[[boot-features]]
= Spring Boot features

[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-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. By default, an `AnnotationConfigApplicationContext` or
`AnnotationConfigServletWebServerApplicationContext` is used, depending on whether you
are developing a web application or not.

The algorithm used to determine a "`web environment`" is fairly simplistic (it is based
on the presence of a few classes).  If you need to override the default, you can use
`setWebEnvironment(boolean webEnvironment)`.

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 `setWebEnvironment(false)` 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.
. {dc-spring-boot-test}/context/SpringBootTest.{dc-ext}[`@SpringBootTest#properties`]
annotation attribute on your tests.
. 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-external-config-yaml]]
=== Using YAML Instead of Properties
http://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
http://www.snakeyaml.org/[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: http://dev.example.com
			name: Developer Setup
		prod:
			url: http://another.example.com
			name: My Cool App
----

The preceding example would be transformed into the following properties:

[source,properties,indent=0]
----
	environments.dev.url=http://dev.example.com
	environments.dev.name=Developer Setup
	environments.prod.url=http://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 the Spring `DataBinder` 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;
		}
	}
----

[NOTE]
====
When lists are configured in more than one place, overriding works by replacing the entire
list. In the preceding example, when `my.servers` is defined in several places, the
entire list from the `PropertySource` with higher precedence overrides any other
configuration for that list. Both comma-separated lists and YAML lists can be used for
completely overriding the contents of the list.
====



[[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
	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` profile is active, the
`server.address` property is `192.168.1.120`. If the `development` and `production`
profiles are *not* enabled, then the value for the property is `192.168.1.100`.

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.



[[boot-features-external-config-complex-type-merge]]
==== Merging YAML Lists
As <<boot-features-external-config-loading-yaml,we showed earlier>>, any YAML content is
ultimately transformed to properties. That process may be counter-intuitive when
overriding "`list`" properties through a profile.

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 collection 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`).



[[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, 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`.

[NOTE]
====
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.
====

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

You also need to list the properties classes to register in the
`@EnableConfigurationProperties` annotation, as shown in the following example:

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

[NOTE]
====
When the `@ConfigurationProperties` bean is registered that way, 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`.
====

Even if the preceding configuration creates a regular bean for `AcmeProperties`, we
recommend that `@ConfigurationProperties` only deal with the environment and, in
particular, does not inject other beans from the context. Having said that, the
`@EnableConfigurationProperties` annotation is _also_ automatically applied to your
project so that any _existing_ bean annotated with `@ConfigurationProperties` is
configured from the `Environment`. You could shortcut `MyConfiguration` by making sure
`AcmeProperties` is already a bean, as shown in the following example:

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

		// ... see the preceding example

	}
----

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
<<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 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.firstName`
|Standard camel case syntax.

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

|`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`.


[[boot-features-external-config-conversion]]
==== Properties Conversion
Spring 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-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

	}
----

In order to validate the values of nested properties, you must annotate the associated
field as `@Valid` to trigger its validation. 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-configuration-metadata.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
	@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 http://commons.apache.org/logging[Commons Logging] for all internal
logging but leaves the underlying log implementation open. Default configurations are
provided for
https://docs.oracle.com/javase/8/docs/api/java/util/logging/package-summary.html[Java Util
Logging], http://logging.apache.org/log4j/2.x/[Log4J2], and
http://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` or `logging.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` |`logging.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.

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.*=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-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.
System properties and the conventional Spring Boot external configuration files work
fine.)

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

|`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
http://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. Multiple profiles can be specified with a
comma-separated list. 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-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.web.HttpMessageConverters;
	import org.springframework.context.annotation.*;
	import org.springframework.http.converter.*;

	@Configuration
	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
http://wiki.fasterxml.com/JacksonHowToCustomDeserializers[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 http://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` dependency.
Then declare your Webjar. Using jQuery as an example, adding
`"/webjars/jquery/dist/jquery.min.js"` results in
`"/webjars/jquery/x.y.z/dist/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`. 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.content-negotiation.favor-parameter=true

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

	# We can also register additional file extensions/media types with:
	spring.mvc.content-negotiation.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.content-negotiation.favor-path-extension=true

	# You can also restrict that feature to known extensions only
	# spring.mvc.path-match.use-registered-suffix-pattern=true

	# We can also register additional file extensions/media types with:
	# spring.mvc.content-negotiation.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.org/docs/[FreeMarker]
 * http://docs.groovy-lang.org/docs/next/html/documentation/template-engines.html#_the_markuptemplateengine[Groovy]
 * http://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 http://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
	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 http://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
	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
	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 http://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:

