目标无法到达，标识符为"Bean名称".解析为空 [英] Target Unreachable, identifier "Bean Name" resolved to null
问题描述
我低于错误.我是JSF的新手.
I m getting below error. I m new to JSF.
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>
推荐答案
在 h:outputLabel ，在JSF生命周期的早期阶段，与可以评估表达式"#{userbean.userName}"相比，for属性必须对String求值.因此，您需要给它一个这样的String值:
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"/>
关于JSF生命周期，请参见此链接 :
See this link about JSF lifecycle:
还原视图阶段 在此阶段，JavaServer Faces实现将构建页面视图. 如果对页面的请求是初始请求，则JavaServer Faces实施在此阶段会创建一个空视图，并且 生命周期进入渲染响应"阶段，在此阶段 空视图中填充了标记所引用的组件 页面.
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.
因此，当已经建立了(空)视图时，不会在渲染响应"阶段之前评估bean的值.
So, the bean value is evaluated not before the Render Response phase, when the (empty) view has already been built.
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