目标不可达标识符解析为空 [英] Target Unreachable identifier resolved to null

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本文介绍了目标不可达标识符解析为空的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

大家好，我是jsp的新手，这是我学习的第一个项目，即托管bean，导航规则和其他内容，我看不到这里存在什么问题.我所有的代码都是这些.请帮助我，因为我快要找到这个了.错误是/pages/login.jsp(31,2)'#{employee.username}'无法到达目标，标识符'employee'解析为空

hi everyone Im new at jsp and this is my first project I learned managed beans, navigation rules and stuff and I cant see what the problem is in here. all my codes are those. Please help me because Im going crazy trying to find this. ERROR is /pages/login.jsp(31,2) '#{employee.username}' Target Unreachable, identifier 'employee' resolved to null

Employee.java 

package com;

public class Employee {
    private String username;
    private String password;
    private String name;
       private String department;
       private int age;
       private double salary;
       private boolean canEdit;

       public Employee (String username,String password,String name,String department,int age,double salary){
          this.username = username;
          this.password = password;
          this.name = name;
          this.department = department;
          this.age = age;
          this.salary = salary;
          canEdit = false;
       }

       public String getUsername() {
          return username;
       }
       public void setUsername(String username) {
          this.username = username;
       }
       public String getPassword() {
          return password;
       }
       public void setPassword(String password) {
          this.password = password;
       }
       public String getName() {
          return name;
       }
       public void setName(String name) {
          this.name = name;
       }

       public String getDepartment() {
          return department;
       }

       public void setDepartment(String department) {
          this.department = department;
       }

       public int getAge() {
          return age;
       }

       public void setAge(int age) {
          this.age = age;
       }

       public double getSalary() {
          return salary;
       }

       public void setSalary(double salary) {
          this.salary = salary;
       }

       public boolean isCanEdit() {
          return canEdit;
       }

       public void setCanEdit(boolean canEdit) {
          this.canEdit = canEdit;
       }    

}

UserData.java 

package com;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;

public class UserData implements Serializable {

private static final long serialVersionUID = 1L;

   private String username;
   private String password;
   private String name;
   private String department;
   private int age;
   private double salary;

   private static final ArrayList<Employee> employees
      = new ArrayList<Employee>(Arrays.asList(
      new Employee("1","1","John", "Marketing", 30,2000.00),
      new Employee("2","2","Robert", "Marketing", 35,3000.00),
      new Employee("3","3","Mark", "Sales", 25,2500.00),
      new Employee("4","4","Chris", "Marketing", 33,2500.00),
      new Employee("5","5","Peter", "Customer Care", 20,1500.00)
   ));  


   public ArrayList<Employee> getEmployees() {
      return employees;
   }

   public String addEmployee() {         
      Employee employee = new Employee(username,password,name,department,age,salary);
      employees.add(employee);
      return null;
   }

   public String deleteEmployees(Employee employee) {
      employees.remove(employee);       
      return null;
   }

   public String editEmployee(Employee employee){
      employee.setCanEdit(true);
      return null;
   }
   public String saveEmployees(){
      for (Employee employee : employees){
         employee.setCanEdit(false);
      }     
      return null;
   }
       public String getUsername() {
          return username;
       }
       public void setUsername(String username) {
          this.username = username;
       }
       public String getPassword() {
          return password;
       }
       public void setPassword(String password) {
          this.password = password;
       }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public String getDepartment() {
      return department;
   }
   public void setDepartment(String department) {
      this.department = department;
   }

   public int getAge() {
      return age;
   }

   public void setAge(int age) {
      this.age = age;
   }

   public double getSalary() {
      return salary;
   }

   public void setSalary(double salary) {
      this.salary = salary;
   }
   public String loginAction(){
         String action = null;

         if (username.equalsIgnoreCase("admin") && password.equalsIgnoreCase("a"))
             action = "loginAdmin";
         else
             action = "loginUser";

         return action;
     }
}

home.jsp 

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="f" uri="http://java.sun.com/jsf/core"%>
<%@ taglib prefix="h" uri="http://java.sun.com/jsf/html"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<style>
.employeeTable{   
   border-collapse:collapse;
   border:1px solid #000000;
}

