访问其他bean或属性时，Jsf NullPointerException ManagedBean

Question

在搜索了几个小时之后，我终于找到了导致nullpointerexception的原因。 这是我在QuestionController.create（）中使用属性Survey。 当我注释掉getSurvey（）行时，页面工作得很好。 所有其他功能也可以正常工作。 只有QuestionController.create（）不起作用。 我知道我注入的managedProperty可以在页面上正确显示surveyname（questionController.survey.surveyName）。

有没有人知道为什么我的QuestionController在尝试使用create（）函数时会变为Null？

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;
}

questionCreate.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>

谢谢你看看！

Answer 1

您正在@PostConstruct中设置Survey

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

但 Survey survey; 对于SessionController为null您必须初始化它，因此您必须首先在构造函数中实例化Survey或确保它在使用之前不为null。

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

---

评论后编辑：

好吧，我认为getSurvey().getQuestions()返回null ，这是导致NPE的原因。

Answer 2

也许调查的问题清单尚未初始化。 所以在你有问题之前，你应该检查一下survey.getQuestions（）是否为null，如果你是初始化它。