[[howto]]
= '`How-to`' guides

[partintro]
--
This section provides answers to some common '`how do I do that...`' questions
that often arise when using Spring Boot. Its coverage is not exhaustive, but it
does cover quite a lot.

If you have a specific problem that we do not cover here, you might want to check out
https://stackoverflow.com/tags/spring-boot[stackoverflow.com] to see if someone has
already provided an answer. This is also a great place to ask new questions (please use
the `spring-boot` tag).

We are also more than happy to extend this section. If you want to add a '`how-to`',
send us a {github-code}[pull request].
--



[[howto-spring-boot-application]]
== Spring Boot Application

This section includes topics relating directly to Spring Boot applications.



[[howto-failure-analyzer]]
=== Create Your Own FailureAnalyzer
{dc-spring-boot}/diagnostics/FailureAnalyzer.{dc-ext}[`FailureAnalyzer`] is a great way
to intercept an exception on startup and turn it into a human-readable message, wrapped
in a {dc-spring-boot}/diagnostics/FailureAnalysis.{dc-ext}[`FailureAnalysis`]. Spring
Boot provides such an analyzer for application-context-related exceptions, JSR-303
validations, and more. You can also create your own.

`AbstractFailureAnalyzer` is a convenient extension of `FailureAnalyzer` that checks the
presence of a specified exception type in the exception to handle. You can extend from
that so that your implementation gets a chance to handle the exception only when it is
actually present. If, for whatever reason, you cannot handle the exception, return `null`
to give another implementation a chance to handle the exception.

`FailureAnalyzer` implementations must be registered in `META-INF/spring.factories`.
The following example registers `ProjectConstraintViolationFailureAnalyzer`:

[source,properties,indent=0]
----
	org.springframework.boot.diagnostics.FailureAnalyzer=\
	com.example.ProjectConstraintViolationFailureAnalyzer
----

NOTE: If you need access to the `BeanFactory` or the `Environment`, your `FailureAnalyzer`
can simply implement `BeanFactoryAware` or `EnvironmentAware` respectively.



[[howto-troubleshoot-auto-configuration]]
=== Troubleshoot Auto-configuration
The Spring Boot auto-configuration tries its best to "`do the right thing`", but
sometimes things fail, and it can be hard to tell why.

There is a really useful `ConditionEvaluationReport` available in any Spring Boot
`ApplicationContext`. You can see it if you enable `DEBUG` logging output. If you use
the `spring-boot-actuator` (see <<production-ready-features.adoc,the Actuator  chapter>>),
there is also a `conditions` endpoint that renders the report in JSON. Use that endpoint
to debug the application and see what features have been added (and which have not been
added) by Spring Boot at runtime.

Many more questions can be answered by looking at the source code and the Javadoc. When
reading the code, remember the following rules of thumb:

* Look for classes called `+*AutoConfiguration+` and read their sources. Pay special
attention to the `+@Conditional*+` annotations to find out what features they enable and
when. Add `--debug` to the command line or a System property `-Ddebug` to get a log on the
console of all the auto-configuration decisions that were made in your app. In a running
Actuator app, look at the `conditions` endpoint (`/actuator/conditions` or the JMX
equivalent) for the same information.
* Look for classes that are `@ConfigurationProperties` (such as
{sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[`ServerProperties`])
and read from there the available external configuration options. The
`@ConfigurationProperties` annotation has a `name` attribute that acts as a prefix to
external properties. Thus, `ServerProperties` has `prefix="server"` and its configuration
properties are `server.port`, `server.address`, and others. In a running Actuator app,
look at the `configprops` endpoint.
* Look for uses of the `bind` method on the `Binder` to pull configuration values
explicitly out of the `Environment` in a relaxed manner. It is often used with a prefix.
* Look for `@Value` annotations that bind directly to the `Environment`.
* Look for `@ConditionalOnExpression` annotations that switch features on and off in
response to SpEL expressions, normally evaluated with placeholders resolved from the
`Environment`.



[[howto-customize-the-environment-or-application-context]]
=== Customize the Environment or ApplicationContext Before It Starts
A `SpringApplication` has `ApplicationListeners` and `ApplicationContextInitializers` that
are used to apply customizations to the context or environment. Spring Boot loads a number
of such customizations for use internally from `META-INF/spring.factories`. There is more
than one way to register additional customizations:

* Programmatically, per application, by calling the `addListeners` and `addInitializers`
methods on `SpringApplication` before you run it.
* Declaratively, per application, by setting the `context.initializer.classes` or
`context.listener.classes` properties.
* Declaratively, for all applications, by adding a `META-INF/spring.factories` and packaging
a jar file that the applications all use as a library.

The `SpringApplication` sends some special `ApplicationEvents` to the listeners (some
even before the context is created) and then registers the listeners for events published
by the `ApplicationContext` as well. See
"`<<spring-boot-features.adoc#boot-features-application-events-and-listeners>>`" in the
'`Spring Boot features`' section for a complete list.

It is also possible to customize the `Environment` before the application context is
refreshed by using `EnvironmentPostProcessor`. Each implementation should be registered in
`META-INF/spring.factories`, as shown in the following example:

[source,properties,indent=0]
----
	org.springframework.boot.env.EnvironmentPostProcessor=com.example.YourEnvironmentPostProcessor
----

The implementation can load arbitrary files and add them to the `Environment`. For
instance, the following example loads a YAML configuration file from the classpath:


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

TIP: The `Environment` has already been prepared with all the usual property sources
that Spring Boot loads by default. It is therefore possible to get the location of the
file from the environment. The preceding example adds the `custom-resource` property
source at the end of the list so that a key defined in any of the usual other locations
takes precedence. A custom implementation may define another order.

CAUTION: While using `@PropertySource` on your `@SpringBootApplication` may seem to be a
convenient and easy way to load a custom resource in the `Environment`, we do not
recommend it, because Spring Boot prepares the `Environment` before the
`ApplicationContext` is refreshed. Any key defined with `@PropertySource` is loaded too
late to have any effect on auto-configuration.



[[howto-build-an-application-context-hierarchy]]
=== Build an ApplicationContext Hierarchy (Adding a Parent or Root Context)
You can use the `ApplicationBuilder` class to create parent/child `ApplicationContext`
hierarchies. See "`<<spring-boot-features.adoc#boot-features-fluent-builder-api>>`"
in the '`Spring Boot features`' section for more information.



[[howto-create-a-non-web-application]]
=== Create a Non-web Application
Not all Spring applications have to be web applications (or web services). If you want to
execute some code in a `main` method but also bootstrap a Spring application to set up
the infrastructure to use, you can use the `SpringApplication` features of Spring
Boot. A `SpringApplication` changes its `ApplicationContext` class, depending on whether
it thinks it needs a web application or not. The first thing you can do to help it is to
leave server-related dependencies (e.g. servlet API) off the classpath. If you cannot do
that (for example, you run two applications from the same code base) then you can
explicitly call `setWebApplicationType(WebApplicationType.NONE)` on your
`SpringApplication` instance or set the `applicationContextClass` property (through the
Java API or with external properties). Application code that you want to run as your
business logic can be implemented as a `CommandLineRunner` and dropped into the context as
a `@Bean` definition.



[[howto-properties-and-configuration]]
== Properties and Configuration

This section includes topics about setting and reading properties and configuration
settings and their interaction with Spring Boot applications.

[[howto-automatic-expansion]]
=== Automatically Expand Properties at Build Time
Rather than hardcoding some properties that are also specified in your project's build
configuration, you can automatically expand them by instead using the existing build
configuration. This is possible in both Maven and Gradle.



[[howto-automatic-expansion-maven]]
==== Automatic Property Expansion Using Maven
You can automatically expand properties from the Maven project by using resource
filtering. If you use the `spring-boot-starter-parent`, you can then refer to your
Maven '`project properties`' with `@..@` placeholders, as shown in the following example:

[source,properties,indent=0]
----
	app.encoding=@project.build.sourceEncoding@
	app.java.version=@java.version@
----

NOTE: Only production configuration is filtered that way (in other words, no filtering is
applied on `src/test/resources`).

TIP: If you enable the `addResources` flag, the `spring-boot:run` goal can add
`src/main/resources` directly to the classpath (for hot reloading purposes). Doing so
circumvents the resource filtering and this feature. Instead, you can use the `exec:java`
goal or customize the plugin's configuration. See the
{spring-boot-maven-plugin-site}/usage.html[plugin usage page] for more details.

If you do not use the starter parent, you need to include the following  element inside
the `<build/>` element of your `pom.xml`:

[source,xml,indent=0]
----
	<resources>
		<resource>
			<directory>src/main/resources</directory>
			<filtering>true</filtering>
		</resource>
	</resources>
----

You also need to include the following element inside `<plugins/>`:

[source,xml,indent=0]
----
	<plugin>
		<groupId>org.apache.maven.plugins</groupId>
		<artifactId>maven-resources-plugin</artifactId>
		<version>2.7</version>
		<configuration>
			<delimiters>
				<delimiter>@</delimiter>
			</delimiters>
			<useDefaultDelimiters>false</useDefaultDelimiters>
		</configuration>
	</plugin>
----

NOTE: The `useDefaultDelimiters` property is important if you use standard Spring
placeholders (such as `${placeholder}`) in your configuration. If that property is not
set to `false`, these may be expanded by the build.



[[howto-automatic-expansion-gradle]]
==== Automatic Property Expansion Using Gradle
You can automatically expand properties from the Gradle project by configuring the
Java plugin's `processResources` task to do so, as shown in the following example:

[source,groovy,indent=0]
----
	processResources {
		expand(project.properties)
	}
----

You can then refer to your Gradle project's properties by using placeholders, as shown in the
following example:

[source,properties,indent=0]
----
	app.name=${name}
	app.description=${description}
----

NOTE: Gradle's `expand` method uses Groovy's `SimpleTemplateEngine`, which transforms
`${..}` tokens. The `${..}` style conflicts with Spring's own property placeholder
mechanism. To use Spring property placeholders together with automatic expansion, escape
the Spring property placeholders as follows: `\${..}`.




[[howto-externalize-configuration]]
=== Externalize the Configuration of `SpringApplication`
A `SpringApplication` has bean properties (mainly setters), so you can use its Java API as
you create the application to modify its behavior. Alternatively, you can externalize the
configuration by setting properties in `+spring.main.*+`. For example, in
`application.properties`, you might have the following settings:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.main.web-application-type=none
	spring.main.banner-mode=off
----

Then the Spring Boot banner is not printed on startup, and the application is not starting
an embedded web server.

Properties defined in external configuration override the values specified with the Java
API, with the notable exception of the sources used to create the `ApplicationContext`.
Consider the following application:

[source,java,indent=0]
----
	new SpringApplicationBuilder()
		.bannerMode(Banner.Mode.OFF)
		.sources(demo.MyApp.class)
		.run(args);
----

Now consider the following configuration:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.main.sources=com.acme.Config,com.acme.ExtraConfig
	spring.main.banner-mode=console
----

The actual application _now_ shows the banner (as overridden by configuration) and uses
three sources for the `ApplicationContext` (in the following order): `demo.MyApp`,
`com.acme.Config`, and `com.acme.ExtraConfig`.



[[howto-change-the-location-of-external-properties]]
=== Change the Location of External Properties of an Application
By default, properties from different sources are added to the Spring `Environment` in a
defined order (see "`<<spring-boot-features.adoc#boot-features-external-config>>`" in
the '`Spring Boot features`' section for the exact order).

A nice way to augment and modify this ordering is to add `@PropertySource` annotations to your
application sources. Classes passed to the `SpringApplication` static convenience
methods and those added using `setSources()` are inspected to see if they have
`@PropertySources`. If they do, those properties are added to the `Environment` early
enough to be used in all phases of the `ApplicationContext` lifecycle. Properties added
in this way have lower priority than any added by using the default locations (such as
`application.properties`), system properties, environment variables, or the command line.

You can also provide the following System properties (or environment variables) to change
the behavior:

* `spring.config.name` (`SPRING_CONFIG_NAME`): Defaults to `application` as the root of
the file name.
* `spring.config.location` (`SPRING_CONFIG_LOCATION`): The file to load (such as a
classpath resource or a URL). A separate `Environment` property source is set up for this
document and it can be overridden by system properties, environment variables, or the
command line.

No matter what you set in the environment, Spring Boot always loads
`application.properties` as described above. By default, if YAML is used, then files with
the '`.yml`' extension are also added to the list.

Spring Boot logs the configuration files that are loaded at the `DEBUG` level and the
candidates it has not found at `TRACE` level.

See {sc-spring-boot}/context/config/ConfigFileApplicationListener.{sc-ext}[`ConfigFileApplicationListener`]
for more detail.



[[howto-use-short-command-line-arguments]]
=== Use '`Short`' Command Line Arguments
Some people like to use (for example) `--port=9000` instead of `--server.port=9000` to
set configuration properties on the command line. You can enable this behavior by using
placeholders in `application.properties`, as shown in the following example:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	server.port=${port:8080}
----

TIP: If you inherit from the `spring-boot-starter-parent` POM, the default filter
token of the `maven-resources-plugins` has been changed from `+${*}+` to `@` (that is,
`@maven.token@` instead of `${maven.token}`) to prevent conflicts with Spring-style
placeholders. If you have enabled Maven filtering for the `application.properties`
directly, you may want to also change the default filter token to use
https://maven.apache.org/plugins/maven-resources-plugin/resources-mojo.html#delimiters[other
delimiters].

NOTE: In this specific case, the port binding works in a PaaS environment such as Heroku
or Cloud Foundry. In those two platforms, the `PORT` environment variable is set
automatically and Spring can bind to capitalized synonyms for `Environment` properties.



[[howto-use-yaml-for-external-properties]]
=== Use YAML for External Properties
YAML is a superset of JSON and, as such, is a convenient syntax for storing external
properties in a hierarchical format, as shown in the following example:

[source,yaml,indent=0,subs="verbatim,quotes,attributes"]
----
	spring:
		application:
			name: cruncher
		datasource:
			driverClassName: com.mysql.jdbc.Driver
			url: jdbc:mysql://localhost/test
	server:
		port: 9000
----

Create a file called `application.yml` and put it in the root of your classpath.
Then add `snakeyaml` to your dependencies (Maven coordinates `org.yaml:snakeyaml`, already
included if you use the `spring-boot-starter`). A YAML file is parsed to a Java
`Map<String,Object>` (like a JSON object), and Spring Boot flattens the map so that it
is one level deep and has period-separated keys, as many people are used to with
`Properties` files in Java.

