无法使用jstl将对象arraylist从servlet发送或传递给jsp

Question

Hey guys I m trying to show list of users from the database table by passing arraylist object from servlet to jsp but unable to do so.

1.> Login.java

package com.pms.servlet;

public class Login {

int id;
String fname;
String mname;
String lname;
String uname;
String utype;
String emailid;
String mobno;
String address;
String password1;
String password2;


public int getUid()
{
    return id;
}
public void setUid(int id)
{
    this.id=id;
}
public String getFname()
{
    return fname;
}
public void setFname(String fname)
{
    this.fname=fname;
}
public String getMname()
{
    return mname;
}
public void setMname(String mname)
{
    this.mname=mname;
}
public String getLname()
{
    return lname;
}
public void setLname(String lname)
{
    this.lname=lname;
}
public String getUname()
{
    return uname;
}
public void setUname(String uname)
{
    this.uname=uname;
}
public String getUtype()
{
    return utype;
}
public void setUtype(String utype)
{
    this.utype=utype;
}
public String getEmailid()
{
    return emailid;
}
public void setEmailid(String emailid)
{
    this.emailid=emailid;
}
public String getMobno()
{
    return mobno;
}
public void setMobno(String mobno)
{
    this.mobno=mobno;
}
public String getAddress()
{
    return address;
}
public void setAddress(String address)
{
    this.address=address;
}
public String getPassword1()
{
    return password1;
}
public void setPassword1(String password1)
{
    this.password1=password1;
}
public String getPassword2()
{
    return password2;
}
public void setPassword2(String password2)
{
    this.password2=password2;
}
}

2.> Delete.java

package com.pms.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;

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 javax.servlet.http.HttpSession;
import javax.swing.text.html.HTMLDocument.Iterator;

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

/**
 * @see HttpServlet#HttpServlet()
 */
public Delete() {
    super();
    // TODO Auto-generated constructor stub
}

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub

        Connection conn=null;
        String url="jdbc:mysql://localhost:3306/";
        String dbName="projectmanagement";
        String driver="com.mysql.jdbc.Driver";
        String dbUserName="root";
        String dbPassword="root";

        try{
        Class.forName(driver).newInstance();
        conn = DriverManager.getConnection(url+dbName,dbUserName,dbPassword);
        String strQuery="select * from user";
        System.out.println("The sql is " +strQuery);
    Statement st= conn.createStatement();
        ResultSet rs= st.executeQuery(strQuery);

        ArrayList<Login> al=new ArrayList<Login>();

    while(rs.next())
    {
        Login l=new Login();
        //l.setUid(rs.getInt("uid"));
        l.setFname(rs.getString("fname"));
        l.setMname(rs.getString("mname"));
        l.setLname(rs.getString("lname"));
        l.setUname(rs.getString("uname"));
        l.setUtype(rs.getString("utype"));
        l.setEmailid(rs.getString("emailid"));
        l.setMobno(rs.getString("mobno"));
        l.setAddress(rs.getString("address"));
        System.out.println(l);
        System.out.println(al);
        al.add(l);

        request.setAttribute("ual",al);
        System.out.println(al);
        }

        rs.close();
        st.close();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }



        response.setContentType("text/html");


    }

 }

3.> successful.jsp

 <%@ 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" %>
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"   "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <body>

 <form name="delete-user" action="Delete" method="post">
        <p><b><i>List of user details:</i></b></p>
        <table border="1">

            <tr>
            <th>First Name</th>
            <th>Middle Name</th>
            <th>Last Name</th>
            <th>User Name</th>
            <th>Usertype</th>
            <th>Email id</th>
            <th>Mobile No</th>
            <th>Address</th>
            <th>Delete User</th>
            </tr>
        <c:forEach items="${ual}" var="u">
            <tr>
            <td><c:out value="${u.fname}"></c:out></td>
            <td><c:out value="${u.mname}"></c:out></td>
            <td><c:out value="${u.lname}"></c:out></td>
            <td><c:out value="${u.uname}"></c:out></td>
            <td><c:out value="${u.utype}"></c:out></td>
            <td><c:out value="${u.emailid}"></c:out></td>
            <td><c:out value="${u.mobno}"></c:out></td>
            <td><c:out value="${u.address}"></c:out></td>
                <td><input type="button" name="delete" value="Delete User"/>    </td>
            </tr> 
        </c:forEach>
        </table>
        </form>
  </body>
  </html>

Here, I m unable to pass the object arraylist for list of users from servlet to jsp. There no run time or compile time error. I m able to show list of users by writing query in jstl sql tag but unable to do so in java servlet code. :(

In web.xml also everything is fine and database connectivity is also properly done. Then where m I going wrong.

I checked various catch's and tutorial's but unable to do so.

Please Help.

Answer 1

You have a serious misconception. The servlet is only called when the form is submitted. So you can't expect, in the JSP, to have access to a list that should have been created and stored in the request, since the servlet doing that has never been called.

Your servlet never forwards to the JSP. All it does is send the content type of the response to text/html.

Moreover, you're storing the same list in a request attribute at every iteration of the loop, instead of doing it just once, when the loop has ended:

while(rs.next()) {
    ...
}
request.setAttribute("ual", al);

Here's what you should have:

1. A ShowUsers servlet. This servlet should have a doGet() method which gets the users, stores them in a request attribute, then forwards to a showUsers.jsp page
2. The showUsers.jsp should have one form per user (and not a single form with all the users inside). Each form should have the ID of the user to delete in a hidden input field, and a submit button to delete the user. The form should have the path of the DeleteUser servlet.
3. The DeleteUser servlet should have a doPost() method, which should take the ID of the user to delete as request parameter, delete this user from the database, and redirect to the ShowUsers servlet.