.employeeTableHeader{
   text-align:center;
   background:none repeat scroll 0 0 #B5B5B5;
   border-bottom:1px solid #000000;  
   padding:2px;
}

.employeeTableOddRow{
   text-align:center;
   background:none repeat scroll 0 0 #FFFFFFF;  
}

.employeeTableEvenRow{
   text-align:center;
   background:none repeat scroll 0 0 #D3D3D3;
}</style>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
      <title>DataTable</title>      
</head>
<body><f:view>
   <h2>DataTable Example</h2>
   <h:form>
      <h:dataTable value="#{userData.employees}" var="employee"
         styleClass="employeeTable"
         headerClass="employeeTableHeader"
         rowClasses="employeeTableOddRow,employeeTableEvenRow">
         <h:column>                 
            <f:facet name="header">Name</f:facet>                   
            <h:inputText id="name" value="#{employee.name}"></h:inputText>
         </h:column>
         <h:column>
            <f:facet name="header">Department</f:facet>
            <h:inputText id="department" value="#{employee.department}"></h:inputText>
         </h:column>
         <h:column>
            <f:facet name="header">Age</f:facet>
            <h:inputText id="age" value="#{employee.age}"></h:inputText>
         </h:column>
         <h:column>
            <f:facet name="header">Salary</f:facet>
            <h:inputText id="salary" value="#{employee.salary}"></h:inputText>
         </h:column>
         <h:column>

               <h:commandButton value="Delete" 
                  action="#{userData.deleteEmployee}" >                
                  <f:setPropertyActionListener 
                     target="#{userData.employees}" value="#{employee}" />
               </h:commandButton>

         </h:column>
      </h:dataTable>
      <h3>Add Employee</h3>
      <hr/>
      <table>
      <tr>
           <td>Name :</td>
           <td><h:inputText size="10" value="#{userData.name}" /></td>
      </tr>
      <tr>
           <td>Department :</td>
           <td><h:inputText size="20" value="#{userData.department}" /></td>
      </tr>
      <tr>
           <td>Age :</td>
           <td><h:inputText size="5" value="#{userData.age}" /></td>
      </tr>
      <tr>
           <td>Salary :</td>
           <td><h:inputText size="5" value="#{userData.salary}" /></td>
      </tr>
      <tr>
           <td> </td>
           <td><h:commandButton value="Add Employee" 
              action="#{userData.addEmployee}" /></td>
      </tr>
      </table>
   </h:form></f:view>
</body>
</html>

login.jsp 

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<f:view>
    <b><h:outputText value="USER Login"> </h:outputText></b>
    <p>
    <h:messages style="color: blue"/></p>
 <h:form>
    <h:panelGrid  columns="2">
    <h:dataTable value="#{userData.employees}" var="employee"></h:dataTable>
    <%-- 
    <h:dataTable value="#{userData.employees}" var="employee"></h:dataTable>
    <h:column>                  
            <h:outputText id="header" value="username"></h:outputText>                  
            <h:inputText id="username" value="#{employee.username}"></h:inputText>
     <br><br>                   
            <h:outputText id="header" value="password"></h:outputText>                  
            <h:inputText id="password" value="#{employee.password}"></h:inputText>
     </h:column>
    --%>
    <h:column>
    <h:outputText value="username :"></h:outputText>
    <h:inputText id="username"  value="#{employee.username}">
    </h:inputText>
 <br>
    <h:outputText value="password :"></h:outputText>
    <h:inputText id="password" value="#{employee.password}" >
    </h:inputText>
    </h:column>
    </h:panelGrid>
    <h:commandButton value="Login" action="#{userData.loginAction}"></h:commandButton><br/>
    <h:outputLink value="pages/sign.jsf"><h:outputText value="Go for Sign up."/></h:outputLink>
 </h:form>
</f:view>
</body>
</html>

