter is
present, all actuators other than `/health` and `/info` are secured by Spring Boot
auto-configuration. If you define a custom `WebSecurityConfigurerAdapter`, 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-reference}#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`. 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.
. If neither HikariCP nor the Tomcat pooling datasource are available and if
https://commons.apache.org/proper/commons-dbcp/[Commons DBCP2] is available, we use it.

If you use the `spring-boot-starter-jdbc` or `spring-boot-starter-data-jpa` "`starters`",
you automatically get a dependency to `HikariCP`.

NOTE: You can bypass that algorithm completely and specify the connection pool to use by
setting the `spring.datasource.type` property. This is especially important if you run
your application in a Tomcat container, as `tomcat-jdbc` is provided by default.

TIP: Additional connection pools can always be configured manually. If you define your
own `DataSource` bean, auto-configuration does not occur.

DataSource configuration is controlled by external configuration properties in
`+spring.datasource.*+`. For example, you might declare the following section in
`application.properties`:

[source,properties,indent=0]
----
	spring.datasource.url=jdbc:mysql://localhost/test
	spring.datasource.username=dbuser
	spring.datasource.password=dbpass
	spring.datasource.driver-class-name=com.mysql.jdbc.Driver
----

NOTE: You should at least specify the URL by setting the `spring.datasource.url`
property. Otherwise, Spring Boot tries to auto-configure an embedded database.

TIP: You often do not need to specify the `driver-class-name`, since Spring Boot can
deduce it for most databases from the `url`.

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
{sc-spring-boot-autoconfigure}/jdbc/DataSourceProperties.{sc-ext}[`DataSourceProperties`]
for more of the supported options. These are the standard options that work regardless of
the actual implementation. It is also possible to fine-tune implementation-specific
settings by using their respective prefix (`+spring.datasource.hikari.*+`,
`+spring.datasource.tomcat.*+`, and `+spring.datasource.dbcp2.*+`). Refer to the
documentation of the connection pool implementation you are using for more details.

For instance, if you use the
https://tomcat.apache.org/tomcat-8.0-doc/jdbc-pool.html#Common_Attributes[Tomcat
connection pool], you could customize many additional settings, as shown in the following
example:


[source,properties,indent=0]
----
	# Number of ms to wait before throwing an exception if no connection is available.
	spring.datasource.tomcat.max-wait=10000

	# Maximum number of active connections that can be allocated from this pool at the same time.
	spring.datasource.tomcat.max-active=50

	# Validate the connection before borrowing it from the pool.
	spring.datasource.tomcat.test-on-borrow=true
----



[[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 `spring.datasource.jndi-name` property can be used as an alternative to the
`spring.datasource.url`, `spring.datasource.username`, and `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,properties,indent=0]
----
	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,properties,indent=0]
----
	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: Makes it easy to implement JPA-based repositories.
* Spring ORMs: 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-javadoc}/repository/Query.html[`Query`] annotation.

Spring Data repositories usually extend from the
{spring-data-commons-javadoc}/repository/Repository.html[`Repository`] or
{spring-data-commons-javadoc}/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
`spring.data.jpa.repositories.bootstrap-mode` 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.

TIP: We have barely scratched the surface of Spring Data JPA. For complete details, see
the https://docs.spring.io/spring-data/jpa/docs/current/reference/html/[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-javadoc}/orm/jpa/support/OpenEntityManagerInViewInterceptor.{dc-ext}[`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
https://projects.spring.io/spring-data-jdbc/[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 `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 `spring.h2.console.path` property.



[[boot-features-jooq]]
=== Using jOOQ
Java 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.



==== 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-manual}/#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>
----



==== 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);
	}
----



==== jOOQ SQL Dialect
Unless the `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.



==== 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`
* `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-nosql]]
== Working with NoSQL Technologies
Spring Data provides additional projects that help you access a variety of NoSQL
technologies, including:
https://projects.spring.io/spring-data-mongodb/[MongoDB],
https://projects.spring.io/spring-data-neo4j/[Neo4J],
https://github.com/spring-projects/spring-data-elasticsearch/[Elasticsearch],
https://projects.spring.io/spring-data-solr/[Solr],
https://projects.spring.io/spring-data-redis/[Redis],
https://projects.spring.io/spring-data-gemfire/[Gemfire],
https://projects.spring.io/spring-data-cassandra/[Cassandra],
https://projects.spring.io/spring-data-couchbase/[Couchbase] and
https://projects.spring.io/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
https://projects.spring.io/spring-data[projects.spring.io/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). By default, if `commons-pool2` is on the classpath, you
get a pooled connection factory.



[[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 Mongo databases, you can inject an auto-configured
`org.springframework.data.mongodb.MongoDbFactory`. 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.MongoDbFactory;
	import com.mongodb.DB;

	@Component
	public class MyBean {

		private final MongoDbFactory mongo;

		@Autowired
		public MyBean(MongoDbFactory mongo) {
			this.mongo = mongo;
		}

		// ...

		public void example() {
			DB db = mongo.getDb();
			// ...
		}

	}
----

You can set the `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]
----
	spring.data.mongodb.uri=mongodb://user:secret@mongo1.example.com:12345,mongo2.example.com:23456/test
----

Alternatively, as long as you use Mongo 2.x, you can specify a `host`/`port`. For
example, you might declare the following settings in your `application.properties`:

[source,properties,indent=0]
----
	spring.data.mongodb.host=mongoserver
	spring.data.mongodb.port=27017
----

If you have defined your own `MongoClient`, it will be used to auto-configure a suitable
`MongoDbFactory`. Both `com.mongodb.MongoClient` and `com.mongodb.client.MongoClient`
are supported.

