Wrap using-spring-boot.adoc at 90 characters

Closes gh-10765
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Andy Wilkinson 2017-10-28 12:14:05 +01:00
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@ -7,12 +7,11 @@ This section goes into more detail about how you should use Spring Boot. It cove
such as build systems, auto-configuration, and how to run your applications. We also cover such as build systems, auto-configuration, and how to run your applications. We also cover
some Spring Boot best practices. Although there is nothing particularly special about some Spring Boot best practices. Although there is nothing particularly special about
Spring Boot (it is just another library that you can consume), there are a few Spring Boot (it is just another library that you can consume), there are a few
recommendations that, when followed, make your development process a recommendations that, when followed, make your development process a little easier.
little easier.
If you are starting out with Spring Boot, you should probably read the If you are starting out with Spring Boot, you should probably read the
_<<getting-started.adoc#getting-started, Getting Started>>_ guide before diving into _<<getting-started.adoc#getting-started, Getting Started>>_ guide before diving into this
this section. section.
-- --
@ -20,26 +19,25 @@ this section.
[[using-boot-build-systems]] [[using-boot-build-systems]]
== Build Systems == Build Systems
It is strongly recommended that you choose a build system that supports It is strongly recommended that you choose a build system that supports
<<using-boot-dependency-management,_dependency management_>> and <<using-boot-dependency-management,_dependency management_>> and that can consume
that can consume artifacts published to the "`Maven Central`" repository. We artifacts published to the "`Maven Central`" repository. We would recommend that you
would recommend that you choose Maven or Gradle. It is possible to get Spring Boot to choose Maven or Gradle. It is possible to get Spring Boot to work with other build systems
work with other build systems (Ant, for example), but they are not particularly well (Ant, for example), but they are not particularly well supported.
supported.
[[using-boot-dependency-management]] [[using-boot-dependency-management]]
=== Dependency Management === Dependency Management
Each release of Spring Boot provides a curated list of dependencies that it supports. In Each release of Spring Boot provides a curated list of dependencies that it supports. In
practice, you do not need to provide a version for any of these dependencies in your practice, you do not need to provide a version for any of these dependencies in your build
build configuration, as Spring Boot is managing that for you. When you upgrade Spring configuration, as Spring Boot is managing that for you. When you upgrade Spring Boot
Boot itself, these dependencies are upgraded as well in a consistent way. itself, these dependencies are upgraded as well in a consistent way.
NOTE: You can still specify a version and override Spring Boot's recommendations if you NOTE: You can still specify a version and override Spring Boot's recommendations if you
need to do so. need to do so.
The curated list contains all the spring modules that you can use with Spring Boot as The curated list contains all the spring modules that you can use with Spring Boot as well
well as a refined list of third party libraries. The list is available as a standard as a refined list of third party libraries. The list is available as a standard
<<using-boot-maven-without-a-parent,Bills of Materials (`spring-boot-dependencies`)>> <<using-boot-maven-without-a-parent,Bills of Materials (`spring-boot-dependencies`)>>
that can be used with both <<using-boot-maven-parent-pom,Maven>> and that can be used with both <<using-boot-maven-parent-pom,Maven>> and
<<using-boot-gradle,Gradle>>. <<using-boot-gradle,Gradle>>.
@ -57,20 +55,21 @@ defaults. The parent project provides the following features:
* Java 1.8 as the default compiler level. * Java 1.8 as the default compiler level.
* UTF-8 source encoding. * UTF-8 source encoding.
* A <<using-boot-dependency-management,Dependency Management section>>, inherited from * A <<using-boot-dependency-management,Dependency Management section>>, inherited from
the spring-boot-dependencies pom, that manages the versions of common dependencies. This the spring-boot-dependencies pom, that manages the versions of common dependencies. This
dependency management lets you omit <version> tags for those dependencies when used dependency management lets you omit <version> tags for those dependencies when used in
in your own pom. your own pom.
* Sensible https://maven.apache.org/plugins/maven-resources-plugin/examples/filter.html[resource filtering]. * Sensible https://maven.apache.org/plugins/maven-resources-plugin/examples/filter.html[resource
filtering].
* Sensible plugin configuration (http://www.mojohaus.org/exec-maven-plugin/[exec plugin], * Sensible plugin configuration (http://www.mojohaus.org/exec-maven-plugin/[exec plugin],
https://github.com/ktoso/maven-git-commit-id-plugin[Git commit ID], and https://github.com/ktoso/maven-git-commit-id-plugin[Git commit ID], and
http://maven.apache.org/plugins/maven-shade-plugin/[shade]). http://maven.apache.org/plugins/maven-shade-plugin/[shade]).
