JPA 2.0 : Adding entity classes to PersistenceUnit *from different jar* automatically

There are several way to solve it:

1. As described in Do I need <class> elements in persistence.xml?, you can set hibernate.archive.autodetection property and Hibernate should be able to look up all annotated classes from classpath. However, that’s not JPA spec compliant.
2. If you are using Spring, from Spring 3.1.2 (or probably even a bit earlier), in LocalContainerEntityManagerFactoryBean, you can define packageToScan which will ask LocalContainerEntityManagerFactoryBean to scan in classpath to find all annotated classes. Again, not JPA spec compliant.