How To make a proxy?

Are there any tutorials on how to make one? I know java and I wanted to start making my own proxy for this game. Any help is appreciated.

What is with all the fuss about jdom? How does that help one make a proxy? jDom afaik is a library for dealing with xml data, which is helpful but not necessary to make a proxy at all...

So we all should download this library, decompile it (when source is available), and somehow turn this into a rotmg proxy?