The Ruby community has produced a lovely library called Tilt. It's basically an abstraction over template engines, so that rather than supporting individual templating engines, a web framework only has to support Tilt, and by doing so supports everything Tilt supports.
Does Java offer anything similar? Possibly as a Servlet component, possibly not -- not sure if it's relevant yet.
I'm prototyping my own web framework, and rather than implementing adapters for a smattering of template engines (rewriting that particular wheel, again), it'd be great to implement just one abstraction.