NOTE: If you use the Mongo 3.0 Java driver, `spring.data.mongodb.host` and
`spring.data.mongodb.port` are not supported. In such cases, `spring.data.mongodb.uri`
should be used to provide all of the configuration.

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 Mongo, you can inject `com.mongodb.MongoClient` beans
instead of using `MongoDbFactory`. If you want to take complete control of establishing
the MongoDB connection, you can also declare your own `MongoDbFactory` 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-mongo}[Spring Data MongoDB] provides a
{spring-data-mongo-javadoc}/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.beans.factory.annotation.Autowired;
	import org.springframework.data.mongodb.core.MongoTemplate;
	import org.springframework.stereotype.Component;

	@Component
	public class MyBean {

		private final MongoTemplate mongoTemplate;

		@Autowired
		public MyBean(MongoTemplate mongoTemplate) {
			this.mongoTemplate = mongoTemplate;
		}

		// ...

	}
----

See the
https://docs.spring.io/spring-data/mongodb/docs/current/api/org/springframework/data/mongodb/core/MongoOperations.html[`MongoOperations`
Javadoc] for complete details.



[[boot-features-spring-data-mongo-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 Mongo 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 https://projects.spring.io/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 `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.ogm.session.Session`. 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 `Session`:

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

		private final Session session;

		@Autowired
		public MyBean(Session session) {
			this.session = session;
		}

		// ...

	}
----

You can configure the uri and credentials to use by setting the `spring.data.neo4j.*`
properties, as shown in the following example:

[source,properties,indent=0]
----
	spring.data.neo4j.uri=bolt://my-server:7687
	spring.data.neo4j.username=neo4j
	spring.data.neo4j.password=secret
----

You can take full control over the session creation by adding a
`org.neo4j.ogm.config.Configuration` `@Bean`. Also, adding a `@Bean` of type
`SessionFactory` disables the auto-configuration and gives you full control.



[[boot-features-connecting-to-neo4j-embedded]]
==== Using the Embedded Mode
If you add `org.neo4j:neo4j-ogm-embedded-driver` to the dependencies of your application,
Spring Boot automatically configures an in-process embedded instance of Neo4j that does
not persist any data when your application shuts down.

[NOTE]
====
As the embedded Neo4j OGM  driver  does not provide the Neo4j kernel itself, you have
to declare `org.neo4j:neo4j` as dependency yourself. Refer to
https://neo4j.com/docs/ogm-manual/current/reference/#reference:getting-started[the
Neo4j OGM documentation] for a list of compatible versions.
====

The embedded driver takes precedence over the other drivers when there are multiple
drivers on the classpath. You can explicitly disable the embedded mode by setting
`spring.data.neo4j.embedded.enabled=false`.

<<boot-features-testing-spring-boot-applications-testing-autoconfigured-neo4j-test,Data Neo4j Tests>>
automatically make use of an embedded Neo4j instance if the embedded driver and Neo4j
kernel are on the classpath as described above.

[NOTE]
====
You can enable persistence for the embedded mode by providing a path to a database file
in your configuration, e.g. `spring.data.neo4j.uri=file://var/tmp/graph.db`.
====



[[boot-features-neo4j-ogm-native-types]]
==== Using Native Types
Neo4j-OGM can map some types, like those in `java.time.*`, to `String`-based properties
or to one of the native types that Neo4j provides. For backwards compatibility reasons
the default for Neo4j-OGM is to use a `String`-based representation. To use native types,
add a dependency on either `org.neo4j:neo4j-ogm-bolt-native-types` or
`org.neo4j:neo4j-ogm-embedded-native-types`, and configure the
`spring.data.neo4j.use-native-types` property as shown in the following example:

[source,properties,indent=0]
----
	spring.data.neo4j.use-native-types=true
----



[[boot-features-neo4j-ogm-session]]
==== Neo4jSession
By default, if you are running a web application, the session is bound to the thread for
the entire processing of the request (that is, it uses the "Open Session in View"
pattern). If you do not want this behavior, add the following line to your
`application.properties` file:

[source,properties,indent=0]
----
	spring.data.neo4j.open-in-view=false
----



[[boot-features-spring-data-neo4j-repositories]]
==== Spring Data Neo4j Repositories
Spring Data includes repository support for Neo4j.

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 Neo4j OGM `@NodeEntity` 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. You can customize the locations to look for repositories and
entities by using `@EnableNeo4jRepositories` and `@EntityScan` respectively on a
`@Configuration`-bean.

TIP: For complete details of Spring Data Neo4j, including its object mapping
technologies, refer to the https://projects.spring.io/spring-data-neo4j/[reference
documentation].



[[boot-features-gemfire]]
=== Gemfire
https://github.com/spring-projects/spring-data-gemfire[Spring Data Gemfire] provides
convenient Spring-friendly tools for accessing the
https://pivotal.io/big-data/pivotal-gemfire#details[Pivotal Gemfire] data management
platform. There is a `spring-boot-starter-data-gemfire` "`Starter`" for collecting the
dependencies in a convenient way. There is currently no auto-configuration support for
Gemfire, but you can enable Spring Data Repositories with a
https://github.com/spring-projects/spring-data-gemfire/blob/master/src/main/java/org/springframework/data/gemfire/repository/config/EnableGemfireRepositories.java[single annotation: `@EnableGemfireRepositories`].



