NPE atP：PrimeFaces组件中的pickList

Question

我在使用 Primefaces 中的Pojo支持组件p:pickList时遇到问题 我在primeface Demo of pickList

中看到了代码

所以，我不知道为什么我在stacktrace中遇到这个问题：

mai 29, 2013 3:27:10 PM com.sun.faces.application.view.FaceletViewHandlingStrategy handleRenderException
SEVERE: Error Rendering View[/pages/protected/admin/function/Project/activateProject.xhtml]
java.lang.NullPointerException
    at org.primefaces.component.picklist.PickListRenderer.encodeMarkup(PickListRenderer.java:86)
    at org.primefaces.component.picklist.PickListRenderer.encodeEnd(PickListRenderer.java:59)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:63)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:47)
    at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:202)
    at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:119)
    at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:56)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:63)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:47)
    at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:202)
    at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:119)
    at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:56)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:851)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:439)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:124)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
    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:594)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.test.ems2.filter.AdminPagesFilter.doFilter(AdminPagesFilter.java:31)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.test.ems2.filter.LoginCheckFilter.doFilter(LoginCheckFilter.java:69)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    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:462)
    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:395)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
    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.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

mai 29, 2013 3:27:10 PM com.sun.faces.context.ExceptionHandlerImpl throwIt
INFO: Exception when handling error trying to reset the response.
java.lang.NullPointerException
    at org.primefaces.component.picklist.PickListRenderer.encodeMarkup(PickListRenderer.java:86)
    at org.primefaces.component.picklist.PickListRenderer.encodeEnd(PickListRenderer.java:59)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:63)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:47)
    at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:202)
    at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:119)
    at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:56)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:63)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:47)
    at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:202)
    at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:119)
    at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:56)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:851)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:439)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:124)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
    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:594)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.test.ems2.filter.AdminPagesFilter.doFilter(AdminPagesFilter.java:31)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.test.ems2.filter.LoginCheckFilter.doFilter(LoginCheckFilter.java:69)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    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:462)
    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:395)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
    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.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

mai 29, 2013 3:27:10 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [Faces Servlet] in context with path [/EMS2App] threw exception [null] with root cause
java.lang.NullPointerException
    at org.primefaces.component.picklist.PickListRenderer.encodeMarkup(PickListRenderer.java:86)
    at org.primefaces.component.picklist.PickListRenderer.encodeEnd(PickListRenderer.java:59)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:63)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:47)
    at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:202)
    at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:119)
    at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:56)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:63)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:47)
    at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:202)
    at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:119)
    at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:56)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:881)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:851)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:439)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:124)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
    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:594)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.test.ems2.filter.AdminPagesFilter.doFilter(AdminPagesFilter.java:31)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.test.ems2.filter.LoginCheckFilter.doFilter(LoginCheckFilter.java:69)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    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:462)
    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:395)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
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.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

.xhml代码：

<p:panel>
                        <div>
                            <p:pickList id="pojoPickListTask" value="#{taskMB.taskDual}"
                                var="task" itemValue="#{taskMB.task}"
                                itemLabel="#{task.task.nameTask}" converter="taskConverter"  showSourceControls="true"
                                showTargetControls="true" showSourceFilter="true"
                                showTargetFilter="true" filterMatchMode="contains">

                                <f:facet name="sourceCaption">Task Added</f:facet>
                                <f:facet name="targetCaption">Task Removed</f:facet>
                                <p:ajax event="transfer" listener="#{taskMB.onTransfer}"
                                    update="msg" />
                                <p:column>  
                                       #{task.nameTask}  
                                </p:column>
                            </p:pickList>
                        </div>
                    </p:panel>