* Sensible resource filtering for `application.properties` and `application.yml` including * Sensible resource filtering for `application.properties` and `application.yml` including
profile-specific files (for example, `application-foo.properties` and `application-foo.yml`) profile-specific files (for example, `application-foo.properties` and
`application-foo.yml`)
Note that, since the `application.properties` and `application.yml` files accept Note that, since the `application.properties` and `application.yml` files accept Spring
Spring style placeholders (`${...}`), the Maven filtering is changed to style placeholders (`${...}`), the Maven filtering is changed to use `@..@` placeholders.
use `@..@` placeholders. (You can override that by setting a Maven property called (You can override that by setting a Maven property called `resource.delimiter`.)
`resource.delimiter`.)
@ -93,8 +92,8 @@ NOTE: You should need to specify only the Spring Boot version number on this dep
If you import additional starters, you can safely omit the version number. If you import additional starters, you can safely omit the version number.
With that setup, you can also override individual dependencies by overriding a property With that setup, you can also override individual dependencies by overriding a property
in your own project. For instance, to upgrade to another Spring Data release train, you would in your own project. For instance, to upgrade to another Spring Data release train, you
add the following to your `pom.xml`: would add the following to your `pom.xml`:
[source,xml,indent=0,subs="verbatim,quotes,attributes"] [source,xml,indent=0,subs="verbatim,quotes,attributes"]
---- ----
@ -134,11 +133,11 @@ dependency, as follows:
</dependencyManagement> </dependencyManagement>
---- ----
The preceding sample setup does not let you override individual dependencies by using a property, as The preceding sample setup does not let you override individual dependencies by using a
explained above. To achieve the same result, you need to add an entry in the property, as explained above. To achieve the same result, you need to add an entry in the
`dependencyManagement` of your project **before** the `spring-boot-dependencies` `dependencyManagement` of your project **before** the `spring-boot-dependencies` entry.
entry. For instance, to upgrade to another Spring Data release train, you could add the For instance, to upgrade to another Spring Data release train, you could add the following
following element to your `pom.xml`: element to your `pom.xml`:
[source,xml,indent=0,subs="verbatim,quotes,attributes"] [source,xml,indent=0,subs="verbatim,quotes,attributes"]
---- ----
@ -163,16 +162,16 @@ following element to your `pom.xml`:
</dependencyManagement> </dependencyManagement>
---- ----
NOTE: In the preceding example, we specify a _BOM_, but any dependency type can be overridden NOTE: In the preceding example, we specify a _BOM_, but any dependency type can be
in the same way. overridden in the same way.
[[using-boot-maven-plugin]] [[using-boot-maven-plugin]]
==== Using the Spring Boot Maven Plugin ==== Using the Spring Boot Maven Plugin
Spring Boot includes a <<build-tool-plugins.adoc#build-tool-plugins-maven-plugin, Maven plugin>> Spring Boot includes a <<build-tool-plugins.adoc#build-tool-plugins-maven-plugin, Maven
that can package the project as an executable jar. Add the plugin to your `<plugins>` plugin>> that can package the project as an executable jar. Add the plugin to your
section if you want to use it, as shown in the following example: `<plugins>` section if you want to use it, as shown in the following example:
[source,xml,indent=0,subs="verbatim,quotes,attributes"] [source,xml,indent=0,subs="verbatim,quotes,attributes"]
---- ----
@ -187,8 +186,8 @@ section if you want to use it, as shown in the following example:
---- ----
NOTE: If you use the Spring Boot starter parent pom, you need to add only the plugin. NOTE: If you use the Spring Boot starter parent pom, you need to add only the plugin.
There is no need to configure it unless you want to change the settings defined in There is no need to configure it unless you want to change the settings defined in the
the parent. parent.
@ -207,7 +206,8 @@ It is possible to build a Spring Boot project using Apache Ant+Ivy. The
`spring-boot-antlib` "`AntLib`" module is also available to help Ant create executable `spring-boot-antlib` "`AntLib`" module is also available to help Ant create executable
jars. jars.
To declare dependencies, a typical `ivy.xml` file looks something like the following example: To declare dependencies, a typical `ivy.xml` file looks something like the following
example:
[source,xml,indent=0] [source,xml,indent=0]
---- ----
@ -288,11 +288,11 @@ search dependencies by name. For example, with the appropriate Eclipse or STS pl
installed, you can simply hit `ctrl-space` in the POM editor and type installed, you can simply hit `ctrl-space` in the POM editor and type
"`spring-boot-starter`" for a complete list. "`spring-boot-starter`" for a complete list.
As explained in the <<spring-boot-features#boot-features-custom-starter,Creating Your Own Starter>> As explained in the <<spring-boot-features#boot-features-custom-starter,Creating Your Own
section, third party starters should not start with `spring-boot`, as it is reserved for Starter>> section, third party starters should not start with `spring-boot`, as it is
official Spring Boot artifacts. Rather, a third-party starter typically starts with the reserved for official Spring Boot artifacts. Rather, a third-party starter typically
name of the project. For example, a third-party starter project called `thirdpartyproject` starts with the name of the project. For example, a third-party starter project called
would typically be named `thirdpartyproject-spring-boot-starter`. `thirdpartyproject` would typically be named `thirdpartyproject-spring-boot-starter`.