[[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.


[[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.

TIP: For complete details of Spring Data Solr, refer to the
https://projects.spring.io/spring-data-solr/[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 HTTP clients:

* The official Java "Low Level" and "High Level" REST clients
* https://github.com/searchbox-io/Jest[Jest]

The transport client is still being used by
https://github.com/spring-projects/spring-data-elasticsearch[Spring Data Elasticsearch],
which you can start using with the `spring-boot-starter-data-elasticsearch` "`Starter`".

[[boot-features-connecting-to-elasticsearch-rest]]
==== Connecting to Elasticsearch by 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.

If you have the `org.elasticsearch.client:elasticsearch-rest-client` dependency on the
classpath, Spring Boot will auto-configure and register a `RestClient` bean that
by default targets `http://localhost:9200`.
You can further tune how `RestClient` is configured, as shown in the following example:

[source,properties,indent=0]
----
	spring.elasticsearch.rest.uris=https://search.example.com:9200
	spring.elasticsearch.rest.username=user
	spring.elasticsearch.rest.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 `RestClient` bean.

If you have the `org.elasticsearch.client:elasticsearch-rest-high-level-client` dependency
on the classpath, Spring Boot will auto-configure a `RestHighLevelClient`, which wraps
any existing `RestClient` bean, reusing its HTTP configuration.


[[boot-features-connecting-to-elasticsearch-jest]]
==== Connecting to Elasticsearch by Using Jest
If you have `Jest` on the classpath, you can inject an auto-configured `JestClient` that
by default targets `http://localhost:9200`. You can further tune how the client is
configured, as shown in the following example:

[source,properties,indent=0]
----
	spring.elasticsearch.jest.uris=https://search.example.com:9200
	spring.elasticsearch.jest.read-timeout=10000
	spring.elasticsearch.jest.username=user
	spring.elasticsearch.jest.password=secret
----

You can also register an arbitrary number of beans that implement
`HttpClientConfigBuilderCustomizer` for more advanced customizations. The following
example tunes additional HTTP settings:

[source,java,indent=0]
----
include::{code-examples}/elasticsearch/jest/JestClientCustomizationExample.java[tag=customizer]
----

To take full control over the registration, define a `JestClient` bean.



[[boot-features-connecting-to-elasticsearch-spring-data]]
==== Connecting to Elasticsearch by Using Spring Data
To connect to Elasticsearch, you must provide the address of one or more cluster nodes.
The address can be specified by setting the `spring.data.elasticsearch.cluster-nodes`
property to a comma-separated `host:port` list. With this configuration in place, an
`ElasticsearchTemplate` or `TransportClient` can be injected like any other Spring bean,
as shown in the following example:

[source,properties,indent=0]
----
	spring.data.elasticsearch.cluster-nodes=localhost:9300
----

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

		private final ElasticsearchTemplate template;

		public MyBean(ElasticsearchTemplate template) {
			this.template = template;
		}

		// ...

	}
----

If you add your own `ElasticsearchTemplate` or `TransportClient` `@Bean`, it replaces the
default.



[[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
https://docs.spring.io/spring-data/elasticsearch/docs/[reference documentation].



[[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 `Session` 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` properties, as shown in the following example:

[source,properties,indent=0]
----
	spring.data.cassandra.keyspace-name=mykeyspace
	spring.data.cassandra.contact-points=cassandrahost1,cassandrahost2
----

You can also register an arbitrary number of beans that implement
`ClusterBuilderCustomizer` for more advanced customizations.

The following code listing shows how to inject a Cassandra bean:

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

		private CassandraTemplate template;

		@Autowired
		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 `Bucket` and `Cluster` by adding the Couchbase SDK and some configuration.
The `spring.couchbase.*` properties can be used to customize the connection. Generally,
you provide the bootstrap hosts, bucket name, and password, as shown in the following
example:

[source,properties,indent=0]
----
	spring.couchbase.bootstrap-hosts=my-host-1,192.168.1.123
	spring.couchbase.bucket.name=my-bucket
	spring.couchbase.bucket.password=secret
----

[TIP]
====
You need to provide _at least_ the bootstrap host(s), in which case the bucket name is
`default` and the password is an empty String. Alternatively, you can define your own
`org.springframework.data.couchbase.config.CouchbaseConfigurer` `@Bean` to take control
over the whole configuration.
====

It is also possible to customize some of the `CouchbaseEnvironment` settings. For
instance, the following configuration changes the timeout to use to open a new `Bucket`
and enables SSL support:

[source,properties,indent=0]
----
	spring.couchbase.env.timeouts.connect=3000
	spring.couchbase.env.ssl.key-store=/location/of/keystore.jks
	spring.couchbase.env.ssl.key-store-password=secret
----

Check the `spring.couchbase.env.*` properties for more details.



[[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
https://docs.spring.io/spring-data/couchbase/docs/current/reference/html/[reference
documentation].

You can inject an auto-configured `CouchbaseTemplate` instance as you would with any
other Spring Bean, provided a _default_ `CouchbaseConfigurer` is available (which
happens when you enable Couchbase support, as explained earlier).