The preceding example YAML corresponds to the following `application.properties` file:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.application.name=cruncher
	spring.datasource.driverClassName=com.mysql.jdbc.Driver
	spring.datasource.url=jdbc:mysql://localhost/test
	server.port=9000
----

See "`<<spring-boot-features.adoc#boot-features-external-config-yaml>>`" in
the '`Spring Boot features`' section for more information
about YAML.

[[howto-set-active-spring-profiles]]
=== Set the Active Spring Profiles
The Spring `Environment` has an API for this, but you would normally set a System property
(`spring.profiles.active`) or an OS environment variable (`SPRING_PROFILES_ACTIVE`).
Also, you can launch your application with a `-D` argument (remember to put it before the
main class or jar archive), as follows:

[indent=0,subs="verbatim,quotes,attributes"]
----
	$ java -jar -Dspring.profiles.active=production demo-0.0.1-SNAPSHOT.jar
----

In Spring Boot, you can also set the active profile in `application.properties`, as shown
in the following example:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	spring.profiles.active=production
----

A value set this way is replaced by the System property or environment variable setting
but not by the `SpringApplicationBuilder.profiles()` method. Thus, the latter Java API can
be used to augment the profiles without changing the defaults.

See "`<<spring-boot-features.adoc#boot-features-profiles>>`" in
the "`Spring Boot features`" section for more information.



[[howto-change-configuration-depending-on-the-environment]]
=== Change Configuration Depending on the Environment
A YAML file is actually a sequence of documents separated by `---` lines, and each
document is parsed separately to a flattened map.

If a YAML document contains a `spring.profiles` key, then the profiles value
(a comma-separated list of profiles) is fed into the Spring
`Environment.acceptsProfiles()` method. If any of those profiles is active, that document
is included in the final merge (otherwise, it is not), as shown in the following example:

[source,yaml,indent=0,subs="verbatim,quotes,attributes"]
----
	server:
		port: 9000
	---

	spring:
		profiles: development
	server:
		port: 9001

	---

	spring:
		profiles: production
	server:
		port: 0
----

In the preceding example, the default port is 9000. However, if the Spring profile called
'`development`' is active, then the port is 9001. If '`production`' is active, then the
port is 0.

NOTE: The YAML documents are merged in the order in which they are encountered. Later
values override earlier values.

To do the same thing with properties files, you can use
`application-${profile}.properties` to specify profile-specific values.



[[howto-discover-build-in-options-for-external-properties]]
=== Discover Built-in Options for External Properties
Spring Boot binds external properties from `application.properties` (or `.yml` files and
other places) into an application at runtime. There is not (and technically cannot be) an
exhaustive list of all supported properties in a single location, because contributions
can come from additional jar files on your classpath.

A running application with the Actuator features has a `configprops` endpoint that shows
all the bound and bindable properties available through `@ConfigurationProperties`.

The appendix includes an <<appendix-application-properties#common-application-properties,
`application.properties`>> example with a list of the most common properties supported by
Spring Boot. The definitive list comes from searching the source code for
`@ConfigurationProperties` and `@Value` annotations as well as the occasional use of
`Binder`. For more about the exact ordering of loading properties, see
"<<spring-boot-features#boot-features-external-config>>".



[[howto-embedded-web-servers]]
== Embedded Web Servers

Each Spring Boot web application includes an embedded web server. This feature leads to a
number of how-to questions, including how to change the embedded server and how to
configure the embedded server. This section answers those questions.

[[howto-use-another-web-server]]
=== Use Another Web Server
Many Spring Boot starters include default embedded containers.

* For servlet stack applications, the `spring-boot-starter-web` includes Tomcat by including
`spring-boot-starter-tomcat`, but you can use `spring-boot-starter-jetty` or
`spring-boot-starter-undertow` instead.
* For reactive stack applications, the `spring-boot-starter-webflux` includes  Reactor Netty
by including `spring-boot-starter-reactor-netty`, but you can use `spring-boot-starter-tomcat`,
`spring-boot-starter-jetty`, or `spring-boot-starter-undertow` instead.

When switching to a different HTTP server, you need to exclude the default dependencies
in addition to including the one you need. Spring Boot provides separate starters for
HTTP servers to help make this process as easy as possible.

The following Maven example shows how to exclude Tomcat and include Jetty for Spring MVC:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<properties>
		<servlet-api.version>3.1.0</servlet-api.version>
	</properties>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
		<exclusions>
			<!-- Exclude the Tomcat dependency -->
			<exclusion>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-starter-tomcat</artifactId>
			</exclusion>
		</exclusions>
	</dependency>
	<!-- Use Jetty instead -->
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-jetty</artifactId>
	</dependency>
----

NOTE: The version of the Servlet API has been overridden as, unlike Tomcat 9 and Undertow
2.0, Jetty 9.4 does not support Servlet 4.0.

The following Gradle example shows how to exclude Netty and include Undertow for Spring
WebFlux:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	configurations {
		// exclude Reactor Netty
		compile.exclude module: 'spring-boot-starter-reactor-netty'
	}

	dependencies {
		compile 'org.springframework.boot:spring-boot-starter-webflux'
		// Use Undertow instead
		compile 'org.springframework.boot:spring-boot-starter-undertow'
		// ...
	}
----

NOTE: `spring-boot-starter-reactor-netty` is required to use the `WebClient` class, so
you may need to keep a dependency on Netty even when you need to include a different HTTP
server.



[[howto-disable-web-server]]
=== Disabling the Web Server
If your classpath contains the necessary bits to start a web server, Spring Boot will
automatically start it. To disable this behaviour configure the `WebApplicationType` in
your `application.properties`, as shown in the following example:

[source,properties,indent=0]
----
	spring.main.web-application-type=none
----



[[howto-change-the-http-port]]
=== Change the HTTP Port
In a standalone application, the main HTTP port defaults to `8080` but can be set with
`server.port` (for example, in `application.properties` or as a System property). Thanks
to relaxed binding of `Environment` values, you can also use `SERVER_PORT` (for example,
as an OS environment variable).

To switch off the HTTP endpoints completely but still create a `WebApplicationContext`,
use `server.port=-1`. (Doing so is sometimes useful for testing.)

For more details, see
"`<<spring-boot-features.adoc#boot-features-customizing-embedded-containers>>`"
in the '`Spring Boot features`' section, or the
{sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[`ServerProperties`] source
code.



[[howto-user-a-random-unassigned-http-port]]
=== Use a Random Unassigned HTTP Port
To scan for a free port (using OS natives to prevent clashes) use `server.port=0`.



[[howto-discover-the-http-port-at-runtime]]
=== Discover the HTTP Port at Runtime
You can access the port the server is running on from log output or from the
`ServletWebServerApplicationContext` through its `WebServer`. The best way to get that and
be sure that it has been initialized is to add a `@Bean` of type
`ApplicationListener<ServletWebServerInitializedEvent>` and pull the container
out of the event when it is published.

Tests that use `@SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT)` can
also inject the actual port into a field by using the `@LocalServerPort` annotation, as
shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@RunWith(SpringJUnit4ClassRunner.class)
	@SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT)
	public class MyWebIntegrationTests {

		@Autowired
		ServletWebServerApplicationContext server;

		@LocalServerPort
		int port;

		// ...

	}
----

[NOTE]
====
`@LocalServerPort` is a meta-annotation for `@Value("${local.server.port}")`. Do not try
to inject the port in a regular application. As we just saw, the value is set only after
the container has been initialized. Contrary to a test, application code callbacks are
processed early (before the value is actually available).
====



[[how-to-enable-http-response-compression]]
=== Enable HTTP Response Compression
HTTP response compression is supported by Jetty, Tomcat, and Undertow. It can be enabled
in `application.properties`, as follows:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	server.compression.enabled=true
----

By default, responses must be at least 2048 bytes in length for compression to be
performed. You can configure this behavior by setting the
`server.compression.min-response-size` property.

By default, responses are compressed only if their content type is one of the
following:

* `text/html`
* `text/xml`
* `text/plain`
* `text/css`
* `text/javascript`
* `application/javascript`
* `application/json`
* `application/xml`

You can configure this behavior by setting the `server.compression.mime-types` property.



[[howto-configure-ssl]]
=== Configure SSL
SSL can be configured declaratively by setting the various `+server.ssl.*+` properties,
typically in `application.properties` or `application.yml`. The following example shows
setting SSL properties in `application.properties`:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	server.port=8443
	server.ssl.key-store=classpath:keystore.jks
	server.ssl.key-store-password=secret
	server.ssl.key-password=another-secret
----

See {sc-spring-boot}/web/server/Ssl.{sc-ext}[`Ssl`] for details of all of the
supported properties.

Using configuration such as the preceding example means the application no longer supports
a plain HTTP connector at port 8080. Spring Boot does not support the configuration of
both an HTTP connector and an HTTPS connector through `application.properties`. If you
want to have both, you need to configure one of them programmatically. We recommend using
`application.properties` to configure HTTPS, as the HTTP connector is the easier of the
two to configure programmatically. See the
{github-code}/spring-boot-samples/spring-boot-sample-tomcat-multi-connectors[`spring-boot-sample-tomcat-multi-connectors`]
sample project for an example.



[[howto-configure-http2]]
=== Configure HTTP/2
You can enable HTTP/2 support in your Spring Boot application with the
`+server.http2.enabled+` configuration property. This support depends on the chosen web
server and the application environment, since that protocol is not supported
out-of-the-box by JDK8.

[NOTE]
====
Spring Boot does not support `h2c`, the cleartext version of the HTTP/2 protocol. So you
must <<howto-configure-ssl, configure SSL first>>.
====



[[howto-configure-http2-undertow]]
==== HTTP/2 with Undertow
As of Undertow 1.4.0+, HTTP/2 is supported without any additional requirement on JDK8.



[[howto-configure-http2-jetty]]
==== HTTP/2 with Jetty
As of Jetty 9.4.8, HTTP/2 is also supported with the
https://www.conscrypt.org/[Conscrypt library].
To enable that support, your application needs to have two additional dependencies:
`org.eclipse.jetty:jetty-alpn-conscrypt-server` and `org.eclipse.jetty.http2:http2-server`.



[[howto-configure-http2-tomcat]]
==== HTTP/2 with Tomcat
Spring Boot ships by default with Tomcat 9.0.x which supports HTTP/2 out of the box when
using JDK 9 or later. Alternatively, HTTP/2 can be used on JDK 8 if the `libtcnative`
library and its dependencies are installed on the host operating system.

The library folder must be made available, if not already, to the JVM library path. You
can do so with a JVM argument such as
`-Djava.library.path=/usr/local/opt/tomcat-native/lib`. More on this in the
https://tomcat.apache.org/tomcat-9.0-doc/apr.html[official Tomcat documentation].

Starting Tomcat 9.0.x on JDK 8 without that native support logs the following error:

[indent=0,subs="attributes"]
----
	ERROR 8787 --- [           main] o.a.coyote.http11.Http11NioProtocol      : The upgrade handler [org.apache.coyote.http2.Http2Protocol] for [h2] only supports upgrade via ALPN but has been configured for the ["https-jsse-nio-8443"] connector that does not support ALPN.
----

This error is not fatal, and the application still starts with HTTP/1.1 SSL support.



[[howto-configure-http2-netty]]
==== HTTP/2 with Reactor Netty
The `spring-boot-webflux-starter` is using by default Reactor Netty as a server.
Reactor Netty can be configured for HTTP/2 using the JDK support with JDK 9 or later.
For JDK 8 environments, or for optimal runtime performance, this server also supports
HTTP/2 with native libraries. To enable that, your application needs to have an
additional dependency.

Spring Boot manages the version for the
`io.netty:netty-tcnative-boringssl-static` "uber jar", containing native libraries for
all platforms. Developers can choose to import only the required dependencies using
a classifier (see http://netty.io/wiki/forked-tomcat-native.html[the Netty official
documentation]).



[[howto-configure-webserver]]
=== Configure the Web Server

Generally, you should first consider using one of the many available configuration keys
and customize your web server by adding new entries in your `application.properties` (or
`application.yml`, or environment, etc. see
"`<<howto-discover-build-in-options-for-external-properties>>`"). The `server.{asterisk}`
namespace is quite useful here, and it includes namespaces like `server.tomcat.{asterisk}`,
`server.jetty.{asterisk}` and others, for server-specific features.
See the list of <<common-application-properties>>.

The previous sections covered already many common use cases, such as compression, SSL
or HTTP/2. However, if a configuration key doesn't exist for your use case, you should
then look at
{dc-spring-boot}/web/server/WebServerFactoryCustomizer.html[`WebServerFactoryCustomizer`].
You can declare such a component and get access to the server factory relevant to your
choice: you should select the variant for the chosen Server (Tomcat, Jetty, Reactor Netty,
Undertow) and the chosen web stack (Servlet or Reactive).

The example below is for Tomcat with the `spring-boot-starter-web` (Servlet stack):

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Component
	public class MyTomcatWebServerCustomizer
			implements WebServerFactoryCustomizer<TomcatServletWebServerFactory> {

		@Override
		public void customize(TomcatServletWebServerFactory factory) {
			// customize the factory here
		}
	}
----

In addition Spring Boot provides:

[[howto-configure-webserver-customizers]]
[cols="1,2,2", options="header"]
|===
| Server | Servlet stack | Reactive stack

| Tomcat
| `TomcatServletWebServerFactory`
| `TomcatReactiveWebServerFactory`

| Jetty
| `JettyServletWebServerFactory`
| `JettyReactiveWebServerFactory`

| Undertow
| `UndertowServletWebServerFactory`
| `UndertowReactiveWebServerFactory`

| Reactor
| N/A
| `NettyReactiveWebServerFactory`

|===

Once you've got access to a `WebServerFactory`, you can often add customizers to it to
configure specific parts, like connectors, server resources, or the server itself - all
using server-specific APIs.

As a last resort, you can also declare your own `WebServerFactory` component, which will
override the one provided by Spring Boot. In this case, you can't rely on configuration
properties in the `server` namespace anymore.



[[howto-add-a-servlet-filter-or-listener]]
=== Add a Servlet, Filter, or Listener to an Application
In a servlet stack application, i.e. with the `spring-boot-starter-web`, there are two
ways to add `Servlet`, `Filter`, `ServletContextListener`, and the other listeners
supported by the Servlet API to your application:

* <<howto-add-a-servlet-filter-or-listener-as-spring-bean>>
* <<howto-add-a-servlet-filter-or-listener-using-scanning>>



[[howto-add-a-servlet-filter-or-listener-as-spring-bean]]
==== Add a Servlet, Filter, or Listener by Using a Spring Bean
To add a `Servlet`, `Filter`, or Servlet `*Listener` by using a Spring bean, you must
provide a `@Bean` definition for it. Doing so can be very useful when you want to inject
configuration or dependencies. However, you must be very careful that they do not cause
eager initialization of too many other beans, because they have to be installed in the
container very early in the application lifecycle. (For example, it is not a good idea to
have them depend on your `DataSource` or JPA configuration.) You can work around such
restrictions by initializing the beans lazily when first used instead of on
initialization.

