you can just rip the XML parsing part from the slick source and use it on the server.
The reason it doesnt work out of the box is because slick of course wants an opengl context, but your server has no graphic output like this normally
so you wanna do data structure stuff but no graphics
^ Try this. Because Slick2d's TiledMap class even handles the data decompression as well, and will offer you the ability to make sure you keep all the data collected in the same kind of data format. It will just make things easier all around for you.
It'll also give you some insight on how XML parsing works, and if you're like me, you'll find that XML parsing is annoyingly confusing at first.