Maven assembly Plugin

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Internal

Overview

The assembly plugin provide a standard way to aggregate complex artifacts using the project modules artifacts, dependencies, documentation and arbitrary files. The plugin produces a single distributable archive. A module has only one artifact - usually a JAR - but we may want to distribute that JAR together with documentation, source and supporting scripts in the form or an "atomic" archive, usually created for an official release. The assembly plugin does that.

Concepts

Assembly

An assembly is an single artifact produced by aggregating artifacts produced by modules, dependencies, documentation and arbitrary files. The assembly is built according to a specification formalized in the assembly descriptor.

The Name of the Assembly Artifact

By default, the name of the assembly artifact is generated according to the pattern artifactId-version-assemblyId.extension, where:

  • "artifactId" is the value of the <artifactId> element for the project (root or sub-module) that executes the assembly plugin.
  • "version" is the value of the <version> element for the project (root or sub-module) that executes the assembly plugin.
  • "assemblyId" is the value of the <id> element for the assembly descriptor that drives the plugin. The assembly ID is used as a classifier in the artifact name. In some cases, you may not want that; to configure Maven not to include it, see section "Prevent the Use of assemblyId in the Artifact Name" below. For more details on the <id> element, see Custom Maven Assembly Descriptors - the AssemblyID.
  • "extension" is dictated by the <format> element of the assembly descriptor. For more details see Custom Maven Assembly Descriptors.

<finalName>

The base name of the assembly artifact can be overridden using the <finalName> assembly plugin configuration element:

  ...
  <configuration>
      <finalName>someFinalName</finalName>
      ...
  </configuration>
  ...

For the configuration presented above, the value specified as <finalName> is prepended to the assemblyId classifier and the extension, as follows: someFinalName-assemblyId.extension Note that the <finalName> may include system properties, such as ${project.version}, which will be de-referenced.

Experience has shown that is best if we use <finalName> to name the assembly artifact. It offers more flexibility, as particular values for "artifactId" may interfere with the build process. We recommend using a "release" module with a "release" artifactId, and naming the assembly with <finalName>. However, as explained in the "<finalName>" section, the custom finalName is only used to generate the artifact file in the local target directory. The artifact file installed in the artifact repository will still be named "release-..."

Prevent the Use of assemblyId in the Artifact Name

In order to prevent the inclusion of the assemblyId value in the artifact name, use the following configuration element:

  ...
  <configuration>
      <finalName>someFinalName</finalName>
      <appendAssemblyId>false</appendAssemblyId>
      ...
  </configuration>
  ...

For more details about the plugin configuration, see "Plugin Configuration" section, below.

Assembly Descriptor

An assembly descriptor specifies the type of assembly archive to create, the contents of the assembly, and the ways in which dependencies or its modules are bundled with an assembly. It can also contain instructions to set specific permissions, etc. Maven offers a set of predefined assembly descriptors, described below. Custom assembly descriptors can also be created.

Pre-defined Assembly Descriptors

Custom Assembly Descriptors

Custom Maven Assembly Descriptors

Plugin Configuration

<project>
    ...
    <build>
        ...
        <plugins>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.6</version>
                <configuration>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                </configuration>
            </plugin>
        </plugins>
        ...
    </build>
    ...      
</project>

Always update the plugin version to the latest stable version, to get reproducible builds.

Use <descriptorRefs> (one or more) when the pre-defined assembly descriptors are sufficient. For a list of available pre-defined assembly descriptors, see "Pre-defined Assembly Descriptors" section.

In case a custom assembly descriptor is needed, it is declared as follows:

    ...
    <configuration>
        <descriptors>
             <descriptor>src/assembly/release.xml</descriptor>
        </descriptors>
    </configuration>
    ...

For more details on custom assembly descriptors, see the "Assembly Descriptor" section.

Plugin Execution

The plugin has a single goal "single". The assembly plugin can be executed in isolation, or it can be executed during the build process of the project.

To execute the plugin in isolation:

mvn assembly:single

To execute the plugin as part of the build process, the plugin has to be first declared and configured, as described in the "Plugin Configuration" section, and then its "single" goal must be bound to the project lifecycle by associating it usually with the "package" phase, as follows:

<project>
    ...
    <build>
        <plugins>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>...</version>
                <configuration>
                    ...
                </configuration>
                <executions>
                    <execution>
                        <id>assembly-execution</id>
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
       ...
</project>

Once the plug-in is bound to the project lifecycle, simply execute the normal package phase from the default lifecycle to create a project assembly:

mvn package

When this build completes, the assembly file is available in the target directory and has a name similar to the following: artifactId-version-jar-with-dependencies.jar (if "jar-with-dependencies" pre-defined assembly descriptor was used).

In case the assembly doesn't require binaries, so the package phase does not need to be executed, the assembly's goal can be bound to a different project phase. You should be careful to make sure the resources included in your assembly exist before that assembly is created.

The "single" Goal

More details available here: http://maven.apache.org/components/plugins/maven-assembly-plugin/single-mojo.html

Creating Two Assemblies for the Same Project

In order to create two (or more) assemblies for the same project, specify two (or more) <executions> elements.

Other Assembly Use Cases

ZIP Artifact
JAR with Dependencies
Executable JAR
Building a Maven Complex Release Artifact