[[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, letting you package executable jar or war archives and run an
application "`in-place`". To use it, you must use Maven 3.2 (or later).

NOTE: See 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, include the appropriate XML in the `plugins`
section of your `pom.xml`, as shown in the following example:

[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 https://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>
----

The preceding configuration repackages 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 do not include the `<execution/>` configuration, as shown in the prior example, you
can run the plugin on its own (but only if the package goal is used as well), as shown in
the following 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 use a milestone or snapshot release, you also need to add the appropriate
`pluginRepository` elements, as shown in the following listing:

[source,xml,indent=0,subs="verbatim,attributes"]
----
	<pluginRepositories>
		<pluginRepository>
			<id>spring-snapshots</id>
			<url>https://repo.spring.io/snapshot</url>
		</pluginRepository>
		<pluginRepository>
			<id>spring-milestones</id>
			<url>https://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 automatically
tries to rewrite archives to make them executable by using the `spring-boot:repackage`
goal. You should configure your project to build a jar or war (as appropriate) by using
the usual `packaging` element, as shown in the following example:

[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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
		<!-- ... -->
		<packaging>jar</packaging>
		<!-- ... -->
	</project>
----

Your existing archive is enhanced by Spring Boot during the `package` phase. The main
class that you want to launch can be specified either by using a configuration option or
by adding a `Main-Class` attribute to the manifest in the usual way. If you do not specify
a main class, the plugin searches 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`", as shown in the
following example:

[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 https://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>
----

TIP: See the "`<<howto-create-a-deployable-war-file>>`" section for more details on how to
create a deployable war file.

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, letting you package
executable jar or war archives, run Spring Boot applications, and use the dependency
management provided by `spring-boot-dependencies`. It requires Gradle 4.4 or later. Please
refer to the plugin's documentation to learn more:

* Reference ({spring-boot-gradle-plugin}/reference/html[HTML] and
  {spring-boot-gradle-plugin}/reference/pdf/spring-boot-gradle-plugin-reference.pdf[PDF])
* {spring-boot-gradle-plugin}/api[API]



[[build-tool-plugins-antlib]]
== Spring Boot AntLib Module
The Spring Boot AntLib module provides basic Spring Boot support for Apache Ant. You can
use the module to create executable jars. To use the module, you need to declare an
additional `spring-boot` namespace in your `build.xml`, as shown in the following example:

[source,xml,indent=0]
----
	<project xmlns:ivy="antlib:org.apache.ivy.ant"
		xmlns:spring-boot="antlib:org.springframework.boot.ant"
		name="myapp" default="build">
		...
	</project>
----

You need to remember to start Ant using the `-lib` option, as shown in the following
example:

[indent=0,subs="verbatim,quotes,attributes"]
----
	$ ant -lib <folder containing spring-boot-antlib-{spring-boot-version}.jar>
----

TIP: The "`Using Spring Boot`" section includes a more complete example of
<<using-spring-boot.adoc#using-boot-ant, using Apache Ant with `spring-boot-antlib`>>.


=== Spring Boot Ant Tasks
Once the `spring-boot-antlib` namespace has been declared, the following additional tasks
are available:

* <<spring-boot-ant-exejar>>
* <<spring-boot-ant-findmainclass>>

[[spring-boot-ant-exejar]]
==== `spring-boot:exejar`
You can use the `exejar` task to create a Spring Boot executable jar. The following
attributes are supported by the task:

[cols="1,2,2"]
|====
|Attribute |Description |Required

|`destfile`
|The destination jar file to create
|Yes

|`classes`
|The root directory of Java class files
|Yes

|`start-class`
|The main application class to run
|No _(the default is the first class found that declares a `main` method)_
|====

The following nested elements can be used with the task:

[cols="1,4"]
|====
|Element |Description

|`resources`
|One or more {ant-manual}/Types/resources.html#collection[Resource Collections] describing
a set of {ant-manual}/Types/resources.html[Resources] that should be added to the content
of the created +jar+ file.

|`lib`
|One or more {ant-manual}/Types/resources.html#collection[Resource Collections] that
should be added to the set of jar libraries that make up the runtime dependency classpath
of the application.
|====



==== Examples

This section shows two examples of Ant tasks.

.Specify +start-class+
[source,xml,indent=0]
----
	<spring-boot:exejar destfile="target/my-application.jar"
			classes="target/classes" start-class="com.example.MyApplication">
		<resources>
			<fileset dir="src/main/resources" />
		</resources>
		<lib>
			<fileset dir="lib" />
		</lib>
	</spring-boot:exejar>
----

.Detect +start-class+
[source,xml,indent=0]
----
	<exejar destfile="target/my-application.jar" classes="target/classes">
		<lib>
			<fileset dir="lib" />
		</lib>
	</exejar>
----


[[spring-boot-ant-findmainclass]]
=== `spring-boot:findmainclass`
The `findmainclass` task is used internally by `exejar` to locate a class declaring a
`main`. If necessary, you can also use this task directly in your build. The following
attributes are supported:

[cols="1,2,2"]
|====
|Attribute |Description |Required

|`classesroot`
|The root directory of Java class files
|Yes _(unless `mainclass` is specified)_

|`mainclass`
|Can be used to short-circuit the `main` class search
|No

|`property`
|The Ant property that should be set with the result
|No _(result will be logged if unspecified)_
|====



==== Examples

This section contains three examples of using `findmainclass`.

.Find and log
[source,xml,indent=0]
----
	<findmainclass classesroot="target/classes" />
----

.Find and set
[source,xml,indent=0]
----
	<findmainclass classesroot="target/classes" property="main-class" />
----

.Override and set
[source,xml,indent=0]
----
	<findmainclass mainclass="com.example.MainClass" property="main-class" />
----



[[build-tool-plugins-other-build-systems]]
== Supporting Other Build Systems
If you want to use a build tool other than Maven, Gradle, or Ant, you 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. If you need to, you may use this library directly.



[[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 by using the
`org.springframework.boot.loader.tools.Libraries` interface. We do not 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 do not use `Repackager.setMainClass()` to specify a main class, the repackager
uses https://asm.ow2.org/[ASM] to read class files and tries 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
The following example shows a typical repackage implementation:

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

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