The Java Persistence API

The Java Persistence API - A Simpler Programming Model for Entity Persistence

The major theme of version 5 of the Java Platform, Enterprise Edition (Java EE, formerly referred to as J2EE) is ease of development. Changes throughout the platform make the development of enterprise Java technology applications much easier, with far less coding. Significantly, these simplifications have not changed the platform's power: The Java EE 5 platform maintains all the functional richness of the previous version, J2EE 1.4.

Enterprise developers should notice dramatic simplification in Enterprise JavaBeans (EJB) technology. Previous articles, such asIntroduction to the Java EE 5 Platform and Ease of Development in Enterprise JavaBeans Technology have described the simplifications made in EJB 3.0 technology, an integral part of the Java EE 5 platform.

A major enhancement in EJB technology is the addition of the new Java Persistence API, which simplifies the entity persistence model and adds capabilities that were not in EJB 2.1 technology. The Java Persistence API deals with the way relational data is mapped to Java objects ("persistent entities"), the way that these objects are stored in a relational database so that they can be accessed at a later time, and the continued existence of an entity's state even after the application that uses it ends. In addition to simplifying the entity persistence model, the Java Persistence API standardizes object-relational mapping.

In short, EJB 3.0 is much easier to learn and use than was EJB 2.1, the technology's previous version, and should result in faster development of applications. With the inclusion of the Java Persistence API, EJB 3.0 technology also offers developers an entity programming model that is both easier to use and yet richer.

The Java Persistence API draws on ideas from leading persistence frameworks and APIs such as Hibernate, Oracle TopLink, and Java Data Objects (JDO), and well as on the earlier EJB container-managed persistence. The Expert Group for the Enterprise JavaBeans 3.0 Specification (JSR 220)has representation from experts in all of these areas as well as from other individuals of note in the persistence community.

This article supplements the earlier articles by focusing on entity-related code. Here you'll be able to examine EJB 2.1 entity beans in an application and compare them to EJB 3.0 entities in an equivalent application. More specifically, you'll be able to view side by side the source code for EJB 2.1 entity beans that use container-managed persistence and relationships and compare them to the source code for equivalently functioning EJB 3.0 entities written to the Java Persistence API. Note that in the Java Persistence API, what used to be called entity beans are now simply called entities. You'll see how much easier and streamlined the EJB 3.0 technology code is.

The article highlights some of the important features that simplify the EJB 3.0 version of the code. Although this article focuses on the Java Persistence API and its use in an EJB 3.0 container, the API can also be used outside the container -- for instance, in applications for the Java Platform, Standard Edition (Java SE, formerly referred to as J2SE). The API also provides support for pluggable, third-party persistence providers. For example, a persistence implementation from one vendor can be used with an EJB container from another vendor, provided that the container and the persistence implementation both conform to JSR 220.

This article assumes that you're familiar with the basic concepts of EJB technology that underlie EJB 2.1. If you're not, see the chapter "Enterprise Beans" in the J2EE 1.4 Tutorial. For more information about EJB 3.0 and Java Persistence concepts, see the chapter "Enterprise Beans" in the Java EE 5 Tutorial.