 * http://freemarker.org/docs/[FreeMarker]
 * http://www.thymeleaf.org[Thymeleaf]
 * http://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 implemented `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] 1.x and
http://cxf.apache.org/[Apache CXF] work quite well out of the box if you register their
`Servlet` or `Filter` as a `@Bean` in your application context. Jersey 2.x 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 2.x, 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 `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. There is also a
{github-code}/spring-boot-samples/spring-boot-sample-jersey1[Jersey 1.x sample]. Note
that, in the Jersey 1.x sample, the spring-boot maven plugin has been configured to
unpack some Jersey jars so that they can be scanned by the JAX-RS implementation (because
the sample asks for them to be scanned in its `Filter` registration). If any of your
JAX-RS resources are packaged as nested jars, you may need to do the same.



[[boot-features-embedded-container]]
=== Embedded Servlet Container Support
Spring Boot includes support for embedded http://tomcat.apache.org/[Tomcat],
https://www.eclipse.org/jetty/[Jetty], and http://undertow.io/[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`.

WARNING: If you choose to use Tomcat on https://www.centos.org/[CentOS], be aware that, by
default, a temporary directory is used to store compiled JSPs, file uploads, and so on.
This directory may be deleted by `tmpwatch` while your application is running, leading to
failures. To avoid this behavior, you may want to customize your `tmpwatch` configuration
such that `tomcat.*` directories are not deleted or configure `server.tomcat.basedir` such
that embedded Tomcat uses a different location.



[[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
`FilterRegistrationBean.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. Dedicated variants exist for Tomcat, Jetty, and Undertow. 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);
		}

	}
----



[[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 Tomcat, it should work if you use war packaging. That is, an executable war works
and is also deployable to a standard container (not limited to, but including Tomcat).
An executable jar does not work because of a hard-coded file pattern in Tomcat.

* With Jetty, it should work if you use war packaging. That is, an executable war works,
and is also deployable to any standard container.

* 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-security]]
== Security
If {spring-security}[Spring Security] is on the classpath, then web applications are
secure 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 `AuthenticationManager` 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 Content-Type) 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 in
the classes imported from there (`SpringBootWebSecurityConfiguration` for web security
and `AuthenticationManagerConfiguration` for authentication configuration, 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 authentication manager configuration or Actuator's security).

To also switch off the authentication manager 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
The default security configuration is implemented in `ReactiveSecurityAutoConfiguration` and in
the classes imported from there (`WebFluxSecurityConfiguration` for web security
and `ReactiveAuthenticationManagerConfiguration` for authentication configuration, 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 authentication manager configuration or Actuator's security).

To also switch off the authentication manager 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.


[[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 Client. This configuration
makes use of the properties under `OAuth2ClientProperties`.

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=http://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=http://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=http://my-auth-server/oauth/authorize
	spring.security.oauth2.client.provider.my-oauth-provider.token-uri=http://my-auth-server/oauth/token
	spring.security.oauth2.client.provider.my-oauth-provider.user-info-uri=http://my-auth-server/userinfo
	spring.security.oauth2.client.provider.my-oauth-provider.jwk-set-uri=http://my-auth-server/token_keys
	spring.security.oauth2.client.provider.my-oauth-provider.user-name-attribute=name
----

By default, Spring Security's `OAuth2LoginAuthenticationFilter` only processes URLs
matching `/login/oauth2/code/*`. If you want to customize the `redirect-uri-template` to
use a different pattern, you need to provide configuration to process that custom pattern.
For example, 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");
	}
}
----

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 ID of your client matches the
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-actuator]]
=== Actuator Security
For security purposes, all actuators other than `/health` and `/info` are disabled by default.
The `management.endpoints.web.expose` flag can be used to enable the actuators.
If Spring Security is on the classpath and no other WebSecurityConfigurerAdapter is present,
the actuators are secured by Spring Boot auto-config. If you define a custom `WebSecurityConfigurerAdapter`,
Spring Boot auto-config will back off and you will be in full control of actuator access rules.

NOTE: Before setting the `management.endpoints.web.expose`, 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-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 http://www.h2database.com[H2],
http://hsqldb.org/[HSQL], and http://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
http://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`"
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.country = country;
		}

		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
{http://projects.spring.io/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 findByNameAndCountryAllIgnoringCase(String name, String country);

	}
----

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-sql-h2-console]]
=== Using H2's Web Console
The http://www.h2database.com[H2 database] provides a
http://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 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 (http://www.jooq.org/[jOOQ]) is a popular product from
http://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
http://www.jooq.org/doc/3.6/manual-single-page/#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`
* `TransactionProvider`
* `RecordMapperProvider`
* `RecordListenerProvider`
* `ExecuteListenerProvider`
* `VisitListenerProvider`

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
http://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
http://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
----

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 findByNameAndCountryAllIgnoringCase(String name, String country);

	}
----

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.