In the case of `Filters` and `Servlets`, you can also add mappings and init parameters by
adding a `FilterRegistrationBean` or a `ServletRegistrationBean` instead of or in
addition to the underlying component.

[NOTE]
====
If no `dispatcherType` is specified on a filter registration, `REQUEST` is used. This
aligns with the Servlet Specification's default dispatcher type.
====

Like any other Spring bean, you can define the order of Servlet filter beans; please
make sure to check the
"`<<spring-boot-features.adoc#boot-features-embedded-container-servlets-filters-listeners-beans>>`"
section.



[[howto-disable-registration-of-a-servlet-or-filter]]
===== Disable Registration of a Servlet or Filter
As <<howto-add-a-servlet-filter-or-listener-as-spring-bean,described earlier>>, any
`Servlet` or `Filter` beans are registered with the servlet container automatically. To
disable registration of a particular `Filter` or `Servlet` bean, create a registration
bean for it and mark it as disabled, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Bean
	public FilterRegistrationBean registration(MyFilter filter) {
		FilterRegistrationBean registration = new FilterRegistrationBean(filter);
		registration.setEnabled(false);
		return registration;
	}
----



[[howto-add-a-servlet-filter-or-listener-using-scanning]]
==== Add Servlets, Filters, and Listeners by Using Classpath Scanning
`@WebServlet`, `@WebFilter`, and `@WebListener` annotated classes can be automatically
registered with an embedded servlet container by annotating a `@Configuration` class
with `@ServletComponentScan` and specifying the package(s) containing the components
that you want to register. By default, `@ServletComponentScan` scans from the package
of the annotated class.



[[howto-configure-accesslogs]]
=== Configure Access Logging
Access logs can be configured for Tomcat, Undertow, and Jetty through their respective
namespaces.

For instance, the following settings log access on Tomcat with a
{tomcat-documentation}/config/valve.html#Access_Logging[custom pattern].

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	server.tomcat.basedir=my-tomcat
	server.tomcat.accesslog.enabled=true
	server.tomcat.accesslog.pattern=%t %a "%r" %s (%D ms)
----

NOTE: The default location for logs is a `logs` directory relative to the Tomcat base
directory. By default, the `logs` directory is a temporary directory, so you may want to
fix Tomcat's base directory or use an absolute path for the logs. In the preceding
example, the logs are available in `my-tomcat/logs` relative to the working directory of
the application.

Access logging for Undertow can be configured in a similar fashion, as shown in the
following example:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	server.undertow.accesslog.enabled=true
	server.undertow.accesslog.pattern=%t %a "%r" %s (%D ms)
----

Logs are stored in a `logs` directory relative to the working directory of the
application. You can customize this location by setting the
`server.undertow.accesslog.directory` property.

Finally, access logging for Jetty can also be configured as follows:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	server.jetty.accesslog.enabled=true
	server.jetty.accesslog.filename=/var/log/jetty-access.log
----

By default, logs are redirected to `System.err`. For more details, see
{jetty-documentation}/configuring-jetty-request-logs.html[the Jetty documentation].



[[howto-use-behind-a-proxy-server]]
[[howto-use-tomcat-behind-a-proxy-server]]
=== Running Behind a Front-end Proxy Server
Your application might need to send `302` redirects or render content with absolute links
back to itself. When running behind a proxy, the caller wants a link to the proxy and not
to the physical address of the machine hosting your app. Typically, such situations are
handled through a contract with the proxy, which adds headers to tell the back end how to
construct links to itself.

If the proxy adds conventional `X-Forwarded-For` and `X-Forwarded-Proto` headers (most
proxy servers do so), the absolute links should be rendered correctly, provided
`server.use-forward-headers` is set to `true` in your `application.properties`.

NOTE: If your application runs in Cloud Foundry or Heroku, the
`server.use-forward-headers` property defaults to `true`. In all
other instances, it defaults to `false`.



[[howto-customize-tomcat-behind-a-proxy-server]]
==== Customize Tomcat's Proxy Configuration
If you use Tomcat, you can additionally configure the names of the headers used to
carry "`forwarded`" information, as shown in the following example:

[indent=0]
----
	server.tomcat.remote-ip-header=x-your-remote-ip-header
	server.tomcat.protocol-header=x-your-protocol-header
----

Tomcat is also configured with a default regular expression that matches internal
proxies that are to be trusted. By default, IP addresses in `10/8`, `192.168/16`,
`169.254/16` and `127/8` are trusted. You can customize the valve's configuration by
adding an entry to `application.properties`, as shown in the following example:

[indent=0]
----
	server.tomcat.internal-proxies=192\\.168\\.\\d{1,3}\\.\\d{1,3}
----

NOTE: The double backslashes are required only when you use a properties file for
configuration. If you use YAML, single backslashes are sufficient, and a value
equivalent to that shown in the preceding example would be `192\.168\.\d{1,3}\.\d{1,3}`.

NOTE: You can trust all proxies by setting the `internal-proxies` to empty (but do not do
so in production).

You can take complete control of the configuration of Tomcat's `RemoteIpValve` by
switching the automatic one off (to do so, set `server.use-forward-headers=false`) and
adding a new valve instance in a `TomcatServletWebServerFactory` bean.



[[howto-enable-multiple-connectors-in-tomcat]]
=== Enable Multiple Connectors with Tomcat
You can add an `org.apache.catalina.connector.Connector` to the
`TomcatServletWebServerFactory`, which can allow multiple connectors, including HTTP and
HTTPS connectors, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Bean
	public ServletWebServerFactory servletContainer() {
		TomcatServletWebServerFactory tomcat = new TomcatServletWebServerFactory();
		tomcat.addAdditionalTomcatConnectors(createSslConnector());
		return tomcat;
	}

	private Connector createSslConnector() {
		Connector connector = new Connector("org.apache.coyote.http11.Http11NioProtocol");
		Http11NioProtocol protocol = (Http11NioProtocol) connector.getProtocolHandler();
		try {
			File keystore = new ClassPathResource("keystore").getFile();
			File truststore = new ClassPathResource("keystore").getFile();
			connector.setScheme("https");
			connector.setSecure(true);
			connector.setPort(8443);
			protocol.setSSLEnabled(true);
			protocol.setKeystoreFile(keystore.getAbsolutePath());
			protocol.setKeystorePass("changeit");
			protocol.setTruststoreFile(truststore.getAbsolutePath());
			protocol.setTruststorePass("changeit");
			protocol.setKeyAlias("apitester");
			return connector;
		}
		catch (IOException ex) {
			throw new IllegalStateException("can't access keystore: [" + "keystore"
					+ "] or truststore: [" + "keystore" + "]", ex);
		}
	}
----



[[howto-use-tomcat-legacycookieprocessor]]
=== Use Tomcat's LegacyCookieProcessor
By default, the embedded Tomcat used by Spring Boot does not support "Version 0" of the
Cookie format, so you may see the following error:

[indent=0]
----
	java.lang.IllegalArgumentException: An invalid character [32] was present in the Cookie value
----

If at all possible, you should consider updating your code to only store values
compliant with later Cookie specifications. If, however, you cannot change the
way that cookies are written, you can instead configure Tomcat to use a
`LegacyCookieProcessor`. To switch to the `LegacyCookieProcessor`, use an
`WebServerFactoryCustomizer` bean that adds a `TomcatContextCustomizer`, as shown
in the following example:

[source,java,indent=0]
----
include::{code-examples}/context/embedded/TomcatLegacyCookieProcessorExample.java[tag=customizer]
----



[[howto-enable-multiple-listeners-in-undertow]]
=== Enable Multiple Listeners with Undertow
Add an `UndertowBuilderCustomizer` to the `UndertowServletWebServerFactory` and
add a listener to the `Builder`, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Bean
	public UndertowServletWebServerFactory servletWebServerFactory() {
		UndertowServletWebServerFactory factory = new UndertowServletWebServerFactory();
		factory.addBuilderCustomizers(new UndertowBuilderCustomizer() {

			@Override
			public void customize(Builder builder) {
				builder.addHttpListener(8080, "0.0.0.0");
			}

		});
		return factory;
	}
----



[[howto-create-websocket-endpoints-using-serverendpoint]]
=== Create WebSocket Endpoints Using @ServerEndpoint
If you want to use `@ServerEndpoint` in a Spring Boot application that used an embedded
container, you must declare a single `ServerEndpointExporter` `@Bean`, as shown in the
following example:

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

The bean shown in the preceding example registers any `@ServerEndpoint` annotated beans
with the underlying WebSocket container. When deployed to a standalone servlet container,
this role is performed by a servlet container initializer, and the
`ServerEndpointExporter` bean is not required.



[[howto-spring-mvc]]
== Spring MVC

Spring Boot has a number of starters that include Spring MVC. Note that some starters
include a dependency on Spring MVC rather than include it directly. This section answers
common questions about Spring MVC and Spring Boot.

[[howto-write-a-json-rest-service]]
=== Write a JSON REST Service
Any Spring `@RestController` in a Spring Boot application should render JSON response by
default as long as Jackson2 is on the classpath, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@RestController
	public class MyController {

		@RequestMapping("/thing")
		public MyThing thing() {
				return new MyThing();
		}

	}
----

As long as `MyThing` can be serialized by Jackson2 (true for a normal POJO or Groovy
object), then `http://localhost:8080/thing` serves a JSON representation of it by
default. Note that, in a browser, you might sometimes see XML responses, because browsers
tend to send accept headers that prefer XML.



[[howto-write-an-xml-rest-service]]
=== Write an XML REST Service
If you have the Jackson XML extension (`jackson-dataformat-xml`) on the classpath, you
can use it to render XML responses. The previous example that we used for JSON would
work. To use the Jackson XML renderer, add the following dependency to your project:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>com.fasterxml.jackson.dataformat</groupId>
		<artifactId>jackson-dataformat-xml</artifactId>
	</dependency>
----

You may also want to add a dependency on Woodstox. It is faster than the default StAX
implementation provided by the JDK and also adds pretty-print support and improved
namespace handling. The following listing shows how to include a dependency on
https://github.com/FasterXML/woodstox[Woodstox]:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>org.codehaus.woodstox</groupId>
		<artifactId>woodstox-core-asl</artifactId>
	</dependency>
----

If Jackson's XML extension is not available, JAXB (provided by default in the JDK) is
used, with the additional requirement of having `MyThing` annotated as
`@XmlRootElement`, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@XmlRootElement
	public class MyThing {
		private String name;
		// .. getters and setters
	}
----

To get the server to render XML instead of JSON, you might have to send an
`Accept: text/xml` header (or use a browser).



[[howto-customize-the-jackson-objectmapper]]
=== Customize the Jackson ObjectMapper
Spring MVC (client and server side) uses `HttpMessageConverters` to negotiate content
conversion in an HTTP exchange. If Jackson is on the classpath, you already get the
default converter(s) provided by `Jackson2ObjectMapperBuilder`, an instance of which
is auto-configured for you.

The `ObjectMapper` (or `XmlMapper` for Jackson XML converter) instance (created by
default) has the following customized properties:

* `MapperFeature.DEFAULT_VIEW_INCLUSION` is disabled
* `DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES` is disabled
* `SerializationFeature.WRITE_DATES_AS_TIMESTAMPS` is disabled

Spring Boot also has some features to make it easier to customize this behavior.

You can configure the `ObjectMapper` and `XmlMapper` instances by using the environment.
Jackson provides an extensive suite of simple on/off features that can be used to
configure various aspects of its processing. These features are described in six enums (in
Jackson) that map onto properties in the environment:

|===
|Enum|Property|Values

|`com.fasterxml.jackson.databind.DeserializationFeature`
|`spring.jackson.deserialization.<feature_name>`
|`true`, `false`

|`com.fasterxml.jackson.core.JsonGenerator.Feature`
|`spring.jackson.generator.<feature_name>`
|`true`, `false`

|`com.fasterxml.jackson.databind.MapperFeature`
|`spring.jackson.mapper.<feature_name>`
|`true`, `false`

|`com.fasterxml.jackson.core.JsonParser.Feature`
|`spring.jackson.parser.<feature_name>`
|`true`, `false`

|`com.fasterxml.jackson.databind.SerializationFeature`
|`spring.jackson.serialization.<feature_name>`
|`true`, `false`

|`com.fasterxml.jackson.annotation.JsonInclude.Include`
|`spring.jackson.default-property-inclusion`
|`always`, `non_null`, `non_absent`, `non_default`, `non_empty`
|===

For example, to enable pretty print, set `spring.jackson.serialization.indent_output=true`.
Note that, thanks to the use of <<boot-features-external-config-relaxed-binding,
relaxed binding>>, the case of `indent_output` does not have to match the case of the
corresponding enum constant, which is `INDENT_OUTPUT`.

This environment-based configuration is applied to the auto-configured
`Jackson2ObjectMapperBuilder` bean and applies to any mappers created by
using the builder, including the auto-configured `ObjectMapper` bean.

The context's `Jackson2ObjectMapperBuilder` can be customized by one or more
`Jackson2ObjectMapperBuilderCustomizer` beans. Such customizer beans can be ordered
(Boot's own customizer has an order of 0), letting additional customization be applied
both before and after Boot's customization.

Any beans of type `com.fasterxml.jackson.databind.Module` are automatically registered
with the auto-configured `Jackson2ObjectMapperBuilder` and are applied to any `ObjectMapper`
instances that it creates. This provides a global mechanism for contributing custom
modules when you add new features to your application.

If you want to replace the default `ObjectMapper` completely, either define a `@Bean` of
that type and mark it as `@Primary` or, if you prefer the builder-based
approach, define a `Jackson2ObjectMapperBuilder` `@Bean`. Note that, in either case,
doing so disables all auto-configuration of the `ObjectMapper`.

If you provide any `@Beans` of type `MappingJackson2HttpMessageConverter`,
they replace the default value in the MVC configuration. Also, a convenience bean of type
`HttpMessageConverters` is provided (and is always available if you use the default MVC
configuration). It has some useful methods to access the default and user-enhanced
message converters.

