Jsf 2 javax.faces.el.EvaluationException:我的jsf web应用程序中的java.lang.NullPointerException

我正在开发一个动态Web应用程序，作为第一步，我想使用我的jsf页面在数据库中保存一个新组。我正在连接一个Oracle 10g数据库，在eclipse Kepler上使用Glassfish4，并使用primefaces 4.0。这就是StackTrace

                  2013-12-07T00:38:34.028+0100|Avertissement: #{groupeBean.createGroupe}: java.lang.NullPointerException
                 javax.faces.FacesException: #{groupeBean.createGroupe}: java.lang.NullPointerException
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
at javax.faces.component.UICommand.broadcast(UICommand.java:315)
at javax.faces.component.UIData.broadcast(UIData.java:1108)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:790)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1282)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
at java.lang.Thread.run(Thread.java:724)
           Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:101)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
... 35 more
         Caused by: java.lang.NullPointerException
at com.portail.dao.DaoGroupe.ajouter(DaoGroupe.java:21)
at com.portail.managedBeans.GroupeBean.createGroupe(GroupeBean.java:24)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.sun.el.parser.AstValue.invoke(AstValue.java:275)
at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:304)
at org.jboss.weld.util.el.ForwardingMethodExpression.invoke(ForwardingMethodExpression.java:40)
at org.jboss.weld.el.WeldMethodExpression.invoke(WeldMethodExpression.java:50)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
... 36 more

这是managedBean的代码

                @ManagedBean
                @ViewScoped
              public class GroupeBean {
               private Groupe newGroupe=new Groupe();
                public Groupe getNewGroupe() {
            return newGroupe;
               }
          public void setNewGroupe(Groupe newGroupe) {
      this.newGroupe = newGroupe;
            }
          private DaoGroupe gdao= new DaoGroupe();
        public void createGroupe()
          {
        gdao.ajouter(newGroupe);
            }}

这是Dao类的代码

            public class DaoGroupe {
private static final String JPA_UNIT_NAME="Portail";
private EntityManager entityManager;
protected EntityManager getEntityManager() {
    if (entityManager == null) {
        entityManager = Persistence.createEntityManagerFactory(
                JPA_UNIT_NAME).createEntityManager();
    }
    return entityManager;
}
 public   void ajouter(Groupe g)
    {
        EntityTransaction tx = entityManager.getTransaction();
        tx.begin();
        entityManager.persist(g);
        tx.commit();}}

这是我的jsf页面中的insert选项卡

                  <p:tab title="Groupe">
            <h:form>
                <h:panelGrid columns="2">
                    <h:outputText value="Nom : *" />
                    <p:inputText value="#{groupeBean.newGroupe.nom}" required="true"
                        label="nomgrp" validatorMessage="Nom de Groupe Obligatoire" />
                        <h:outputText value="Numéro : *" />
                    <p:inputText value="#{groupeBean.newGroupe.idGroupe}" required="true"
                        label="numgrp" validatorMessage="Numéro de Groupe Obligatoire" />
                </h:panelGrid>
                <p:commandButton value="Ajouter"
                    style="width:205px;margin-left:10%"
                    action="#{groupeBean.createGroupe}" />
            </h:form>

        </p:tab>   

---

在方法

ajouter

中的DaoGroupe类中，您会得到一个NullPointerException。 我猜原因是

entityManager.getTransaction（）

，因为entityManager没有在任何地方填充。将其替换为使用

getEntityManager（）

-方法可能是开始调试的第一步

EntityTransaction tx = getEntityManager().getTransaction();

---

希望对你有帮助

您正在使用GlassFish，它支持开箱即用的EJB。为什么您仍在手动创建实体管理器并手动管理事务？这很痛苦。只需使用EJB，代码就会比现在少2-3倍，因为GlassFish将自动执行注入和事务管理。这实际上是一个大学项目，我需要从头开始构建该项目，并认为我是一个初学者，我的教授给了我一个项目的模型，我应该继续下去，在最后期限之前完成这个项目。这实际上是一件好事，将来您将更好地理解EJB可以从您身上带走什么样的样板文件/混乱。祝你好运：）