@PersistenceContext, EntityManager and NullPointerException

syco · **Joined:** Wed Apr 13, 2011 10:03 am **Posts:** 3

hi,
I know it's a problem widely discussed, but I read forums from two days and everything looks correct, please help me.
I have netbeans 7, tomcat 7, hibernate 3.6.3 and JavaServer Faces 2.

this is the structure of the project:

Code:

./src:
conf  java

./src/conf:
MANIFEST.MF  persistence.xml

./src/java:
AppBean.java  Bundle.properties  Bundles  Controller  Converter  DB  Utils

./src/java/Bundles:
Operatore.properties

./src/java/Controller:
OperatoreController.java

./src/java/Converter:
OperatoreConverter.java

./src/java/DB:
Operatore.java

./web:
index.xhtml  META-INF  operatore.xhtml  WEB-INF

./web/META-INF:
context.xml

./web/WEB-INF:
beans.xml  faces-config.xml  web.xml

and this OperatoreController.java:

Code:

package Controller;


import DB.Operatore;
import java.io.Serializable;
import java.util.List;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@ManagedBean(name = "OperatoreController")
@SessionScoped
public class OperatoreController implements Serializable {

    @PersistenceContext(unitName = "mPU")
    private EntityManager entityManager;
    private Operatore x = new Operatore();

    public EntityManager getEntityManager() {
        return entityManager;
    }

    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    public Operatore getX() {
        return x;
    }

    public void setX(Operatore x) {
        this.x = x;
    }

    public void aggiungi() {
        if (x.getId() == 0) {
            x.setId(null);
        }
        entityManager.persist(x);
    }

    public void modifica(Object id) {
        x = entityManager.find(Operatore.class, id);
    }

    public void elimina(Object id) {
        entityManager.remove(entityManager.find(Operatore.class, id));
    }

    public List<Operatore> list() {
        System.err.println("\n\n" + entityManager + "\n\n");
        List<Operatore> list = entityManager.createQuery("FROM Operatore").getResultList();
        return list;
    }

    public Operatore get(Integer id) {
        Operatore list = (Operatore) entityManager.createQuery("FROM Operatore AS x WHERE x.id = :id").setParameter("id", id).getSingleResult();
        return list;
    }
}

from this file I use only "list" function.

this is my persistance.xml:

Code:

<?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="mPU" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>DB.Operatore</class>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <shared-cache-mode>NONE</shared-cache-mode>
    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/MY_DB"/>
      <property name="javax.persistence.jdbc.password" value="MY_PWD"/>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
      <property name="javax.persistence.jdbc.user" value="MY_USER"/>
    </properties>
  </persistence-unit>
</persistence>

and finally this is the stack trace:

Code:

java.lang.NullPointerException
   at Controller.OperatoreController.list(OperatoreController.java:117)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
   at java.lang.reflect.Method.invoke(Method.java:597)
   at javax.el.BeanELResolver.invoke(BeanELResolver.java:467)
   at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:161)
   at org.apache.el.parser.AstValue.getValue(AstValue.java:159)
   at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
   at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
   at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:193)
   at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:181)
   at javax.faces.component.UIData.getValue(UIData.java:557)
   at javax.faces.component.UIData.getDataModel(UIData.java:1297)
   at javax.faces.component.UIData.setRowIndex(UIData.java:450)
   at com.sun.faces.renderkit.html_basic.TableRenderer.encodeBegin(TableRenderer.java:81)
   at javax.faces.component.UIComponentBase.encodeBegin(UIComponentBase.java:828)
   at javax.faces.component.UIData.encodeBegin(UIData.java:940)
   at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:55)
   at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:46)
   at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:225)
   at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:148)
   at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:75)
   at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:883)
   at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1659)
   at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
   at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:853)
   at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1652)
   at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1655)
   at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1655)
   at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:399)
   at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
   at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
   at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
   at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
   at javax.faces.webapp.FacesServlet.service(FacesServlet.java:313)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
   at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
   at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
   at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:498)
   at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
   at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
   at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
   at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
   at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:394)
   at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
   at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
   at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
   at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
   at java.lang.Thread.run(Thread.java:662)

Thanks to all

ngomo · **Joined:** Tue Sep 14, 2010 4:29 pm **Posts:** 16

Hi syco,

the persistence.xml has to be present in the META-INF folder. Check the the resulting war/jar or the exploded webapp folders, if its there. I am not familiar with project structure under Netbeans, but I think moving the persistence.xml from ./src/conf to ./web/META-INF might do the trick.

