如何解决java.lang.NullPointerException？

时间：2014-06-06 10:57:49

标签： spring jsf primefaces nullpointerexception

我的应用程序使用jsf2 primefaces5和spring，我尝试实现一个惰性数据表， 当我在惰性数据表中选择一行时，我收到以下错误：

Avertissement: java.lang.NullPointerException
javax.el.ELException: java.lang.NullPointerException
    at com.sun.el.parser.AstValue.invoke(AstValue.java:238)
    at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:297)
    at org.primefaces.behavior.ajax.AjaxBehaviorListenerImpl.processCustomListener(AjaxBehaviorListenerImpl.java:87)
    at org.primefaces.behavior.ajax.AjaxBehaviorListenerImpl.processArgListener(AjaxBehaviorListenerImpl.java:72)
    at org.primefaces.behavior.ajax.AjaxBehaviorListenerImpl.processAjaxBehavior(AjaxBehaviorListenerImpl.java:56)
    at org.primefaces.event.SelectEvent.processListener(SelectEvent.java:40)
    at javax.faces.component.behavior.BehaviorBase.broadcast(BehaviorBase.java:98)
    at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:764)
    at javax.faces.component.UIData.broadcast(UIData.java:890)
    at javax.faces.component.UIData.broadcast(UIData.java:912)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:781)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1246)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:77)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:308)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:113)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at com.gestion.projet.web.jsf.Lazy.onRowSelect(Lazy.java:68)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.sun.el.parser.AstValue.invoke(AstValue.java:234)
    ... 38 more

javax.faces.FacesException: java.lang.NullPointerException
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:85)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:308)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:113)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: javax.el.ELException: java.lang.NullPointerException
    at com.sun.el.parser.AstValue.invoke(AstValue.java:238)
    at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:297)
    at org.primefaces.behavior.ajax.AjaxBehaviorListenerImpl.processCustomListener(AjaxBehaviorListenerImpl.java:87)
    at org.primefaces.behavior.ajax.AjaxBehaviorListenerImpl.processArgListener(AjaxBehaviorListenerImpl.java:72)
    at org.primefaces.behavior.ajax.AjaxBehaviorListenerImpl.processAjaxBehavior(AjaxBehaviorListenerImpl.java:56)
    at org.primefaces.event.SelectEvent.processListener(SelectEvent.java:40)
    at javax.faces.component.behavior.BehaviorBase.broadcast(BehaviorBase.java:98)
    at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:764)
    at javax.faces.component.UIData.broadcast(UIData.java:890)
    at javax.faces.component.UIData.broadcast(UIData.java:912)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:781)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1246)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:77)
    ... 26 more
Caused by: java.lang.NullPointerException
    at com.gestion.projet.web.jsf.Lazy.onRowSelect(Lazy.java:68)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.sun.el.parser.AstValue.invoke(AstValue.java:234)
    ... 38 more

然后是与以下bean方法关联的代码：

@ManagedBean(name="lazyBean")
    @ViewScoped
    public class Lazy extends LazyDataModel<Projet>  {
 public void onRowSelect(SelectEvent event) {
            FacesMessage msg = new FacesMessage("Projet Selected", ((Projet) event.getObject()).getIdprojet().toString());
            FacesContext.getCurrentInstance().addMessage(null, msg);
        }

这是xhtml页面：

<h:form id="form">
            <p:dataTable var="current" value="#{ProjetComponent.lazyModel}"  
                paginator="true" rows="10" 
                paginatorTemplate="{RowsPerPageDropdown} {FirstPageLink} {PreviousPageLink} {CurrentPageReport} {NextPageLink} {LastPageLink}"
                rowsPerPageTemplate="5,10,15" selectionMode="single"
                selection="#{ProjetComponent.projet}" id="projetTable" lazy="true">
                <p:ajax event="rowSelect" listener="#{ProjetComponent.onRowSelect}"
                    update=":form:projetDetail" oncomplete="PF('projetDialog').show()" />
                <p:column headerText="Id" sortBy="#{current.idprojet}" filterBy="#{current.idprojet}">
                    <h:outputText value="#{current.idprojet}" />
                </p:column>
                <p:column headerText="Nom" sortBy="#{current.nomprojet}"
                    filterBy="#{current.nomprojet}">
                    <h:outputText value="#{current.nomprojet}" />
                </p:column>

            </p:dataTable>

            <p:dialog header="Projet Detail" widgetVar="projetDialog" modal="true"
                showEffect="fade" hideEffect="fade" resizable="false">
                <p:outputPanel id="projetDetail" style="text-align:center;">
                    <p:panelGrid columns="2"
                        rendered="#{not empty ProjetComponent.projet}"
                        columnClasses="label,value">
                        <f:facet name="header">

                        </f:facet>

                        <h:outputText value="Id:" />
                        <h:outputText value="#{ProjetComponent.projet.idprojet}" />

                        <h:outputText value="Nom:" />
                        <h:outputText value="#{ProjetComponent.projet.nomprojet}" />

                    </p:panelGrid>
                </p:outputPanel>
            </p:dialog>
        </h:form>

2 个答案:

答案 0 :(得分：-1)

你的问题是这个方法返回null 

 @Override
    public Projet getRowData(String rowKey) {
        for(Projet projet : datasource) {
            if(projet.getIdprojet().equals(rowKey))
                return projet;
        }

        return null;
    }

删除它并尝试

答案 1 :(得分：-2)

根据您的堆栈跟踪，

at com.gestion.projet.web.jsf.Lazy.onRowSelect(Lazy.java:68)，

我想，第68行是FacesMessage msg = new FacesMessage("Projet Selected", ((Projet) event.getObject()).getIdprojet().toString());

所以看起来SelectEvent event，你的参数是null，检查你传递给这个方法的内容并添加一个if语句：

public void onRowSelect(SelectEvent event) {
    if (event != null){
        FacesMessage msg = new FacesMessage("Projet Selected", ((Projet) event.getObject()).getIdprojet().toString());
        FacesContext.getCurrentInstance().addMessage(null, msg);
    }
}

您应该阅读What is a NullReferenceException, and how do I fix it?

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