代码之家  ›  专栏  ›  技术社区  ›  Tankske

访问其他bean或属性时的Jsf NullPointerException ManagedBean

managed-bean nullpointerexception jsf java
  •  4
  • Tankske  · 技术社区  · 10 年前

    搜索了几个小时后,我终于找到了导致nullpointerexception的原因。这是在QuestionController.create()中使用属性Survey。当我注释掉getSurvey()行时。。该页面工作正常。所有其他功能也很好。只有QuestionController.create()不起作用。我知道我注入的managedProperty在页面上正确显示surveyname(questionController.surveyname)时工作。

    有人知道为什么我的QuestionController在尝试使用create()函数时变为Null吗? 

    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)
at javax.faces.component.UICommand.broadcast(UICommand.java:315)
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: java.lang.NullPointerException
at com.survey.jsfController.QuestionController.create(QuestionController.java:69)
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 javax.el.ELUtil.invokeMethod(ELUtil.java:326)
at javax.el.BeanELResolver.invoke(BeanELResolver.java:536)
at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:256)
at com.sun.el.parser.AstValue.invoke(AstValue.java:269)
at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:304)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
... 35 more

    我的托管bean QuestionController 

    @SessionScoped
@ManagedBean(name = "questionController")
public class QuestionController extends Controller  implements Serializable {

private QuestionService questionService;
private QuestionTypeService questionTypeService;

public QuestionController() {
    setQuestionService(ApplicationController.getQuestionService());
    setQuestionTypeService(ApplicationController.getQuestionTypeService());
    question = new Question();
}

@PostConstruct
private void init(){
    setSurvey(getSessionController().getSurvey());
}

private static final long serialVersionUID = 1L;

private Question question;

private Survey survey;

private String surveyId;

@ManagedProperty("#{sessionController}")
private SessionController sessionController;

public Question getQuestion() {
    return question;
}

public void setQuestion(Question question) {
    this.question = question;
}

public List<Question> getQuestions() {
        return getQuestionService().retrieveAll();
}

public List<QuestionType> getQuestionTypes() {
        return getQuestionTypeService().retrieveAll();
}

public void create() {
    //TODO: link survey with this question
    getSurvey().getQuestions().add(getQuestion());
    //surveyService.update(survey);
    questionService.create(getQuestion());
    FacesContext.getCurrentInstance().addMessage("questionCreation", new FacesMessage("Question has been created succesfully!"));
}

public String update() {
    questionService.update(question);
    FacesContext.getCurrentInstance().addMessage("questionCreation", new FacesMessage("Question has been updated succesfully!"));
    return "overview";
}

public String delete() throws RemoteException {
    getQuestionService().delete(question);
    FacesContext.getCurrentInstance().addMessage("questionDeletion",
            new FacesMessage("Question has been deleted succesfully!"));
    return "overview";
}

public String show(Question question){
    if (question != null) setQuestion(question);
    return "detail";
}

public String update(Question question){
    if (question != null) setQuestion(question);
    return "update";
}

public String delete(Question question){
    if (question != null) setQuestion(question);
    return "delete";
}

public void setSurveyId(String survey) {
    this.surveyId = survey;
}

public String getSurveyId() {
    return this.surveyId;
}

@Override
public void clear(){
    setQuestion(null);
    FacesContext.getCurrentInstance().addMessage("formClearing", new FacesMessage("Form cleared!!", "The answer creation has been submitted successfully"));
}

public SessionController getSessionController() {
    return sessionController;
}

public void setSessionController(SessionController sessionController) {
    this.sessionController = sessionController;
}

public Survey getSurvey() {
    return survey;
}

public void setSurvey(Survey survey) {
    this.survey = survey;
}

public QuestionService getQuestionService() {
    return questionService;
}

public void setQuestionService(QuestionService questionService) {
    this.questionService = questionService;
}

public QuestionTypeService getQuestionTypeService() {
    return questionTypeService;
}

public void setQuestionTypeService(QuestionTypeService questionTypeService) {
    this.questionTypeService = questionTypeService;
}