**** ****
The following application starters are provided by Spring Boot under the The following application starters are provided by Spring Boot under the
@ -307,15 +307,16 @@ _<<production-ready-features.adoc#production-ready, production ready>>_ features
.Spring Boot production starters .Spring Boot production starters
include::../../../target/generated-resources/production-starters.adoc[] include::../../../target/generated-resources/production-starters.adoc[]
Finally, Spring Boot also includes the following starters that can be used if you want to exclude Finally, Spring Boot also includes the following starters that can be used if you want to
exclude
or swap specific technical facets: or swap specific technical facets:
.Spring Boot technical starters .Spring Boot technical starters
include::../../../target/generated-resources/technical-starters.adoc[] include::../../../target/generated-resources/technical-starters.adoc[]
TIP: For a list of additional community contributed starters, see the TIP: For a list of additional community contributed starters, see the
{github-master-code}/spring-boot-project/spring-boot-starters/README.adoc[README file] in the {github-master-code}/spring-boot-project/spring-boot-starters/README.adoc[README file] in
`spring-boot-starters` module on GitHub. the `spring-boot-starters` module on GitHub.
@ -331,11 +332,11 @@ best practices that help.
When a class does not include a `package` declaration, it is considered to be in the When a class does not include a `package` declaration, it is considered to be in the
"`default package`". The use of the "`default package`" is generally discouraged and "`default package`". The use of the "`default package`" is generally discouraged and
should be avoided. It can cause particular problems for Spring Boot applications that should be avoided. It can cause particular problems for Spring Boot applications that
use the `@ComponentScan`, `@EntityScan`, or `@SpringBootApplication` annotations, since every use the `@ComponentScan`, `@EntityScan`, or `@SpringBootApplication` annotations, since
class from every jar is read. every class from every jar is read.
TIP: We recommend that you follow Java's recommended package naming conventions TIP: We recommend that you follow Java's recommended package naming conventions and use a
and use a reversed domain name (for example, `com.example.project`). reversed domain name (for example, `com.example.project`).
@ -347,9 +348,9 @@ main class, and it implicitly defines a base "`search package`" for certain item
example, if you are writing a JPA application, the package of the example, if you are writing a JPA application, the package of the
`@EnableAutoConfiguration` annotated class is used to search for `@Entity` items. `@EnableAutoConfiguration` annotated class is used to search for `@Entity` items.
Using a root package also lets the `@ComponentScan` annotation be used without Using a root package also lets the `@ComponentScan` annotation be used without needing to
needing to specify a `basePackage` attribute. You can also use the specify a `basePackage` attribute. You can also use the `@SpringBootApplication`
`@SpringBootApplication` annotation if your main class is in the root package. annotation if your main class is in the root package.
The following listing shows a typical layout: The following listing shows a typical layout:
@ -402,9 +403,9 @@ The `Application.java` file would declare the `main` method, along with the basi
[[using-boot-configuration-classes]] [[using-boot-configuration-classes]]
== Configuration Classes == Configuration Classes
Spring Boot favors Java-based configuration. Although it is possible to use Spring Boot favors Java-based configuration. Although it is possible to use
`SpringApplication` with XML sources, we generally recommend that your primary `SpringApplication` with XML sources, we generally recommend that your primary source be a
source be a single `@Configuration` class. Usually the class that defines the `main` single `@Configuration` class. Usually the class that defines the `main` method is a good
method is a good candidate as the primary `@Configuration`. candidate as the primary `@Configuration`.
TIP: Many Spring configuration examples have been published on the Internet that use XML TIP: Many Spring configuration examples have been published on the Internet that use XML
configuration. If possible, always try to use the equivalent Java-based configuration. configuration. If possible, always try to use the equivalent Java-based configuration.
@ -414,9 +415,9 @@ Searching for `+Enable*+` annotations can be a good starting point.
[[using-boot-importing-configuration]] [[using-boot-importing-configuration]]
=== Importing Additional Configuration Classes === Importing Additional Configuration Classes
You need not put all your `@Configuration` into a single class. The `@Import` You need not put all your `@Configuration` into a single class. The `@Import` annotation
annotation can be used to import additional configuration classes. Alternatively, you can be used to import additional configuration classes. Alternatively, you can use
can use `@ComponentScan` to automatically pick up all Spring components, including `@ComponentScan` to automatically pick up all Spring components, including
`@Configuration` classes. `@Configuration` classes.
@ -424,8 +425,8 @@ can use `@ComponentScan` to automatically pick up all Spring components, includi
[[using-boot-importing-xml-configuration]] [[using-boot-importing-xml-configuration]]
=== Importing XML Configuration === Importing XML Configuration
If you absolutely must use XML based configuration, we recommend that you still start If you absolutely must use XML based configuration, we recommend that you still start
with a `@Configuration` class. You can then use an `@ImportResource` with a `@Configuration` class. You can then use an `@ImportResource` annotation to load
annotation to load XML configuration files. XML configuration files.
