Recently I got two books on Google App Engine for Java. Programming Google App Engine by Oreilly and Beginning Google App Engine by Apress. There is less material and comprehensive online tutorials available on this. So its better that you read book on it. I started reading Oreilly’s book. I completed some of the basic components so quickly by given code examples in the book. Its always a good start on some new technology, if you have books in your pocket.
You guys can share your feedback if you read any book or any material on it.