See the "`<<howto-customize-the-responsebody-rendering>>`" section and the
{sc-spring-boot-autoconfigure}/web/servlet/WebMvcAutoConfiguration.{sc-ext}[`WebMvcAutoConfiguration`]
source code for more details.



[[howto-customize-the-responsebody-rendering]]
=== Customize the @ResponseBody Rendering
Spring uses `HttpMessageConverters` to render `@ResponseBody` (or responses from
`@RestController`). You can contribute additional converters by adding beans of the
appropriate type in a Spring Boot context. If a bean you add is of a type that would have
been included by default anyway (such as `MappingJackson2HttpMessageConverter` for JSON
conversions), it replaces the default value. A convenience bean of type
`HttpMessageConverters` is provided and is always available if you use the default MVC
configuration. It has some useful methods to access the default and user-enhanced message
converters (For example, it can be useful if you want to manually inject them into a
custom `RestTemplate`).

As in normal MVC usage, any `WebMvcConfigurer` beans that you provide can also
contribute converters by overriding the `configureMessageConverters` method. However, unlike
with normal MVC, you can supply only additional converters that you need (because Spring
Boot uses the same mechanism to contribute its defaults). Finally, if you opt out of the
Spring Boot default MVC configuration by providing your own `@EnableWebMvc` configuration,
you can take control completely and do everything manually by using
`getMessageConverters` from `WebMvcConfigurationSupport`.

See the
{sc-spring-boot-autoconfigure}/web/servlet/WebMvcAutoConfiguration.{sc-ext}[`WebMvcAutoConfiguration`]
source code for more details.



[[howto-multipart-file-upload-configuration]]
=== Handling Multipart File Uploads
Spring Boot embraces the Servlet 3 `javax.servlet.http.Part` API to support uploading
files. By default, Spring Boot configures Spring MVC with a maximum size of 1MB per
file and a maximum of 10MB of file data in a single request. You may override these
values, the location to which intermediate data is stored (for example, to the `/tmp`
directory), and the threshold past which data is flushed to disk by using the properties
exposed in the `MultipartProperties` class. For example, if you want to specify that
files be unlimited, set the `spring.servlet.multipart.max-file-size` property to `-1`.

The multipart support is helpful when you want to receive multipart encoded file data as
a `@RequestParam`-annotated parameter of type `MultipartFile` in a Spring MVC controller
handler method.

See the
{sc-spring-boot-autoconfigure}/web/servlet/MultipartAutoConfiguration.{sc-ext}[`MultipartAutoConfiguration`]
source for more details.

NOTE: It is recommended to use the container's built-in support for multipart uploads
rather than introducing an additional dependency such as Apache Commons File Upload.



[[howto-switch-off-the-spring-mvc-dispatcherservlet]]
=== Switch Off the Spring MVC DispatcherServlet
By default, all content is served from the root of your application (`/`). If you
would rather map to a different path, you can configure one as follows:

[source,properties,indent=0,subs="verbatim"]
----
	spring.mvc.servlet.path=/acme
----

If you have additional servlets you can declare a `@Bean` of type `Servlet` or
`ServletRegistrationBean` for each and Spring Boot will register them transparently to the
container. Because servlets are registered that way, they can be mapped to a sub-context
of the `DispatcherServlet` without invoking it.

Configuring the `DispatcherServlet` yourself is unusual but if you really need to do it, a
`@Bean` of type `DispatcherServletPath` must be provided as well to provide the path of
your custom `DispatcherServlet`.



[[howto-switch-off-default-mvc-configuration]]
=== Switch off the Default MVC Configuration
The easiest way to take complete control over MVC configuration is to provide your own
`@Configuration` with the `@EnableWebMvc` annotation. Doing so leaves all MVC
configuration in your hands.



[[howto-customize-view-resolvers]]
=== Customize ViewResolvers
A `ViewResolver` is a core component of Spring MVC, translating view names in
`@Controller` to actual `View` implementations. Note that `ViewResolvers` are mainly
used in UI applications, rather than REST-style services (a `View` is not used to render
a `@ResponseBody`). There are many implementations of `ViewResolver` to choose from, and
Spring on its own is not opinionated about which ones you should use. Spring Boot, on the
other hand, installs one or two for you, depending on what it finds on the classpath and
in the application context. The `DispatcherServlet` uses all the resolvers it finds in
the application context, trying each one in turn until it gets a result, so, if you
add your own, you have to be aware of the order and in which position your resolver is
added.

`WebMvcAutoConfiguration` adds the following `ViewResolvers` to your context:

* An `InternalResourceViewResolver` named '`defaultViewResolver`'. This one locates
physical resources that can be rendered by using the `DefaultServlet` (including static
resources and JSP pages, if you use those). It applies a prefix and a suffix to the
view name and then looks for a physical resource with that path in the servlet context
(the defaults are both empty but are accessible for external configuration through
`spring.mvc.view.prefix` and `spring.mvc.view.suffix`). You can override it by
providing a bean of the same type.
* A `BeanNameViewResolver` named '`beanNameViewResolver`'. This is a useful member of the
view resolver chain and picks up any beans with the same name as the `View` being
resolved. It should not be necessary to override or replace it.
* A `ContentNegotiatingViewResolver` named '`viewResolver`' is added only if there *are*
actually beans of type `View` present. This is a '`master`' resolver, delegating to all
the others and attempting to find a match to the '`Accept`' HTTP header sent by the
client. There is a useful
https://spring.io/blog/2013/06/03/content-negotiation-using-views[blog about
`ContentNegotiatingViewResolver`] that you might like to study to learn more, and you
might also look at the source code for detail. You can switch off the auto-configured
`ContentNegotiatingViewResolver` by defining a bean named '`viewResolver`'.
* If you use Thymeleaf, you also have a `ThymeleafViewResolver` named
'`thymeleafViewResolver`'. It looks for resources by surrounding the view name with a
prefix and suffix. The prefix is `spring.thymeleaf.prefix`, and the suffix is
`spring.thymeleaf.suffix`. The values of the prefix and suffix default to
'`classpath:/templates/`' and '`.html`', respectively. You can override
`ThymeleafViewResolver` by providing a bean of the same name.
* If you use FreeMarker, you also have a `FreeMarkerViewResolver` named
'`freeMarkerViewResolver`'. It looks for resources in a loader path (which is
externalized to `spring.freemarker.templateLoaderPath` and has a default value of
'`classpath:/templates/`') by surrounding the view name with a prefix and a suffix. The
prefix is externalized to `spring.freemarker.prefix`, and the suffix is externalized to
`spring.freemarker.suffix`. The default values of the prefix and suffix are empty and
'`.ftl`', respectively. You can override `FreeMarkerViewResolver` by providing a bean
of the same name.
* If you use Groovy templates (actually, if `groovy-templates` is on your classpath), you
also have a `GroovyMarkupViewResolver` named '`groovyMarkupViewResolver`'. It looks for
resources in a loader path by surrounding the view name with a prefix and suffix
(externalized to `spring.groovy.template.prefix` and `spring.groovy.template.suffix`).
The prefix and suffix have default values of '`classpath:/templates/`' and '`.tpl`',
respectively. You can override `GroovyMarkupViewResolver` by providing a bean of the
same name.

For more detail, see the following sections:

* {sc-spring-boot-autoconfigure}/web/servlet/WebMvcAutoConfiguration.{sc-ext}[`WebMvcAutoConfiguration`]
* {sc-spring-boot-autoconfigure}/thymeleaf/ThymeleafAutoConfiguration.{sc-ext}[`ThymeleafAutoConfiguration`]
* {sc-spring-boot-autoconfigure}/freemarker/FreeMarkerAutoConfiguration.{sc-ext}[`FreeMarkerAutoConfiguration`]
* {sc-spring-boot-autoconfigure}/groovy/template/GroovyTemplateAutoConfiguration.{sc-ext}[`GroovyTemplateAutoConfiguration`]



[[howto-use-test-with-spring-security]]
== Testing With Spring Security
Spring Security provides support for running tests as a specific user.
For example, the test in the snippet below will run with an authenticated user
that has the `ADMIN` role.

[source,java,indent=0]
----
	@Test
	@WithMockUser(roles="ADMIN")
	public void requestProtectedUrlWithUser() throws Exception {
		mvc
			.perform(get("/"))
			...
	}
----

Spring Security provides comprehensive integration with Spring MVC Test and
this can also be used when testing controllers using the `@WebMvcTest` slice and `MockMvc`.

For additional details on Spring Security's testing support, refer to Spring Security's
https://docs.spring.io/spring-security/site/docs/current/reference/htmlsingle/#test[reference documentation]).



[[howto-jersey]]
== Jersey



[[howto-jersey-spring-security]]
=== Secure Jersey endpoints with Spring Security
Spring Security can be used to secure a Jersey-based web application in much the same
way as it can be used to secure a Spring MVC-based web application. However, if you want
to use Spring Security's method-level security with Jersey, you must configure Jersey to
use `setStatus(int)` rather `sendError(int)`. This prevents Jersey from committing the
response before Spring Security has had an opportunity to report an authentication or
authorization failure to the client.

The `jersey.config.server.response.setStatusOverSendError` property must be set to `true`
on the application's `ResourceConfig` bean, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/jersey/JerseySetStatusOverSendErrorExample.java[tag=resource-config]
----



[[howto-http-clients]]
== HTTP Clients

Spring Boot offers a number of starters that work with HTTP clients. This section answers
questions related to using them.

[[howto-http-clients-proxy-configuration]]
=== Configure RestTemplate to Use a Proxy
As described in <<spring-boot-features.adoc#boot-features-resttemplate-customization>>,
you can use a `RestTemplateCustomizer` with `RestTemplateBuilder` to build a customized
`RestTemplate`. This is the recommended approach for creating a `RestTemplate` configured
to use a proxy.

The exact details of the proxy configuration depend on the underlying client request
factory that is being used. The following example configures
`HttpComponentsClientRequestFactory` with an `HttpClient` that uses a proxy for all hosts
except `192.168.0.5`:

[source,java,indent=0]
----
include::{code-examples}/web/client/RestTemplateProxyCustomizationExample.java[tag=customizer]
----



[[howto-logging]]
== Logging

Spring Boot has no mandatory logging dependency, except for the Commons Logging API, which
is typically provided by Spring Framework's `spring-jcl` module. To use
http://logback.qos.ch[Logback], you need to include it and `spring-jcl` on the classpath.
The simplest way to do that is through the starters, which all depend on
`spring-boot-starter-logging`. For a web application, you need only
`spring-boot-starter-web`, since it depends transitively on the logging starter. If you
use Maven, the following dependency adds logging for you:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
----

Spring Boot has a `LoggingSystem` abstraction that attempts to configure logging based on
the content of the classpath. If Logback is available, it is the first choice.

If the only change you need to make to logging is to set the levels of various loggers,
you can do so in `application.properties` by using the "logging.level" prefix, as shown
in the following example:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	logging.level.org.springframework.web=DEBUG
	logging.level.org.hibernate=ERROR
----

You can also set the location of a file to which to write the log (in addition to the
console) by using "logging.file".

To configure the more fine-grained settings of a logging system, you need to use the native
configuration format supported by the `LoggingSystem` in question. By default, Spring Boot
picks up the native configuration from its default location for the system (such as
`classpath:logback.xml` for Logback), but you can set the location of the config file by
using the "logging.config" property.



[[howto-configure-logback-for-logging]]
=== Configure Logback for Logging
If you put a `logback.xml` in the root of your classpath, it is picked up from there (or
from `logback-spring.xml`, to take advantage of the templating features provided by
Boot). Spring Boot provides a default base configuration that you can include if you
want to set levels, as shown in the following example:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<?xml version="1.0" encoding="UTF-8"?>
	<configuration>
		<include resource="org/springframework/boot/logging/logback/base.xml"/>
		<logger name="org.springframework.web" level="DEBUG"/>
	</configuration>
----

If you look at `base.xml` in the spring-boot jar, you can see that it uses
some useful System properties that the `LoggingSystem` takes care of creating for you:

* `${PID}`: The current process ID.
* `${LOG_FILE}`: Whether `logging.file` was set in Boot's external configuration.
* `${LOG_PATH}`: Whether `logging.path` (representing a directory for
   log files to live in) was set in Boot's external configuration.
* `${LOG_EXCEPTION_CONVERSION_WORD}`: Whether `logging.exception-conversion-word` was set
   in Boot's external configuration.

Spring Boot also provides some nice ANSI color terminal output on a console (but not in
a log file) by using a custom Logback converter. See the default `base.xml` configuration
for details.

If Groovy is on the classpath, you should be able to configure Logback with
`logback.groovy` as well. If present, this setting is given preference.



[[howto-configure-logback-for-logging-fileonly]]
==== Configure Logback for File-only Output
If you want to disable console logging and write output only to a file, you need a custom
`logback-spring.xml` that imports `file-appender.xml` but not `console-appender.xml`, as
shown in the following example:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<?xml version="1.0" encoding="UTF-8"?>
	<configuration>
		<include resource="org/springframework/boot/logging/logback/defaults.xml" />
		<property name="LOG_FILE" value="${LOG_FILE:-${LOG_PATH:-${LOG_TEMP:-${java.io.tmpdir:-/tmp}}/}spring.log}"/>
		<include resource="org/springframework/boot/logging/logback/file-appender.xml" />
		<root level="INFO">
			<appender-ref ref="FILE" />
		</root>
	</configuration>
----

You also need to add `logging.file` to your `application.properties`, as shown in the
following example:

[source,properties,indent=0,subs="verbatim,quotes,attributes"]
----
	logging.file=myapplication.log
----



[[howto-configure-log4j-for-logging]]
=== Configure Log4j for Logging
Spring Boot supports http://logging.apache.org/log4j/2.x[Log4j 2] for logging
configuration if it is on the classpath. If you use the starters for
assembling dependencies, you have to exclude Logback and then include log4j 2
instead. If you do not use the starters, you need to provide (at least) `spring-jcl` in
addition to Log4j 2.

The simplest path is probably through the starters, even though it requires some
jiggling with excludes. The following example shows how to set up the starters in Maven:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter</artifactId>
		<exclusions>
			<exclusion>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-starter-logging</artifactId>
			</exclusion>
		</exclusions>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-log4j2</artifactId>
	</dependency>
----

And the following example shows one way to set up the starters in Gradle:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	dependencies {
		compile 'org.springframework.boot:spring-boot-starter-web'
		compile 'org.springframework.boot:spring-boot-starter-log4j2'
	}

	configurations {
		all {
			exclude group: 'org.springframework.boot', module: 'spring-boot-starter-logging'
		}
	}
----

NOTE: The Log4j starters gather together the dependencies for common logging
requirements (such as having Tomcat use `java.util.logging` but configuring the
output using Log4j 2). See the
{github-code}/spring-boot-samples/spring-boot-sample-actuator-log4j2[Actuator Log4j 2]
samples for more detail and to see it in action.

