Glen’s “from the trenches” experience is ideally complemented by Peter’s insider knowledge, which he has shown thousands of times when answering questions on the Grails user mailing list. If anybody on this planet knows what people ask about Grails, he does.
Writing a good book on Grails is a challenge. As an author, you are tempted to present the full cornucopia of features, but you would like to also get across the simplicity that Grails brings to Java web application development.
Glen and Peter have found an excellent balance between providing a low-barrier entry into the Grails world and covering the issues that you are likely to encounter when using Grails in more demanding scenarios.
Grails in Action takes a practical stance. It leads you through the process of creating a Grails application and explains the sights along the way. This applies to the various pieces of technology: models, tests, views, controllers, services, and the like, but also—and maybe even more importantly—to the sequence of when and how you go from one to the next.