I did a side project in Play! some time ago. While it was generally OK to use, Java in Play is definitely a second class citizen compared to Scala. Most documentation (which btw is sorely lacking) concerns how to do stuff with Scala and you'll have to figure out how to do the same in Java yourself.

Even worse, breaking backwards compatibility between even minor releases seems to be standard for this framework. So once you've finally managed to find some piece of documentation from some random source on the net (as again, the official documentation is pretty much a joke) you'll find that it doesn't work at all because it was written with Play! 2.0 in mind which is different from 2.1 which is different from 2.2 and so on.

Once you figure it out, it's a pretty nice framework. It's a shame so little attention seems to be paid to exposing that in a better fashion.