Question

I have a multi-module maven project with an installer sub-project. The installer will be distributed as an executable JAR. It will setup the DB and extract the WAR file to the app server. I would like to use maven to assemble this jar like so:

/META-INF/MANIFEST.MF
/com/example/installer/Installer.class
/com/example/installer/…
/server.war

The manifest will have a main-class entry pointing to the installer class. How might I get maven to build the jar in this fashion?

Answer 1

You can build the jar using the Maven Assembly Plugin.

First, you’ll need to add some information to your pom.xml plugins section to make the resulting jar executable:

<plugin>   <artifactId>maven-assembly-plugin</artifactId>   <configuration>     <archive>       <manifest>         <mainClass>com.example.installer.Installer</mainClass>       </manifest>     </archive>   </configuration> </plugin> 

I recommend using a separate assembly descriptor to build the actual installer jar. Here’s an example:

<assembly>   <id>installer</id>    <formats>     <format>jar</format>   </formats>    <baseDirectory></baseDirectory>    <dependencySets>     <dependencySet>       <outputDirectory>/</outputDirectory>       <includes>         <!-- this references your installer sub-project -->         <include>com.example:installer</include>       </includes>       <!-- must be unpacked inside the installer jar so it can be executed -->       <unpack>true</unpack>       <scope>runtime</scope>     </dependencySet>     <dependencySet>       <outputDirectory>/</outputDirectory>       <includes>         <!-- this references your server.war and any other dependencies -->         <include>com.example:server</include>       </includes>       <unpack>false</unpack>       <scope>runtime</scope>     </dependencySet>   </dependencySets> </assembly> 

If you’ve saved the assembly descriptor as ‘installer.xml’ you can build your jar by running the assembly like this:

mvn clean package assembly:single -Ddescriptor=installer.xml

Hope this helps. Here are some additional links that you might find useful:

• Maven Assembly Plugin – Configuration and Usage
• Creating Executable JARs using the Maven Assembly Plugin
• Creating executable jars with Maven