}

    我的托管bean SessionController 

    @SessionScoped
@ManagedBean(name = "sessionController")
public class SessionController extends Controller{

private Survey survey;

private String emailAddress;

private String password;


public String getEmailAddress() {
    return emailAddress;
}

public void setEmailAddress(String emailAddress) {
    this.emailAddress = emailAddress;
}

public String getPassword() {
    return password;
}

public void setPassword(String password) {
    this.password = password;
}

public String login() {

    return "about";
}

public String logout() {
    FacesContext.getCurrentInstance().getExternalContext().invalidateSession();
    return "login";
}

public Survey getSurvey() {
    return survey;
}

public void setSurvey(Survey survey) {
    this.survey = survey;
}

    问题Create.xhtml 

            <p>Step 1: Created survey: #{questionController.surveyId}</p>
        <p>
            <strong>Step 2: Create questions</strong>
        </p>
        <p>Step 3: Create benchmark</p>
        <p>Step 4: Create graph per question</p>

        <p:panelGrid columns="2">

            <f:facet name="header">Create question for survey #{questionController.survey.surveyName} </f:facet>

            <h:outputText value="#{msg['question']}" for="question" />
            <h:inputText id="question"
                value="#{questionController.question.question}"></h:inputText>

            <h:outputText value="#{msg['selectType']}" for="questionType" />
            <p:selectOneMenu id="questionType"
                value="#{questionController.question.questionType}" effect="fold"
                editable="true" converter="questionTypeConverter">
                <!-- selectItem used to display as reset value/empty value -->
                <f:selectItem itemLabel="select questionType" itemValue=""/>
                <!-- selectItems used to fill with value from a collection -->
                <f:selectItems value="#{questionController.questionTypes}" var="q"
                    itemLabel="#{q.typeName}" />
            </p:selectOneMenu>

            <f:facet name="footer">
                <h:panelGroup>
                    <h:commandButton value="#{msg['createButton']}"
                        action="#{questionController.create()}"/>
                    <h:commandButton value="Clear"
                        action="#{questionController.clear()}" immediate="true">
                        <f:resetValues render="form form:question" />
                    </h:commandButton>
                </h:panelGroup>
            </f:facet>
        </p:panelGrid>

        <h:messages style="color:red" />

        <p />

        <ui:include src="listRetrieveComponent.xhtml"></ui:include>


    </ui:define>

    谢谢你看一看!

    2 回复  |  直到 10 年前
        1
  •  1
  •   pamps    10 年前

    也许调查的问题列表尚未初始化。因此,在你有问题之前,你应该检查survey.getQuestions()是否为空,如果为空,你应该初始化它。

        2
  •  1
  •   akash    10 年前

    您正在设置 Survey 在里面 @PostConstruct 

    @PostConstruct
private void init(){
    setSurvey(getSessionController().getSurvey());
    //But Survey survey; is null of SessionController
    //getSessionController().getSurvey() is giving you null
}

    但是 Survey survey; 属于 SessionController 是 null 您必须初始化它,以便首先实例化 调查 在构造函数中,或者在使用它之前确保它不为空。 

    public class SessionController extends Controller{
   private Survey survey;//Not Initialized
   private String emailAddress;
   private String password;
   ...

    注释后编辑:

    比我想象的好 getSurvey().getQuestions() 正在返回 无效的 这就是原因 NPE .

    推荐文章
    Chathura Buddhika  ·  如何将JSF InputText值传递给ajax侦听器
    6 年前
    Luis Pavez  ·  在actionListener完成之前更新组件
    6 年前
    Sandeep YS  ·  primefaces-使用额外下拉菜单上载多个文件
    6 年前
    Pascal  ·  Primefaces更改延迟输出面板内inputSwitch的值
    6 年前
    Bruno A  ·  未调用Primefaces dialog over dialog方法
    6 年前
    Filou  ·  Omnifaces validateBean:无法获取ShowMessage以使AtterBute正常工作
    6 年前
    Sechanris  ·  使用JSF selectOneListbox存储Liferay 7 portlet首选项
    6 年前
    Atul  ·  两个不同h:commandButton操作的条件呈现
    6 年前
    J Dev  ·  自定义p:dataTable的导出输出格式
    6 年前
    ecdhe  ·  Forward方法是在页面加载时激发的,而不是在链接点击时激发的
    6 年前
    关于   移动版
    代码之家 - 一站式码农服务社区
    沪ICP备11025650号