I am currently working on a Java multiplayer game. The game itself (single player) already works perfectly fine and so does the chat. The only thing that is really missing is the multiplayer part. Sadly I am absolutely clueless on where to start with that. I roughly know that I will have to work with packages, and I also know many things about streaming etc (chat is already working). Oh and it should - according to this article - be a UDP server. My problem is that I can't find any resources on how to do this. A tutorial (book or website) would be perfect, alternatively a good example of an open source client/server (in Java of course) would be fine as well. If you feel like doing something helpful I'd also really appreciate someone "privately" teaching me via email or some chat program :)

Thank you!