Java Web Development and Automatic Feedback

I've been having a (ironic) play around with the Play Framework and have been impressed thus far. I was just curious as to what other Java frameworks are out there that have a开发者_开发技巧 similar feature to Play in that you are able to get immediate feedback when making changes to your code base without having to re-build or re-deploy your app?

For the "immediate feedback" (see changes without lengthy rebuild and redeploy) part, I've used JRebel with some decent success. Definitely worth a look.