Well the maps are 600 by 480... so about 290,000 tiles worst case, but in general probably about 100k solid tiles.
All same size, square, not rotation, just need to check collision and if possible solve the collision with objects. There will be moving objects to collide with the tiles, they don't rotate but are various sizes.

The engines all in place, the previous server ran off action script, so we're hoping to gain a lot of performance gain switching to Java.

I'm currently migrating our game server to Java, and  I had a really clean library using Quad trees to keep collisions minimized.
I'm looking for a simple Java solution, the main problem being that the game is based on a tile map, so options like jBox2D, I assume, would get bogged down with so many little objects.
Any suggestions.
I could be wrong about jBox2D if it has some option to simplify the calls on stationary objects, but I havent touched anything box2D related since the AS3 port many years back.