JPA/EJB3 Relationship

Question

I have been reading about JPA and EJB3 and would like to confirm that my understanding of their relationship is correct. Here's what I think I know...

JPA is a specification that has been implemented by a number of vendors including:

• JBoss/Hibernate
• Oracle/TopLink Essentials (now EclipseLink)
• Apache/OpenJPA

EJB3 is a specification that is implemented in Application Servers including:

• Glassfish
• JBoss

Is this correct?

Answer 1

The Java Persistence API introduced in Java EE 5 is a subset of EJB 3 and replaces the persistence solution of EJB 2.0 CMP. JPA 1.0 has been defined as part of the EJB 3.0 specification ( JSR 220 ) but can be used without and outside an EJB container. In Java EE 6, JPA 2.0 has its separate specification ( JSR 317 ), outside the EJB 3.1 specification ( JSR 318 ). So to summarize:

• JPA is a subset of EJB 3 and implementations are provided by persistence providers like Toplink Essentials / EclipseLink, Hibernate, Kodo / OpenJPA (Kodo is the project from which the OpenJPA source code was derived and Kodo is now, in turn, based on OpenJPA), etc.

• EJB 3 is a wider specification and implementations are provided by the EJB container of application servers that rely on persistence providers:

  • The default persistence provider of GlassFish v3 is EclipseLink
  • The default persistence provider of JBoss is Hibernate
  • The default persistence provider of WebLogic 10.3.1+ is OpenJPA/Kodo or EclipseLink
  • The default persistence provider of WebSphere 6.1+ is (based on) OpenJPA

Answer 2

Yes, and JPA1 and JPA2 is also implemented by DataNucleus which also implements JDO1, JDO2, JDO3, as well as the OGC Simple Feature spec; and is also the only truly independent implementation (not tied to a large software vendor). Obviously, users are free to slot in whichever JPA implementation they wish into their EJB3 environment

Answer 3

是的，我也使用过Google OpenJPA，但这是正确的