NOTE: To ensure that debug logging performed using `java.util.logging` is routed into
Log4j 2, configure its https://logging.apache.org/log4j/2.0/log4j-jul/index.html[JDK
logging adapter] by setting the `java.util.logging.manager` system property to
`org.apache.logging.log4j.jul.LogManager`.



[[howto-configure-log4j-for-logging-yaml-or-json-config]]
==== Use YAML or JSON to Configure Log4j 2
In addition to its default XML configuration format, Log4j 2 also supports YAML and JSON
configuration files. To configure Log4j 2 to use an alternative configuration file format,
add the appropriate dependencies to the classpath and name your
configuration files to match your chosen file format, as shown in the following example:

[cols="10,75,15"]
|===
|Format|Dependencies|File names

|YAML
a| `com.fasterxml.jackson.core:jackson-databind` +
   `com.fasterxml.jackson.dataformat:jackson-dataformat-yaml`
a| `log4j2.yaml` +
   `log4j2.yml`

|JSON
a| `com.fasterxml.jackson.core:jackson-databind`
a| `log4j2.json` +
   `log4j2.jsn`
|===

[[howto-data-access]]
== Data Access

Spring Boot includes a number of starters for working with data sources. This section
answers questions related to doing so.

[[howto-configure-a-datasource]]
=== Configure a Custom DataSource
To configure your own `DataSource`, define a `@Bean` of that type in your configuration.
Spring Boot reuses your `DataSource` anywhere one is required, including database
initialization. If you need to externalize some settings, you can bind your
`DataSource` to the environment (see
"`<<spring-boot-features.adoc#boot-features-external-config-3rd-party-configuration>>`").

The following example shows how to define a data source in a bean:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Bean
	@ConfigurationProperties(prefix="app.datasource")
	public DataSource dataSource() {
		return new FancyDataSource();
	}
----

The following example shows how to define a data source by setting properties:

[source,properties,indent=0]
----
	app.datasource.url=jdbc:h2:mem:mydb
	app.datasource.username=sa
	app.datasource.pool-size=30
----

Assuming that your `FancyDataSource` has regular JavaBean properties for the URL, the
username, and the pool size, these settings are bound automatically before the
`DataSource` is made available to other components. The regular
<<howto-initialize-a-database-using-spring-jdbc,database initialization>> also happens
(so the relevant sub-set of `spring.datasource.*` can still be used with your custom
configuration).

Spring Boot also provides a utility builder class, called `DataSourceBuilder`, that can
be used to create one of the standard data sources (if it is on the classpath). The
builder can detect the one to use based on what's available on the classpath. It also
auto-detects the driver based on the JDBC URL.

The following example shows how to create a data source by using a `DataSourceBuilder`:

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

To run an app with that `DataSource`, all you need is the connection
information. Pool-specific settings can also be provided. Check the implementation that
is going to be used at runtime for more details.

The following example shows how to define a JDBC data source by setting properties:

[source,properties,indent=0]
----
	app.datasource.url=jdbc:mysql://localhost/test
	app.datasource.username=dbuser
	app.datasource.password=dbpass
	app.datasource.pool-size=30
----

However, there is a catch. Because the actual type of the connection pool is not exposed,
no keys are generated in the metadata for your custom `DataSource` and no completion is
available in your IDE (because the `DataSource` interface exposes no properties). Also, if
you happen to have Hikari on the classpath, this basic setup does not work, because Hikari
has no `url` property (but does have a `jdbcUrl` property). In that case, you must rewrite
your configuration as follows:

[source,properties,indent=0]
----
	app.datasource.jdbc-url=jdbc:mysql://localhost/test
	app.datasource.username=dbuser
	app.datasource.password=dbpass
	app.datasource.maximum-pool-size=30
----

You can fix that by forcing the connection pool to use and return a dedicated
implementation rather than `DataSource`. You cannot change the implementation
at runtime, but the list of options will be explicit.

The following example shows how create a `HikariDataSource` with `DataSourceBuilder`:

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

You can even go further by leveraging what `DataSourceProperties` does for you -- that is,
by providing a default embedded database with a sensible username and password if no URL
is provided. You can easily initialize a `DataSourceBuilder` from the state of any
`DataSourceProperties` object, so you could also inject the DataSource that Spring Boot
creates automatically. However, that would split your configuration into two namespaces:
`url`, `username`, `password`, `type`, and `driver` on `spring.datasource` and the rest on
your custom namespace (`app.datasource`). To avoid that, you can redefine a custom
`DataSourceProperties` on your custom namespace, as shown in the following example:

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

This setup puts you _in sync_ with what Spring Boot does for you by default, except that
a dedicated connection pool is chosen (in code) and its settings are exposed in the
`app.datasource.configuration` sub namespace. Because `DataSourceProperties` is taking
care of the `url`/`jdbcUrl` translation for you, you can configure it as follows:

[source,properties,indent=0]
----
	app.datasource.url=jdbc:mysql://localhost/test
	app.datasource.username=dbuser
	app.datasource.password=dbpass
	app.datasource.configuration.maximum-pool-size=30
----

TIP: Spring Boot will expose Hikari-specific settings to `spring.datasource.hikari`. This
example uses a more generic `configuration` sub namespace as the example does not support
multiple datasource implementations.

NOTE: Because your custom configuration chooses to go with Hikari, `app.datasource.type`
has no effect. In practice, the builder is initialized with whatever value you
might set there and then overridden by the call to `.type()`.

See "`<<spring-boot-features.adoc#boot-features-configure-datasource>>`" in the
"`Spring Boot features`" section and the
{sc-spring-boot-autoconfigure}/jdbc/DataSourceAutoConfiguration.{sc-ext}[`DataSourceAutoConfiguration`]
class for more details.



[[howto-two-datasources]]
=== Configure Two DataSources
If you need to configure multiple data sources, you can apply the same tricks that are
described in the previous section. You must, however, mark one of the `DataSource`
instances as `@Primary`, because various auto-configurations down the road expect to be
able to get one by type.

If you create your own `DataSource`, the auto-configuration backs off. In the following
example, we provide the _exact_ same feature set as the auto-configuration provides
on the primary data source:

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

TIP: `firstDataSourceProperties` has to be flagged as `@Primary` so that the database
initializer feature uses your copy (if you use the initializer).

Both data sources are also bound for advanced customizations. For instance, you could
configure them as follows:

[source,properties,indent=0]
----
	app.datasource.first.url=jdbc:mysql://localhost/first
	app.datasource.first.username=dbuser
	app.datasource.first.password=dbpass
	app.datasource.first.configuration.maximum-pool-size=30

	app.datasource.second.url=jdbc:mysql://localhost/second
	app.datasource.second.username=dbuser
	app.datasource.second.password=dbpass
	app.datasource.second.max-total=30
----

You can apply the same concept to the secondary `DataSource` as well, as shown in the
following example:

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

The preceding example configures two data sources on custom namespaces with the same
logic as Spring Boot would use in auto-configuration. Note that each `configuration` sub
namespace provides advanced settings based on the chosen implementation.



[[howto-use-spring-data-repositories]]
=== Use Spring Data Repositories
Spring Data can create implementations of `@Repository` interfaces of various flavors.
Spring Boot handles all of that for you, as long as those `@Repositories` are included in
the same package (or a sub-package) of your `@EnableAutoConfiguration` class.

For many applications, all you need is to put the right Spring Data dependencies on
your classpath (there is a `spring-boot-starter-data-jpa` for JPA and a
`spring-boot-starter-data-mongodb` for Mongodb) and create some repository interfaces to
handle your `@Entity` objects. Examples are in the
{github-code}/spring-boot-samples/spring-boot-sample-data-jpa[JPA sample] and the
{github-code}/spring-boot-samples/spring-boot-sample-data-mongodb[Mongodb sample].

Spring Boot tries to guess the location of your `@Repository` definitions, based on the
`@EnableAutoConfiguration` it finds. To get more control, use the `@EnableJpaRepositories`
annotation (from Spring Data JPA).

For more about Spring Data, see the {spring-data}[Spring Data project page].



[[howto-separate-entity-definitions-from-spring-configuration]]
=== Separate @Entity Definitions from Spring Configuration
Spring Boot tries to guess the location of your `@Entity` definitions, based on the
`@EnableAutoConfiguration` it finds. To get more control, you can use the `@EntityScan`
annotation, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Configuration
	@EnableAutoConfiguration
	@EntityScan(basePackageClasses=City.class)
	public class Application {

		//...

	}
----



[[howto-configure-jpa-properties]]
=== Configure JPA Properties
Spring Data JPA already provides some vendor-independent configuration options (such as
those for SQL logging), and Spring Boot exposes those options and a few more for Hibernate
as external configuration properties. Some of them are automatically detected according to
the context so you should not have to set them.

The `spring.jpa.hibernate.ddl-auto` is a special case, because, depending on runtime
conditions, it has different defaults. If an embedded database is used and no schema
manager (such as Liquibase or Flyway) is handling the `DataSource`, it defaults to
`create-drop`. In all other cases, it defaults to `none`.

The dialect to use is also automatically detected based on the current `DataSource`, but
you can set `spring.jpa.database` yourself if you want to be explicit and bypass that
check on startup.

NOTE: Specifying a `database` leads to the configuration of a well-defined Hibernate
dialect. Several databases have more than one `Dialect`, and this may not suit your needs.
In that case, you can either set `spring.jpa.database` to `default` to let Hibernate
figure things out or set the dialect by setting the `spring.jpa.database-platform`
property.

The most common options to set are shown in the following example:

[indent=0,subs="verbatim,quotes,attributes"]
----
	spring.jpa.hibernate.naming.physical-strategy=com.example.MyPhysicalNamingStrategy
	spring.jpa.show-sql=true
----

In addition, all properties in `+spring.jpa.properties.*+` are passed through as normal
JPA properties (with the prefix stripped) when the local `EntityManagerFactory` is
created.

TIP: If you need to apply advanced customization to Hibernate properties, consider
registering a `HibernatePropertiesCustomizer` bean that will be invoked prior to creating
the `EntityManagerFactory`. This takes precedence to anything that is applied by the
auto-configuration.



[[howto-configure-hibernate-naming-strategy]]
=== Configure Hibernate Naming Strategy
Hibernate uses {hibernate-documentation}#naming[two different naming strategies] to map
names from the object model to the corresponding database names. The fully qualified
class name of the physical and the implicit strategy implementations can be configured by
setting the `spring.jpa.hibernate.naming.physical-strategy` and
`spring.jpa.hibernate.naming.implicit-strategy` properties, respectively. Alternatively,
if `ImplicitNamingStrategy` or `PhysicalNamingStrategy` beans are available in the
application context, Hibernate will be automatically configured to use them.

By default, Spring Boot configures the physical naming strategy with
`SpringPhysicalNamingStrategy`. This implementation provides the same table structure as
Hibernate 4: all dots are replaced by underscores and camel casing is replaced by
underscores as well. By default, all table names are generated in lower case, but it is
possible to override that flag if your schema requires it.

For example, a `TelephoneNumber` entity is mapped to the `telephone_number` table.

If you prefer to use Hibernate 5's default instead, set the following property:

[indent=0,subs="verbatim,quotes,attributes"]
----
	spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
----

Alternatively, you can configure the following bean:

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

See {sc-spring-boot-autoconfigure}/orm/jpa/HibernateJpaAutoConfiguration.{sc-ext}[`HibernateJpaAutoConfiguration`]
and {sc-spring-boot-autoconfigure}/orm/jpa/JpaBaseConfiguration.{sc-ext}[`JpaBaseConfiguration`]
for more details.



[[howto-configure-hibernate-second-level-caching]]
=== Configure Hibernate Second-Level Caching
Hibernate {hibernate-documentation}#caching[second-level cache] can be configured for a
range of cache providers. Rather than configuring Hibernate to lookup the cache provider
again, it is better to provide the one that is available in the context whenever possible.

If you're using JCache, this is pretty easy. First, make sure that
`org.hibernate:hibernate-jcache` is available on the classpath. Then, add a
`HibernatePropertiesCustomizer` bean as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/jpa/HibernateSecondLevelCacheExample.java[tag=configuration]
----

This customizer will configure Hibernate to use the same `CacheManager` as the one that
the application uses. It is also possible to use separate `CacheManager` instances, refer
to {hibernate-documentation}#caching-provider-jcache[the Hibernate user guide].



[[howto-use-dependency-injection-hibernate-components]]
=== Use Dependency Injection in Hibernate Components
By default, Spring Boot registers a `BeanContainer` implementation that uses the
`BeanFactory` so that converters and entity listeners can use regular dependency
injection.

You can disable or tune this behaviour by registering a `HibernatePropertiesCustomizer`
that removes or changes the `hibernate.resource.beans.container` property.



[[howto-use-custom-entity-manager]]
=== Use a Custom EntityManagerFactory
To take full control of the configuration of the `EntityManagerFactory`, you need to add
a `@Bean` named '`entityManagerFactory`'. Spring Boot auto-configuration switches off its
entity manager in the presence of a bean of that type.



[[howto-use-two-entity-managers]]
=== Use Two EntityManagers
Even if the default `EntityManagerFactory` works fine, you need to define a new one.
Otherwise, the presence of the second bean of that type switches off the
default. To make it easy to do, you can use the convenient `EntityManagerBuilder`
provided by Spring Boot. Alternatively, you can just the
`LocalContainerEntityManagerFactoryBean` directly from Spring ORM, as shown in the
following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	// add two data sources configured as above

	@Bean
	public LocalContainerEntityManagerFactoryBean customerEntityManagerFactory(
			EntityManagerFactoryBuilder builder) {
		return builder
				.dataSource(customerDataSource())
				.packages(Customer.class)
				.persistenceUnit("customers")
				.build();
	}

	@Bean
	public LocalContainerEntityManagerFactoryBean orderEntityManagerFactory(
			EntityManagerFactoryBuilder builder) {
		return builder
				.dataSource(orderDataSource())
				.packages(Order.class)
				.persistenceUnit("orders")
				.build();
	}
----

The configuration above almost works on its own. To complete the picture, you need to
configure `TransactionManagers` for the two `EntityManagers` as well. If you mark one of
them as `@Primary`, it could be picked up by the default `JpaTransactionManager` in Spring
Boot. The other would have to be explicitly injected into a new instance. Alternatively,
you might be able to use a JTA transaction manager that spans both.