faces-config.xml 

<?xml version="1.0" encoding="UTF-8"?>
<faces-config version="1.2" xmlns="http://java.sun.com/xml/ns/javaee"
 xmlns:xi="http://www.w3.org/2001/XInclude"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_1_2.xsd">
 <managed-bean>
  <managed-bean-name>userData</managed-bean-name>
  <managed-bean-class>com.UserData</managed-bean-class>
  <managed-bean-scope>session</managed-bean-scope>
 </managed-bean>
 <navigation-rule>
  <from-view-id>/pages/login.jsp</from-view-id>
  <navigation-case>
   <from-outcome>loginAdmin</from-outcome>
   <to-view-id>/pages/home.jsp</to-view-id>
  </navigation-case>
  <navigation-case>
   <from-outcome>loginUser</from-outcome>
   <to-view-id>/pages/welcome.jsp</to-view-id>
  </navigation-case>
 </navigation-rule>
</faces-config>

index.jsp 

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<jsp:forward page="/pages/login.jsf" />
</body>
</html>

错误消息 

11:45:47,704 WARN  [lifecycle]   executePhase(PROCESS_VALIDATIONS 3,com.sun.faces.context.FacesContextImpl@23ccb9) threw exception
javax.faces.FacesException: /pages/login.jsp(31,2) '#{employee.username}' Target Unreachable, identifier 'employee' resolved to null
    at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:108)
    at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:117)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:244)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179)
    at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
    at java.lang.Thread.run(Unknown Source)
Caused by: org.apache.jasper.el.JspPropertyNotFoundException: /pages/login.jsp(31,2) '#{employee.username}' Target Unreachable, identifier 'employee' resolved to null
    at org.apache.jasper.el.JspValueExpression.getType(JspValueExpression.java:61)
    at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:81)
    at javax.faces.component.UIInput.getConvertedValue(UIInput.java:934)
    at javax.faces.component.UIInput.validate(UIInput.java:860)
    at javax.faces.component.UIInput.executeValidate(UIInput.java:1065)
    at javax.faces.component.UIInput.processValidators(UIInput.java:666)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1033)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1033)
    at javax.faces.component.UIForm.processValidators(UIForm.java:229)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1033)
    at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:662)
    at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:100)
    ... 21 more
11:45:47,704 ERROR [[Faces Servlet]]   Servlet.service() for servlet Faces Servlet threw exception
org.apache.jasper.el.JspPropertyNotFoundException: /pages/login.jsp(31,2) '#{employee.username}' Target Unreachable, identifier 'employee' resolved to null
    at org.apache.jasper.el.JspValueExpression.getType(JspValueExpression.java:61)
    at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:81)
    at javax.faces.component.UIInput.getConvertedValue(UIInput.java:934)
    at javax.faces.component.UIInput.validate(UIInput.java:860)
    at javax.faces.component.UIInput.executeValidate(UIInput.java:1065)
    at javax.faces.component.UIInput.processValidators(UIInput.java:666)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1033)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1033)
    at javax.faces.component.UIForm.processValidators(UIForm.java:229)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1033)
    at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:662)
    at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:100)
    at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:117)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:244)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179)
    at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
    at java.lang.Thread.run(Unknown Source)

推荐答案

正如BalusC所说，这是很久以前就已弃用的.除了他提到的资源外，我认为您应该在自己的博客上搜索Google，在这里您将找到学习JSF所需的一切.
关于您的实际问题，请注意，在login.jsp页面中，您将关闭在datatable定义employee var的位置:

As BalusC said, this is since long time ago deprecated. And in addition to the resources he mentioned, I think you should google his own blog where you will find everything you need to learn JSF.
As for your real problem, notice that in your login.jsp page you are closing the datatable where you defined the employee var: 

<h:dataTable value="#{userData.employees}" var="employee"></h:dataTable>

在评论部分之前.然后您在呼叫

right before the commented part. And then you are calling 

<h:inputText id="username"  value="#{employee.username}">

这很正常，不会识别employee变种.

This is very normal that the employee var will not be recognised.

这篇关于目标不可达标识符解析为空的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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