Entity Classes Reverse Engineering - JPA Modeler
Home Page : http://plugins.netbeans.org/plugin/53...
You can also use the JPA modeler on old sources ( no need to create a new project from scratch to use JPA Modeler ). And, whenever the diagram becomes out of date, you can simply regenerate it, from the current state of your sources.
Screencast info[JPA Modeler v0.5 and Netbeans 8.0]