I think most beginning Rails books cover the Ruby language as well. (You can check out some reviews in
The Bunkhouse.) I think it might be worthwhile to spend a little time just getting to know the language though, before you start looking at the Rails and how to develop web apps. I worked through some of the Project Euler problems using Ruby, just working from online references. It's an interesting language, and if you're coming from a
Java background as I was,
you should definitely try to get comfortable with concepts like closures and lambda functions, duck typing, and bolt-ons. Have fun!