The following examples shows how to inject a Couchbase 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 `CouchbaseTemplate` `@Bean` with a name of `couchbaseTemplate`.
* An `IndexManager` `@Bean` with a name of `couchbaseIndexManager`.
* A `CustomConversions` `@Bean` with a name of `couchbaseCustomConversions`.

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(...);
		}

		// ...

	}
----

TIP: If you want to fully bypass the auto-configuration for Spring Data Couchbase,
provide your own implementation of
`org.springframework.data.couchbase.config.AbstractCouchbaseDataConfiguration`.



[[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://www.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,properties,indent=0]
----
	spring.ldap.urls=ldap://myserver:1235
	spring.ldap.username=admin
	spring.ldap.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 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://www.ldap.com/unboundid-ldap-sdk-for-java[UnboundID]. To configure the server,
add a dependency to `com.unboundid:unboundid-ldapsdk` and declare a `base-dn` property, as
follows:

[source,properties,indent=0]
----
	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:

[source,yaml,indent=0]
----
	spring.ldap.embedded.base-dn:
	  - dc=spring,dc=io
	  - dc=pivotal,dc=io
----

In properties files, you must include the index as part of the property name:

[source,properties,indent=0]
----
	spring.ldap.embedded.base-dn[0]=dc=spring,dc=io
	spring.ldap.embedded.base-dn[1]=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 `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 `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 `spring.ldap.embedded.validation.enabled` property.
If you have custom attributes, you can use `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,properties,indent=0]
----
	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-reference}integration.html#cache[relevant section] of the Spring
Framework reference for more details.

In a nutshell, adding caching to an operation of your service is as easy as adding 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 `spring.cache.cache-names` property.

TIP: It is also possible to transparently
{spring-reference}integration.html#cache-annotations-put[update] or
{spring-reference}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-javadoc}/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
`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 Guava 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,properties,indent=0]
----
    # Only necessary if more than one provider is present
	spring.cache.jcache.provider=com.acme.MyCachingProvider
	spring.cache.jcache.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 `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 `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,properties,indent=0]
----
	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,properties,indent=0]
----
	spring.cache.infinispan.config=infinispan.xml
----

Caches can be created on startup by setting the `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 the https://www.couchbase.com/[Couchbase] Java client and the `couchbase-spring-cache`
implementation are available and Couchbase is <<boot-features-couchbase,configured>>, a
`CouchbaseCacheManager` is auto-configured. It is also possible to create additional
caches on startup by setting the `spring.cache.cache-names` property. These caches
operate on the `Bucket` that was auto-configured. You can _also_ create additional caches
on another `Bucket` by using the customizer. Assume you need two caches (`cache1` and
`cache2`) on the "main" `Bucket` and one (`cache3`) cache with a custom time to live of 2
seconds on the "`another`" `Bucket`. You can create the first two caches through
configuration, as follows:

[source,properties,indent=0]
----
	spring.cache.cache-names=cache1,cache2
----

Then you can define a `@Configuration` class to configure the extra `Bucket` and the
`cache3` cache, as follows:


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

		private final Cluster cluster;

		public CouchbaseCacheConfiguration(Cluster cluster) {
			this.cluster = cluster;
		}

		@Bean
		public Bucket anotherBucket() {
			return this.cluster.openBucket("another", "secret");
		}

		@Bean
		public CacheManagerCustomizer<CouchbaseCacheManager> cacheManagerCustomizer() {
			return c -> {
				c.prepareCache("cache3", CacheBuilder.newInstance(anotherBucket())
						.withExpiration(2));
			};
		}

	}
----

This sample configuration reuses the `Cluster` that was created through
auto-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
`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,properties,indent=0]
----
	spring.cache.cache-names=cache1,cache2
	spring.cache.redis.time-to-live=600000
----

[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 configuration by adding a `RedisCacheConfiguration`
`@Bean` of your own. This can be useful if you're looking for customizing the
serialization strategy.



[[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 `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,properties,indent=0]
----
	spring.cache.cache-names=cache1,cache2
	spring.cache.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,properties,indent=0]
----
	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,properties,indent=0]
----
	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-reference}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,properties,indent=0]
----
	spring.activemq.broker-url=tcp://192.168.1.210:9876
	spring.activemq.user=admin
	spring.activemq.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,properties,indent=0]
----
	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,properties,indent=0]
----
	spring.activemq.pool.enabled=true
	spring.activemq.pool.max-connections=50
----

TIP: See
{sc-spring-boot-autoconfigure}/jms/activemq/ActiveMQProperties.{sc-ext}[`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]]
==== Artemis Support
Spring Boot can auto-configure a `ConnectionFactory` when it detects that
https://activemq.apache.org/artemis/[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 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.

Artemis configuration is controlled by external configuration properties in
`+spring.artemis.*+`. For example, you might declare the following section in
`application.properties`:

[source,properties,indent=0]
----
	spring.artemis.mode=native
	spring.artemis.host=192.168.1.210
	spring.artemis.port=9876
	spring.artemis.user=admin
	spring.artemis.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,properties,indent=0]
----
	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,properties,indent=0]
----
	spring.artemis.pool.enabled=true
	spring.artemis.pool.max-connections=50
----

See
{sc-spring-boot-autoconfigure}/jms/artemis/ArtemisProperties.{sc-ext}[`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 `spring.jms.jndi-name`
property if you need to specify an alternative location, as shown in the following
example:

