I love to use Processing.org for all my Ludum Dare games, its somewhat of a Java library or framework that takes most of the hassle out of writing games (you don’t need to worry about setting up the window, or a graphics canvas, etc)

I have one that I’ve written myself, and I’m in the process of upgrading it right now. The current stable version uses LWJGL 2 and all of it for you. It only has open support for 2D things right now, all of the 3D implementations are untested and left almost untouchable, but it runs pretty well and I’ve never had real problems with it, very easy to set up and use.

^ I don’t have a link to it, haven’t uploaded, but if anyone wants to see it I can do that

For both entry LD30 and LD31 we used libgdx together with tiled.

I’ll just leave this little plug here. I find Mercury to be a nice, simple, easy to use Java game lib.