If you're looking for the short answer, go check out the Spring Data JPA project. This is an incredible product that offers a tremendous productivity boost for projects using JPA. If you're interested in the more gory details, read on below :)
I've been a Hibernate user since 2005 and have used JPA + Hibernate Annotations since 2006 when 1.0 of the JPA spec was released. Unlike many others I did not immediately jump to the JPA APIs (EntityManager, PersistenceContext, etc) and continued using the native Hibernate APIs (Session, SessionFactory, etc). JPA was still missing quite a few useful features such as a Criteria API and I wasn't ready to give that up just to use a "standard API." When JPA 2.0 was released in late 2009 the feature sets of the two products were generally comparable making the decision a little tougher. But since I've never really bought into the "vendor portability" promise of JPA, I continued happily on with native Hibernate APIs to much success.
Over the past month or two, I've come to the decision it's time to fully embrace JPA.
JPA has grown beyond its original purpose as an object-relational mapping framework into a more generic persistence API. NoSQL / data grid solutions have become incredibly important and popular over the past few years. Several JPA-based implemenations for these solutions have already been developed, including Google App Engine / Big Table and Hibernate's own Object/Grid Mapper (OGM). I started to experiment with GAE about a month ago and was surprised how quickly I could be productive with its JPA implementation. While JPA likely isn't the best fit for the diverse range of NoSQL implementations out there, the ease of use for JPA developers is undeniable.
While industry trends are important, I've finally found the killer app for JPA: the Spring Data JPA project. At its core, SDJ is about generating JPQL at runtime so you don't have to write tedious queries. Some of the awesome features include:
- Out-of-the-box support for data pagination and sorting.
- Query creation from method names. Creating a method signature of findByEmailAddressAndLastName(String emailAddress, String lastName) creating a backing query that does exactly what you'd expect.
- Specification API to define and combine predicates in a manner similar to the Criteria API.
Check out the reference documentation for Spring Data JPA. The project just dropped its first 1.0 release candidate. I'm excited to see what they'll come up with in future releases.