Thanks for the nice utility!
I hacked up a little command line client and a build script to assemble a runnable jar. It's yours to add to your project if you want it. Download it here:
http://beach.traxel.com/junrar-cli.tar.gz
Works as follows:
$ java -jar dist/unrar.jar
Usage:
java -jar unrar.jar archive.rar [destination_directory]
unrar.jar: the name of this jar...