@ -447,20 +448,20 @@ recommend that you add it to your primary `@Configuration` class.
[[using-boot-replacing-auto-configuration]] [[using-boot-replacing-auto-configuration]]
=== Gradually Replacing Auto-configuration === Gradually Replacing Auto-configuration
Auto-configuration is noninvasive. At any point, you can start to define your own Auto-configuration is noninvasive. At any point, you can start to define your own
configuration to replace specific parts of the auto-configuration. For example, if configuration to replace specific parts of the auto-configuration. For example, if you add
you add your own `DataSource` bean, the default embedded database support backs away. your own `DataSource` bean, the default embedded database support backs away.
If you need to find out what auto-configuration is currently being applied, and why, If you need to find out what auto-configuration is currently being applied, and why, start
start your application with the `--debug` switch. Doing so enables debug logs for a your application with the `--debug` switch. Doing so enables debug logs for a selection of
selection of core loggers and logs an auto-configuration report to the console. core loggers and logs an auto-configuration report to the console.
[[using-boot-disabling-specific-auto-configuration]] [[using-boot-disabling-specific-auto-configuration]]
=== Disabling Specific Auto-configuration Classes === Disabling Specific Auto-configuration Classes
If you find that specific auto-configuration classes that you do not want are being applied, If you find that specific auto-configuration classes that you do not want are being
you can use the exclude attribute of `@EnableAutoConfiguration` to disable them, as shown applied, you can use the exclude attribute of `@EnableAutoConfiguration` to disable them,
in the following example: as shown in the following example:
[source,java,indent=0] [source,java,indent=0]
---- ----
@ -474,10 +475,10 @@ in the following example:
} }
---- ----
If the class is not on the classpath, you can use the `excludeName` attribute of If the class is not on the classpath, you can use the `excludeName` attribute of the
the annotation and specify the fully qualified name instead. Finally, you can also annotation and specify the fully qualified name instead. Finally, you can also control the
control the list of auto-configuration classes to exclude by using the list of auto-configuration classes to exclude by using the `spring.autoconfigure.exclude`
`spring.autoconfigure.exclude` property. property.
TIP: You can define exclusions both at the annotation level and by using the property. TIP: You can define exclusions both at the annotation level and by using the property.
@ -536,8 +537,8 @@ example:
} }
---- ----
TIP: Notice how using constructor injection lets the `riskAssessor` field be marked TIP: Notice how using constructor injection lets the `riskAssessor` field be marked as
as `final`, indicating that it cannot be subsequently changed. `final`, indicating that it cannot be subsequently changed.
@ -545,8 +546,9 @@ as `final`, indicating that it cannot be subsequently changed.
== Using the @SpringBootApplication Annotation == Using the @SpringBootApplication Annotation
Many Spring Boot developers always have their main class annotated with `@Configuration`, Many Spring Boot developers always have their main class annotated with `@Configuration`,
`@EnableAutoConfiguration`, and `@ComponentScan`. Since these annotations are so frequently `@EnableAutoConfiguration`, and `@ComponentScan`. Since these annotations are so frequently
used together (especially if you follow the <<using-boot-structuring-your-code, best practices>> used together (especially if you follow the <<using-boot-structuring-your-code, best
above), Spring Boot provides a convenient `@SpringBootApplication` alternative. practices>> above), Spring Boot provides a convenient `@SpringBootApplication`
alternative.
The `@SpringBootApplication` annotation is equivalent to using `@Configuration`, The `@SpringBootApplication` annotation is equivalent to using `@Configuration`,
`@EnableAutoConfiguration`, and `@ComponentScan` with their default attributes, as shown `@EnableAutoConfiguration`, and `@ComponentScan` with their default attributes, as shown
@ -589,18 +591,18 @@ application as a war file, you should refer to your server and IDE documentation
[[using-boot-running-from-an-ide]] [[using-boot-running-from-an-ide]]
=== Running from an IDE === Running from an IDE
You can run a Spring Boot application from your IDE as a simple Java application. However, You can run a Spring Boot application from your IDE as a simple Java application. However,
you first need to import your project. Import steps vary depending on your IDE you first need to import your project. Import steps vary depending on your IDE and build
and build system. Most IDEs can import Maven projects directly. For example, Eclipse users system. Most IDEs can import Maven projects directly. For example, Eclipse users can
can select `Import...` -> `Existing Maven Projects` from the `File` menu. select `Import...` -> `Existing Maven Projects` from the `File` menu.
