Question

In the following code, a Null pointer exception is raised when I try to call beginTransaction method. I thought that JBoss would init my transaction… apparently not :\

What am I missing ?

JBoss 5.1.0.GA
JPA 1
JDK 6

---

import javax.annotation.Resource;
import javax.persistence.EntityManagerFactory;
import javax.persistence.PersistenceUnit;
import javax.transaction.UserTransaction;

public abstract class AbstractDAO {
    @PersistenceUnit(unitName = "miniDS")
    protected static EntityManagerFactory emf;
    @Resource
    protected UserTransaction t;

    public AbstractDAO() {

    }

    protected void beginTransaction() throws Throwable {
        t.begin();
    }

    protected void commitTransaction() throws Throwable {
        t.commit();
    }

    protected void rollbackTransaction() throws Throwable {
        t.rollback();
    }
}

Answer 1

Your AbstractDAO does not seem to be managed. Injection only works in container managed objects. This is not specific to injection of UserTransaction, but injection in general. As result emf is null as well. Java EE specification lists following classes to be able to use injection:

• Servlet: servlets, servlet filters, event listeners
• JSP: tag handlers, tag library event listeners
• JSF: scoped managed beans
• JAX-WS: service endpoints, handlers
• EJB: beans, interceptors
• Managed Beans: managed beans
• CDI: CDI-style managed beans, decorators
• Java EE Platform: main class (static), login callback handler

Possible workaround are to move injection of resources to managed class or use JNDI lookup.