[[boot-features-neo4j]]
=== Neo4j
http://neo4j.com/[Neo4j] is an open-source NoSQL graph database that uses a rich data
model of nodes related 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
You can inject an auto-configured `Neo4jSession`, `Session`, or `Neo4jOperations`
instance as you would any other Spring Bean. By default, the instance tries to connect to
a Neo4j server at `localhost:7474`. The following example shows how to inject a Neo4j
bean:

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

		private final Neo4jTemplate neo4jTemplate;

		@Autowired
		public MyBean(Neo4jTemplate neo4jTemplate) {
			this.neo4jTemplate = neo4jTemplate;
		}

		// ...

	}
----

You can take full control of the configuration by adding a
`org.neo4j.ogm.config.Configuration` `@Bean` of your own. Also, adding a `@Bean` of type
`Neo4jOperations` disables the auto-configuration.

You can configure the user 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=http://my-server:7474
	spring.data.neo4j.username=neo4j
	spring.data.neo4j.password=secret
----



[[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. You can explicitly disable that
mode by setting `spring.data.neo4j.embedded.enabled=false`. You can also enable
persistence for the embedded mode by providing a path to a database file, as shown in the
following example:

----
	spring.data.neo4j.uri=file://var/tmp/graph.db
----

[NOTE]
====
The Neo4j OGM embedded driver does not provide the Neo4j kernel. Users are expected to
provide this dependency manually. See
http://neo4j.com/docs/ogm-manual/current/reference/#reference:getting-started[the
documentation] for more details.
====


[[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.

In fact, both Spring Data JPA and Spring Data Neo4j share the same common infrastructure.
You could take the JPA example from earlier and, assuming that `City` is now a Neo4j OGM
`@NodeEntity` rather than a JPA `@Entity`, it works in the same way.

TIP: You can customize entity scanning locations by using the `@EntityScan` annotation.

To enable repository support (and optionally support for `@Transactional`), add the
following two annotations to your Spring configuration:

[source,java,indent=0]
----
	@EnableNeo4jRepositories(basePackages = "com.example.myapp.repository")
	@EnableTransactionManagement
----

==== Repository Example

The following example shows an interface definition for a Neo4j repository:

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

	import org.springframework.data.domain.*;
	import org.springframework.data.repository.*;

	public interface CityRepository extends GraphRepository<City> {

		Page<City> findAll(Pageable pageable);

		City findByNameAndCountry(String name, String country);

	}
----

TIP: For complete details of Spring Data Neo4j, including its rich 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
http://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
http://www.elasticsearch.org/[Elasticsearch] is an open source, distributed, real-time
search and analytics engine. Spring Boot offers basic auto-configuration for
Elasticsearch and the abstractions on top of it provided by
https://github.com/spring-projects/spring-data-elasticsearch[Spring Data Elasticsearch].
There is a `spring-boot-starter-data-elasticsearch` "`Starter`" for collecting the
dependencies in a convenient way. Spring Boot also supports
https://github.com/searchbox-io/Jest[Jest].



[[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=http://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
http://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
----

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
http://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
	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.



[[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
----

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=http://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 `OkHttpClient.Builder` 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.


NOTE: If you use the cache infrastructure with beans that are not interface-based, make
sure to enable the `proxyTargetClass` attribute of `@EnableCaching`.


=== 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
http://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
http://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
	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 http://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 http://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
----

You can also pool JMS resources by adding a dependency to
`org.apache.activemq:activemq-pool` and configuring the `PooledConnectionFactory`
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
http://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.

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
	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
----

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). Retries are disabled by default.



[[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
	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.

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
http://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 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.*`. Also, if a `RecordMessageConverter` bean is defined, it is
automatically associated to the default factory.

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) {
			// ...
		}

	}
----



[[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 both producers and consumers but can be
specified at the producer or consumer level if you wish to use different values for each.
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 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
----

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` and the `prop.four` producer property to `fourth`.

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=org.foo.Invoice
spring.kafka.consumer.properties.spring.json.trusted.packages=org.foo,org.bar
----

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 MyBean(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.basicAuthorization("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 create your own client instance with the builder,
`WebClient.create()`. See the {spring-reference}web.html#web-reactive-client[relevant
section on WebClient].