If you cannot directly import your project into your IDE, you may be able to generate IDE If you cannot directly import your project into your IDE, you may be able to generate IDE
metadata by using a build plugin. Maven includes plugins for metadata by using a build plugin. Maven includes plugins for
http://maven.apache.org/plugins/maven-eclipse-plugin/[Eclipse] and http://maven.apache.org/plugins/maven-eclipse-plugin/[Eclipse] and
http://maven.apache.org/plugins/maven-idea-plugin/[IDEA]. Gradle offers plugins http://maven.apache.org/plugins/maven-idea-plugin/[IDEA]. Gradle offers plugins for
for {gradle-user-guide}/userguide.html[various IDEs]. {gradle-user-guide}/userguide.html[various IDEs].
TIP: If you accidentally run a web application twice, you see a "`Port already in TIP: If you accidentally run a web application twice, you see a "`Port already in use`"
use`" error. STS users can use the `Relaunch` button rather than the `Run` button to ensure that error. STS users can use the `Relaunch` button rather than the `Run` button to ensure that
any existing instance is closed. any existing instance is closed.
@ -616,7 +618,8 @@ run your application using `java -jar`, as shown in the following example:
---- ----
It is also possible to run a packaged application with remote debugging support enabled. It is also possible to run a packaged application with remote debugging support enabled.
Doing so lets you attach a debugger to your packaged application, as shown in the following example: Doing so lets you attach a debugger to your packaged application, as shown in the
following example:
[indent=0,subs="attributes"] [indent=0,subs="attributes"]
---- ----
@ -636,7 +639,8 @@ and run your application. Applications run in an exploded form, as they do in yo
$ mvn spring-boot:run $ mvn spring-boot:run
---- ----
You might also want to use the `MAVEN_OPTS` operating system environment variable, as shown in the following example: You might also want to use the `MAVEN_OPTS` operating system environment variable, as
shown in the following example:
[indent=0,subs="attributes"] [indent=0,subs="attributes"]
---- ----
@ -647,8 +651,8 @@ You might also want to use the `MAVEN_OPTS` operating system environment variabl
[[using-boot-running-with-the-gradle-plugin]] [[using-boot-running-with-the-gradle-plugin]]
=== Using the Gradle Plugin === Using the Gradle Plugin
The Spring Boot Gradle plugin also includes a `bootRun` task that can be used to run The Spring Boot Gradle plugin also includes a `bootRun` task that can be used to run your
your application in an exploded form. The `bootRun` task is added whenever you apply the application in an exploded form. The `bootRun` task is added whenever you apply
the `org.springframework.boot` and `java` plugins and is shown in the following example: the `org.springframework.boot` and `java` plugins and is shown in the following example:
[indent=0,subs="attributes"] [indent=0,subs="attributes"]
@ -656,7 +660,8 @@ the `org.springframework.boot` and `java` plugins and is shown in the following
$ gradle bootRun $ gradle bootRun
---- ----
You might also want to use the `JAVA_OPTS` operating system environment variable, as shown in the following example: You might also want to use the `JAVA_OPTS` operating system environment variable, as shown
in the following example:
[indent=0,subs="attributes"] [indent=0,subs="attributes"]
---- ----
@ -684,7 +689,8 @@ See the <<using-boot-devtools>> section below and the
Spring Boot includes an additional set of tools that can make the application Spring Boot includes an additional set of tools that can make the application
development experience a little more pleasant. The `spring-boot-devtools` module can be development experience a little more pleasant. The `spring-boot-devtools` module can be
included in any project to provide additional development-time features. To include included in any project to provide additional development-time features. To include
devtools support, add the module dependency to your build, as shown in the following listings for Maven and Gradle: devtools support, add the module dependency to your build, as shown in the following
listings for Maven and Gradle:
.Maven .Maven
[source,xml,indent=0,subs="verbatim,quotes,attributes"] [source,xml,indent=0,subs="verbatim,quotes,attributes"]
@ -724,9 +730,9 @@ Maven and Gradle plugins.
[[using-boot-devtools-property-defaults]] [[using-boot-devtools-property-defaults]]
=== Property Defaults === Property Defaults
Several of the libraries supported by Spring Boot use caches to improve performance. For Several of the libraries supported by Spring Boot use caches to improve performance. For
example, <<spring-boot-features#boot-features-spring-mvc-template-engines,template engines>> example, <<spring-boot-features#boot-features-spring-mvc-template-engines,template
cache compiled templates to avoid repeatedly parsing template files. engines>> cache compiled templates to avoid repeatedly parsing template files. Also,
Also, Spring MVC can add HTTP caching headers to responses when serving static resources. Spring MVC can add HTTP caching headers to responses when serving static resources.
While caching is very beneficial in production, it can be counter-productive during While caching is very beneficial in production, it can be counter-productive during
development, preventing you from seeing the changes you just made in your application. development, preventing you from seeing the changes you just made in your application.
@ -734,8 +740,8 @@ For this reason, spring-boot-devtools disables the caching options by default.
Cache options are usually configured by settings in your `application.properties` file. Cache options are usually configured by settings in your `application.properties` file.
