In an article for IBM's developerWorks site, Aaron Rustad, technical architect at Anassina, Inc., takes a look at Ruby on Rails from the perspective of a J2EE developer. He includes a couple of useful diagrams showing the differences between the two styles of hierarchy between the frameworks, useful for Rails and J2EE developers alike who aren't familiar with each other's platforms. Rustad ultimately concludes:
Should you dispense with J2EE altogether in favor of Rails? Absolutely not. J2EE is a well-established standard with several solid implementations and, most importantly, is a proven technology. But I do suggest that you download a copy of Rails and start hacking away. Many of the tutorials that are available are introductory and will get you up and running in no time. Again, I don't guaranteeing that you'll experience joy as a result of working with Rails, but I do bet you'll find contentment.
Rustad doesn't look at the Ruby or Java languages, in particularly, instead choosing to focus on the framework hierarchies instead, making this a useful article for those higher-up the decision-making chain.