Spring Boot creates and pre-configures such a builder for you. For example, client HTTP
codecs are configured in the same fashion as the server ones (see
<<boot-features-webflux-httpcodecs,WebFlux HTTP codecs auto-configuration>>).

The following code shows a typical example:

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

		private final WebClient webClient;

		public MyBean(WebClient.Builder webClientBuilder) {
			this.webClient = webClientBuilder.baseUrl("http://example.org").build();
		}

		public Mono<Details> someRestCall(String name) {
			return this.webClient.get().url("/{name}/details", name)
							.retrieve().bodyToMono(Details.class);
		}

	}
----



[[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
----



[[boot-features-jta]]
== Distributed Transactions with JTA
Spring Boot supports distributed JTA transactions across multiple XA resources by using
either an http://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-narayana]]
=== Using a Narayana Transaction Manager
http://narayana.io/[Narayana] is a popular open source JTA transaction manager
implementation supported by JBoss. You can use the `spring-boot-starter-jta-narayana`
starter to add the appropriate Narayana dependencies to your project. As with Atomikos and
Bitronix, Spring Boot automatically configures Narayana and post-processes your beans to
ensure that startup and shutdown ordering is correct.

By default, Narayana transaction logs are written to a `transaction-logs` directory in
your application 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.narayana.properties` can also be used to customize the Narayana
configuration. See the
{dc-spring-boot}/jta/narayana/NarayanaProperties.{dc-ext}[`NarayanaProperties` Javadoc]
for complete details.

NOTE: To ensure that multiple transaction managers can safely coordinate the same
resource managers, each Narayana instance must be configured with a unique ID. By
default, this ID is set to `1`. 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}/jta/XAConnectionFactoryWrapper.{sc-ext}[`XAConnectionFactoryWrapper`]
and {sc-spring-boot}/jta/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
http://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
http://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
----

NOTE: By default, the database is detected and initialized by using the standard scripts
provided with the Quartz library. It is also possible to provide a custom script by
setting the `spring.quartz.jdbc.schema` property.

Quartz Scheduler configuration can be customized by using Quartz configuration properties
()`spring.quartz.properties.*`) and `SchedulerFactoryBeanCustomizer` beans, which allow
programmatic `SchedulerFactoryBean` customization.

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-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.



[[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 Spring Session is available, 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
----



[[boot-features-jmx]]
== Monitoring and Management over JMX
Java Management Extensions (JMX) provide a standard mechanism to monitor and manage
applications. By default, Spring Boot creates an `MBeanServer` bean with an ID of
`mbeanServer` and exposes any of your beans that are annotated with Spring JMX
annotations (`@ManagedResource`, `@ManagedAttribute`, or `@ManagedOperation`).

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:

* http://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.
* http://joel-costigliola.github.io/assertj/[AssertJ]: A fluent assertion library.
* http://hamcrest.org/JavaHamcrest/[Hamcrest]: A library of matcher objects (also known
as constraints or predicates).
* http://mockito.org/[Mockito]: A Java mocking framework.
* https://github.com/skyscreamer/JSONassert[JSONassert]: An assertion library for JSON.
* https://github.com/jayway/JsonPath[JsonPath]: XPath for JSON.

We generally find these common libraries to be useful when writing tests. If these
libraries do not suit your needs, you can add additional test dependencies of your own.



[[boot-features-testing-spring-applications]]
=== Testing Spring Applications
One of the major advantages of dependency injection is that it should make your code
easier to unit test. You can instantiate objects by using the `new` operator without
even involving Spring. You can also use _mock objects_ instead of real dependencies.

Often, you need to move beyond unit testing and start integration testing (with
a Spring `ApplicationContext`). It is useful to be able to perform integration testing
without requiring deployment of your application or needing to connect to other
infrastructure.

The Spring Framework includes a dedicated test module for such integration testing. You
can declare a dependency directly to `org.springframework:spring-test` or use the
`spring-boot-starter-test` "`Starter`" to pull it in transitively.

If you have not used the `spring-test` module before, you should start by reading the
{spring-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 creating the `ApplicationContext` used in your
tests through `SpringApplication`.

You can use the `webEnvironment` attribute of `@SpringBootTest` to further refine how
your tests run:

* `MOCK`: Loads a `WebApplicationContext` and provides a mock servlet environment.
Embedded servlet containers are not started when using this annotation. If servlet APIs
are not on your classpath, this mode transparently falls back to creating a regular
non-web `ApplicationContext`. It can be used in conjunction with
`@AutoConfigureMockMvc` for `MockMvc`-based testing of your application.
* `RANDOM_PORT`: Loads an `ServletWebServerApplicationContext` and provides a real
servlet environment. Embedded servlet containers are started and listen on a random
port.
* `DEFINED_PORT`: Loads a `ServletWebServerApplicationContext` and provides a real
servlet environment. Embedded servlet containers 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_ servlet 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: In addition to `@SpringBootTest`, a number of other annotations are also provided
for testing more specific slices of an application. You can find more detail throughout
this chapter.