For example, Thymeleaf offers the `spring.thymeleaf.cache` property. Rather than needing For example, Thymeleaf offers the `spring.thymeleaf.cache` property. Rather than needing
to set these properties manually, the `spring-boot-devtools` module automatically to set these properties manually, the `spring-boot-devtools` module automatically applies
applies sensible development-time configuration. sensible development-time configuration.
TIP: For a complete list of the properties that are applied by the devtools, see TIP: For a complete list of the properties that are applied by the devtools, see
{sc-spring-boot-devtools}/env/DevToolsPropertyDefaultsPostProcessor.{sc-ext}[DevToolsPropertyDefaultsPostProcessor]. {sc-spring-boot-devtools}/env/DevToolsPropertyDefaultsPostProcessor.{sc-ext}[DevToolsPropertyDefaultsPostProcessor].
@ -744,35 +750,35 @@ TIP: For a complete list of the properties that are applied by the devtools, see
[[using-boot-devtools-restart]] [[using-boot-devtools-restart]]
=== Automatic Restart === Automatic Restart
Applications that use `spring-boot-devtools` automatically restart whenever files Applications that use `spring-boot-devtools` automatically restart whenever files on the
on the classpath change. This can be a useful feature when working in an IDE, as it gives classpath change. This can be a useful feature when working in an IDE, as it gives a very
a very fast feedback loop for code changes. By default, any entry on the classpath that fast feedback loop for code changes. By default, any entry on the classpath that points to
points to a folder is monitored for changes. Note that certain resources, such as a folder is monitored for changes. Note that certain resources, such as static assets and
static assets and view templates, <<using-boot-devtools-restart-exclude, do not need to view templates, <<using-boot-devtools-restart-exclude, do not need to restart the
restart the application>>. application>>.
.Triggering a restart .Triggering a restart
**** ****
As DevTools monitors classpath resources, the only way to trigger a restart is to update As DevTools monitors classpath resources, the only way to trigger a restart is to update
the classpath. The way in which you cause the classpath to be updated depends on the IDE the classpath. The way in which you cause the classpath to be updated depends on the IDE
that you are using. In Eclipse, saving a modified file causes the classpath to be that you are using. In Eclipse, saving a modified file causes the classpath to be updated
updated and triggers a restart. In IntelliJ IDEA, building the project (`Build +->+ Make and triggers a restart. In IntelliJ IDEA, building the project (`Build +->+ Make Project`)
Project`) will have the same effect. will have the same effect.
**** ****
[NOTE] [NOTE]
==== ====
As long as forking is enabled, you can also start your application by using the supported As long as forking is enabled, you can also start your application by using the supported
build plugins (Maven and Gradle), since DevTools needs an isolated application build plugins (Maven and Gradle), since DevTools needs an isolated application classloader
classloader to operate properly. By default, Gradle and Maven do that when they detect to operate properly. By default, Gradle and Maven do that when they detect DevTools on the
DevTools on the classpath. classpath.
==== ====
TIP: Automatic restart works very well when used with LiveReload. TIP: Automatic restart works very well when used with LiveReload.
<<using-boot-devtools-livereload,See the LiveReload section>> for details. If you use JRebel, automatic <<using-boot-devtools-livereload,See the LiveReload section>> for details. If you use
restarts are disabled in favor of dynamic class reloading. Other devtools features JRebel, automatic restarts are disabled in favor of dynamic class reloading. Other
(such as LiveReload and property overrides) can still be used. devtools features (such as LiveReload and property overrides) can still be used.
NOTE: DevTools relies on the application context's shutdown hook to close it during a NOTE: DevTools relies on the application context's shutdown hook to close it during a
restart. It does not work correctly if you have disabled the shutdown hook restart. It does not work correctly if you have disabled the shutdown hook
@ -789,9 +795,9 @@ the `getResource` method on the `ApplicationContext` is not supported.
[[using-spring-boot-restart-vs-reload]] [[using-spring-boot-restart-vs-reload]]
.Restart vs Reload .Restart vs Reload
**** ****
The restart technology provided by Spring Boot works by using two classloaders. The restart technology provided by Spring Boot works by using two classloaders. Classes
Classes that do not change (for example, those from third-party jars) are loaded into a that do not change (for example, those from third-party jars) are loaded into a _base_
_base_ classloader. Classes that you are actively developing are loaded into a _restart_ classloader. Classes that you are actively developing are loaded into a _restart_
classloader. When the application is restarted, the _restart_ classloader is thrown away classloader. When the application is restarted, the _restart_ classloader is thrown away
and a new one is created. This approach means that application restarts are typically much and a new one is created. This approach means that application restarts are typically much
faster than "`cold starts`", since the _base_ classloader is already available and faster than "`cold starts`", since the _base_ classloader is already available and
@ -844,8 +850,9 @@ If you do not want to use the restart feature, you can disable it by using the
watch for file changes). watch for file changes).
