title: NullPointerException in JPA
body: <p>I am creating a Java EE application using jpa.</p>
  
  <p>I am getting the following error when the code is run on server</p>
  
  <pre><code>    [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)
  </code></pre>
  
  <p>Line no 41 in UserBean.java is :</p>
  
  <p>//within UserBean.java, containing UserBean a stateless EJB</p>
  
  <pre><code>    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=&gt;  Query query=manager.createQuery("from User");
  
          List&lt;User&gt; results = query.getResultList();
  
          if(results.size()!=0){
              Iterator&lt;User&gt; 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";
  
      }
      }
  </code></pre>
  
  <p>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.</p>