JSP ForEach 循环和 PropertyNotFoundExceptions 中的错误

Question

我是 java 的新手，我正在使用 Eclipse IDE。我正在做一个项目，其中管理员正在向系统添加员工。我需要通过从数据库中检索数据并在单独的 table（单独的 jsp 页面）中查看来显示员工列表。即使数据已添加到数据库中，我也无法检索它。我在 jsp 页面中使用了 for each 循环。当调用视图页面 jspPropertyNotFoundException 时。

型号类

public class Person {

    private String Nic;
    private String Name;
    private String Email;
    private String Phone;
    private String Address;


   public Person(String Nic, String Name, String Email, String Phone, String Address) {

        this.Nic = Nic;
        this.Name = Name;
        this.Email = Email;
        this.Phone = Phone;
        this.Address = Address;
    }

    public void setNic(String Nic) {
        this.Nic = Nic;
    }

    public String getNic() {
        return Nic;
    }

public class Employee extends Person  {


    private String YearsOfExperience;
    private String Specialization;
    private String Salary;




    public Employee(String Nic, String Name, String Email, String Phone, String Address, String YearsOfExperience,
            String Specialization, String Salary) {
        super(Nic, Name, Email, Phone, Address);
        this.YearsOfExperience = YearsOfExperience;
        this.Specialization = Specialization;
        this.Salary = Salary;
    }

    public String getYearsOfExperience() {
        return YearsOfExperience;
    }

jsp页面我要显示数据(EmployeeList.jsp)

 <%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<table>
 <c:forEach var="emp" items="${employeeDetails}">

                                 <c:set var="Nic" value="${emp.Nic}"/>
                                 <c:set var="Name" value="${emp.Name}"/>
                                 <c:set var="Email" value="${emp.Email}"/>
                                 <c:set var="Phone" value="${emp.Phone}"/>
                                 <c:set var="Address" value="${emp.Address}"/>
                                 <c:set var="YearsOfExperience" value="${emp.YearsOfExperience}"/>
                                 <c:set var="Specialization" value="${emp.Specialization}"/> 
                                 <c:set var="Salary" value="${emp.Salary}"/>


                  <tbody>
                    <tr>
                            <td>${emp.Nic}</td>
                            <td>${emp.Name}</td>
                            <td>${emp.Email}</td>
                            <td>${emp.Phone}</td>
                            <td>${emp.Address}</td>
                            <td>${emp.YearsOfExperience}</td>
                            <td>${emp.Specialization}</td>
                            <td>${emp.Salary}</td>

                    </tr>


                  </tbody>
                  </c:forEach>
</table>

添加员工 Servlet

@WebServlet("/addEmployeeServlet")
public class addEmployeeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String Nic= request.getParameter("Nic");
        String Name= request.getParameter("Name");
        String Email= request.getParameter("Email");
        String Phone= request.getParameter("Phone");
        String Address= request.getParameter("Address");
        String YearsOfExperience= request.getParameter("YearsOfExperience");
        String Specialization = request.getParameter("Specialization");
        String Salary= request.getParameter("Salary");

        boolean isTrue;

        isTrue = EmployeeDBUtil.AddEmployee(Nic,Name,Email,Phone,Address,YearsOfExperience,Specialization,Salary);

        //if inserted to database
        if(isTrue == true) {

            List <Employee> employeeDetails = EmployeeDBUtil.viewAllEmployee();
            request.setAttribute("employeeDetails",employeeDetails);


            RequestDispatcher dis1 =request.getRequestDispatcher("EmployeeList.jsp");
            dis1.forward(request, response);

        }
        else {
            RequestDispatcher dis2 =request.getRequestDispatcher("Unsuccess.jsp");
            dis2.forward(request, response);

        }

    }

EmployeeDBUtil

public class EmployeeDBUtil {

    private static Connection con= null;
    private static Statement stmt = null;
    private static ResultSet rs = null;
    private static boolean isSuccess;

    // data from the database
    public static List<Employee> viewAllEmployee()  {


          ArrayList <Employee> emp = new ArrayList<>();

            try {
                con = DBconnection.getConnection();
                stmt = con.createStatement(); 
                String sql = "Select * from employee";
                rs= stmt.executeQuery(sql);



                while(rs.next()) {
                    String Nic= rs.getString(1);
                    String Name = rs.getString(2);
                    String Email = rs.getString(3);
                    String Phone =rs.getString(4);
                    String Address =rs.getString(5);
                    String YearsOfExperience =rs.getString(6);
                    String Specialization =rs.getString(7);
                    String Salary =rs.getString(8);

                    Employee e = new Employee(Nic,Name,Email,Phone,Address,YearsOfExperience,Specialization,Salary);
                    emp.add(e);

                    System.out.println("im here");
                }
            }catch(Exception e){
                e.printStackTrace();
         }


         return emp;

