Wicket, I suggest.
With proper mark-up/logic separation, a POJO data model, and a refreshing lack of XML, Wicket makes developing web-apps in Java simple and enjoyable again. Swap the boilerplate, complex debugging and brittle code for powerful, reusable components written with plain Java and HTML.
It's V1.3.0 coming.
I started looking at feasibility of using Grails to provide required functionality.
Benefits of Grails:
Risks and cons:
The team at Sun have done some great work on JRuby.
I know that Alfresco is Java and Groovy + Grails has a Java heritage, but reading through the WSF wiki goals I think JRuby better meets your needs.