Data persistence is a cornerstone of scalable application delivery in enterprise environments. In this final article of his series introducing Google App Engine for Java™, Rick Hightower takes on the challenges of App Engine's current Java-based persistence framework. Learn the nuts and bolts of why Java persistence in the current preview release isn't quite ready for prime time, while also getting a working demonstration of what you can do to persist data in App Engine for Java applications. Note that you will need to have the contact-management application from Part 2 up and running as you learn how to use the JDO API to persist, query, update, and delete Contact objects.