JPOX provides transparent persistence of Java objects. It fully complies with the JDO1.0/JDO2.0/JDO2.1/JPA1 specifications. It supports persistence to all of the major RDBMSs on the market today, as well as DB4O. It allows querying using JDOQL, SQL, or JPQL. It comes with its own byte-code enhancer. Its 1.1 release is Sun's "Reference Implementation" (RI) for JDO2.0, and its 1.2 release is the RI for JDO2.1. It is highly extensible, using OSGi technology and providing a wide range of value-adding plugins.
Some issues with detachment have been fixed. Support for the SCO List.remove(int) method has been made consistent. Behavior of SCO Maps have been made consistent for the instantiation type. Use of application identity where the PK was not at the start of the class has been fixed. Identity generation in non-default schema for PostgreSQL has been improved. This is likely the final release of JPOX, and future development is under the name "DataNucleus".
URL: Java Persistent Objects (JPOX)