As I wrote 2 days ago I was looking into Google Web Toolkit (GWT) in combination with Google App Engine. Google recently released support for Java on App Engine and a plugin for Eclipse fro GWT and App Engine. This provides a very slick development environment. Deploying your web app is just pushing one button and your app is deployed. Actually you can deploy multiple versions of the same web app. So you can first test drive the app before making it the live version.
The really cool thing is that all the code on both client and server is Java, which make development and debugging a breeze.
If you want to know a bit more I can recommend you watching: