NullPointerException in JPA

Question

I am creating a Java EE application using jpa.

I am getting the following error when the code is run on server

    [2/25/12 22:56:31:371 IST] 00000047 SystemOut     O hello
    [2/25/12 22:56:31:375 IST] 00000047 SystemOut     O Error...:(
    [2/25/12 22:56:31:371 IST] 00000047 SystemErr     R java.lang.NullPointerException
    [2/25/12 22:56:31:371 IST] 00000047 SystemErr     R     at plh.service.ejb.UserBean.getUserDetails(UserBean.java:41)
    [2/25/12 22:56:31:372 IST] 00000047 SystemErr     R     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    [2/25/12 22:56:31:372 IST] 00000047 SystemErr     R     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:45)
    [2/25/12 22:56:31:372 IST] 00000047 SystemErr     R     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
    [2/25/12 22:56:31:372 IST] 00000047 SystemErr     R     at java.lang.reflect.Method.invoke(Method.java:599)
    [2/25/12 22:56:31:372 IST] 00000047 SystemErr     R     at com.ibm.etools.utc.model.ReflectionMethodModel.invoke(ReflectionMethodModel.java:65)
    [2/25/12 22:56:31:372 IST] 00000047 SystemErr     R     at com.ibm.etools.utc.servlet.InvokeServlet.invoke(InvokeServlet.java:113)
    [2/25/12 22:56:31:372 IST] 00000047 SystemErr     R     at com.ibm.etools.utc.servlet.InvokeServlet.doPost(InvokeServlet.java:374)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at javax.servlet.http.HttpServlet.service(HttpServlet.java:738)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at javax.servlet.http.HttpServlet.service(HttpServlet.java:831)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1443)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:790)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:443)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:175)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.servlet.CacheServletWrapper.handleRequest(CacheServletWrapper.java:91)
    [2/25/12 22:56:31:373 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:859)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1557)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:173)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:455)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewInformation(HttpInboundLink.java:384)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.ws.http.channel.inbound.impl.HttpICLReadCallback.complete(HttpICLReadCallback.java:83)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
    [2/25/12 22:56:31:374 IST] 00000047 SystemErr     R     at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
    [2/25/12 22:56:31:375 IST] 00000047 SystemErr     R     at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
    [2/25/12 22:56:31:375 IST] 00000047 SystemErr     R     at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:202)
    [2/25/12 22:56:31:375 IST] 00000047 SystemErr     R     at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:766)
    [2/25/12 22:56:31:375 IST] 00000047 SystemErr     R     at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:896)
    [2/25/12 22:56:31:375 IST] 00000047 SystemErr     R     at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1527)

Line no 41 in UserBean.java is :

//within UserBean.java, containing UserBean a stateless EJB

    public class UserBean implements UserBeanInterface {

      /**
      * Default constructor. 
      */
@PersistenceContext
    private EntityManager manager;

public UserBean() {
}
public String authenticate(String name){
    return null;
}
public String changePassword(){
    return null;
}
public String setUserDetails(){
    return null;
}
public String getUserDetails(){
    System.out.println("hello");
    try{
41=>  Query query=manager.createQuery("from User");

        List<User> results = query.getResultList();

        if(results.size()!=0){
            Iterator<User> stIterator=results.iterator();
            while(stIterator.hasNext()){
                User st=stIterator.next();
                System.out.print("User Id:"+st.getUserId());
                System.out.print("Type:"+st.getUserType());
                System.out.print("Detail:"+st.getUserProfile());
            }
        }
        else
        {
            System.out.println("Record not found.");
        }
    }
    catch(Exception e)
    {
        e.printStackTrace();
        System.out.println("Error...:(");
    }
    return "hi";

    }
    }

The User class, User has been generated automatically from the database tables. There is a USER table in the database. Please help on what the possible reason for this error could be.

Please show the entire class (especially the `manager` property). — ndeverge, Feb 25 '12 at 18:11
manager is the only thing that could be null there, how are you getting access to the persistence manager? — chrislatimer, Feb 25 '12 at 18:22
@nico_ekito I've added the entire UserBean class... pls help... — nkvp, Feb 25 '12 at 18:29

perissf · Accepted Answer · 2012-02-25T20:06:21.760

5

Your EntityManager manager is no-interface an Enterprise Java Bean injected in your client UserBean. EJBs should be injected in classes whose lifecycle is managed by the application server.

The client must be either a web component or another enterprise bean. In your case, the client UserBean is a POJO (Plain Old Java Object). See here for further details about how to use EJBs.

A possible simple solution is to make UserBean a Stateless Session Bean by adding the annotation javax.ejb.Stateless before the class definition. And you should eventually inject UserBean into your ManagedBean with the EJB annotation.

edited Feb 25 '12 at 20:06

answered Feb 25 '12 at 18:54

perissf

15,979
14
80
117

ok... but i dont get it fully. How am I supposed to inject javax.persistence.EntityManager?? – nkvp Feb 25 '12 at 19:25
1

A possible simple solution is to make UserBeanInterface a Stateless Session Bean by adding the annotation javax.ejb.Stateless before the class definition. And you should eventually inject UserBeanInterface into your ManagedBean with the EJB annotation. – perissf Feb 25 '12 at 19:29
how to make an interface a Stateless Session Bean ? – nkvp Feb 25 '12 at 20:00
i still don't understand... can u pls give an example...? – nkvp Feb 25 '12 at 21:05

score 1 · Answer 2 · answered Jun 22 '12 at 12:39

1

in such cases make sure you write the@EJB annotation before creating the object of the class containing the entity manager. the reason for the null pointer exception is generally because the entitymanager is not initialised. @EJB annotation does that.

In your case the class where you declare an object of user class write @EJB above it.this should solve the problem.

answered Jun 22 '12 at 12:39

jairaj

1,789
5
19
32

well, this is an old post. I solved it long back using the answer above. Anyways, thanks for posting. – nkvp Jun 25 '12 at 05:09

NullPointerException in JPA

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