This tutorial will show you how to use the maven-jar-plugin to create a manifest file, and package / add it into the final jar file. The manifest file is normally used to define following tasks :

1. Define the entry point of the Application, make the Jar executable.

When you run the command mvn package to package project into a Jar, the following meta-inf/manifest.mf file will be generated and added into the final Jar file automatically.

Manifest-Version: 1.0
Built-By: ${user.name} Build-Jdk:${java.version}
Created-By: Apache Maven
Archiver-Version: Plexus Archiver

## Make the Jar executable

Define maven-jar-plugin in pom.xml, and configure the manifest file via configuration tag.

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<configuration>
<archive>
<manifest>
<mainClass>com.mkyong.core.App</mainClass>
</manifest>
</archive>
</configuration>
</plugin>

Following manifest file will be generated. If you run this Jar, it will execute the com.mkyong.core.App.

anifest-Version: 1.0
Built-By: mkyong
Build-Jdk: 1.6.0_35
Created-By: Apache Maven
Main-Class: com.mkyong.core.App
Archiver-Version: Plexus Archiver

Most Java projects need dependency, and it can define in manifest file easily. Normally, you will use maven-dependency-plugin to copy project dependencies to somewhere else.

  <plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<configuration>
<archive>
<manifest>
<mainClass>com.mkyong.core.App</mainClass>
<classpathPrefix>dependency-jars/</classpathPrefix>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.5.1</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory>
\${project.build.directory}/dependency-jars/
</outputDirectory>
</configuration>
</execution>
</executions>
</plugin>

Following manifest file will be generated. The project dependencies will be copied to {project}/target/dependency-jars/.

manifest-Version: 1.0
Built-By: mkyong
Build-Jdk: 1.6.0_35
Class-Path: dependency-jars/log4j-1.2.17.jar
Created-By: Apache Maven
Main-Class: com.mkyong.core.App
Archiver-Version: Plexus Archiver

When using the above maven-dependency-plugin, Eclipse’s m2e plugin will report an error:

maven-dependency-plugin (goals "copy-dependencies", "unpack") is not supported by m2e.

This is a problem of M2E for Eclipse M2E plugin execution not covered.

To solve this problem, all you got to do is to map the lifecycle it doesn’t recognize and instruct M2E to execute it.

You should add this after your plugins, inside the build.

<pluginManagement>
<plugins>
<plugin>
<groupId>org.eclipse.m2e</groupId>
<artifactId>lifecycle-mapping</artifactId>
<version>1.0.0</version>
<configuration>
<pluginExecutions>
<pluginExecution>
<pluginExecutionFilter>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<versionRange>[2.0,)</versionRange>
<goals>
<goal>copy-dependencies</goal>
</goals>
</pluginExecutionFilter>
<action>
<execute />
</action>
</pluginExecution>
</pluginExecutions>
</pluginManagement>
This will remove the error and make M2E recognize the goal copy-depencies of maven-dependency-plugin and make the POM work as expected, copying dependencies to folder every time Eclipse build it. If you just want to ignore the error, then you change <execute /> for <ignore />. No need for enclosing your maven-dependency-plugin into pluginManagement, as suggested before.