The Window Matching Agent is a simple java agent that uses bytecode manipulation to change the value sun.awt.X11.XToolkit assigns to the WM_CLASS property
Make sure you have have maven installed then from the commandline run :
mvn package
the generated agent.jar file will end up in the target folder
You can download a v1.0 here
To use it add the following argument to your commandline
-javaagent:agent.jar=YOUR_APPLICATION_IDENTIFIER
and assure that asm v3.3.1 is in the classpath