If you use Spring Data, you need to configure `@EnableJpaRepositories` accordingly,
as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Configuration
	@EnableJpaRepositories(basePackageClasses = Customer.class,
			entityManagerFactoryRef = "customerEntityManagerFactory")
	public class CustomerConfiguration {
		...
	}

	@Configuration
	@EnableJpaRepositories(basePackageClasses = Order.class,
			entityManagerFactoryRef = "orderEntityManagerFactory")
	public class OrderConfiguration {
		...
	}
----



[[howto-use-traditional-persistence-xml]]
=== Use a Traditional `persistence.xml` File
Spring Boot will not search for or use a `META-INF/persistence.xml` by default. If you
prefer to use a traditional `persistence.xml`, you need to define your own `@Bean` of
type `LocalEntityManagerFactoryBean` (with an ID of '`entityManagerFactory`') and set the
persistence unit name there.

See
{sc-spring-boot-autoconfigure}/orm/jpa/JpaBaseConfiguration.{sc-ext}[`JpaBaseConfiguration`]
for the default settings.



[[howto-use-spring-data-jpa--and-mongo-repositories]]
=== Use Spring Data JPA and Mongo Repositories

Spring Data JPA and Spring Data Mongo can both automatically create `Repository`
implementations for you. If they are both present on the classpath, you might have to do
some extra configuration to tell Spring Boot which repositories to create. The most
explicit way to do that is to use the standard Spring Data `+@EnableJpaRepositories+` and
`+@EnableMongoRepositories+` annotations and provide the location of your `Repository`
interfaces.

There are also flags (`+spring.data.*.repositories.enabled+` and
`+spring.data.*.repositories.type+`) that you can use to switch the auto-configured
repositories on and off in external configuration. Doing so is useful, for instance, in
case you want to switch off the Mongo repositories and still use the auto-configured
`MongoTemplate`.

The same obstacle and the same features exist for other auto-configured Spring Data
repository types (Elasticsearch, Solr, and others). To work with them, change the names of
the annotations and flags accordingly.



[[howto-use-customize-spring-datas-web-support]]
=== Customize Spring Data's Web Support
Spring Data provides web support that simplifies the use of Spring Data repositories in a
web application. Spring Boot provides properties in the `spring.data.web` namespace
for customizing its configuration. Note that if you are using Spring Data REST, you must
use the properties in the `spring.data.rest` namespace instead.


[[howto-use-exposing-spring-data-repositories-rest-endpoint]]
=== Expose Spring Data Repositories as REST Endpoint
Spring Data REST can expose the `Repository` implementations as REST endpoints for you,
provided Spring MVC has been enabled for the application.

Spring Boot exposes a set of useful properties (from the `spring.data.rest` namespace)
that customize the
{spring-data-rest-javadoc}/core/config/RepositoryRestConfiguration.{dc-ext}[`RepositoryRestConfiguration`].
If you need to provide additional customization, you should use a
{spring-data-rest-javadoc}/webmvc/config/RepositoryRestConfigurer.{dc-ext}[`RepositoryRestConfigurer`]
bean.

NOTE: If you do not specify any order on your custom `RepositoryRestConfigurer`, it runs
after the one Spring Boot uses internally. If you need to specify an order, make sure it
is higher than 0.



[[howto-configure-a-component-that-is-used-by-JPA]]
=== Configure a Component that is Used by JPA
If you want to configure a component that JPA uses, then you need to ensure
that the component is initialized before JPA. When the component is auto-configured,
Spring Boot takes care of this for you. For example, when Flyway is auto-configured,
Hibernate is configured to depend upon Flyway so that Flyway has a chance to
initialize the database before Hibernate tries to use it.

If you are configuring a component yourself, you can use an
`EntityManagerFactoryDependsOnPostProcessor` subclass as a convenient way of setting up
the necessary dependencies. For example, if you use Hibernate Search with
Elasticsearch as its index manager, any `EntityManagerFactory` beans must be
configured to depend on the `elasticsearchClient` bean, as shown in the following example:

[source,java,indent=0]
----
include::{code-examples}/elasticsearch/HibernateSearchElasticsearchExample.java[tag=configuration]
----



[[howto-configure-jOOQ-with-multiple-datasources]]
=== Configure jOOQ with Two DataSources
If you need to use jOOQ with multiple data sources, you should create your own
`DSLContext` for each one. Refer to
{sc-spring-boot-autoconfigure}/jooq/JooqAutoConfiguration.{sc-ext}[JooqAutoConfiguration]
for more details.

TIP: In particular, `JooqExceptionTranslator` and `SpringTransactionProvider` can be
reused to provide similar features to what the auto-configuration does with a single
`DataSource`.



[[howto-database-initialization]]
== Database Initialization
An SQL database can be initialized in different ways depending on what your stack is.
Of course, you can also do it manually, provided the database is a separate process.



[[howto-initialize-a-database-using-jpa]]
=== Initialize a Database Using JPA
JPA has features for DDL generation, and these can be set up to run on startup against the
database. This is controlled through two external properties:

* `spring.jpa.generate-ddl` (boolean) switches the feature on and off and is vendor
independent.
* `spring.jpa.hibernate.ddl-auto` (enum) is a Hibernate feature that controls the
behavior in a more fine-grained way. This feature is described in more detail later in
this guide.



[[howto-initialize-a-database-using-hibernate]]
=== Initialize a Database Using Hibernate
You can set `spring.jpa.hibernate.ddl-auto` explicitly and the standard Hibernate property
values are `none`, `validate`, `update`, `create`, and `create-drop`. Spring Boot chooses
a default value for you based on whether it thinks your database is embedded. It defaults
to `create-drop` if no schema manager has been detected or `none` in all other cases. An
embedded database is detected by looking at the `Connection` type. `hsqldb`, `h2`, and
`derby` are embedded, and others are not. Be careful when switching from in-memory to a
'`real`' database that you do not make assumptions about the existence of the tables and
data in the new platform. You either have to set `ddl-auto` explicitly or use one of the
other mechanisms to initialize the database.

NOTE: You can output the schema creation by enabling the `org.hibernate.SQL` logger. This
is done for you automatically if you enable the
<<boot-features-logging-console-output,debug mode>>.

In addition, a file named `import.sql` in the root of the classpath is executed on
startup if Hibernate creates the schema from scratch (that is, if the `ddl-auto` property
is set to `create` or `create-drop`). This can be useful for demos and for testing if you
are careful but is probably not something you want to be on the classpath in production.
It is a Hibernate feature (and has nothing to do with Spring).


[[howto-initialize-a-database-using-spring-jdbc]]
=== Initialize a Database
Spring Boot can automatically create the schema (DDL scripts) of your `DataSource` and
initialize it (DML scripts). It loads SQL from the standard root classpath locations:
`schema.sql` and `data.sql`, respectively. In addition, Spring Boot processes the
`schema-${platform}.sql` and `data-${platform}.sql` files (if present), where `platform`
is the value of `spring.datasource.platform`. This allows you to switch to
database-specific scripts if necessary. For example, you might choose to set it to the
vendor name of the database (`hsqldb`, `h2`, `oracle`, `mysql`, `postgresql`, and so on).

[NOTE]
====
Spring Boot automatically creates the schema of an embedded `DataSource`. This behaviour
can be customized by using the `spring.datasource.initialization-mode` property. For
instance, if you want to always initialize the `DataSource` regardless of its type:

[indent=0,subs="verbatim,quotes,attributes"]
----
	spring.datasource.initialization-mode=always
----
====

By default, Spring Boot enables the fail-fast feature of the Spring JDBC initializer. This
means that, if the scripts cause exceptions, the application fails to start. You can tune
that behavior by setting `spring.datasource.continue-on-error`.

NOTE: In a JPA-based app, you can choose to let Hibernate create the schema or use
`schema.sql`, but you cannot do both. Make sure to disable
`spring.jpa.hibernate.ddl-auto` if you use `schema.sql`.



[[howto-initialize-a-spring-batch-database]]
=== Initialize a Spring Batch Database
If you use Spring Batch, it comes pre-packaged with SQL initialization scripts for most
popular database platforms. Spring Boot can detect your database type and execute those
scripts on startup. If you use an embedded database, this happens by default. You can also
enable it for any database type, as shown in the following example:

[indent=0,subs="verbatim,quotes,attributes"]
----
	spring.batch.initialize-schema=always
----

You can also switch off the initialization explicitly by setting
`spring.batch.initialize-schema=never`.



[[howto-use-a-higher-level-database-migration-tool]]
=== Use a Higher-level Database Migration Tool
Spring Boot supports two higher-level migration tools: https://flywaydb.org/[Flyway]
and http://www.liquibase.org/[Liquibase].

[[howto-execute-flyway-database-migrations-on-startup]]
==== Execute Flyway Database Migrations on Startup
To automatically run Flyway database migrations on startup, add the
`org.flywaydb:flyway-core` to your classpath.

The migrations are scripts in the form `V<VERSION>__<NAME>.sql` (with `<VERSION>` an
underscore-separated version, such as '`1`' or '`2_1`'). By default, they are in a folder
called `classpath:db/migration`, but you can modify that location by setting
`spring.flyway.locations`. This is a comma-separated list of one or more `classpath:`
or `filesystem:` locations. For example, the following configuration would search for
scripts in both the default classpath location and the `/opt/migration` directory:

[source,properties,indent=0]
----
	spring.flyway.locations=classpath:db/migration,filesystem:/opt/migration
----

You can also add a special `{vendor}` placeholder to use vendor-specific scripts. Assume
the following:

[source,properties,indent=0]
----
	spring.flyway.locations=classpath:db/migration/{vendor}
----

Rather than using `db/migration`, the preceding configuration sets the folder to use
according to the type of the database (such as `db/migration/mysql` for MySQL). The list
of supported databases is available in
{sc-spring-boot}/jdbc/DatabaseDriver.{sc-ext}[`DatabaseDriver`].

{sc-spring-boot-autoconfigure}/flyway/FlywayProperties.{sc-ext}[`FlywayProperties`]
provides most of Flyway's settings and a small set of additional properties that can be
used to disable the migrations or switch off the location checking. If you need more
control over the configuration, consider registering a `FlywayConfigurationCustomizer`
bean.

Spring Boot calls `Flyway.migrate()` to perform the database migration. If you would like
more control, provide a `@Bean` that implements
{sc-spring-boot-autoconfigure}/flyway/FlywayMigrationStrategy.{sc-ext}[`FlywayMigrationStrategy`].

Flyway supports SQL and Java https://flywaydb.org/documentation/callbacks.html[callbacks].
To use SQL-based callbacks, place the callback scripts in the `classpath:db/migration`
folder. To use Java-based callbacks, create one or more beans that implement
`Callback`. Any such beans are automatically registered with `Flyway`. They can be
ordered by using `@Order` or by implementing `Ordered`. Beans that implement the
deprecated `FlywayCallback` interface can also be detected, however they cannot be used
alongside `Callback` beans.

By default, Flyway autowires the (`@Primary`) `DataSource` in your context and
uses that for migrations. If you like to use a different `DataSource`, you can create
one and mark its `@Bean` as `@FlywayDataSource`. If you do so and want two data sources,
remember to create another one and mark it as `@Primary`. Alternatively, you can use
Flyway's native `DataSource` by setting `spring.flyway.[url,user,password]`
in external properties. Setting either `spring.flyway.url` or `spring.flyway.user`
is sufficient to cause Flyway to use its own `DataSource`. If any of the three
properties has not be set, the value of its equivalent `spring.datasource` property will
be used.

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

You can also use Flyway to provide data for specific scenarios. For example, you can
place test-specific migrations in `src/test/resources` and they are run only when your
application starts for testing. Also, you can use profile-specific configuration to
customize `spring.flyway.locations` so that certain migrations run only when a particular
profile is active. For example, in `application-dev.properties`, you might specify the
following setting:

[source,properties,indent=0]
----
	spring.flyway.locations=classpath:/db/migration,classpath:/dev/db/migration
----

With that setup, migrations in `dev/db/migration` run only when the `dev` profile is
active.



[[howto-execute-liquibase-database-migrations-on-startup]]
==== Execute Liquibase Database Migrations on Startup
To automatically run Liquibase database migrations on startup, add the
`org.liquibase:liquibase-core` to your classpath.

By default, the master change log is read from `db/changelog/db.changelog-master.yaml`,
but you can change the location by setting `spring.liquibase.change-log`. In addition to
YAML, Liquibase also supports JSON, XML, and SQL change log formats.

By default, Liquibase autowires the (`@Primary`) `DataSource` in your context and uses
that for migrations. If you need to use a different `DataSource`, you can create one and
mark its `@Bean` as `@LiquibaseDataSource`. If you do so and you want two data sources,
remember to create another one and mark it as `@Primary`. Alternatively, you can use
Liquibase's native `DataSource` by setting `spring.liquibase.[url,user,password]` in
external properties. Setting either `spring.liquibase.url` or `spring.liquibase.user`
is sufficient to cause Liquibase to use its own `DataSource`. If any of the three
properties has not be set, the value of its equivalent `spring.datasource` property will
be used.

See
{sc-spring-boot-autoconfigure}/liquibase/LiquibaseProperties.{sc-ext}[`LiquibaseProperties`]
for details about available settings such as contexts, the default schema, and others.

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



[[howto-messaging]]
== Messaging

Spring Boot offers a number of starters that include messaging. This section answers
questions that arise from using messaging with Spring Boot.

[[howto-jms-disable-transaction]]
=== Disable Transacted JMS Session
If your JMS broker does not support transacted sessions, you have to disable the
support of transactions altogether. If you create your own `JmsListenerContainerFactory`,
there is nothing to do, since, by default it cannot be transacted. If you want to use
the `DefaultJmsListenerContainerFactoryConfigurer` to reuse Spring Boot's default, you
can disable transacted sessions, as follows:

[source,java,indent=0]
----
	@Bean
	public DefaultJmsListenerContainerFactory jmsListenerContainerFactory(
			ConnectionFactory connectionFactory,
			DefaultJmsListenerContainerFactoryConfigurer configurer) {
		DefaultJmsListenerContainerFactory listenerFactory =
				new DefaultJmsListenerContainerFactory();
		configurer.configure(listenerFactory, connectionFactory);
		listenerFactory.setTransactionManager(null);
		listenerFactory.setSessionTransacted(false);
		return listenerFactory;
	}
----

The preceding example overrides the default factory, and it should be applied to any
other factory that your application defines, if any.



