在JSP中找不到屬性異常EL

Question

非常討厭。不知道爲什麼會出現這個錯誤。在下面的代碼

NOTE: 

if I only use <td>${user.id}</td> than its printing id properly but on ${user.username} property generating error. See below JSP page code. 

If I use below code in JSP page like to test than I get all the objects and properties 


<c:forEach var="user" items="${users}" varStatus="i"> 
    <tr> 
     <td>${users[i.index]}</td> 
    </tr>      
</c:forEach> 

Result: 

User[id=1,username=u1,password=p1,firstname=f1,lastname=l1,dob=2012-07-01,age=40] 
User[id=2,username=u2,password=p2,firstname=f2,lastname=l2,dob=2012-07-02,age=39] 
User[id=3,username=u3,password=p3,firstname=f3,lastname=l3,dob=2012-07-03,age=38] 

ERROR：

09:49:49,047 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/crud_jsp_servlet_cdi_jdbc_tagfile].[jsp]] (http-localhost-127.0.0.1-8080-1) Servlet.service() for servlet jsp threw exception: javax.el.PropertyNotFoundException: The class 'com.myapp.dao.User' does not have the property 'username'. 
    at javax.el.BeanELResolver.getBeanProperty(BeanELResolver.java:661) [jboss-el-api_2.2_spec-1.0.0.Final.jar:1.0.0.Final] 
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:290) [jboss-el-api_2.2_spec-1.0.0.Final.jar:1.0.0.Final] 
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:175) [jboss-el-api_2.2_spec-1.0.0.Final.jar:1.0.0.Final] 
    at org.apache.el.parser.AstValue.getValue(AstValue.java:169) [jbossweb-7.0.13.Final.jar:] 
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189) [jbossweb-7.0.13.Final.jar:] 
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:935) [jbossweb-7.0.13.Final.jar:] 
    at org.apache.jsp.WEB_002dINF.admin.UserList_jsp._jspx_meth_c_005fforEach_005f0(UserList_jsp.java:137) 
    at org.apache.jsp.WEB_002dINF.admin.UserList_jsp.access$1(UserList_jsp.java:114) 
    at org.apache.jsp.WEB_002dINF.admin.UserList_jsp$Helper.invoke1(UserList_jsp.java:215) 
    at org.apache.jsp.WEB_002dINF.admin.UserList_jsp$Helper.invoke(UserList_jsp.java:240) 
    at org.apache.jsp.tag.web.layout_tag.doTag(layout_tag.java:120) 
    at org.apache.jsp.WEB_002dINF.admin.UserList_jsp._jspx_meth_tags_005flayout_005f0(UserList_jsp.java:96) 
    at org.apache.jsp.WEB_002dINF.admin.UserList_jsp._jspService(UserList_jsp.java:69) 
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) [jbossweb-7.0.13.Final.jar:] 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final] 

JSP頁：

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" 
    pageEncoding="ISO-8859-1"%> 

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%> 
<%@ taglib prefix="tags" tagdir="/WEB-INF/tags"%> 

<tags:layout path="${pageContext.request.contextPath}"> 
    <jsp:attribute name="search"> 
     <tags:search /> 
    </jsp:attribute> 
    <jsp:body> 
     <div class="mainDiv"> 
      <table class="table table-striped table-bordered table-condensed"> 
       <thead> 
        <tr> 
         <th>Id</th> 
         <th>UserName</th> 
         <th>Password</th> 
         <th>FirstName</th> 
         <th>LastName</th> 
         <th>Date of Birth</th> 
         <th>Age</th> 
         <th>Actions</th> 
        </tr> 
       </thead> 
       <tbody> 
        <c:forEach var="user" items="${users}"> 
         <tr> 
          <td>${user.id}</td> 
          <td>${user.username}</td> 
          <td>${user.password}</td> 
          <td>${user.firstname}</td> 
          <td>${user.lastname}</td> 
          <td>${user.dob}</td> 
          <td>${user.age}</td> 
          <td><a href="#"><i class="icon-edit"></i></a> <a href="#"><i 
            class="icon-trash"></i></a></td> 
         </tr> 
        </c:forEach> 
       </tbody> 
      </table> 
     </div> 
    </jsp:body> 
</tags:layout> 

User.java

package com.myapp.dao; 

import java.sql.Date; 


public class User { 

    private Long id; 
    private String username; 
    private String password; 
    private String firstname; 
    private String lastname; 
    private Date dob; 
    private int age; 

    public User(){ 
    }; 

    public User(Long id, String username, String password, String firstname, String lastname, Date dob, int age){ 

     this.id = id; 
     this.username = username; 
     this.password = password; 
     this.firstname = firstname; 
     this.lastname = lastname; 
     this.dob = dob; 
     this.age = age; 
    } 

    public Long getId(){ 
     return id; 
    } 

    public void setId(Long id){ 
     this.id = id; 
    } 

    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 getFirstName(){ 
     return firstname; 
    } 

    public void setFirstName(String firstname){ 
     this.firstname = firstname; 
    } 

    public String getLastName(){ 
     return lastname; 
    } 

    public void setLastName(String lastname){ 
     this.lastname = lastname; 
    } 

    public Date getDob(){ 
     return dob; 
    } 

    public void setDob(Date dob){ 
     this.dob = dob; 
    } 

    public int getAge(){ 
     return age; 
    } 

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

    public String getFullName(){ 
     return this.firstname + " " + this.lastname; 
    } 

} 

Selvlet：

List<User> users = null; 
     userDAO = new UserDAOJDBC(); 

     users = userDAO.listUsers(); 
     request.setAttribute("users", users); 

     String path = "/WEB-INF/admin/UserList.jsp"; 
     getServletContext().getRequestDispatcher(path).forward(request, response); 

Answer 1

案例事項的Java Bean的屬性。在EL中，您嘗試訪問屬性username，但在bean中您有getUserName/setUserName。改用getUsername/setUsername（小寫'n'）。