Suggestions for debugging mafia

I haven't done much Java programming in forever and then some.
I am successfully building and modifying mafia.
Can someone suggest a good free interactive debugger that runs on Windows for use in debugging mafia and possibly any interesting setup instructions.

Well.. The JDK is a must, obviously.

Eclipse is alright for a free IDE I guess, although I don't really use it.

The utilities that come with JDK are good for most of the things I want to do