EntityManager not injected and nullpointer

[ordeal]

Hello

I have a simple Ejb application consisting of 3 entities and 3 stateless SB, web tier is based on a jsp page which accesses the  DB making some simple operations.

The application has been deployed as an ear  file to jboss-5.1.0.GA.

The only jar on default/lib directory is the mysql connector mysql-connector-java-5.1.15-bin.jar, used to map queries to a mysql dbms.

Here is my persistence.xml

<?xml version="1.0" encoding="UTF-8"?>

 <persistence xmlns="http://java.sun.com/xml/ns/persistence"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
          http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
        version="1.0">
    <persistence-unit name="SampleProjectUnit" >
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <jta-data-source>java:/MyDB</jta-data-source>        
        <properties>
         <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
        </properties>
    </persistence-unit>
</persistence>

The Error i get from logs is java.lang.NullPointerException while invoking em.createQuery, where em is my container-managed entity manager, using jdpa i can see em as a null pointer, as not being injected.

This is the SB where i call the entitymanager :

@Stateless @TransactionManagement(TransactionManagementType.CONTAINER)

public class PublisherDAOBean implements PublisherDAO {

    @PersistenceContext(unitName = "SampleProjectUnit")EntityManager em;


    @SuppressWarnings("unchecked")
    public List<Publisher> findAllPublishers() {
        return em.createQuery("SELECT a FROM Publisher a" ).getResultList(); // here i get the nullpointer exception
    }

...

Can anyone tell me how to solve this issue ?

Thanks, Rino

Attached files:

Progetto_EJB3.ear is the app as deployed to jboss

source.zip contains the source files

server.log is the jboss log from server startup

[jaikiran]

Rino, welcome to the forums!

public class EJB3DaoFactory extends DAOFactory {

    @Override
    public AuthorDAO getAuthorDAO() {
        // TODO Auto-generated method stub
        return new AuthorDAOBean();
    }

    @Override
    public BookDAO getBookDAO() {
        // TODO Auto-generated method stub
        return new BookDAOBean();
    }

    @Override
    public PublisherDAO getPublisherDAO() {
        // TODO Auto-generated method stub
        return new PublisherDAOBean();
    }

}

Never instantiate (using "new") a container managed component (like an EJB). The container (application server) is responsible for doing the instantiation and injecting it with the necessary resources and give you that fully injected instance. Typically, such a injected instance of the managed component is available through JNDI. So all you have to do is lookup that instance in JNDI at  a some specific JNDI key.

See these for more details:

http://community.jboss.org/message/367375#367375

http://community.jboss.org/thread/110303?tstart=0#4158957

[ordeal]

Thanks for the reply,

I had forgotten to make the container inject those SB instances in the factory before calling those getter methods.

Now instead of calling a classical JNDI lookup, i would rather use a @EJB annotation to have those SB injected, i've tried this approach but unfortunately i get a nullpointer too:

public class EJB3DaoFactory extends DAOFactory {
@EJB private AuthorDAOBean a; 
@EJB private BookDAOBean b;
@EJB private PublisherDAOBean p;

//a,b and p turn out to be null

    @Override
    public AuthorDAO getAuthorDAO() {
        return a;
    }

    @Override
    public BookDAO getBookDAO() {
        return b;
    }

    @Override
    public PublisherDAO getPublisherDAO() {
        return p;
    }
}

How can i fix it ?

[jaikiran]

That's because injection works only in container managed components. EJB3DaoFactory isn't a container managed component. If you want to access those beans in a non-container managed class like that factory, then use the JNDI lookup.

[ordeal]

Ok, everything is working now,

in order to use @EJB  i had to rearrange the whole project having the SB directly injected in a servlet like this:

public class EJBServlet extends HttpServlet {


    private static final long serialVersionUID = -3583166529015480243L;
    @EJB(mappedName= "Progetto_EJB3/BookDAOBean/local") 
    private BookDAO bookSB;
    @EJB(mappedName= "Progetto_EJB3/PublisherDAOBean/local")
    private PublisherDAO publisherSB;
    @EJB(mappedName= "Progetto_EJB3/AuthorDAOBean/local")
    private AuthorDAO authorSB;

and then forward the fetched data to a jsp page according to MVC pattern.

Thanks