When I was doing JSF development, I found the real problem was that libraries were often developed without an awareness of how to make it reload-safe. So yeah, it's theoretically possible to hit Save and Refresh and have Tomcat automatically pick up your changes, but in practice I found that all sorts of strange things happened in the 3rd party libraries that made up the middle of our technology stack.

I think one of the main strengths of the Python/Ruby communities is that it's expected that you'll be able to edit a file and immediately have the changes reflected. If this doesn't happen, people complain! While in the Java world, a lot of people (including myself, eventually) just accept it as business as usual, because so many libraries and apps don't work like that.