(UPDATED for version 1.3.0. See below.)

Problem

If you have ever tried doing this before with Maven, you have probably used maven-assembly-plugin, which would leave the door open for classpath problems!

It would extract all your dependency jars in one directory together with all your class files and all other classpath resources. The problem is that everything ended up in a big mix, with classpath resources possibly overwriting each other. For example, if two dependencies each had a log4j.properties file in their jar, one log4j.properties would overwrite the other.

No more of that mess!

Solution

Enter maven-onejar-plugin. It lets all your dependency jars stay jars, and your code is in its own jar. All of those jars are put in a bigger jar, which is made executable.

Configuration

It may sound weird, but it's quite elegant! Just put this in your pom.xml's <plugins> tag to make it work:

<plugin>
  <groupId>org.dstovall</groupId>
  <artifactId>onejar-maven-plugin</artifactId>
  <version>1.3.0</version>
  <executions>
    <execution>
      <configuration>
        <mainClass>your.package.YourMainClass</mainClass>
      </configuration>
      <goals>
        <goal>one-jar</goal>
      </goals>
    </execution>
  </executions>
</plugin>

You also need to add this to the pom:

<pluginRepositories>
  <pluginRepository>
    <id>onejar-maven-plugin.googlecode.com</id>
    <url>http://onejar-maven-plugin.googlecode.com/svn/mavenrepo</url>
  </pluginRepository>
</pluginRepositories>

Please note the new Maven repository URL. Me and onejar-maven-plugin founder Drew Stovall just recently moved the project to Google Code to make it more open and easier for others (like me!) to pitch in. Yesterday, I released version 1.2.3 of onejar-maven-plugin to our new Maven repo at Google Code. UPDATE: Just released version 1.3.0 with optional support for including and autoloading native libraries such as .dll files. (detailed usage instructions.)

Make sure you get the <pluginRepository> URL right so that the latest version will be available to you!

Use

Then do this to build everything:

mvn install

That will build both your normal jar, as well as another jar. You will get these:

Standalone one-jar.jar file, along with the original .jar file.

myApp.one-jar.jar is the big executable that includes both myApp.jar, and all dependency jars.

You can run it standalone without any extra files, like this:

java -jar target/myApp.one-jar.jar

If you found this interesting, you might find my post about winstone-maven-plugin enlightning as well. It shows you how to make an executable .war file.

Credits

Thank you Drew Stovall for creating this Maven plugin in the first place, and thank you to the other contributors who have also submitted patches.

Project homepage: http://onejar-maven-plugin.googlecode.com

If your project is configured with a Maven pom.xml and the module has <packaging>war</packaging>, you can just add this little piece of XML inside the pom's <plugins> tag:

<plugin>
    <groupId>net.sf.alchim</groupId>
    <artifactId>winstone-maven-plugin</artifactId>
    <executions>
        <execution>
            <goals>
                <goal>embed</goal>
            </goals>
            <phase>package</phase>
        </execution>
    </executions>
</plugin>

Then, when you run...

mvn install

...winstone-maven-plugin will automatically create a *-standalone.jar file for you, which contains your web application.

Standalone .jar file, along with the .war file.

You can run that .jar file as a standalone application, which runs your included web application on port 8080 by default:

java -jar target/*-standalone.jar

No web server installation necessary! No external files required! (You don't even need the .war file anymore.)

The resulting .jar file is actually the servlet container Winstone, with your .war file deployed inside it.

There are more configuration options on winstone-maven-plugin's usage page.

I want to disable some default features of Winstone for security reasons, because they are not needed: ajp13 listener on a separate port, servlet invoker and directory listings. This is the complete plugin configuration I usually use myself:

<plugin>
    <groupId>net.sf.alchim</groupId>
    <artifactId>winstone-maven-plugin</artifactId>
    <version>1.2</version>
    <configuration>
        <cmdLineOptions>
            <property>
                <name>httpPort</name>
                <value>8080</value>
            </property>
            <property>
                <name>ajp13Port</name>
                <value>-1</value>
            </property>
            <property>
                <name>controlPort</name>
                <value>-1</value>
            </property>
            <property>
                <name>directoryListings</name>
                <value>false</value>
            </property>
            <property>
                <name>useInvoker</name>
                <value>false</value>
            </property>
        </cmdLineOptions>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>embed</goal>
            </goals>
            <phase>package</phase>
        </execution>
    </executions>
</plugin>

You can temporarily override these configuration parameters if you like, using command-line options when executing the standalone .jar file. Find them with --help when you run the .jar.