Both lookup and injection of an EntityManagerFactory can be configured via the @PersistenceUnit annotation or <persistence-unit-ref> in xml. Annotations and xml have equal function in both lookup and injection.
Injection and Lookup
Via annotation
Usable by EJB, Interceptor, Servlet, Filter, or Listener
package org.superbiz; import javax.persistence.PersistenceUnit; import javax.persistence.EntityManagerFactory; import javax.ejb.Stateless; import javax.naming.InitialUnit; @Stateless public class MyBean implements MyInterface { @PersistenceUnit(unitName = "bar-unit") private EntityManagerFactory myBarEntityManagerFactory; public void someBusinessMethod() throws Exception { if (myBarEntityManagerFactory == null) throw new NullPointerException("myBarEntityManagerFactory not injected"); // Both can be looked up from JNDI as well InitialContext unit = new InitialContext(); EntityManagerFactory barEntityManagerFactory = (EntityManagerFactory) context.lookup("java:comp/env/org.superbiz.MyBean/myBarEntityManagerFactory"); } }
Via xml
The above @PersistenceUnit annotation usage is 100% equivalent to the following xml.
ejb-jar.xml or web.xml
<persistence-unit-ref> <persistence-unit-ref-name>org.superbiz.calculator.MyBean/myBarEntityManagerFactory</persistence-unit-ref-name> <persistence-unit-name>bar-unit</persistence-unit-name> <persistence-unit-type>Transaction</persistence-unit-type> <injection-target> <injection-target-class>org.superbiz.calculator.MyBean</injection-target-class> <injection-target-name>myBarEntityManagerFactory</injection-target-name> </injection-target> </persistence-unit-ref>
Lookup only
Via annotation
Usable by EJB, Interceptor, Servlet, Filter, or Listener
package org.superbiz; import javax.persistence.PersistenceUnit; import javax.persistence.EntityManagerFactory; import javax.ejb.Stateless; import javax.naming.InitialUnit; @Stateless @PersistenceUnit(name = "myFooEntityManagerFactory", unitName = "foo-unit") public class MyBean implements MyInterface { public void someBusinessMethod() throws Exception { InitialContext context = new InitialContext(); EntityManagerFactory fooEntityManagerFactory = (EntityManagerFactory) context.lookup("java:comp/env/myFooEntityManagerFactory"); } }
Via xml
The above @PersistenceUnit annotation usage is 100% equivalent to the following xml.
ejb-jar.xml or web.xml
<persistence-unit-ref> <persistence-unit-ref-name>myFooEntityManagerFactory</persistence-unit-ref-name> <persistence-unit-name>foo-unit</persistence-unit-name> <persistence-unit-type>Transaction</persistence-unit-type> </persistence-unit-ref>