Van Riper posted a good suggestion the other day which may warrant your attention. If you'd like to see support for Java and/or Groovy added to the new Google App Engine, then here's something you should do. Head on over to Google Code and "star" this issue. It's easy and quick, and your input there will send a clear signal to the powers-that-be in the Googleplex that you'd like Java/Groovy support to be added. Please note Van's request:
Important Note: Please do *not* add a "+1" comment to this issue like many others have already done. All that is necessary is to star the issue. Comments are intended to provide more information about an issue and everyone that stars an issue sees these comments. So, it ends up generating essentially spam email for everyone that has starred the issue.
There are over 300 stars there already, and with your help the number will climb. Add your star now, and pass the word along.