Which persistence framework to use (JPA, JDO, Hibernate, Toplink) ?

With multiple persistence technologies in Java world, it was always difficult to evaluate all the existing frameworks and choose the best (& mature) one. Sun came up with unsuccessful technologies like entity beans and JDO. BEA created its own framework JDO based Kodo framework. Oracle's Toplink is another mature framework, which is in use for last several years. Open source communities create great persistence frameworks (Hibernate, iBATIS), which are being used heavily.

Java is an Object Oriented programming language, and it  was an unanimous desire to have a good object-relational mapping (OR Mapping) based persistence framework. In last few years, it has been established that Hibernate & Toplink are winner in this race. These are now considered as de-facto standard for persistence-framework. For last four years, I've seen Hibernate being used on all enterprise projects (except one, which was on iBATIS).

To compete with Hibernate and Toplink, Sun came up with OR-Mapping based framework "JDO". However, it failed to create an impression on java-community. BEA created its product Kodo based on JDO specification. Gavin King has highlighted few shortcomings in JDO in his article (Link: Gavin's Article). Currently, JDO provides more facilities than JPA (see comparison). However, Sun has indicated that JPA is the standard specification for OR-mapping based persistence. Here is one of FAQ from Sun (Link: JPA FAQ):

Q: What will happen to other data persistence APIs now that the Java Persistence API is available?

A: The Java Persistence API is now the standard API for persistence and object/relational mapping for the Java EE platform. Earlier APIs of course will not go away, but we expect that they will become less interesting once this new standard API is available.

Finally, experts from all popular frameworks (Hibernate, Toplink etc.) sat together to come up with a specification to define common APIs, that would be implemented or supported by the existing popular frameworks. And, JPA 1.0 was born. Hibernate, Toplink and other products were enhanced to support JPA specification.

With JPA, it is possible not to use one common APIs for many persistence frameworks. If the application is using JPA with Hibernate, it would not require any change in the code to replace Hibernate with Toplink or any other JPA based framework. Apache is working on another JPA based framework named as OpenJPA.

BEA and IBM are shipping OpenJPA as JPA implementation in their application servers WebLogic and WebSphere respectively. Oracle  has Toplink in its application server.

Conclusion

JPA is not the standard specification for OR-Mapping based persistence framework. It has support from all the major vendors including IBM, BEA, Oracle, SUN etc. Hibernate and Toplink are enhanced to support JPA. These two frameworks are in use for last several years and are mature now. It is easy to find developers with experience with these two frameworks. IBM and BEA are shipping a new OpenJPA framework, which it not proven as a mature product so far. So, in my opinion, the new projects should use Hibernate or Toplink with JPA even if the application would be deployed on WebLogic or WebSphere Application Server. And, while building the application, caution should be taken not to use any proprietary API from Hibernate or Toplink to provide portability in future.