Hibernate is not an official part of the J2EE specification. It is an Object/Relational Mapper that hides the complexity of marshalling and unmarshalling JavaBeans and ResultSets.
Hibernate is unique because it can run either in a J2EE container such as JBoss, or as a standalone service. JBoss 4.0.2 ships standard with Hibernate 3.0.2. This chapter focuses on integrating the two to streamline the persistence tier of your application. (For a more detailed look at installing and running Hibernate, see Hibernate: A Developer's Notebook by James Elliott (O'Reilly).)