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我得到以下错误。我是 JSF 的新手。

Jul 21, 2013 6:24:04 PM com.sun.faces.lifecycle.ProcessValidationsPhase execute
WARNING: /index.xhtml @18,65 value="#{userbean.userName}": Target Unreachable, identifier 'userbean' resolved to null
javax.el.PropertyNotFoundException: /index.xhtml @18,65 value="#{userbean.userName}": Target Unreachable, identifier 'userbean' resolved to null
    at com.sun.faces.facelets.el.TagValueExpression.getType(TagValueExpression.java:100)
    at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:95)
    at javax.faces.component.UIInput.getConvertedValue(UIInput.java:1030)
    at javax.faces.component.UIInput.validate(UIInput.java:960)
    at javax.faces.component.UIInput.executeValidate(UIInput.java:1233)
    at javax.faces.component.UIInput.processValidators(UIInput.java:698)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
    at javax.faces.component.UIForm.processValidators(UIForm.java:253)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
    at org.primefaces.component.panel.Panel.processValidators(Panel.java:284)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
    at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1172)
    at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:76)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Unknown Source)

这是我的代码：

package com.jsf.dev.bean;

import java.io.Serializable;

import javax.faces.bean.ManagedBean;

@ManagedBean(name = "userbean")
public class UserBean implements Serializable {

    private static final long serialVersionUID = 1L;
    private String userName;
    private String userPassword;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getUserPassword() {
        return userPassword;
    }

    public void setUserPassword(String userPassword) {
        this.userPassword = userPassword;
    }

    public String login(){
        return "login";
    }
}

XHTML：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3c.org/1999/xhtml"
      xmlns:f="http://java.sun.com/jsf/core"
      xmlns:h="http://java.sun.com/jsf/html"
      xmlns:p="http://primefaces.org/ui">

<h:head>

</h:head>
<h:body>
    <center>
        <p:panel header="Login Form" style="width:350;">
            <h:form>
                <h:panelGrid columns="2" cellpadding="2">
                    <h:outputLabel for="#{userbean.userName}" value="UserName" />
                    <h:inputText value="#{userbean.userName}" label="UserName"></h:inputText>
                    <h:outputLabel for="#{userbean.userPassword}" value="Password" />
                    <h:inputSecret value="#{userbean.userPassword}"></h:inputSecret>
                    <h:commandButton type="submit" value="Login"
                        action="#{userbean.login}"></h:commandButton>
                </h:panelGrid>
            </h:form>
        </p:panel>
        <div>
            <h:messages></h:messages>
        </div>
    </center>
</h:body>
</html>
4

1 回答 1

4

In h:outputLabel, the for attribute must evaluate to String in an earlier phase of the JSF lifecycle than when the expression "#{userbean.userName}" can be evaluated. Therefore, you need to give it a String value like this:

<h:outputLabel for="userName" value="UserName" />
<h:inputText id="userName" value="#{userbean.userName}" label="UserName"/>

See this link about JSF lifecycle:

Restore View Phase During this phase, the JavaServer Faces implementation builds the view of the page ... If the request for the page is an initial request, the JavaServer Faces implementation creates an empty view during this phase and the lifecycle advances to the Render Response phase, during which the empty view is populated with the components referenced by the tags in the page.

So, the bean value is evaluated not before the Render Response phase, when the (empty) view has already been built.

于 2013-07-21T10:51:47.677 回答