[[build-tool-plugins]]
= Build tool plugins

[partintro]
--
Spring Boot provides build tool plugins for Maven and Gradle. The plugins offer a
variety of features, including the packaging of executable jars. This section provides
more details on both plugins, as well as some help should you need to extend an
unsupported build system. If you are just getting started, you might want to read
``<<using-spring-boot.adoc#using-boot-build-systems>>'' from the
<<using-spring-boot.adoc#using-boot>> section first.
--



[[build-tool-plugins-maven-plugin]]
== Spring Boot Maven plugin
The {spring-boot-maven-plugin-site}/[Spring Boot Maven Plugin] provides Spring Boot
support in Maven, allowing you to package executable jar or war archives and run an
application ``in-place''. To use it you must be using Maven 3 (or better).

NOTE: Refer to the {spring-boot-maven-plugin-site}/[Spring Boot Maven Plugin Site]
for complete plugin documentation.



[[build-tool-plugins-include-maven-plugin]]
=== Including the plugin
To use the Spring Boot Maven Plugin simply include the appropriate XML in the `plugins`
section of your `pom.xml`

[source,xml,indent=0,subs="verbatim,attributes"]
----
	<?xml version="1.0" encoding="UTF-8"?>
	<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
		<modelVersion>4.0.0</modelVersion>
		<!-- ... -->
		<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>
	</project>
----

This configuration will repackage a jar or war that is built during the `package` phase of
the Maven lifecycle. The following example shows both the repackaged jar, as well as the
original jar, in the `target` directory:

[indent=0]
----
	$ mvn package
	$ ls target/*.jar
	target/myproject-1.0.0.jar target/myproject-1.0.0.jar.original
----


If you don't include the `<execution/>` configuration as above, you can run the plugin on
its own (but only if the package goal is used as well). For example:

[indent=0]
----
	$ mvn package spring-boot:repackage
	$ ls target/*.jar
	target/myproject-1.0.0.jar target/myproject-1.0.0.jar.original
----

If you are using a milestone or snapshot release you will also need to add appropriate
`pluginRepository` elements:

[source,xml,indent=0,subs="verbatim,attributes"]
----
	<pluginRepositories>
		<pluginRepository>
			<id>spring-snapshots</id>
			<url>http://repo.spring.io/snapshot</url>
		</pluginRepository>
		<pluginRepository>
			<id>spring-milestones</id>
			<url>http://repo.spring.io/milestone</url>
		</pluginRepository>
	</pluginRepositories>
----



[[build-tool-plugins-maven-packaging]]
=== Packaging executable jar and war files
Once `spring-boot-maven-plugin` has been included in your `pom.xml` it will automatically
attempt to rewrite archives to make them executable using the `spring-boot:repackage`
goal. You should configure your project to build a jar or war (as appropriate) using the
usual `packaging` element:

[source,xml,indent=0,subs="verbatim,attributes"]
----
	<?xml version="1.0" encoding="UTF-8"?>
	<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
		<!-- ... -->
		<packaging>jar</packaging>
		<!-- ... -->
	</project>
----

Your existing archive will be enhanced by Spring Boot during the `package` phase. The
main class that you want to launch can either be specified using a configuration option,
or by adding a `Main-Class` attribute to the manifest in the usual way. If you don't
specify a main class the plugin will search for a class with a
`public static void main(String[] args)` method.

To build and run a project artifact, you can type the following:

[indent=0]
----
	$ mvn package
	$ java -jar target/mymodule-0.0.1-SNAPSHOT.jar
----

To build a war file that is both executable and deployable into an external container you
need to mark the embedded container dependencies as ``provided'', e.g:

[source,xml,indent=0,subs="verbatim,attributes"]
----
	<?xml version="1.0" encoding="UTF-8"?>
	<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
		<!-- ... -->
		<packaging>war</packaging>
		<!-- ... -->
		<dependencies>
			<dependency>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-starter-web</artifactId>
			</dependency>
			<dependency>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-starter-tomcat</artifactId>
				<scope>provided</scope>
			</dependency>
			<!-- ... -->
		</dependencies>
	</project>
----

Advanced configuration options and examples are available in the
{spring-boot-maven-plugin-site}/[plugin info page].



[[build-tool-plugins-gradle-plugin]]
== Spring Boot Gradle plugin
The Spring Boot Gradle Plugin provides Spring Boot support in Gradle, allowing you to
package executable jar or war archives, run Spring Boot applications and omit version
information from your `build.gradle` file for ``blessed'' dependencies.



