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Cannot get data from the same servlet using request.getParameter () or request.getAttributes (), tried how to get only null

I send the flag = update to call the update method with a URL, and also send the ID of the current record which user wants to edit the record. My problem here is that I cannot get the parameter values ​​(fname, lname, email, pass, cno) from the edit method . Each time it returns null from the update method.

I think something is wrong with the update method or the editing method. Please study this question. I want to understand why this problem has occurred since I try the last few hours.

I know what I can use request.getAttributes();instead request.getParameter();to retrieve data in the same servlet, but let me know if there is any simple way or not? and please help solve my problem. Thanks in advance.

Registration.html

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Registration Page</title>
</head>
<body>

<form action="Controller1" >

First Name : <input type="text" name="fName"><br/> 
Last Name : <input type="text" name="lName"><br/>
Email : <input type="text" name="eMail"><br/>
Password : <input type="password" name="password"><br/>
Contact No : <input type="text" name="cNo"><br/><br/>

<input type="submit"  value="Register">
<input type="hidden" name="flag" value="register">

 &nbsp;&nbsp;&nbsp;<a href="Controller1?flag=login">Login</a>
</form>

</body>
</html>

login.html

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Login Page</title>
</head>
<body>

<form action="Controller1">

Email : <input type="text" name="lin_Email" value="insert your registered EmailID"><br/>
Password : <input type="text" name="lin_Pass" value="enter your registered password"><br/>

<input type="submit" value="Login">
<input type="hidden" name="flag" value="loginValidate">

</form>

</body>
</html>

Controller1.java

import java.io.IOException;

import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

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

/**
 * Servlet implementation class Controller1
 */
@WebServlet("/Controller1")
public class Controller1 extends HttpServlet {
    private static final long serialVersionUID = 1L;
    int id;
    String fname, lname, email, pass, cno, flag;
    PrintWriter out;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Controller1() {
        super();
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        flag = request.getParameter("flag");

        if (flag.equals("register")) {
            register(request, response);
        } else if (flag.equals("login")) {
            response.sendRedirect("/JDBC_Registration/Login.html");
        }

        else if (flag.equals("loginValidate")) {
            loginValidate(request, response);
        } else if (flag.equals("view")) {
            try {
                view(request, response);
            } catch (SQLException e) {
                                e.printStackTrace();
            }
        } else if (flag.equals("edit")) {
            try {
                edit(request, response);
            } catch (SQLException e) {

                e.printStackTrace();
            }
        } else if (flag.equals("delete")) {
            delete(request, response);
        }
        else if (flag.equals("update")) {
            try {
                update(request, response);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    private void update(HttpServletRequest request, HttpServletResponse response) throws IOException, SQLException, ServletException {
        response.setContentType("text/html");
        out = response.getWriter();

        id = Integer.parseInt(request.getParameter("id"));
//
//      String fname = request.getParameter("t1");
//      String lname = request.getParameter("t2");
//      String email = request.getParameter("t3");
//      String pass = request.getParameter("t4");
//      String cno = request.getParameter("t5");

        fname = (String) request.getAttribute("t1");
        lname = (String) request.getAttribute("t2");
        email = (String) request.getAttribute("t3");
        pass = (String) request.getAttribute("t4");
        cno = (String) request.getAttribute("t5");
        System.out.println("updated values... "+fname+"  "+lname+" "+email+" "+pass+" "+cno);
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test2","root","root");
            Statement stm = con.createStatement();

            stm.executeUpdate("update registration set FirstName='"+fname+"',LastName='"+lname+"',Email='"+email+"',Password='"+pass+"',ContactNo='"+cno+"' where id='"+id+"'");
            view(request, response);

        } catch (ClassNotFoundException e) {

            e.printStackTrace();
        }
    }

    private void delete(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/html");
        out = response.getWriter();
        id = Integer.parseInt(request.getParameter("id"));
        System.out.println("delete record ID....."+id);

        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test2","root","root");
            Statement stm = con.createStatement();

            stm.executeUpdate("delete from registration where id='"+id+"'");
            System.out.println("successfully deleted...record ID : "+id);
            view(request, response);
        }catch (Exception e) {
            System.out.println(e);
        }
    }

    private void edit(HttpServletRequest request, HttpServletResponse response) throws IOException, SQLException {
        response.setContentType("text/html");
        out = response.getWriter();
        id = Integer.parseInt(request.getParameter("id"));
        System.out.println(""+id);

        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test2","root","root");
            Statement stm = con.createStatement();

