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This chapter is from the book

Architectural Overview

Standards Adherence

OpenJPA is an implementation of the JPA 1.0 Specification that is a subspecification under the SUN EJB 3.0 specification, developed under JSR 220. At the time of this writing, JPA 2.0 is being developed under its own JSR 317, and EJB 3.1 is being developed under JSR 318. The website is the definitive source for the JPA 2.0 specifications [JPA 2].

Platforms Required

Before Java EE 5.0 and EJB 3.0, the persistence layer of the Java EE platform required a full-blown Java EE Application Server. JPA changes this. OpenJPA applications can be written to run in both Java SE and Java EE environments. However, there are some differences in JPA applications hosted inside a Java EE environment as opposed to a Java SE environment. Rather than discuss the differences here, we will highlight them where they exist throughout the remainder of this chapter.

Other Dependencies

OpenJPA comes bundled with several other JARs needed to make it run. Like many Apache projects, it makes use of other Apache licensed packages:

  • Several of the Apache Commons projects :commons-lang, commons-logging, commons-pool, and commons-collections. Please refer to the Apache Commons website for more information [Apache].
  • Apache OpenJPA relies on the Serp project for Java "bytecode enhancement" to add persistence behavior to annotated Java files as a separate step. The Serp JAR comes bundled with OpenJPA. We discuss this step in the later section "Development Process for the Common Example." You can read more about Serp at their website [Serp].
  • A valid JDBC database driver.
  • For Java EE applications, any JARs required to run OpenJPA in a target Java EE Server.

Vendors and Licenses

OpenJPA is distributed under an Apache License. As mentioned in Chapter 2, an Apache License is more liberal in what you can do with the source because you can change parts of the code, and you don't need to distribute them back to the original authors. In addition, several commercial products ship an OpenJPA implementation, such as IBM WebSphere Application Server and BEA WebLogic Server.

It is worth noting that because JPA is a specification, there are other JPA implementations available beyond the OpenJPA version:

  • Hibernate JPA. Refer to Chapter 7, "Hibernate Core," or the Hibernate website [Hibernate] for license information.
  • TopLink Essentials, which is an open-source implementation that Oracle built on top of TopLink. We discussed TopLink briefly in Chapter 1. See their website for more information [TopLink].

Available Literature

OpenJPA is very well documented on their website. In addition, there are several articles available. Table 8.1 shows some examples.

Table 8.1. OpenJPA Resources

Resource

Link

Description

OpenJPA Manuals [OpenJPA 2]

openjpa.apache.org/documentation.html

Comprehensive OpenJPA Module

Integrating OpenJPA with Application Servers [OpenJPA 3]

openjpa.apache.org/integration.html

List of other articles for integrating OpenJPA with other Application Server.

Building EJB 3 Applications with WebSphere Application Server

www.ibm.com/developerworks/websphere/techjournal/0712_barcia/0712_barcia.html

Tutorial on using OpenJPA inside the WebSphere EJB 3 Container

Leveraging OpenJPA with WebSphere Application Server

A.8.1

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www-128.ibm.com/developerworks/websphere/techjournal/0612_barcia/0612_barcia.html

Tutorial on using OpenJPA inside WebSphere Application Server

Java Persistence with Hibernate [Bauer]

A.8.2

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www.amazon.com/Java-Persistence-Hibernate-Christian-Bauer/dp/1932394885/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1201195747&sr=1-1

Book on using Hibernate JPA API

Enterprise JavaBeans, 5th Edition [Monson-Haefel]

www.amazon.com/Enterprise-JavaBeans-3-0-Bill-Burke/dp/059600978X/ref=pd_bbs_sr_2?ie=UTF8&s=books&qid=1201195725&sr=8-2

Comprehensive sourcebook on EJB 3

Migrating Legacy Hibernate Applications to OpenJPA and EJB 3

A.8.3

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www.ibm.com/developerworks/websphere/techjournal/0708_vines/0708_vines.html

Techniques useful to migrate a Hibernate Core Application to OpenJPA

Besides OpenJPA, there are many other resources available on the JPA programming model.

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