[[build-tool-plugins-including-the-gradle-plugin]]
=== Including the plugin
To use the Spring Boot Gradle Plugin simply include a `buildscript` dependency and apply
the `spring-boot` plugin:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	buildscript {
		dependencies {
			classpath("org.springframework.boot:spring-boot-gradle-plugin:{spring-boot-version}")
		}
	}
	apply plugin: 'spring-boot'
----

If you are using a milestone or snapshot release you will also need to add appropriate
`repositories` reference:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	buildscript {
		repositories {
			maven.url "http://repo.spring.io/snapshot"
			maven.url "http://repo.spring.io/milestone"
		}
		// ...
	}
----



[[build-tool-plugins-gradle-dependencies-without-versions]]
=== Declaring dependencies without versions
The `spring-boot` plugin will register a custom Gradle `ResolutionStrategy` with your
build that allows you to omit version numbers when declaring dependencies to ``blessed''
artifacts. To make use of this functionality, simply declare dependencies in the usual way,
but leave the version number empty:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	dependencies {
		compile("org.springframework.boot:spring-boot-starter-web")
		compile("org.thymeleaf:thymeleaf-spring4")
		compile("nz.net.ultraq.thymeleaf:thymeleaf-layout-dialect")
	}
----

NOTE: The version of the `spring-boot` gradle plugin that you declare determines the
actual versions of the ``blessed'' dependencies (this ensures that builds are always
repeatable). You should always set the version of the `spring-boot` gradle plugin to the
actual Spring Boot version that you wish to use. Details of the versions that are
provided can be found in the <<appendix-dependency-versions, appendix>>.

The `spring-boot` plugin will only supply a version where one is not specified. To
use a version of an artifact that differs from the one that the plugin would provide,
simply specify the version when you declare the dependency as you usually would. For
example:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	dependencies {
		compile("org.thymeleaf:thymeleaf-spring4:2.1.1.RELEASE")
	}
----



[[build-tool-plugins-gradle-custom-version-management]]
==== Custom version management
If is possible to customize the versions used by the `ResolutionStrategy` if you need
to deviate from Spring Boot's ``blessed'' dependencies. Alternative version meta-data
is consulted using the `versionManagement` configuration. For example:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	dependencies {
		versionManagement("com.mycorp:mycorp-versions:1.0.0.RELEASE@properties")
		compile("org.springframework.data:spring-data-hadoop")
	}
----

Version information needs to be published to a repository as a `.properties` file. For
the above example `mycorp-versions.properties` file might contain the following:

[source,properties,indent=0,subs="verbatim,attributes"]
----
	org.springframework.data\:spring-data-hadoop=2.0.0.RELEASE
----

The properties file takes precedence over Spring Boot's defaults, and can be used
to override version numbers if necessary.



[[build-tool-plugins-gradle-exclude-rules]]
=== Default exclude rules
Gradle handles ``exclude rules'' in a slightly different way to Maven which can cause
unexpected results when using the starter POMs. Specifically, exclusions declared on
a dependency will not be applied when the dependency can be reached though a different
path. For example, if a starter POM declares the following:

[source,xml,indent=0,subs="verbatim,attributes"]
----
	<dependencies>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-core</artifactId>
			<version>4.0.5.RELEASE</version>
			<exclusions>
				<exclusion>
					<groupId>commons-logging</groupId>
					<artifactId>commons-logging</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
			<version>4.0.5.RELEASE</version>
		</dependency>
	</dependencies>
----

The `commons-logging` jar will *not* be excluded by Gradle because it is pulled in
transitively via `spring-context` (`spring-context` -> `spring-core` -> `commons-logging`)
which does not have an `exclusion` element.

To ensure that correct exclusions are actually applied, the Spring Boot Gradle plugin will
automatically add exclusion rules. All exclusions defined in the
`spring-boot-dependencies` POM and implicit rules for the ``starter'' POMs will be added.

If you don't want exclusion rules automatically applied you can use the following
configuration:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	springBoot {
		applyExcludeRules=false
	}
----



[[build-tool-plugins-gradle-packaging]]
=== Packaging executable jar and war files
Once the `spring-boot` plugin has been applied to your project it will automatically
attempt to rewrite archives to make them executable using the `bootRepackage` task. You
should configure your project to build a jar or war (as appropriate) in the usual way.

The main class that you want to launch can either be specified using a configuration
option, or by adding a `Main-Class` attribute to the manifest. If you don't specify a
main class the plugin will search for a class with a
`public static void main(String[] args)` method.