[source,properties,indent=0]
----
	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-javadoc}/jms/core/JmsMessagingTemplate.{dc-ext}[`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-javadoc}/jms/annotation/EnableJms.{dc-ext}[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,properties,indent=0]
----
	spring.rabbitmq.host=localhost
	spring.rabbitmq.port=5672
	spring.rabbitmq.username=admin
	spring.rabbitmq.password=secret
----

If a `ConnectionNameStrategy` bean exists in the context, it will be automatically used to
name connections created by the auto-configured `ConnectionFactory`. See
{sc-spring-boot-autoconfigure}/amqp/RabbitProperties.{sc-ext}[`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-javadoc}/rabbit/core/RabbitMessagingTemplate.{dc-ext}[`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,properties,indent=0]
----
	spring.rabbitmq.template.retry.enabled=true
	spring.rabbitmq.template.retry.initial-interval=2s
----

Retries are disabled by default. You can also customize the `RetryTemplate`
programmatically by declaring a `RabbitRetryTemplateCustomizer` bean.



[[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
`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-javadoc}/rabbit/annotation/EnableRabbit.{dc-ext}[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,properties,indent=0]
----
	spring.kafka.bootstrap-servers=localhost:9092
	spring.kafka.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 {sc-spring-boot-autoconfigure}/kafka/KafkaProperties.{sc-ext}[`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 `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 `ErrorHandler` or `AfterRollbackProcessor` 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 just 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, simply 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
`spring.kafka.streams.auto-startup` property.



[[boot-features-kafka-extra-props]]
==== Additional Kafka Properties
The properties supported by auto configuration are shown in
<<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,properties,indent=0]
----
	spring.kafka.properties.prop.one=first
	spring.kafka.admin.properties.prop.two=second
	spring.kafka.consumer.properties.prop.three=third
	spring.kafka.producer.properties.prop.four=fourth
	spring.kafka.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,properties,indent=0]
----
spring.kafka.consumer.value-deserializer=org.springframework.kafka.support.serializer.JsonDeserializer
spring.kafka.consumer.properties.spring.json.value.default.type=com.example.Invoice
spring.kafka.consumer.properties.spring.json.trusted.packages=com.example,org.acme
----

Similarly, you can disable the `JsonSerializer` default behavior of sending type
information in headers:

[source,properties,indent=0]
----
spring.kafka.producer.value-serializer=org.springframework.kafka.support.serializer.JsonSerializer
spring.kafka.producer.properties.spring.json.add.type.headers=false
----

IMPORTANT: Properties set in this way override any configuration item that Spring Boot
explicitly supports.

[[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-javadoc}/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, the most extreme (and rarely used) option is to create your own
`RestTemplateBuilder` bean. 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-reference}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-reference}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 easy 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-reference}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
{sc-spring-boot-autoconfigure}/mail/MailProperties.{sc-ext}[`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,properties,indent=0]
----
	spring.mail.properties.mail.smtp.connectiontimeout=5000
	spring.mail.properties.mail.smtp.timeout=3000
	spring.mail.properties.mail.smtp.writetimeout=5000
----

It is also possible to configure a `JavaMailSender` with an existing `Session` from JNDI:

[source,properties,indent=0]
----
	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
either an https://www.atomikos.com/[Atomikos] or https://github.com/bitronix/btm[Bitronix]
embedded transaction manager. 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 `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
`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
{dc-spring-boot}/jta/atomikos/AtomikosProperties.{dc-ext}[`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 `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
https://github.com/bitronix/btm[Bitronix] is a popular open-source JTA transaction
manager implementation. 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 `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 `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, `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 {sc-spring-boot}/jms/XAConnectionFactoryWrapper.{sc-ext}[`XAConnectionFactoryWrapper`]
and {sc-spring-boot}/jdbc/XADataSourceWrapper.{sc-ext}[`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 {sc-spring-boot}/jta/bitronix/BitronixXAConnectionFactoryWrapper.{sc-ext}[BitronixXAConnectionFactoryWrapper]
and {sc-spring-boot}/jta/bitronix/BitronixXADataSourceWrapper.{sc-ext}[BitronixXADataSourceWrapper]
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.

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.xml` configuration file to use through
configuration, as shown in the following example:

[source,properties,indent=0]
----
	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. 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.

If `hazelcast-client` is present on the classpath, 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 `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.

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
`spring.quartz.job-store-type` property is configured accordingly, as shown in the
following example:

[source,properties,indent=0]
----
	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,properties,indent=0]
----
	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
`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.

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 `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,properties,indent=0]
----
	spring.task.execution.pool.max-threads=16
	spring.task.execution.pool.queue-capacity=100
	spring.task.execution.pool.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,properties,indent=0]
----
	spring.integration.jdbc.initialize-schema=always
----

See the
{sc-spring-boot-autoconfigure}/integration/IntegrationAutoConfiguration.{sc-ext}[`IntegrationAutoConfiguration`]
and {sc-spring-boot-autoconfigure}/integration/IntegrationProperties.{sc-ext}[`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

When building a reactive web application, the following stores can be auto-configured:

* Redis
* MongoDB

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 {sc-spring-boot-autoconfigure}/session/StoreType.{sc-ext}[`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,properties,indent=0]
----
    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,properties,indent=0]
----
    spring.session.jdbc.table-name=SESSIONS
----

For setting the timeout of the session you can use the `spring.session.timeout` property.
If that property is not set, the auto-configuration falls back to the value of
`server.servlet.session.timeout`.

