JBoss Application Server 5 fully supports the entire Java 5 Enterprise Edition specification. JBoss Application Server 4.2.2 implemented EJB3 functionality by way of an EJB MBean container running as a plugin in the JBoss Application Server. This had certain implications for application development.

The EJB3 plugin injects references to an EntityManager and @EJB references from one EJB object to another. However this support is limited to the EJB3 MBean and the JAR files it manages. Any JAR files which are loaded from a WAR (such as Servlets, JSF backing beans, and so forth) do not undergo this processing. The Java 5 Enterprise Edition standard specifies that a Servlet can reference a Session Bean through an @EJB annotated reference, this was not implemented in JBoss Application Server 4.2.2.