To build and run a project artifact, you can type the following:

[indent=0]
----
	$ gradle build
	$ java -jar build/libs/mymodule-0.0.1-SNAPSHOT.jar
----

To build a war file that is both executable and deployable into an external container,
you need to mark the embedded container dependencies as belonging to a configuration
named ``providedRuntime'', e.g:

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

	war {
		baseName = 'myapp'
		version =  '0.5.0'
	}

	repositories {
		mavenCentral()
		maven { url "http://repo.spring.io/libs-snapshot" }
	}

	configurations {
		providedRuntime
	}

	dependencies {
		compile("org.springframework.boot:spring-boot-starter-web")
		providedRuntime("org.springframework.boot:spring-boot-starter-tomcat")
		...
	}
----


[[build-tool-plugins-gradle-running-applications]]
=== Running a project in-place
To run a project in place without building a jar first you can use the ``bootRun'' task:

[indent=0]
----
	$ gradle bootRun
----

Running this way makes your static classpath resources (i.e. in `src/main/resources` by
default) reloadable in the live application, which can be helpful at development time.

[[build-tool-plugins-gradle-global-configuration]]
=== Spring Boot plugin configuration
The gradle plugin automatically extends your build script DSL with a `springBoot` element
for global configuration of the Boot plugin. Set the appropriate properties as you would
with any other Gradle extension (see below for a list of configuration options):

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	springBoot {
		backupSource = false
	}
----



[[build-tool-plugins-gradle-repackage-configuration]]
=== Repackage configuration
The plugin adds a `bootRepackage` task which you can also configure directly, e.g.:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	bootRepackage {
		mainClass = 'demo.Application'
	}
----

The following configuration options are available:

[cols="2,4"]
|===
|Name |Description

|`enabled`
|Boolean flag to switch the repackager off (sometimes useful if you
want the other Boot features but not this one)

|`mainClass`
|The main class that should be run. If not specified the `mainClassName` project property
 will be used or, if the no `mainClassName` id defined the archive will be searched for a
 suitable class. "Suitable" means a unique class with a well-formed `main()` method (if
 more than one is found the build will fail). You should also be able to specify the main
 class name via the "run" task (`main` property) and/or the "startScripts"
 (`mainClassName` property) as an alternative to using the "springBoot" configuration.

|`classifier`
|A file name segment (before the extension) to add to the archive, so that the original is
 preserved in its original location. Defaults to null in which case the archive is
 repackaged in place. The default is convenient for many purposes, but if you want to use
 the original jar as a dependency in another project, it's best to use an extension to
 define the executable archive.

|`withJarTask`
|The name or value of the `Jar` task (defaults to all tasks of type `Jar`) which is used
 to locate the archive to repackage.

|`customConfiguration`
|The name of the custom configuration whuch is used to populate the nested lib directory
 (without specifying this you get all compile and runtime dependencies).
|===



[[build-tool-plugins-gradle-repackage-custom-configuration]]
=== Repackage with custom Gradle configuration
Sometimes it may be more appropriate to not package default dependencies resolved from
`compile`, `runtime` and `provided` scopes. If the created executable jar file
is intended to be run as it is, you need to have all dependencies nested inside it;
however, if the plan is to explode a jar file and run the main class manually, you may already
have some of the libraries available via `CLASSPATH`. This is a situation where
you can repackage your jar with a different set of dependencies.

Using a custom
configuration will automatically disable dependency resolving from
`compile`, `runtime` and `provided` scopes. Custom configuration can be either
defined globally (inside the `springBoot` section) or per task.

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	task clientJar(type: Jar) {
		appendix = 'client'
		from sourceSets.main.output
		exclude('**/*Something*')
	}

	task clientBoot(type: BootRepackage, dependsOn: clientJar) {
		withJarTask = clientJar
		customConfiguration = "mycustomconfiguration"
	}
----

In above example, we created a new `clientJar` Jar task to package a customized
file set from your compiled sources. Then we created a new `clientBoot`
BootRepackage task and instructed it to work with only `clientJar` task and
`mycustomconfiguration`.

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	configurations {
		mycustomconfiguration.exclude group: 'log4j'
	}

	dependencies {
		mycustomconfiguration configurations.runtime
	}
----

The configuration that we are referring to in `BootRepackage` is a normal
http://www.gradle.org/docs/current/dsl/org.gradle.api.artifacts.Configuration.html[Gradle
configuration]. In the above example we created a new configuration named
`mycustomconfiguration` instructing it to derive from a `runtime` and exclude the `log4j`
group. If the `clientBoot` task is executed, the repackaged boot jar will have all
dependencies from `runtime` but no `log4j` jars.



