Justin Grammens has published a great overview of using Asterisk and Groovy with Asterisk-Java showing some real-worl examples.
The presentation is also available from SlideShare.
You might also want to have a look at Justin’s blog Localtone. You’ll find lots of information on Asterisk, Ruby and Groovy including the Ruby framework Adhearsion and some screencasts. I recommend his screencast on how to setup Asterisk to any Java or Ruby developer who wants to get started with VoIP and Asterisk.