If you're really comfortable with Java, and you want to get something out of the door, it may not be the best choice to switch languages (as would be the case for rails). If you already know ruby, then go rails by all means.
Instead, you might consider a of Java-rooted option:
The play framework is pretty slick (http://www.playframework.org). The APIs are fairly light and easy to pick up, and the templating system is rather powerful. The documentation is solid, and it's not like you'll need to spend hours in tutorials to get started Play does both Java and Scala, and works fine with either. I'd actually recommend you stick to Play 1.x, as the 2.x docs and stuff aren't as mature and are much more targeted to Scala developers.
Oh, and heroku loves play. https://devcenter.heroku.com/articles/play