AppJar packages Java application in a single executable jar just like Maven Shade Plugin or OneJar Plugin.

Maven Shade Plugin combines severla jars in a single jar combining them.
It's unable to handle properly artifacts that packages more than one jar that contain the same file.
It tries to solve problems with some files like service files combining them, but sometimes this is not enough, for instance, when jars depends on its Manifest information to work.

OneJar Maven Plugin (Maven adaptation for OneJar) packages jars inside other jar without unpacking them.
It uses a classloader to load classes from the inner jars. The way it does that forces to use JarInputStreams and iterate over entries each time it has to read a class, affecting performance.
In the other hand, it uses jar: an file: URL protocols to solve class loading mechanism and it leads to some problems with some software that uses those protocols (I've found some problems with XML default entity resolvers that handles those protocols).

AppJar unpacks all dependencies just like Maven Shade Plugin, but instead of unpacking them into the same folder it unpacks the jars in separate paths inside the jar.

It allows having more than one Manifest inside the main jar.

It register a new protocol to handle the class loading so it doesn't affect software that handle standard protocols directly.

To use AppJar you must configure the plugin in the pom.xml file.

	<plugin>
		<groupId>com.github.emenaceb.appjar</groupId>
		<artifactId>appjar-maven-plugin</artifactId>
		<version>0.9.1</version>
		<executions>
			<execution>
				<id>generate_appjar</id>
				<phase>package</phase>
				<goals>
					<goal>simple</goal>
				</goals>
				<inherited>false</inherited>
			</execution>
		</executions>
	</plugin>

That creates and attach to the Maven build an artifact with app classifier that contains all artifact's dependencies.

It reads from the maven-jar-plugin the Main-Class configuration:

<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-jar-plugin</artifactId>
	<configuration>
		<archive>
			<manifest>
				<mainClass>io.vertx.core.Launcher</mainClass>
				<addDefaultImplementationEntries>true</addDefaultImplementationEntries>
				<addDefaultSpecificationEntries>true</addDefaultSpecificationEntries>
			</manifest>
			<manifestEntries>
				<Main-Verticle>my.project.MainVerticle</Main-Verticle>
			</manifestEntries>
		</archive>
	</configuration>
</plugin>

You also can override this class adding mainClass property to the plugin configuration.

	<plugin>
		<groupId>com.github.emenaceb.appjar</groupId>
		<artifactId>appjar-maven-plugin</artifactId>
		...
		
		<configuration>
			<mainClass>my.project.Main</mainClass>
		</configuration>
		...
	</plugin>

You can change the default app classifier to other:

   <plugin>
   	<groupId>com.github.emenaceb.appjar</groupId>
   	<artifactId>appjar-maven-plugin</artifactId>
   	...
   	
   	<configuration>
   		<alternateClassifier>fat</alternateClassifier>
   	</configuration>
   	...
   </plugin>

In addition to AppJar banner you can add a custom banner to be shown during startup in the starndar output.

   <plugin>
   	<groupId>com.github.emenaceb.appjar</groupId>
   	<artifactId>appjar-maven-plugin</artifactId>
   	...
   	
   	<configuration>
   		<bannerFile>src/main/appjar/banner.txt</bannerFile>
   	</configuration>
   	...
   </plugin>

This banner may contain any Maven Project property like ${project.version}.

If you want to disable the big default AppJar banner, you can do it adding the -Dappjar.noBanner to the command line and the default banner will be replaced with a more discreet message:

 AppJar v 0.9.1  (c) emenaceb 2016
----------------------------------------------------------------------

If you've defined a custom banner the message looks like :

 Powered by AppJar v 0.9.1  (c) emenaceb 2016
----------------------------------------------------------------------

Feel free to disable the default AppJar banner, but keep in mind that every time you do that a little kitty dies.