If you need to _completely_ disable restart support (for example, because it doesn't work If you need to _completely_ disable restart support (for example, because it doesn't work
with a specific library), you need to set the `spring.devtools.restart.enabled` `System` property to `false` before calling with a specific library), you need to set the `spring.devtools.restart.enabled` `System`
`SpringApplication.run(...)`, as shown in the following example: property to `false` before calling `SpringApplication.run(...)`, as shown in the following
example:
[source,java,indent=0] [source,java,indent=0]
---- ----
@ -866,7 +873,8 @@ Changing the file only triggers the check and the restart will only occur if Dev
detected it has to do something. The trigger file can be updated manually or via an IDE detected it has to do something. The trigger file can be updated manually or via an IDE
plugin. plugin.
To use a trigger file, set the `spring.devtools.restart.trigger-file` property to the path of your trigger file. To use a trigger file, set the `spring.devtools.restart.trigger-file` property to the path
of your trigger file.
TIP: You might want to set `spring.devtools.restart.trigger-file` as a TIP: You might want to set `spring.devtools.restart.trigger-file` as a
<<using-boot-devtools-globalsettings,global setting>>, so that all your projects behave <<using-boot-devtools-globalsettings,global setting>>, so that all your projects behave
@ -880,13 +888,13 @@ As described in the <<using-spring-boot-restart-vs-reload>> section above, resta
functionality is implemented by using two classloaders. For most applications, this functionality is implemented by using two classloaders. For most applications, this
approach works well. However, sometimes it can cause classloading issues. approach works well. However, sometimes it can cause classloading issues.
By default, any open project in your IDE is loaded with the "`restart`" classloader, By default, any open project in your IDE is loaded with the "`restart`" classloader, and
and any regular `.jar` file is loaded with the "`base`" classloader. If you work on any regular `.jar` file is loaded with the "`base`" classloader. If you work on a
a multi-module project, and not every module is imported into your IDE, you may need to multi-module project, and not every module is imported into your IDE, you may need to
customize things. To do so, you can create a `META-INF/spring-devtools.properties` file. customize things. To do so, you can create a `META-INF/spring-devtools.properties` file.
The `spring-devtools.properties` file can contain properties prefixed with `restart.exclude` and The `spring-devtools.properties` file can contain properties prefixed with
`restart.include`. The `include` elements are items that should be `restart.exclude` and `restart.include`. The `include` elements are items that should be
pulled up into the "`restart`" classloader, and the `exclude` elements are items that pulled up into the "`restart`" classloader, and the `exclude` elements are items that
should be pushed down into the "`base`" classloader. The value of the property is a regex should be pushed down into the "`base`" classloader. The value of the property is a regex
pattern that is applied to the classpath, as shown in the following example: pattern that is applied to the classpath, as shown in the following example:
@ -908,8 +916,8 @@ package files inside your project, or in the libraries that the project consumes
[[using-boot-devtools-known-restart-limitations]] [[using-boot-devtools-known-restart-limitations]]
==== Known Limitations ==== Known Limitations
Restart functionality does not work well with objects that are deserialized by using a Restart functionality does not work well with objects that are deserialized by using a
standard `ObjectInputStream`. If you need to deserialize data, you may need to use Spring's standard `ObjectInputStream`. If you need to deserialize data, you may need to use
`ConfigurableObjectInputStream` in combination with Spring's `ConfigurableObjectInputStream` in combination with
`Thread.currentThread().getContextClassLoader()`. `Thread.currentThread().getContextClassLoader()`.
Unfortunately, several third-party libraries deserialize without considering the context Unfortunately, several third-party libraries deserialize without considering the context
@ -938,10 +946,10 @@ from your IDE, only the first has LiveReload support.
=== Global Settings === Global Settings
You can configure global devtools settings by adding a file named You can configure global devtools settings by adding a file named
`.spring-boot-devtools.properties` to your `$HOME` folder (note that the filename starts `.spring-boot-devtools.properties` to your `$HOME` folder (note that the filename starts
with "`.`"). Any properties added to this file apply to _all_ Spring Boot with "`.`"). Any properties added to this file apply to _all_ Spring Boot applications on
applications on your machine that use devtools. For example, to configure restart to your machine that use devtools. For example, to configure restart to always use a
always use a <<using-boot-devtools-restart-triggerfile, trigger file>>, you would add <<using-boot-devtools-restart-triggerfile, trigger file>>, you would add the following
the following property: property:
.~/.spring-boot-devtools.properties .~/.spring-boot-devtools.properties
[source,properties,indent=0] [source,properties,indent=0]
@ -955,7 +963,8 @@ the following property:
=== Remote Applications === Remote Applications
The Spring Boot developer tools are not just limited to local development. You can also The Spring Boot developer tools are not just limited to local development. You can also
use several features when running applications remotely. Remote support is opt-in. To use several features when running applications remotely. Remote support is opt-in. To
enable it, you need to make sure that `devtools` is included in the repackaged archive, as shown in the following listing: enable it, you need to make sure that `devtools` is included in the repackaged archive, as
shown in the following listing:
[source,xml,indent=0,subs="verbatim,quotes,attributes"] [source,xml,indent=0,subs="verbatim,quotes,attributes"]
---- ----
@ -972,7 +981,8 @@ enable it, you need to make sure that `devtools` is included in the repackaged a
</build> </build>
---- ----
Then you need to set a `spring.devtools.remote.secret` property, as shown in the following example: Then you need to set a `spring.devtools.remote.secret` property, as shown in the following
example:
[source,properties,indent=0] [source,properties,indent=0]
---- ----
@ -982,18 +992,18 @@ Then you need to set a `spring.devtools.remote.secret` property, as shown in the
WARNING: Enabling `spring-boot-devtools` on a remote application is a security risk. You WARNING: Enabling `spring-boot-devtools` on a remote application is a security risk. You
should never enable support on a production deployment. should never enable support on a production deployment.