[[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
{sc-spring-boot-autoconfigure}/jmx/JmxAutoConfiguration.{sc-ext}[`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, AssertJ, Hamcrest, and a number of other useful
libraries.



[[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[JUnit]: The de-facto standard for unit testing Java applications.
* {spring-reference}testing.html#integration-testing[Spring Test] & Spring Boot Test:
Utilities and integration test support for Spring Boot applications.
* https://joel-costigliola.github.io/assertj/[AssertJ]: A fluent assertion library.
* https://github.com/hamcrest/JavaHamcrest[Hamcrest]: A library of matcher objects (also
known as constraints or predicates).
* https://mockito.github.io[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-reference}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 `@RunWith(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 `spring.main.web-application-type`
property:

[source,java,indent=0]
----
	@RunWith(SpringRunner.class)
	@SpringBootTest(properties = "spring.main.web-application-type=reactive")
	public 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-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]
----
	@RunWith(SpringRunner.class)
	@SpringBootTest
	@Import(MyTestsConfiguration.class)
	public class MyTests {

		@Test
		public void exampleTest() {
			...
		}

	}
----

NOTE: If you directly use `@ComponentScan` (that is, not through
`@SpringBootApplication`) you need to register the `TypeExcludeFilter` with it. See
{dc-spring-boot}/context/TypeExcludeFilter.{dc-ext}[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-reference}/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-reference}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]
----



[[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-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-reference}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-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-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, a listener must be explicitly added, as shown in the following example:

[source,java,indent=0]
----
	@TestExecutionListeners(MockitoTestExecutionListener.class)
----

====

The following example replaces an existing `RemoteService` bean with a mock
implementation:

[source,java,indent=0]
----
	import org.junit.*;
	import org.junit.runner.*;
	import org.springframework.beans.factory.annotation.*;
	import org.springframework.boot.test.context.*;
	import org.springframework.boot.test.mock.mockito.*;
	import org.springframework.test.context.junit4.*;

	import static org.assertj.core.api.Assertions.*;
	import static org.mockito.BDDMockito.*;

	@RunWith(SpringRunner.class)
	@SpringBootTest
	public class MyTests {

		@MockBean
		private RemoteService remoteService;

		@Autowired
		private Reverser reverser;

		@Test
		public 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 {dc-spring-boot-test}/mock/mockito/SpyBean.{dc-ext}[Javadoc] for full details.

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.



[[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.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.*;
	import org.junit.runner.*;
	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 org.springframework.test.context.junit4.*;

	import static org.assertj.core.api.Assertions.*;

	@RunWith(SpringRunner.class)
	@JsonTest
	public class MyJsonTests {

		@Autowired
		private JacksonTester<VehicleDetails> json;

		@Test
		public 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
		public 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`, `WebMvcConfigurer`, and `HandlerMethodArgumentResolver`.
Regular `@Component` beans are not scanned when using this annotation.

TIP: A list of the auto-configuration settings that are enabled by `@WebMvcTest` can be
<<appendix.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.*;
	import org.junit.runner.*;
	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.*;

	@RunWith(SpringRunner.class)
	@WebMvcTest(UserVehicleController.class)
	public class MyControllerTests {

		@Autowired
		private MockMvc mvc;

		@MockBean
		private UserVehicleService userVehicleService;

		@Test
		public 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 or Selenium, auto-configuration also provides an HTMLUnit `WebClient`
bean and/or a `WebDriver` bean. The following example uses HtmlUnit:


[source,java,indent=0]
----
	import com.gargoylesoftware.htmlunit.*;
	import org.junit.*;
	import org.junit.runner.*;
	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.*;

	@RunWith(SpringRunner.class)
	@WebMvcTest(UserVehicleController.class)
	public class MyHtmlUnitTests {

		@Autowired
		private WebClient webClient;

		@MockBean
		private UserVehicleService userVehicleService;

		@Test
		public 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-reference}/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`, and
`WebFluxConfigurer`. Regular `@Component` beans are not scanned when the `@WebFluxTest`
annotation is used.

TIP: A list of the auto-configurations that are enabled by `@WebFluxTest` can be
<<appendix.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-reference}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.Test;
	import org.junit.runner.RunWith;

	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.context.junit4.SpringRunner;
	import org.springframework.test.web.reactive.server.WebTestClient;

	@RunWith(SpringRunner.class)
	@WebFluxTest(UserVehicleController.class)
	public class MyControllerTests {

		@Autowired
		private WebTestClient webClient;

		@MockBean
		private UserVehicleService userVehicleService;

		@Test
		public 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-jpa-test]]
==== Auto-configured Data JPA Tests
You can use the `@DataJpaTest` annotation to test JPA applications. By default, it
configures an in-memory embedded database, scans for `@Entity` classes, and configures
Spring Data JPA repositories. Regular `@Component` beans are not loaded into the
`ApplicationContext`.