[[build-tool-plugins-gradle-configuration-options]]
==== Configuration options
The following configuration options are available:

[cols="2,4"]
|===
|Name |Description

|`mainClass`
|The main class that should be run by the executable archive.

|`providedConfiguration`
|The name of the provided configuration (defaults to `providedRuntime`).

|`backupSource`
|If the original source archive should be backed-up before being repackaged (defaults
 to `true`).

|`customConfiguration`
|The name of the custom configuration.

|`layout`
|The type of archive, corresponding to how the dependencies are laid out inside
 (defaults to a guess based on the archive type).

|`requiresUnpack`
|A list of dependencies (in the form ``groupId:artifactId'' that must be unpacked from
 fat jars in order to run. Items are still packaged into the fat jar, but they will be
 automatically unpacked when it runs.
|===



[[build-tool-plugins-understanding-the-gradle-plugin]]
=== Understanding how the Gradle plugin works
When `spring-boot` is applied to your Gradle project a default task named `bootRepackage`
is created automatically. The `bootRepackage` task depends on Gradle `assemble` task, and
when executed, it tries to find all jar artifacts whose qualifier is empty (i.e. tests and
sources jars are automatically skipped).

Due to the fact that `bootRepackage` finds 'all' created jar artifacts, the order of
Gradle task execution is important. Most projects only create a single jar file, so
usually this is not an issue; however, if you are planning to create a more complex
project setup, with custom `Jar` and `BootRepackage` tasks, there are few tweaks to
consider.

If you are 'just' creating custom jar files from your project you can simply disable
default `jar` and `bootRepackage` tasks:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	jar.enabled = false
	bootRepackage.enabled = false
----

Another option is to instruct the default `bootRepackage` task to only work with a
default `jar` task.

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	bootRepackage.withJarTask = jar
----

If you have a default project setup where the main jar file is created and repackaged,
'and' you still want to create additional custom jars, you can combine your custom
repackage tasks together and use `dependsOn` so that the `bootJars` task will run after
the default `bootRepackage` task is executed:

[source,groovy,indent=0,subs="verbatim,attributes"]
----
	task bootJars
	bootJars.dependsOn = [clientBoot1,clientBoot2,clientBoot3]
	build.dependsOn(bootJars)
----

All the above tweaks are usually used to avoid situations where an already created boot
jar is repackaged again. Repackaging an existing boot jar will not break anything, but
you may find that it includes unnecessary dependencies.



[[build-tool-plugins-other-build-systems]]
== Supporting other build systems
If you want to use a build tool other than Maven or Gradle, you will likely need to develop
your own plugin. Executable jars need to follow a specific format and certain entries need
to be written in an uncompressed form (see the
'<<appendix-executable-jar-format.adoc#executable-jar, executable jar format>>' section
in the appendix for details).

The Spring Boot Maven and Gradle plugins both make use of `spring-boot-loader-tools` to
actually generate jars. You are also free to use this library directly yourself if you
need to.



[[build-tool-plugins-repackaging-archives]]
=== Repackaging archives
To repackage an existing archive so that it becomes a self-contained executable archive
use `org.springframework.boot.loader.tools.Repackager`. The `Repackager` class takes a
single constructor argument that refers to an existing jar or war archive. Use one of the
two available `repackage()` methods to either replace the original file or write to a new
destination. Various settings can also be configured on the repackager before it is
run.



[[build-tool-plugins-nested-libraries]]
=== Nested libraries
When repackaging an archive you can include references to dependency files using the
`org.springframework.boot.loader.tools.Libraries` interface. We don't provide any
concrete implementations of `Libraries` here as they are usually build system specific.

If your archive already includes libraries you can use `Libraries.NONE`.



[[build-tool-plugins-find-a-main-class]]
=== Finding a main class
If you don't use `Repackager.setMainClass()` to specify a main class, the repackager will
use http://asm.ow2.org/[ASM] to read class files and attempt to find a suitable class
with a `public static void main(String[] args)` method. An exception is thrown if more
than one candidate is found.



[[build-tool-plugins-repackage-implementation]]
=== Example repackage implementation
Here is a typical example repackage:

[source,java,indent=0]
----
	Repackager repackager = new Repackager(sourceJarFile);
	repackager.setBackupSource(false);
	repackager.repackage(new Libraries() {
				@Override
				public void doWithLibraries(LibraryCallback callback) throws IOException {
					// Build system specific implementation, callback for each dependency
					// callback.library(new Library(nestedFile, LibraryScope.COMPILE));
				}
			});
----

[[build-tool-plugins-whats-next]]
== What to read next
If you're interested in how the build tool plugins work you can
look at the {github-code}/spring-boot-tools[`spring-boot-tools`] module on GitHub. More
technical details of the <<appendix-executable-jar-format.adoc#executable-jar, executable
jar format>> are covered in the appendix.

If you have specific build-related questions you can check out the
`<<howto.adoc#howto, how-to>>' guides.
