I am not familiar with Ruby, nor java, but this looks like an excellent tool.
I tried to build and use this tool by installing JRuby, and installing the jem as specified. When I tried to run the javac line, I received the errors at : http://pastebin.com/FB8RyLwV
A better requirements and 'how to' would be nice for new users (like me) if someone had the time to make one.
Thank you.