NullPointerException calling EJB in Vaadin 7

Question

I'm using Wildfly 8.2, JavaEE 7 and Vaadin 7. I got NullPointerException when calling the stateless bean findAll() method in the user interface layer. Do you know why? Below are my code.

            @MappedSuperclass
            public abstract class AbstractEntity implements Serializable {
                @Id
                @GeneratedValue(strategy = GenerationType.AUTO)
                private Long id;

                //Getters/Setters are here    
            }

        @Entity
        public class Patient extends AbstractEntity {
            String firstName;
            String lastName;
            Date DOB;

            public Patient() {}
            //Getters/Setters are here
        }

    @Stateless
    public class PatientService {

        @PersistenceContext(unitName="patient-pu")
        private EntityManager em;

        public List<Patient> findAll() {
            CriteriaQuery<Patient> cq = em.getCriteriaBuilder().createQuery(Patient.class);
            cq.select(cq.from(Patient.class));
            return em.createQuery(cq).getResultList();
        }

    }

Here's my persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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_2_0.xsd">
  <persistence-unit name="patient-pu" transaction-type="JTA">
    <jta-data-source>java:jboss/h2</jta-data-source>
    <class>com.example.samples.backend.data.Patient</class>
  </persistence-unit>
</persistence>

Here's my Vaadin UI.

@Viewport("user-scalable=no,initial-scale=1.0")
@Theme("valo")
@Widgetset("com.example.MyAppWidgetset")
public class MyUI extends UI {
    @Inject
    private PatientService patientService;

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        patientService.findAll();
    }

    @WebServlet(urlPatterns = "/*", name = "MyUIServlet", asyncSupported = true)
    @VaadinServletConfiguration(ui = MyUI.class, productionMode = false)
    public static class MyUIServlet extends VaadinServlet {
    }
}

Answer 1

You get a NPE because patientService is null.

The problem is that the MyUI class is not a managed bean, meaning that it's not created by the Java EE container and that's why the @Inject annotation don't have any effect.

The easiest way to make MyUI as a managed bean, is to use the Vaadin CDI addon.