[[howto-batch-applications]]
== Batch Applications

This section answers questions that arise from using Spring Batch with Spring Boot.

NOTE: By default, batch applications require a `DataSource` to store job details. If you
want to deviate from that, you need to implement `BatchConfigurer`. See
{spring-batch-javadoc}/core/configuration/annotation/EnableBatchProcessing.html[The
Javadoc of `@EnableBatchProcessing`] for more details.

For more about Spring Batch, see the https://projects.spring.io/spring-batch/[Spring Batch
project page].



[[howto-execute-spring-batch-jobs-on-startup]]
=== Execute Spring Batch Jobs on Startup
Spring Batch auto-configuration is enabled by adding `@EnableBatchProcessing`
(from Spring Batch) somewhere in your context.

By default, it executes *all* `Jobs` in the application context on startup (see
{sc-spring-boot-autoconfigure}/batch/JobLauncherCommandLineRunner.{sc-ext}[JobLauncherCommandLineRunner]
for details). You can narrow down to a specific job or jobs by specifying
`spring.batch.job.names` (which takes a comma-separated list of job name patterns).

If the application context includes a `JobRegistry`, the jobs in
`spring.batch.job.names` are looked up in the registry instead of being autowired from the
context. This is a common pattern with more complex systems, where multiple jobs are
defined in child contexts and registered centrally.

See
{sc-spring-boot-autoconfigure}/batch/BatchAutoConfiguration.{sc-ext}[BatchAutoConfiguration]
and
https://github.com/spring-projects/spring-batch/blob/master/spring-batch-core/src/main/java/org/springframework/batch/core/configuration/annotation/EnableBatchProcessing.java[@EnableBatchProcessing]
for more details.



[[howto-actuator]]
== Actuator

Spring Boot includes the Spring Boot Actuator. This section answers questions that often
arise from its use.

[[howto-change-the-http-port-or-address-of-the-actuator-endpoints]]
=== Change the HTTP Port or Address of the Actuator Endpoints
In a standalone application, the Actuator HTTP port defaults to the same as the main HTTP
port. To make the application listen on a different port, set the external property:
`management.server.port`. To listen on a completely different network address (such as
when you have an internal network for management and an external one for user
applications), you can also set `management.server.address` to a valid IP address to which
the server is able to bind.

For more detail, see the
{sc-spring-boot-actuator-autoconfigure}/web/server/ManagementServerProperties.{sc-ext}[`ManagementServerProperties`]
source code and
"`<<production-ready-features.adoc#production-ready-customizing-management-server-port>>`"
in the "`Production-ready features`" section.



[[howto-customize-the-whitelabel-error-page]]
=== Customize the '`whitelabel`' Error Page
Spring Boot installs a '`whitelabel`' error page that you see in a browser client if
you encounter a server error (machine clients consuming JSON and other media types should
see a sensible response with the right error code).

NOTE: Set `server.error.whitelabel.enabled=false` to switch the default error page off.
Doing so restores the default of the servlet container that you are using. Note that
Spring Boot still tries to resolve the error view, so you should probably add your own
error page rather than disabling it completely.

Overriding the error page with your own depends on the templating technology that you
use. For example, if you use Thymeleaf, you can add an `error.html` template.
If you use FreeMarker, you can add an `error.ftl` template. In general, you
need a `View` that resolves with a name of `error` or a `@Controller` that handles
the `/error` path. Unless you replaced some of the default configuration, you should find
a `BeanNameViewResolver` in your `ApplicationContext`, so a `@Bean` named `error` would
be a simple way of doing that. See
{sc-spring-boot-autoconfigure}/web/servlet/error/ErrorMvcAutoConfiguration.{sc-ext}[`ErrorMvcAutoConfiguration`]
for more options.

See also the section on "`<<boot-features-error-handling, Error Handling>>`" for details
of how to register handlers in the servlet container.



[[howto-sanitize-sensible-values]]
=== Sanitize sensible values
Information returned by the `env` and `configprops` endpoints can be somewhat sensitive
so keys matching a certain pattern are sanitized by default (i.e. their values are
replaced by `+******+`).

Spring Boot uses sensible defaults for such keys: for instance, any key ending with the
word "password", "secret", "key" or "token" is sanitized. It is also possible to use a
regular expression instead, such as `+*credentials.*+` to sanitize any key that holds the
word `credentials` as part of the key.

The patterns to use can be customized using the `management.endpoint.env.keys-to-sanitize`
and `management.endpoint.configprops.keys-to-sanitize` respectively.



[[howto-security]]
== Security

This section addresses questions about security when working with Spring Boot, including
questions that arise from using Spring Security with Spring Boot.

For more about Spring Security, see the {spring-security}[Spring Security project page].



[[howto-switch-off-spring-boot-security-configuration]]
=== Switch off the Spring Boot Security Configuration
If you define a `@Configuration` with a `WebSecurityConfigurerAdapter` in your application,
it switches off the default webapp security settings in Spring Boot.


[[howto-change-the-user-details-service-and-add-user-accounts]]
=== Change the UserDetailsService and Add User Accounts
If you provide a `@Bean` of type `AuthenticationManager`, `AuthenticationProvider`,
or `UserDetailsService`, the default `@Bean` for `InMemoryUserDetailsManager` is not
created, so you have the full feature set of Spring Security available (such as
https://docs.spring.io/spring-security/site/docs/current/reference/htmlsingle/#jc-authentication[various
authentication options]).

The easiest way to add user accounts is to provide your own `UserDetailsService` bean.



[[howto-enable-https]]
=== Enable HTTPS When Running behind a Proxy Server
Ensuring that all your main endpoints are only available over HTTPS is an important
chore for any application. If you use Tomcat as a servlet container, then
Spring Boot adds Tomcat's own `RemoteIpValve` automatically if it detects some
environment settings, and you should be able to rely on the `HttpServletRequest` to
report whether it is secure or not (even downstream of a proxy server that handles the
real SSL termination). The standard behavior is determined by the presence or absence of
certain request headers (`x-forwarded-for` and `x-forwarded-proto`), whose names are
conventional, so it should work with most front-end proxies. You can switch on the valve
by adding some entries to `application.properties`, as shown in the following example:

[source,properties,indent=0]
----
	server.tomcat.remote-ip-header=x-forwarded-for
	server.tomcat.protocol-header=x-forwarded-proto
----

(The presence of either of those properties switches on the valve. Alternatively, you can
add the `RemoteIpValve` by adding a `TomcatServletWebServerFactory` bean.)

To configure Spring Security to require a secure channel for all (or some)
requests, consider adding your own `WebSecurityConfigurerAdapter` that adds the following
`HttpSecurity` configuration:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@Configuration
	public class SslWebSecurityConfigurerAdapter extends WebSecurityConfigurerAdapter {

		@Override
		protected void configure(HttpSecurity http) throws Exception {
			// Customize the application security
			http.requiresChannel().anyRequest().requiresSecure();
		}

	}
----


[[howto-hotswapping]]
== Hot Swapping

Spring Boot supports hot swapping. This section answers questions about how it works.



[[howto-reload-static-content]]
=== Reload Static Content
There are several options for hot reloading. The recommended approach is to use
<<using-spring-boot.adoc#using-boot-devtools,`spring-boot-devtools`>>, as it provides
additional development-time features, such as support for fast application restarts
and LiveReload as well as sensible development-time configuration (such as template
caching). Devtools works by monitoring the classpath for changes. This means that static
resource changes must be "built" for the change to take affect. By default, this happens
automatically in Eclipse when you save your changes. In IntelliJ IDEA, the Make Project
command triggers the necessary build. Due to the
<<using-spring-boot.adoc#using-boot-devtools-restart-exclude, default restart
exclusions>>, changes to static resources do not trigger a restart of your application.
They do, however, trigger a live reload.

Alternatively, running in an IDE (especially with debugging on) is a good way to do
development (all modern IDEs allow reloading of static resources and usually also allow
hot-swapping of Java class changes).

Finally, the <<build-tool-plugins.adoc#build-tool-plugins, Maven and Gradle plugins>> can
be configured (see the `addResources` property) to support running from the command line
with reloading of static files directly from source. You can use that with an external
css/js compiler process if you are writing that code with higher-level tools.



[[howto-reload-thymeleaf-template-content]]
=== Reload Templates without Restarting the Container
Most of the templating technologies supported by Spring Boot include a configuration
option to disable caching (described later in this document). If you use the
`spring-boot-devtools` module, these properties are
<<using-spring-boot.adoc#using-boot-devtools-property-defaults,automatically configured>>
for you at development time.



[[howto-reload-thymeleaf-content]]
==== Thymeleaf Templates
If you use Thymeleaf, set `spring.thymeleaf.cache` to `false`. See
{sc-spring-boot-autoconfigure}/thymeleaf/ThymeleafAutoConfiguration.{sc-ext}[`ThymeleafAutoConfiguration`]
for other Thymeleaf customization options.



[[howto-reload-freemarker-content]]
==== FreeMarker Templates
If you use FreeMarker, set `spring.freemarker.cache` to `false`. See
{sc-spring-boot-autoconfigure}/freemarker/FreeMarkerAutoConfiguration.{sc-ext}[`FreeMarkerAutoConfiguration`]
for other FreeMarker customization options.



[[howto-reload-groovy-template-content]]
==== Groovy Templates
If you use Groovy templates, set `spring.groovy.template.cache` to `false`. See
{sc-spring-boot-autoconfigure}/groovy/template/GroovyTemplateAutoConfiguration.{sc-ext}[`GroovyTemplateAutoConfiguration`]
for other Groovy customization options.



[[howto-reload-fast-restart]]
=== Fast Application Restarts
The `spring-boot-devtools` module includes support for automatic application restarts.
While not as fast as technologies such as
http://zeroturnaround.com/software/jrebel/[JRebel] it is usually significantly faster than
a "`cold start`". You should probably give it a try before investigating some of the more
complex reload options discussed later in this document.

For more details, see the <<using-spring-boot.adoc#using-boot-devtools>> section.



[[howto-reload-java-classes-without-restarting]]
=== Reload Java Classes without Restarting the Container
Many modern IDEs (Eclipse, IDEA, and others) support hot swapping of bytecode.
Consequently, if you make a change that does not affect class or method signatures, it
should reload cleanly with no side effects.



[[howto-build]]
== Build

Spring Boot includes build plugins for Maven and Gradle. This section answers common
questions about these plugins.



[[howto-build-info]]
=== Generate Build Information
Both the Maven plugin and the Gradle plugin allow generating build information containing
the coordinates, name, and version of the project. The plugins can also be configured
to add additional properties through configuration. When such a file is present,
Spring Boot auto-configures a `BuildProperties` bean.

To generate build information with Maven, add an execution for the `build-info` goal, as
shown in the following example:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<version>{spring-boot-version}</version>
				<executions>
					<execution>
						<goals>
							<goal>build-info</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
		</plugins>
	</build>
----

TIP: See the {spring-boot-maven-plugin-site}[Spring Boot Maven Plugin documentation]
for more details.

The following example does the same with Gradle:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	springBoot {
		buildInfo()
	}
----

TIP: See the
{spring-boot-gradle-plugin-reference}/#integrating-with-actuator-build-info[Spring Boot
Gradle Plugin documentation] for more details.



[[howto-git-info]]
=== Generate Git Information

Both Maven and Gradle allow generating a `git.properties` file containing information
about the state of your `git` source code repository when the project was built.

For Maven users, the `spring-boot-starter-parent` POM includes a pre-configured plugin to
generate a `git.properties` file. To use it, add the following declaration to your POM:

[source,xml,indent=0]
----
	<build>
		<plugins>
			<plugin>
				<groupId>pl.project13.maven</groupId>
				<artifactId>git-commit-id-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
----

Gradle users can achieve the same result by using the
https://plugins.gradle.org/plugin/com.gorylenko.gradle-git-properties[`gradle-git-properties`]
plugin, as shown in the following example:

[source,groovy,indent=0]
----
	plugins {
		id "com.gorylenko.gradle-git-properties" version "1.5.1"
	}
----

TIP: The commit time in `git.properties` is expected to match the following format:
`yyyy-MM-dd'T'HH:mm:ssZ`. This is the default format for both plugins listed above. Using
this format lets the time be parsed into a `Date` and its format, when serialized to JSON,
to be controlled by Jackson's date serialization configuration settings.



[[howto-customize-dependency-versions]]
=== Customize Dependency Versions
If you use a Maven build that inherits directly or indirectly from
`spring-boot-dependencies` (for instance, `spring-boot-starter-parent`) but you want to
override a specific third-party dependency, you can add appropriate `<properties>`
elements. Browse the
{github-code}/spring-boot-project/spring-boot-dependencies/pom.xml[`spring-boot-dependencies`]
POM for a complete list of properties. For example, to pick a different `slf4j` version,
you would add the following property:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<properties>
		<slf4j.version>1.7.5<slf4j.version>
	</properties>
----

NOTE: Doing so only works if your Maven project inherits (directly or indirectly) from
`spring-boot-dependencies`. If you have added `spring-boot-dependencies` in your
own `dependencyManagement` section with `<scope>import</scope>`, you have to redefine
the artifact yourself instead of overriding the property.

WARNING: Each Spring Boot release is designed and tested against this specific set of
third-party dependencies. Overriding versions may cause compatibility issues.

To override dependency versions in Gradle, see {spring-boot-gradle-plugin-reference}/#managing-dependencies-customizing[this section]
of the Gradle plugin's documentation.

[[howto-create-an-executable-jar-with-maven]]
=== Create an Executable JAR with Maven
The `spring-boot-maven-plugin` can be used to create an executable "`fat`" JAR. If you
use the `spring-boot-starter-parent` POM, you can declare the plugin and your jars are
repackaged as follows:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
----

If you do not use the parent POM, you can still use the plugin. However, you must
additionally add an `<executions>` section, as follows:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<version>{spring-boot-version}</version>
				<executions>
					<execution>
						<goals>
							<goal>repackage</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
		</plugins>
	</build>
----

See the {spring-boot-maven-plugin-site}/usage.html[plugin documentation] for full usage
details.


[[howto-create-an-additional-executable-jar]]
=== Use a Spring Boot Application as a Dependency
Like a war file, a Spring Boot application is not intended to be used as a dependency. If
your application contains classes that you want to share with other projects, the
recommended approach is to move that code into a separate module. The separate module can
then be depended upon by your application and other projects.