       }

网页Xml文件

?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
         http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

<servlet>
 <servlet-name>AddEmployee</servlet-name>
 <servlet-class>com.carepoint.servlet.addEmployeeServlet</servlet-class>
</servlet>

<servlet-mapping>
  <servlet-name>AddEmployee</servlet-name>
  <url-pattern>/Add</url-pattern>
</servlet-mapping>

 </web-app>

当我将员工添加到系统时，系统会转到 EmployeeList.jsp 页面，但它会显示 table 或列表。尽管 Nic 是真人模特。这是显示的错误。

May 09, 2020 7:04:31 PM org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet [jsp] threw exception
org.apache.jasper.el.JspPropertyNotFoundException: /EmployeeList.jsp(315,9) '${emp.Nic}' Property [Nic] not found on type [com.carepoint.model.Employee]
    at org.apache.jasper.el.JspValueExpression.getValue(JspValueExpression.java:120)
    at org.apache.jsp.EmployeeList_jsp._jspx_meth_c_005fset_005f0(EmployeeList_jsp.java:659)
    at org.apache.jsp.EmployeeList_jsp._jspx_meth_c_005fforEach_005f0(EmployeeList_jsp.java:558)
    at org.apache.jsp.EmployeeList_jsp._jspService(EmployeeList_jsp.java:441)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:71)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:384)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312)
    at com.carepoint.servlet.addEmployeeServlet.doPost(addEmployeeServlet.java:48)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

May 09, 2020 7:04:31 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [AddEmployee] in context with path [/Care-Point-Service-Station] threw exception [An exception occurred processing [/EmployeeList.jsp] at line [315]

312:                   
313:                   <c:forEach var="emp" items="${employeeDetails}">
314:                                 
315:                                 <c:set var="Nic" value="${emp.Nic}"/>
316:                                 <c:set var="Name" value="${emp.Name}"/>
317:                                 <c:set var="Email" value="${emp.Email}"/>
318:                                 <c:set var="Phone" value="${emp.Phone}"/>


Stacktrace:] with root cause
org.apache.jasper.el.JspPropertyNotFoundException: /EmployeeList.jsp(315,9) '${emp.Nic}' Property [Nic] not found on type [com.carepoint.model.Employee]
    at org.apache.jasper.el.JspValueExpression.getValue(JspValueExpression.java:120)
    at org.apache.jsp.EmployeeList_jsp._jspx_meth_c_005fset_005f0(EmployeeList_jsp.java:659)
    at org.apache.jsp.EmployeeList_jsp._jspx_meth_c_005fforEach_005f0(EmployeeList_jsp.java:558)
    at org.apache.jsp.EmployeeList_jsp._jspService(EmployeeList_jsp.java:441)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:71)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:384)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312)
    at com.carepoint.servlet.addEmployeeServlet.doPost(addEmployeeServlet.java:48)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

为什么我无法检索数据？

Answer 1

在您的代码中解决以下问题：

关注 Java naming conventions 例如Nic 应命名为 nic。您违反了所有变量的约定。
因为已经使用注解@WebServlet，所以不需要在web.xml中声明映射。

下面给出的是 Minimal, Complete, and Verifiable example:

Person.java:

package beans;

public class Person {
    private String nic;
    private String name;
    private String email;
    private String phone;
    private String address;

    public Person(String nic, String name, String email, String phone, String address) {
        this.nic = nic;
        this.name = name;
        this.email = email;
        this.phone = phone;
        this.address = address;
    }
    public String getNic() {
        return nic;
    }
    public void setNic(String nic) {
        this.nic = nic;
    }
}

Employee.java:

package beans;

public class Employee extends Person {
    private String yearsOfExperience;
    private String specialization;
    private String salary;

    public Employee(String nic, String name, String email, String phone, String address, String yearsOfExperience,
            String specialization, String salary) {
        super(nic, name, email, phone, address);
        this.yearsOfExperience = yearsOfExperience;
        this.specialization = specialization;
        this.salary = salary;
    }
}

AddEmployeeServlet.java:

package servlets;

import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import beans.Employee;

@WebServlet("/addEmployeeServlet")
public class AddEmployeeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        List<Employee> employeeDetails = List.of(new Employee("123", null, null, null, null, null, null, null),
                new Employee("456", null, null, null, null, null, null, null));
        request.setAttribute("employeeDetails", employeeDetails);
        request.getRequestDispatcher("employees.jsp").forward(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
}

employees.jsp:

<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<table>
    <c:forEach var="emp" items="${employeeDetails}">
        <tr>
            <td>${emp.nic}</td>
        </tr>
    </c:forEach>
</table>

输出：

JSP ForEach 循环和 PropertyNotFoundExceptions 中的错误

JSP Error in ForEach Loop and PropertyNotFoundExceptions

java

eclipse

foreach

jsp

propertynotfoundexception