TIP: A list of the auto-configuration settings that are enabled by `@DataJpaTest` can be
<<appendix.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-reference}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.Test;
	import org.junit.runner.RunWith;
	import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
	import org.springframework.test.context.junit4.SpringRunner;
	import org.springframework.transaction.annotation.Propagation;
	import org.springframework.transaction.annotation.Transactional;

	@RunWith(SpringRunner.class)
	@DataJpaTest
	@Transactional(propagation = Propagation.NOT_SUPPORTED)
	public class ExampleNonTransactionalTests {

	}
----

Data JPA tests may also inject a
{sc-spring-boot-test-autoconfigure}/orm/jpa/TestEntityManager.{sc-ext}[`TestEntityManager`]
bean, which provides an alternative to the standard JPA `EntityManager` that is
specifically designed for tests. If you want to use `TestEntityManager` outside of
`@DataJpaTest` instances, you can also use the `@AutoConfigureTestEntityManager`
annotation. 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.*;
	import org.junit.runner.*;
	import org.springframework.boot.test.autoconfigure.orm.jpa.*;

	import static org.assertj.core.api.Assertions.*;

	@RunWith(SpringRunner.class)
	@DataJpaTest
	public class ExampleRepositoryTests {

		@Autowired
		private TestEntityManager entityManager;

		@Autowired
		private UserRepository repository;

		@Test
		public 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]
----
	@RunWith(SpringRunner.class)
	@DataJpaTest
	@AutoConfigureTestDatabase(replace=Replace.NONE)
	public 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` beans are not loaded into
the `ApplicationContext`.

TIP: A list of the auto-configurations that are enabled by `@JdbcTest` can be
<<appendix.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-reference}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.Test;
	import org.junit.runner.RunWith;
	import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;
	import org.springframework.test.context.junit4.SpringRunner;
	import org.springframework.transaction.annotation.Propagation;
	import org.springframework.transaction.annotation.Transactional;

	@RunWith(SpringRunner.class)
	@JdbcTest
	@Transactional(propagation = Propagation.NOT_SUPPORTED)
	public 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` beans are not loaded into
the `ApplicationContext`.

TIP: A list of the auto-configurations that are enabled by `@DataJdbcTest` can be
<<appendix.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-reference}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` beans are not loaded into the `ApplicationContext`.

TIP: A list of the auto-configurations that are enabled by `@JooqTest` can be
<<appendix.adoc#test-auto-configuration,found in the appendix>>.

`@JooqTest` configures a `DSLContext`. Regular `@Component` beans are not loaded into the
`ApplicationContext`. The following example shows the `@JooqTest` annotation in use:

[source,java,indent=0]
----
	import org.jooq.DSLContext;
	import org.junit.Test;
	import org.junit.runner.RunWith;
	import org.springframework.boot.test.autoconfigure.jooq.JooqTest;
	import org.springframework.test.context.junit4.SpringRunner;

	@RunWith(SpringRunner.class)
	@JooqTest
	public 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` beans are not loaded into the `ApplicationContext`. (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.adoc#test-auto-configuration,found in the appendix>>.

The following class shows the `@DataMongoTest` annotation in use:

[source,java,indent=0]
----
	import org.junit.runner.RunWith;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
	import org.springframework.data.mongodb.core.MongoTemplate;
	import org.springframework.test.context.junit4.SpringRunner;

	@RunWith(SpringRunner.class)
	@DataMongoTest
	public 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.junit.runner.RunWith;
  import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration;
	import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
	import org.springframework.test.context.junit4.SpringRunner;

	@RunWith(SpringRunner.class)
	@DataMongoTest(excludeAutoConfiguration = EmbeddedMongoAutoConfiguration.class)
	public 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 uses an in-memory
embedded Neo4j (if the embedded driver is available), scans for `@NodeEntity` classes, and
configures Spring Data Neo4j repositories. Regular `@Component` beans are not loaded into
the `ApplicationContext`. (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.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.junit.runner.RunWith;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
	import org.springframework.test.context.junit4.SpringRunner;

	@RunWith(SpringRunner.class)
	@DataNeo4jTest
	public 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-reference}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.Test;
	import org.junit.runner.RunWith;
	import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
	import org.springframework.test.context.junit4.SpringRunner;
	import org.springframework.transaction.annotation.Propagation;
	import org.springframework.transaction.annotation.Transactional;

	@RunWith(SpringRunner.class)
	@DataNeo4jTest
	@Transactional(propagation = Propagation.NOT_SUPPORTED)
	public class ExampleNonTransactionalTests {

	}
----




[[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`
beans are not loaded into the `ApplicationContext`. (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.adoc#test-auto-configuration,found in the appendix>>.

The following example shows the `@DataRedisTest` annotation in use:

[source,java,indent=0]
----
	import org.junit.runner.RunWith;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.redis.DataRedisTest;
	import org.springframework.test.context.junit4.SpringRunner;

	@RunWith(SpringRunner.class)
	@DataRedisTest
	public 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` beans are not
loaded into the `ApplicationContext`. (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.adoc#test-auto-configuration,found in the appendix>>.

The following example shows the `@DataLdapTest` annotation in use:

[source,java,indent=0]
----
	import org.junit.runner.RunWith;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
	import org.springframework.ldap.core.LdapTemplate;
	import org.springframework.test.context.junit4.SpringRunner;

	@RunWith(SpringRunner.class)
	@DataLdapTest
	public 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.junit.runner.RunWith;
	import org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration;
	import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
	import org.springframework.test.context.junit4.SpringRunner;

	@RunWith(SpringRunner.class)
	@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
	public 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` beans are not loaded into
the `ApplicationContext`.

