I would highly recommend Grails. You can get a scaffolded site up in minutes. Grails 1.0.3 was recently released, and the grails-user mailing lists are very active. This is an up-and-coming web framework, but I've been using it for almost a year now (professionally!) and I wouldn't want to create a java web app any other way.
For a Java developer, groovy may seem to be a natural fit. However, before you head down that path, let me suggest Ruby, and ROR:
- Ruby/ROR has less risk, and is more mature than Groovy/ Grails
- While Groovy/Grails community is encouraging, Ruby/Rails community is vibrant and alive with activity
- Ruby/ROR offers you a different paradigm at web development. Groovy/Grails copies/mimics this, sometimes at a loss of functionality
- Ruby and ROR still offer some functionality that Groovy/Grails doesn't (like DB migrations, plethora of helpers, etc)
- Ruby isn't based upon, or restricted by Java (and it's limitations/rules/implementation). Enough said.
- Groovy/ Grails are still gaining acceptance. Ruby/Rails have passed this test.
The point of this post isn't to get you to "choose" Ruby/ROR, but to consider them. I think it's worth your while.