TIP: Do not forget to add `@RunWith(SpringRunner.class)` to your test. Otherwise, the
annotations are ignored.



[[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>>.

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-applications-working-with-random-ports]]
==== Working with Random Ports
If you need to start a full running server for tests, 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 `TestRestTemplate`, which resolves relative links to the
running server, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/test/web/RandomPortTestRestTemplateExampleTests.java[tag=test-random-port]
----

If you prefer to use a {spring-reference}testing.html#webtestclient[`WebTestClient`], you
can use that as well:

[source,java,indent=0]
----
include::{code-examples}/test/web/RandomPortWebTestClientExampleTests.java[tag=test-random-port]
----


[[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");
		}

	}
----

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.


[[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 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`.

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`

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`.

A list of the auto-configuration that is enabled by `@JsonTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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: 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.

A list of the auto-configuration settings that are enabled by `@WebMvcTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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: 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");
		}

	}
----

A list of the auto-configuration that is enabled by `@WebFluxTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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`.

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 {

		// ...

	}
----

A list of the auto-configuration settings that are enabled by `@DataJpaTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[boot-features-testing-spring-boot-applications-testing-autoconfigured-jdbc-test]]
==== Auto-configured JDBC Tests
`@JdbcTest` is similar to `@DataJpaTest` but is for pure JDBC-related tests. By default,
it also configures an in-memory embedded database and a `JdbcTemplate`. Regular
`@Component` beans are not loaded into the `ApplicationContext`.

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>>".)

A list of the auto-configuration that is enabled by `@JdbcTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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.)

`@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>>.

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



[[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.)

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 {

	}
----

A list of the auto-configuration settings that are enabled by `@DataMongoTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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.)

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 {

	}
----


A list of the auto-configuration settings that are enabled by `@DataNeo4jTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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.)

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;

		//
	}
----

A list of the auto-configuration settings that are enabled by `@DataRedisTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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.)

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 {

	}
----

A list of the auto-configuration settings that are enabled by `@DataLdapTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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`. 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");
		}

	}
----

A list of the auto-configuration settings that are enabled by `@RestClientTest` can be
<<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.



[[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 or REST Assured. 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-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-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
	@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.

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 1.1 or later to
benefit from a number of improvements to Spock's Spring Framework and Spring Boot
integration. See http://spockframework.org/spock/docs/1.1/modules.html[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-environment-test-utilities]]
==== EnvironmentTestUtils
`EnvironmentTestUtils` lets you quickly add properties to a
`ConfigurableEnvironment` or `ConfigurableApplicationContext`. You can call it with
`key=value` strings, as follows:

[source,java,indent=0]
----
	EnvironmentTestUtils.addEnvironment(env, "org=Spring", "name=Boot");
----



[[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
`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 = template.getForEntity("http://myhost.com/example", String.class).getHeaders();
			assertThat(headers.getLocation().toString(), containsString("myotherhost"));
		}

	}
----

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]
----
	@RunWith(SpringRunner.class)
	@SpringBootTest
	public class MyTest {

		@Autowired
		private TestRestTemplate template;

		@Test
		public void testRequest() throws Exception {
			HttpHeaders headers = template.getForEntity("/example", String.class).getHeaders();
			assertThat(headers.getLocation().toString(), containsString("myotherhost"));
		}

		@TestConfiguration
		static class Config {

			@Bean
			public RestTemplateBuilder restTemplateBuilder() {
				return new RestTemplateBuilder()
					.additionalMessageConverters(...)
					.customizers(...);
			}

		}

	}
----



[[boot-features-websockets]]
== WebSockets
Spring Boot provides WebSockets auto-configuration for embedded Tomcat 8.5, Jetty
9, 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]
that can be easily accessed through the `spring-boot-starter-websocket` module.



[[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-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
----

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.

[NOTE]
====
Auto-configurations must be loaded that way _only_. Make sure that they are defined in
a specific package space and that, in particular, they are never the target of component
scanning.
====



[[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
be included based on the presence or absence of specific classes. Due to the fact that
annotation metadata is parsed by using http://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.

[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
	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. Using these conditions at the class level is equivalent to
marking each contained `@Bean` method with the annotation.



[[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]
----



==== 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-configuration-metadata#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.



[[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-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>>.
