1 Reply Latest reply on Jan 21, 2007 6:36 PM by A Komulai

    EntityManagerFactory not injected?

    A Komulai Newbie

      Hi,
      I'm new to EJB 3.0 and just learning about the new persistence features. I'm using Eclipse 3.2 with JBoss 4.05 as the application server. I'm currently trying to write a very simple servlet listener class, which should fetch one row from a database using the EntityManagerFactory and EntityManager classes. This is very similar to the material represented in the latest Java EE tutorial (it's using the same database as the web bookstore example). Here's the code for that class:

      public class ContextListener implements ServletContextListener {
       @javax.persistence.PersistenceUnit(unitName="pu") private EntityManagerFactory emf;
      
       public void contextDestroyed(ServletContextEvent arg0) { }
      
       public void contextInitialized(ServletContextEvent arg0) {
       EntityManager em = emf.createEntityManager();
       WebBookstoreBooks b = (WebBookstoreBooks)em.find(WebBookstoreBooks.class, "201");
       System.out.println(b.getTitle());
       }
      }
      


      And here's my persistence.xml file:

      <?xml version="1.0" encoding="UTF-8"?>
      <persistence xmlns="http://java.sun.com/xml/ns/persistence" ...>
       <persistence-unit name="pu">
       <jta-data-source>java:/sqlserver</jta-data-source>
       <class>data.WebBookstoreBooks</class>
       </persistence-unit>
      </persistence>


      After deployment I get NullPointerException from this line:
      EntityManager em = emf.createEntityManager();

      If I understand correctly, this means, that the EntityManagerFactory has not been injected and is null. Anyhow, if I write the same code and add the bolded line there, everything works:

      public class ContextListener implements ServletContextListener {
       @javax.persistence.PersistenceUnit(unitName="pu") private EntityManagerFactory emf;
      
       public void contextDestroyed(ServletContextEvent arg0) { }
      
       public void contextInitialized(ServletContextEvent arg0) {
      
       emf = Persistence.createEntityManagerFactory("pu");
      
       EntityManager em = emf.createEntityManager();
       WebBookstoreBooks b = (WebBookstoreBooks)em.find(WebBookstoreBooks.class, "201");
       System.out.println(b.getTitle());
       }
      }
      


      This is very confusing. Why do I have to "manually" create the EntityManagerFactory by calling Persistence.createEntityManagerFactory? Shouldn't the container (JBoss) do that automatically. I've googled and found dozens of examples, where the EntityManagerFactory is just added with the @persistenceUnit annotation and everything works fine after that without the need for any extra lines of code.

      Could someone explain what is going on here and if I'm doing/understood something wrong?

        • 1. Re: EntityManagerFactory not injected?
          A Komulai Newbie

          Oh no... just found this from project Glassfish FAQ:

          Q. Can I use javax.persistence.Persistence.createEntityManagerFactory() to get hold of an EntityManagerFactory in my web application?

          Yes, but this is not recommended because javax.persistence.Persistence.createEntityManagerFactory() is designed for use in a Java SE environment. In a Java EE environment, you can use dependency injection or JNDI lookup to access an EntityManagerFactory or an EntityManager as discussed earlier in this FAQ. Having said that, if you are using a web container like Tomcat 5.x which does not support Java Persistence API, then you have no option but to use this API. In such a case, we recommend you choose a container like GlassFish which supports the latest spec.


          I'm using JBoss 4.0.5 which uses Tomcat 5.5 as web container. I guess it's goodbye JPA then? Do I have any alternatives left if I'm going to continue using JBoss?

          What a mess :(