Castor

To quote castor.org, Castor is an "Open Source data binding framework for Java[tm]", the "shortest path between Java objects, XML documents and relational tables". We have Java-to-XML binding, Java-to-SQL persistence and more. Looked at in reverse, you can think of it as a Java persistence layer. It was developed by some guys at Intalio, Inc. Castor uses JUnit to build and test components.