TIP: A list of the auto-configuration settings that are enabled by `@RestClientTest` can
be <<appendix.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]
----
	@RunWith(SpringRunner.class)
	@RestClientTest(RemoteVehicleDetailsService.class)
	public class ExampleRestClientTest {

		@Autowired
		private RemoteVehicleDetailsService service;

		@Autowired
		private MockRestServiceServer server;

		@Test
		public 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-rest-docs}[Spring REST
Docs] in your tests with Mock MVC, REST Assured, or WebTestClient. It removes the need for
the JUnit rule 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. 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.Test;
	import org.junit.runner.RunWith;

	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.context.junit4.SpringRunner;
	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.*;

	@RunWith(SpringRunner.class)
	@WebMvcTest(UserController.class)
	@AutoConfigureRestDocs
	public class UserDocumentationTests {

		@Autowired
		private MockMvc mvc;

		@Test
		public 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
	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`. 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]
----



[[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-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 by creating a custom `@AutoConfigure...` annotation or
simply by adding `@ImportAutoConfiguration` to the test as shown in the following example:

[source,java,indent=0]
----
	@RunWith(SpringRunner.class)
	@JdbcTest
	@ImportAutoConfiguration(IntegrationAutoConfiguration.class)
	public 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.



[[boot-features-testing-spring-boot-applications-testing-user-configuration]]
==== User Configuration and Slicing
If you <<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 extends 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 http://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 `Rule` that you can use to capture `System.out` and
`System.err` output. You can declare the capture as a `@Rule` and then use `toString()`
for assertions, as follows:

[source,java,indent=0]
----
	import org.junit.Rule;
	import org.junit.Test;
	import org.springframework.boot.test.rule.OutputCapture;

	import static org.hamcrest.Matchers.*;
	import static org.junit.Assert.*;

	public class MyTest {

		@Rule
		public OutputCapture capture = new OutputCapture();

		@Test
		public void testName() throws Exception {
			System.out.println("Hello World!");
			assertThat(capture.toString(), containsString("World"));
		}

	}
----

[[boot-features-rest-templates-test-utility]]
==== TestRestTemplate

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`.


`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 behaves in a
test-friendly way by not throwing exceptions on server-side errors. 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-reference}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-reference}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-reference}[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,properties,indent=0]
----
	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-reference}#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 {sc-spring-boot-autoconfigure}[`spring-boot-autoconfigure`]
to see the `@Configuration` classes that Spring provides (see the
{github-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
{sc-spring-boot-autoconfigure}/AutoConfigureAfter.{sc-ext}[`@AutoConfigureAfter`] or
{sc-spring-boot-autoconfigure}/AutoConfigureBefore.{sc-ext}[`@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.



[[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.org/[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.



[[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 web application is any application that uses a Spring `WebApplicationContext`,
defines a `session` scope, or has a `StandardServletEnvironment`.



[[boot-features-spel-conditions]]
==== SpEL Expression Conditions
The `@ConditionalOnExpression` annotation lets configuration be included based on the
result of a {spring-reference}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 `Assert4J`.

[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
	public void autoConfigTest {
		ConditionEvaluationReportLoggingListener initializer = new ConditionEvaluationReportLoggingListener(
				LogLevel.INFO);
		ApplicationContextRunner contextRunner = new ApplicationContextRunner()
				.withInitializer(initializer).run((context) -> {
						// Do something...
				});
	}
----



==== 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.



==== 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 full Spring Boot starter for a library may contain the following components:

* The `autoconfigure` module that contains the auto-configuration code.
* The `starter` module that provides a dependency to the `autoconfigure` module as well
as the library and any additional dependencies that are typically useful. In a nutshell,
adding the starter should provide everything needed to start using that library.

TIP: You may combine the auto-configuration code and the dependency management in a
single module if you do not need to separate those two concerns.



[[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-autoconfigure` and the starter `acme-spring-boot-starter`. If
you only have one module that combines the two, name it `acme-spring-boot-starter`.

Also, 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.

Make sure to
<<appendix.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 meta-data (`META-INF/spring-configuration-metadata.json`) to make
sure your keys are properly documented.



[[boot-features-custom-starter-module-autoconfigure]]
==== `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>
----

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-documentation}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-reference}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 supports Kotlin 1.3.x. 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-documentation}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-documentation}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-documentation}java-interop.html#null-safety-and-platform-types[platform types]
for which null-checks are relaxed.
{kotlin-documentation}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-documentation}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.



[[boot-features-kotlin-configuration-properties]]
=== `@ConfigurationProperties`
`@ConfigurationProperties` supports classes with immutable `val` properties as shown in
the following example:

[source,kotlin,indent=0]
----
@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.adoc#configuration-metadata-annotation-processor,your own
metadata>> using the annotation processor, {kotlin-documentation}kapt.html[`kapt` should
be configured] with the `spring-boot-configuration-processor` dependency. Note that some
features (such as detecting the default value or deperecated 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 (the default provided by `spring-boot-starter-test`)
to test Kotlin code, JUnit 5 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
`@BeforeClass` and `@AfterClass` annotations on non-static methods, which is a good fit for
Kotlin.

To use JUnit 5, exclude `junit:junit` dependency from `spring-boot-starter-test`, add
JUnit 5 dependencies, and configure the Maven or Gradle plugin accordingly. See the
{junit5-documentation}/#dependency-metadata-junit-jupiter-samples[JUnit 5
documentation] for more details. You also need to
{junit5-documentation}/#writing-tests-test-instance-lifecycle-changing-default[switch test
instance lifecycle to "per-class"].

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-documentation}[Kotlin language reference]
* https://slack.kotlinlang.org/[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



[[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 {dc-root}[Spring Boot API documentation] or you can browse the
{github-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>>.
