Persistencecontext Entitymanager Injection Nullpointerexception

EntityManager injection - NullPointerException

You can't access the EntityManager within the constructor. Take a look at the @PostConstruct-Annotation

@Service(value="inboxQueryBuilder")
public class InboxQueryBuilder {

@PersistenceContext
EntityManager em;

CriteriaBuilder cb;

public InboxQueryBuilder() {
    // em= null
}

@PostConstruct
public void toSomething(){
    // em set by Container  
    cb = em.getCriteriaBuilder();
}

public TypedQuery<App> getQueryForApps(AppSearchObject aso) {
       ...
}

...
}

EDIT:
After reading your post again, I start to became unsure, if I'm right. I know the Java EE-Dependency-Injection within a JBoss works as I described, but I'm not sure about spring-IOC.

PersistenceContext EntityManager injection NullPointerException

An entity manager can only be injected in classes running inside a transaction. In other words, it can only be injected in a EJB. Other classe must use an EntityManagerFactory to create and destroy an EntityManager.

Since your TestService is not an EJB, the annotation @PersistenceContext is simply ignored. Not only that, in JavaEE 5, it's not possible to inject an EntityManager nor an EntityManagerFactory in a JAX-RS Service. You have to go with a JavaEE 6 server (JBoss 6, Glassfish 3, etc).

Here's an example of injecting an EntityManagerFactory:

package com.test.service;

import java.util.*;
import javax.persistence.*;
import javax.ws.rs.*;

@Path("/service")
public class TestService {

    @PersistenceUnit(unitName = "test")
    private EntityManagerFactory entityManagerFactory;

    @GET
    @Path("/get")
    @Produces("application/json")
    public List get() {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        try {
            return entityManager.createQuery("from TestEntity").getResultList();
        } finally {
            entityManager.close();
        }
    }
}

The easiest way to go here is to declare your service as a EJB 3.1, assuming you're using a JavaEE 6 server.

Related question:
Inject an EJB into JAX-RS (RESTful service)

Injecting EntityManager using Spring ( Null Pointer Exception )

Since you are instantiating TeacherDaoImpl yourself (with the new keyword) within main, Spring is not injecting the EntityManager and hence the NPE.

Annotate the field TeacherDaoImpl.entityManager with @PersistenceContext and annotate the TeacherDaoImpl class with @Component to have Spring instantiate it for you. Then in your main, get a hold of that bean:

TeacherDao dao = applicationContext.getBean(TeacherDao.class);
// ...

Also these two directives seem to be unnecessary:

<context:annotation-config />
<context:spring-configured />

The former is implied when you are using <context:component-scan />. The latter is only useful if you are using @Configurable in your code.

EJB @PersistenceContext EntityManager Throws NullPointerException

The EntityManager instance, is injected when the EJB is deployed in the Container.
If you take a look at the lifecycle of enterprise bean, you will see clearly when dependency injection occurs.
When the Container sees the @Persistencecontext annotation it will inject a container-managed EntityManager.

The problem is that the code executed in this test is not managed by the Container, therefore, no one inject the necessary dependencies.

bookDao = new BookEJB();

When you run the test, the BookEJB class is just a simple POJO, the @Stateless and @PersistenceContext annotations are simply ignored.

You have several alternatives in order to test your EJB, take a look at this link.

---

Related Topics