If you cannot rearrange your code as recommended above, Spring Boot's Maven and Gradle
plugins must be configured to produce a separate artifact that is suitable for use as a
dependency. The executable archive cannot be used as a dependency as the
<<appendix-executable-jar-format.adoc#executable-jar-jar-file-structure,executable jar
format>> packages application classes in `BOOT-INF/classes`. This means
that they cannot be found when the executable jar is used as a dependency.

To produce the two artifacts, one that can be used as a dependency and one that is
executable, a classifier must be specified. This classifier is applied to the name of the
executable archive, leaving the default archive for use as a dependency.

To configure a classifier of `exec` in Maven, you can use the following configuration:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<configuration>
					<classifier>exec</classifier>
				</configuration>
			</plugin>
		</plugins>
	</build>
----



[[howto-extract-specific-libraries-when-an-executable-jar-runs]]
=== Extract Specific Libraries When an Executable Jar Runs
Most nested libraries in an executable jar do not need to be unpacked in order to run.
However, certain libraries can have problems. For example, JRuby includes its own nested
jar support, which assumes that the `jruby-complete.jar` is always directly available as a
file in its own right.

To deal with any problematic libraries, you can flag that specific nested jars should be
automatically unpacked to the "`temp folder`" when the executable jar first runs.

For example, to indicate that JRuby should be flagged for unpacking by using the Maven
Plugin, you would add the following configuration:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<configuration>
					<requiresUnpack>
						<dependency>
							<groupId>org.jruby</groupId>
							<artifactId>jruby-complete</artifactId>
						</dependency>
					</requiresUnpack>
				</configuration>
			</plugin>
		</plugins>
	</build>
----



[[howto-create-a-nonexecutable-jar]]
=== Create a Non-executable JAR with Exclusions
Often, if you have an executable and a non-executable jar as two separate build products,
the executable version has additional configuration files that are not needed in a library
jar. For example, the `application.yml` configuration file might by excluded from the
non-executable JAR.

In Maven, the executable jar must be the main artifact and you can add a classified jar
for the library, as follows:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
			<plugin>
				<artifactId>maven-jar-plugin</artifactId>
				<executions>
					<execution>
						<id>lib</id>
						<phase>package</phase>
						<goals>
							<goal>jar</goal>
						</goals>
						<configuration>
							<classifier>lib</classifier>
							<excludes>
								<exclude>application.yml</exclude>
							</excludes>
						</configuration>
					</execution>
				</executions>
			</plugin>
		</plugins>
	</build>
----



[[howto-remote-debug-maven-run]]
=== Remote Debug a Spring Boot Application Started with Maven
To attach a remote debugger to a Spring Boot application that was started with Maven, you
can use the `jvmArguments` property of the {spring-boot-maven-plugin-site}[maven plugin].

See {spring-boot-maven-plugin-site}/examples/run-debug.html[this example] for more
details.



[[howto-build-an-executable-archive-with-ant]]
=== Build an Executable Archive from Ant without Using `spring-boot-antlib`
To build with Ant, you need to grab dependencies, compile, and then create a jar or war
archive. To make it executable, you can either use the `spring-boot-antlib`
module or you can follow these instructions:

. If you are building a jar, package the application's classes and resources in a nested
`BOOT-INF/classes` directory. If you are building a war, package the application's
classes in a nested `WEB-INF/classes` directory as usual.
. Add the runtime dependencies in a nested `BOOT-INF/lib` directory for a jar or
`WEB-INF/lib` for a war. Remember *not* to compress the entries in the archive.
. Add the `provided` (embedded container) dependencies in a nested `BOOT-INF/lib`
directory for a jar or `WEB-INF/lib-provided` for a war. Remember *not* to compress the
entries in the archive.
. Add the `spring-boot-loader` classes at the root of the archive (so that the `Main-Class`
is available).
. Use the appropriate launcher (such as `JarLauncher` for a jar file) as a `Main-Class`
attribute in the manifest and specify the other properties it needs as manifest entries --
principally, by setting a `Start-Class` property.

The following example shows how to build an executable archive with Ant:

[source,xml,indent=0]
----
	<target name="build" depends="compile">
		<jar destfile="target/${ant.project.name}-${spring-boot.version}.jar" compress="false">
			<mappedresources>
				<fileset dir="target/classes" />
				<globmapper from="*" to="BOOT-INF/classes/*"/>
			</mappedresources>
			<mappedresources>
				<fileset dir="src/main/resources" erroronmissingdir="false"/>
				<globmapper from="*" to="BOOT-INF/classes/*"/>
			</mappedresources>
			<mappedresources>
				<fileset dir="${lib.dir}/runtime" />
				<globmapper from="*" to="BOOT-INF/lib/*"/>
			</mappedresources>
			<zipfileset src="${lib.dir}/loader/spring-boot-loader-jar-${spring-boot.version}.jar" />
			<manifest>
				<attribute name="Main-Class" value="org.springframework.boot.loader.JarLauncher" />
				<attribute name="Start-Class" value="${start-class}" />
			</manifest>
		</jar>
	</target>
----

The {github-code}/spring-boot-samples/spring-boot-sample-ant[Ant Sample] has a
`build.xml` file with a `manual` task that should work if you run it with the following
command:

[indent=0,subs="verbatim,quotes,attributes"]
----
	$ ant -lib <folder containing ivy-2.2.jar> clean manual
----

Then you can run the application with the following command:

[indent=0,subs="verbatim,quotes,attributes"]
----
	$ java -jar target/*.jar
----



[[howto-traditional-deployment]]
== Traditional Deployment

Spring Boot supports traditional deployment as well as more modern forms of deployment.
This section answers common questions about traditional deployment.



[[howto-create-a-deployable-war-file]]
=== Create a Deployable War File

WARNING: Because Spring WebFlux does not strictly depend on the Servlet API and
applications are deployed by default on an embedded Reactor Netty server,
War deployment is not supported for WebFlux applications.

The first step in producing a deployable war file is to provide a
`SpringBootServletInitializer` subclass and override its `configure` method. Doing so
makes use of Spring Framework's Servlet 3.0 support and lets you configure your
application when it is launched by the servlet container. Typically, you should update
your application's main class to extend `SpringBootServletInitializer`, as shown in the
following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@SpringBootApplication
	public class Application extends SpringBootServletInitializer {

		@Override
		protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
			return application.sources(Application.class);
		}

		public static void main(String[] args) throws Exception {
			SpringApplication.run(Application.class, args);
		}

	}
----

The next step is to update your build configuration such that your project produces a war
file rather than a jar file. If you use Maven and `spring-boot-starter-parent` (which
configures Maven's war plugin for you), all you need to do is to modify `pom.xml` to
change the packaging to war, as follows:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<packaging>war</packaging>
----

If you use Gradle, you need to modify `build.gradle` to apply the war plugin to the
project, as follows:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	apply plugin: 'war'
----

The final step in the process is to ensure that the embedded servlet container does not
interfere with the servlet container to which the war file is deployed. To do so, you
need to mark the embedded servlet container dependency as being provided.

If you use Maven, the following example marks the servlet container (Tomcat, in this
case) as being provided:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependencies>
		<!-- … -->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-tomcat</artifactId>
			<scope>provided</scope>
		</dependency>
		<!-- … -->
	</dependencies>
----

If you use Gradle, the following example marks the servlet container (Tomcat, in this
case) as being provided:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	dependencies {
		// …
		providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'
		// …
	}
----

TIP: `providedRuntime` is preferred to Gradle's `compileOnly` configuration. Among other
limitations, `compileOnly` dependencies are not on the test classpath, so any web-based
integration tests fail.

If you use the <<build-tool-plugins.adoc#build-tool-plugins, Spring Boot build tools>>,
marking the embedded servlet container dependency as provided produces an executable war
file with the provided dependencies packaged in a `lib-provided` directory. This means
that, in addition to being deployable to a servlet container, you can also run your
application by using `java -jar` on the command line.

TIP: Take a look at Spring Boot's sample applications for a
{github-code}/spring-boot-samples/spring-boot-sample-traditional/pom.xml[Maven-based
example] of the previously described configuration.




[[howto-convert-an-existing-application-to-spring-boot]]
=== Convert an Existing Application to Spring Boot
For a non-web application, it should be easy to convert an existing Spring application to
a Spring Boot application. To do so, throw away the code that creates your
`ApplicationContext` and replace it with calls to `SpringApplication` or
`SpringApplicationBuilder`. Spring MVC web applications are generally amenable to first
creating a deployable war application and then migrating it later to an executable war
or jar. See the https://spring.io/guides/gs/convert-jar-to-war/[Getting
Started Guide on Converting a jar to a war].

To create a deployable war by extending `SpringBootServletInitializer` (for example, in a
class called `Application`) and adding the Spring Boot `@SpringBootApplication`
annotation, use code similar to that shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@SpringBootApplication
	public class Application extends SpringBootServletInitializer {

		@Override
		protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
			// Customize the application or call application.sources(...) to add sources
			// Since our example is itself a @Configuration class (via @SpringBootApplication)
			// we actually don't need to override this method.
			return application;
		}

	}
----

Remember that, whatever you put in the `sources` is merely a Spring `ApplicationContext`.
Normally, anything that already works should work here. There might be some beans you can
remove later and let Spring Boot provide its own defaults for them, but it should be
possible to get something working before you need to do that.

Static resources can be moved to `/public` (or `/static` or `/resources` or
`/META-INF/resources`) in the classpath root. The same applies to `messages.properties`
(which Spring Boot automatically detects in the root of the classpath).

Vanilla usage of Spring `DispatcherServlet` and Spring Security should require no further
changes. If you have other features in your application (for instance, using other
servlets or filters), you may need to add some configuration to your `Application`
context, by replacing those elements from the `web.xml`, as follows:

* A `@Bean` of type `Servlet` or `ServletRegistrationBean` installs that bean in the
container as if it were a `<servlet/>` and `<servlet-mapping/>` in `web.xml`.
* A `@Bean` of type `Filter` or `FilterRegistrationBean` behaves similarly (as a
`<filter/>` and `<filter-mapping/>`).
* An `ApplicationContext` in an XML file can be added through an `@ImportResource` in
your `Application`. Alternatively, simple cases where annotation configuration is
heavily used already can be recreated in a few lines as `@Bean` definitions.

Once the war file is working, you can make it executable by adding a `main` method to
your `Application`, as shown in the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}
----

[NOTE]
====
If you intend to start your application as a war or as an executable application, you
need to share the customizations of the builder in a method that is both available to the
`SpringBootServletInitializer` callback and in the `main` method in a class similar to the
following:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	@SpringBootApplication
	public class Application extends SpringBootServletInitializer {

		@Override
		protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
			return configureApplication(builder);
		}

		public static void main(String[] args) {
			configureApplication(new SpringApplicationBuilder()).run(args);
		}

		private static SpringApplicationBuilder configureApplication(SpringApplicationBuilder builder) {
			return builder.sources(Application.class).bannerMode(Banner.Mode.OFF);
		}

	}
----
====

Applications can fall into more than one category:

* Servlet 3.0+ applications with no `web.xml`.
* Applications with a `web.xml`.
* Applications with a context hierarchy.
* Applications without a context hierarchy.

All of these should be amenable to translation, but each might require slightly different
techniques.

Servlet 3.0+ applications might translate pretty easily if they already use the Spring
Servlet 3.0+ initializer support classes. Normally, all the code from an existing
`WebApplicationInitializer` can be moved into a `SpringBootServletInitializer`. If your
existing application has more than one `ApplicationContext` (for example, if it uses
`AbstractDispatcherServletInitializer`) then you might be able to combine all your context
sources into a single `SpringApplication`. The main complication you might encounter is if
combining does not work and you need to maintain the context hierarchy. See the
<<howto-build-an-application-context-hierarchy, entry on building a hierarchy>> for
examples. An existing parent context that contains web-specific features usually
needs to be broken up so that all the `ServletContextAware` components are in the child
context.

Applications that are not already Spring applications might be convertible to Spring
Boot applications, and the previously mentioned guidance may help. However, you may yet
encounter problems. In that case, we suggest
https://stackoverflow.com/questions/tagged/spring-boot[asking questions on Stack Overflow
with a tag of `spring-boot`].



[[howto-weblogic]]
===  Deploying a WAR to WebLogic
To deploy a Spring Boot application to WebLogic, you must ensure that your servlet
initializer *directly* implements `WebApplicationInitializer` (even if you extend from a
base class that already implements it).

A typical initializer for WebLogic should resemble the following example:

[source,java,indent=0,subs="verbatim,quotes,attributes"]
----
	import org.springframework.boot.autoconfigure.SpringBootApplication;
	import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
	import org.springframework.web.WebApplicationInitializer;

	@SpringBootApplication
	public class MyApplication extends SpringBootServletInitializer implements WebApplicationInitializer {

	}
----

If you use Logback, you also need to tell WebLogic to prefer the packaged version
rather than the version that was pre-installed with the server. You can do so by adding a
`WEB-INF/weblogic.xml` file with the following contents:

[source,xml,indent=0]
----
	<?xml version="1.0" encoding="UTF-8"?>
	<wls:weblogic-web-app
		xmlns:wls="http://xmlns.oracle.com/weblogic/weblogic-web-app"
		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
			http://java.sun.com/xml/ns/javaee/ejb-jar_3_0.xsd
			http://xmlns.oracle.com/weblogic/weblogic-web-app
			http://xmlns.oracle.com/weblogic/weblogic-web-app/1.4/weblogic-web-app.xsd">
		<wls:container-descriptor>
			<wls:prefer-application-packages>
				<wls:package-name>org.slf4j</wls:package-name>
			</wls:prefer-application-packages>
		</wls:container-descriptor>
	</wls:weblogic-web-app>
----



[[howto-use-jedis-instead-of-lettuce]]
=== Use Jedis Instead of Lettuce
By default, the Spring Boot starter (`spring-boot-starter-data-redis`) uses
https://github.com/lettuce-io/lettuce-core/[Lettuce]. You need to exclude that
dependency and include the https://github.com/xetorthio/jedis/[Jedis] one instead. Spring
Boot manages these dependencies to help make this process as easy as possible.

The following example shows how to do so in Maven:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-data-redis</artifactId>
		<exclusions>
			<exclusion>
				<groupId>io.lettuce</groupId>
				<artifactId>lettuce-core</artifactId>
			</exclusion>
		</exclusions>
	</dependency>
	<dependency>
		<groupId>redis.clients</groupId>
		<artifactId>jedis</artifactId>
	</dependency>
----

The following example shows how to do so in Gradle:

[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
----
	configurations {
		compile.exclude module: "lettuce"
	}

	dependencies {
		compile("redis.clients:jedis")
		// ...
	}
----