            ResultSet rs = stm.executeQuery("select * from registration where id='"+id+"'");

            out.println("<form action='Controller1'><table border=2>");
            out.println(
                    "<tr><td>ID</td><td>FirstName</td><td>LastName</td><td>Email</td><td>Password</td><td>ContactNo</td><td>Action</td></tr>");
            while (rs.next()) {
                out.println("<tr><td>" + rs.getString(1) + "</td><td><input type='text' name='t1' value=" + rs.getString(2) + "></td><td><input type='text' name='t2' value=" + rs.getString(3) + "></td><td><input type='text' name='t3' value=" + rs.getString(4) + "></td><td><input type='text' name='t4' value=" + rs.getString(5) + "></td><td><input type='text' name='t5' value=" + rs.getString(6) + "></td><td>&nbsp;&nbsp;<a href=Controller1?flag=update&id=" + rs.getString(1)
                        + ">Update</a>&nbsp;&nbsp;</td></tr>");
            }

            out.println("</table></form>");

        } catch (ClassNotFoundException e) {

            e.printStackTrace();
        }
    }

    private void view(HttpServletRequest request, HttpServletResponse response)
            throws SQLException, IOException, ServletException {
        response.setContentType("text/html");
        out = response.getWriter();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test2", "root", "root");
            Statement stmt = con.createStatement();

            // RequestDispatcher rd =
            // request.getRequestDispatcher("Welcome.html");
            // rd.include(request, response);

            ResultSet rs = stmt.executeQuery("select * from registration");
            out.println("<form><table border=2>");
            out.println(
                    "<tr><td>ID</td><td>FirstName</td><td>LastName</td><td>Email</td><td>Password</td><td>ContactNo</td><td>Action</td></tr>");
            while (rs.next()) {
                out.println("<tr><td>" + rs.getString(1) + "</td><td>" + rs.getString(2) + "</td><td>" + rs.getString(3)
                        + "</td><td>" + rs.getString(4) + "</td><td>" + rs.getString(5) + "</td><td>" + rs.getString(6)
                        + "</td><td>&nbsp;&nbsp;<a href=Controller1?flag=edit&id=" + rs.getInt(1)
                        + ">Edit</a>&nbsp;&nbsp;&nbsp;&nbsp; <a href=Controller1?flag=delete&id=" + rs.getInt(1)
                        + ">Delete</a>&nbsp;&nbsp;</td></tr>");
            }

            out.println("</table></form>");

        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

    }

    private void loginValidate(HttpServletRequest request, HttpServletResponse response) throws IOException {

        response.setContentType("text/html");
        out = response.getWriter();

        try {
            email = request.getParameter("lin_Email");
            pass = request.getParameter("lin_Pass");
            System.out.println("" + email + pass);

            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test2", "root", "root");
            Statement stmt = con.createStatement();

            ResultSet rs = stmt
                    .executeQuery("select * from registration where Email='" + email + "'and Password='" + pass + "'");

            if (!rs.next()) {
                out.println("<h4 style='color:red'>Please Enter correct Email ID & Password...sq</h4><br/><br/>");
                // response.sendRedirect("/JDBC_Registration/Login.html");
                RequestDispatcher rd = request.getRequestDispatcher("Login.html");
                rd.include(request, response);
            } else {
                // System.out.println("else if called....");
                out.println("<h1>Welcome User :</h1><h3>" + rs.getString(2)
                        + "</h3>&nbsp;&nbsp;&nbsp;<a href=Controller1?flag=view>view</a>");
                RequestDispatcher rd = request.getRequestDispatcher("Welcome.html");
                rd.include(request, response);
            }
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    private void register(HttpServletRequest request, HttpServletResponse response) throws IOException {

        response.setContentType("text/html");
        out = response.getWriter();

        try {
            fname = request.getParameter("fName");
            lname = request.getParameter("lName");
            email = request.getParameter("eMail");
            pass = request.getParameter("password");
            cno = request.getParameter("cNo");

            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test2", "root", "root");
            Statement stmt = con.createStatement();

            stmt.executeUpdate("insert into registration(FirstName,LastName,Email,Password,ContactNo) values('" + fname
                    + "','" + lname + "','" + email + "','" + pass + "','" + cno + "')");
            System.out.println(" INSERT  : : : " + fname + " " + lname + " " + email + " " + pass + " " + cno);

            response.sendRedirect("/JDBC_Registration/Login.html");

            // view(request, response);
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}
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2 answers

it worked for me when I added a submit button instead of a url to call the update method.

<input type='submit'>
<input type='hidden' name='flag' value='update'>
<input type='hidden' name='id' value='"+id+"'>

what happened here, the hyperlink value is not added with the rest of the parameters t1, t2, t3, t4 and t5. By clicking the submit button, it accepts all parameters as read by default using the get () method.

+4

jsp. doGet. update(), getAttributes doGet .

0

Source: https://habr.com/ru/post/1670234/

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