More Advanced Features - Beginning Hibernate: From Novice to Professional - page 233

APPENDIX A
n n n
More Advanced Features
I n this appendix, we discuss some of the features that, strictly speaking, lie outside the scope
of this topic, but that you should be aware of if you go on to use Hibernate in more depth.
EJB 3 and the EntityManager
The third version of the Enterprise Java Beans specification, generally known as EJB 3, has
recently been finalized. Among other features, EJB 3 includes a standard ORM technology that
was significantly influenced by the design of Hibernate.
You encountered this close relationship in Chapter 6 when we discussed Hibernate's use
of the EJB 3 annotations for creating entity mappings. Annotations can be used throughout
your EJB 3 applications to denote various settings. They are also used to mark for injection of
resources from the container in a manner very like that of Spring's dependency injection (see
Appendix C). HQL, which was discussed in Chapter 9, is very similar to the EJB QL used in
EJB 3 environments—generally speaking, your HQL queries can be used as EJB QL queries
without change.
Given these similarities, a Hibernate application can be converted into a portable EJB 3
application with surprisingly few changes. EJB 3 now supports both J2SE environments and
those hosted within J2EE application servers; so even a stand-alone application can be writ-
ten to take advantage of the EJB 3 features.
The standard way to access the ORM components of an EJB 3 application is through the
EntityManager . The Hibernate team provides appropriate libraries for download on their
EntityManager site at http://entitymanager.hibernate.org .
The EntityManager is configured through a standard file called persistence.xml , which
must be provided in a META-INF directory accessible from the classpath (or, in a J2EE environ-
ment, from the root of the deployed archive). This file serves the same purpose as a conventional
Hibernate configuration file ( hibernate.cfg.xml ), although its syntax is somewhat different. An
example file is given in Listing A-1.
Listing A-1. An EJB 3 persistence.xml Configuration File
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
version="1.0">
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