Remote devtools support is provided in two parts: a server-side endpoint that Remote devtools support is provided in two parts: a server-side endpoint that accepts
accepts connections and a client application that you run in your IDE. The server connections and a client application that you run in your IDE. The server component is
component is automatically enabled when the `spring.devtools.remote.secret` property automatically enabled when the `spring.devtools.remote.secret` property is set. The client
is set. The client component must be launched manually. component must be launched manually.
==== Running the Remote Client Application ==== Running the Remote Client Application
The remote client application is designed to be run from within your IDE. You need to run The remote client application is designed to be run from within your IDE. You need to run
`org.springframework.boot.devtools.RemoteSpringApplication` with the same classpath as `org.springframework.boot.devtools.RemoteSpringApplication` with the same classpath as
the remote project that you connect to. the remote project that you connect to. The application's single required argument is the
The application's single required argument is the remote URL to which it connects. remote URL to which it connects.
For example, if you are using Eclipse or STS and you have a project named `my-app` that For example, if you are using Eclipse or STS and you have a project named `my-app` that
you have deployed to Cloud Foundry, you would do the following: you have deployed to Cloud Foundry, you would do the following:
@ -1028,8 +1038,8 @@ NOTE: Because the remote client is using the same classpath as the real applicat
can directly read application properties. This is how the `spring.devtools.remote.secret` can directly read application properties. This is how the `spring.devtools.remote.secret`
property is read and passed to the server for authentication. property is read and passed to the server for authentication.
TIP: It is always advisable to use `https://` as the connection protocol, so that traffic is TIP: It is always advisable to use `https://` as the connection protocol, so that traffic
encrypted and passwords cannot be intercepted. is encrypted and passwords cannot be intercepted.
TIP: If you need to use a proxy to access the remote application, configure the TIP: If you need to use a proxy to access the remote application, configure the
`spring.devtools.remote.proxy.host` and `spring.devtools.remote.proxy.port` properties. `spring.devtools.remote.proxy.host` and `spring.devtools.remote.proxy.port` properties.
@ -1038,12 +1048,11 @@ TIP: If you need to use a proxy to access the remote application, configure the
[[using-boot-devtools-remote-update]] [[using-boot-devtools-remote-update]]
==== Remote Update ==== Remote Update
The remote client monitors your application classpath for changes in the same way as The remote client monitors your application classpath for changes in the same way as the
the <<using-boot-devtools-restart,local restart>>. Any updated resource is pushed <<using-boot-devtools-restart,local restart>>. Any updated resource is pushed to the
to the remote application and (_if required_) triggers a restart. This can be helpful remote application and (_if required_) triggers a restart. This can be helpful if you
if you iterate on a feature that uses a cloud service that you do not have locally. iterate on a feature that uses a cloud service that you do not have locally. Generally,
Generally, remote updates and restarts are much quicker than a full rebuild and deploy remote updates and restarts are much quicker than a full rebuild and deploy cycle.
cycle.
NOTE: Files are only monitored when the remote client is running. If you change a file NOTE: Files are only monitored when the remote client is running. If you change a file
before starting the remote client, it is not pushed to the remote server. before starting the remote client, it is not pushed to the remote server.
@ -1063,9 +1072,8 @@ _<<production-ready-features.adoc#production-ready>>_ for details.
[[using-boot-whats-next]] [[using-boot-whats-next]]
== What to Read Next == What to Read Next
You should now understand how you can use Spring Boot and some best You should now understand how you can use Spring Boot and some best practices that you
practices that you should follow. You can now go on to learn about specific should follow. You can now go on to learn about specific
_<<spring-boot-features#boot-features, Spring Boot features>>_ in depth, or you _<<spring-boot-features#boot-features, Spring Boot features>>_ in depth, or you could skip
could skip ahead and read about the ahead and read about the "`<<production-ready-features#production-ready, production
"`<<production-ready-features#production-ready, production ready>>`" aspects of Spring ready>>`" aspects of Spring Boot.
Boot.