OpenBooks is a Swing based sample (and perhaps, simple) application featuring some of the new features in JPA 2.0.
The source code for OpenBooks is available in OpenJPA SubVersion repository
OpenBooks comes with a an Ant script to build.
svn co https://svn.apache.org/repos/asf/openjpa/trunk/openjpa-examples/openbooks
ant package deploy
ant -f run.xml run