Greetings ngomo

syco · **Joined:** Wed Apr 13, 2011 10:03 am **Posts:** 3

i unpacked the final war, this is the folder tree:

Code:

ls -R
.:
index.xhtml  META-INF  operatore.xhtml  WEB-INF

./META-INF:
context.xml  MANIFEST.MF

./WEB-INF:
beans.xml  classes  faces-config.xml  lib  web.xml

./WEB-INF/classes:
AppBean.class  BUNDLE  Bundle.properties  Controller  Converter  DB  META-INF  Utils

./WEB-INF/classes/BUNDLE:
Operatore.properties

./WEB-INF/classes/Controller:
OperatoreController.class

./WEB-INF/classes/Converter:
OperatoreConverter.class

./WEB-INF/classes/DB:
Operatore.class

./WEB-INF/classes/META-INF:
persistence.xml

./WEB-INF/classes/Utils:
Functions.class

./WEB-INF/lib:
antlr-2.7.6.jar              hibernate-jpa-2.0-api-1.0.0.Final.jar  jsf-impl.jar                         primefaces.jar
commons-collections-3.1.jar  hibernate-testing.jar                  jstl.jar                             slf4j-api-1.6.1.jar
dom4j-1.6.1.jar              javassist-3.12.0.GA.jar                jta-1.1.jar                          standard.jar
hibernate3.jar               jsf-api.jar                            mysql-connector-java-5.1.13-bin.jar

persistance.xml is under a META-INF folder, i have two of them.

i tried to move the file from src/conf to web/META-INF, this is the unpacked result:

Code:

.:
index.xhtml  META-INF  operatore.xhtml  WEB-INF

./META-INF:
context.xml  MANIFEST.MF  persistence.xml

./WEB-INF:
beans.xml  classes  faces-config.xml  lib  web.xml

./WEB-INF/classes:
AppBean.class  Bundle.properties  Bundles  Controller  Converter  DB  Utils

./WEB-INF/classes/Bundles:
Operatore.properties

./WEB-INF/classes/Controller:
OperatoreController.class

./WEB-INF/classes/Converter:
OperatoreConverter.class

./WEB-INF/classes/DB:
Operatore.class

./WEB-INF/classes/Utils:
Functions.class

./WEB-INF/lib:
antlr-2.7.6.jar              hibernate3.jar                         jsf-api.jar   mysql-connector-java-5.1.13-bin.jar
commons-collections-3.1.jar  hibernate-jpa-2.0-api-1.0.0.Final.jar  jsf-impl.jar  primefaces.jar
cupertino-1.0.1.jar          hibernate-testing.jar                  jstl.jar      slf4j-api-1.6.1.jar
dom4j-1.6.1.jar              javassist-3.12.0.GA.jar                jta-1.1.jar   standard.jar

but the error is the same.

ngomo · **Joined:** Tue Sep 14, 2010 4:29 pm **Posts:** 16

I have surfed the web a bit for documentation. I found the chapter Persistence Units in Sun's/Oracle's Java EE5 tutorial located here:http://download.oracle.com/javaee/5/tutorial/doc/bnbqw.html#bnbrj. They write:

Quote:

If you package the persistence unit as a set of classes in a WAR file, persistence.xml should be located in the WAR file’s WEB-INF/classes/META-INF directory.

Your persistence.xml being in WEB-INF/classes/META-INF/ and your entity class being in WEB-INF/classes/DB/ should work.

I thought that dependency injeciton of JSF might be the issue. I have read a bit further up to the chapter located here: http://download.oracle.com/javaee/5/tutorial/doc/bnbrm.html#bnbrp
I found the following paragraph that might be of importance for you:

Quote:

In fact, you can bypass injecting EntityManagerFactory and instead inject the EntityManager directly into BookDBAO. This is because thread safety is not an issue with request-scoped beans. Conversely, developers need to be concerned with thread safety when working with servlets and listeners. Therefore, a servlet or listener needs to inject an EntityManagerFactory instance, which is thread-safe, whereas a persistence context is not thread-safe. The following code shows part of the BookDBAO object included in the JavaServer Faces version of Duke’s Bookstore:

You marked your Managed Bean as SessionScoped which (opposed to RequestScoped) is not thread safe. So maybe this prevents EntityManager from being injected. I suggest trying one of the following. Either mark your Managed Bean RequestScoped or inject the EntityManagerFactory with @PersistenceUnit and get the EntityManager from the factory.

If this does not help, I am sorry to admit that I lack any further ideas.

Cheers ngomo

syco · **Joined:** Wed Apr 13, 2011 10:03 am **Posts:** 3

IT WORKS!
thanks a lot.

and for who has an annoying

Code:

org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags

should substitute java.utils.List with java.utils.Set in Entity declaretion.