How can I print/display error in a nice formatted way?

Question

I'm currently doing a project on java eclipse IDE. I have a servlet shown below with the functionality of password change. As you can see, there are various errors I have programmed it to return based on user input, e.g. "Passwords do not match". But, this is always printed at the top of the screen. Is there any way I can output these errors as an actual formatted error? Maybe in the form of a popup box or at least position it in a proper place?

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class NewPassword extends HttpServlet { 
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

                response.setContentType("text/html;charset=UTF-8");
                PrintWriter out = response.getWriter();

                String oldpassword = request.getParameter("oldpassword"); 
                String newpassword = request.getParameter("newpassword"); 
                String confirmpassword = request.getParameter("confirmpassword"); 

                int newpass = newpassword.length(); 

                HttpSession session = request.getSession(false);
                String employeeid = ""; 

                if(session != null) { 
                    employeeid = (String)session.getAttribute("employeeid"); 
                }

                boolean st = false; 
                try { 
                    Class.forName("com.mysql.jdbc.Driver").newInstance(); 
                    Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/payroll_system", "root", ""); 
                    PreparedStatement ps = con.prepareStatement("SELECT pwd FROM payroll_system.employee_login WHERE employeeID = ?");
                    ps.setString(1, employeeid);
                    ResultSet rs = ps.executeQuery(); 
                    st = rs.next(); 
                    String currentpassword = rs.getString("pwd"); 
                    if(st) { 

                        if((currentpassword.equals(oldpassword)) && newpassword.equals(confirmpassword) && newpass >= 8) { 
                            PreparedStatement pd = con.prepareStatement("UPDATE payroll_system.employee_login SET pwd = ? where employeeID = ?" ); 
                            pd.setString(1, newpassword);
                            pd.setString(2, employeeid);
                            int updated = pd.executeUpdate(); 
                            if(updated > 0){
                                out.println("Password Successfully Updated");
                                RequestDispatcher rd = request.getRequestDispatcher("changePassAdmin.html");
                                rd.include(request, response);
                            }
                        }

                        else if(oldpassword.equals("") || newpassword.equals("")  || confirmpassword.equals("") ) { 
                            out.println("Fields cannot be left blank.");
                            RequestDispatcher rd = request.getRequestDispatcher("changePassAdmin.html");
                            rd.include(request, response);
                        }
                        else if(!currentpassword.equals(oldpassword) && !newpassword.equals(confirmpassword)) { 
                            out.println("Old password is incorrect and passwords do not match, please try again.");
                            RequestDispatcher rd = request.getRequestDispatcher("changePassAdmin.html"); 
                            rd.include(request, response); 
                        }
                        else if(!currentpassword.equals(oldpassword)) { 
                            out.println("Old password entered incorrectly, please try again.");
                            RequestDispatcher rd = request.getRequestDispatcher("changePassAdmin.html");
                            rd.include(request, response);
                        }
                        else if(!newpassword.equals(confirmpassword)) { 
                            out.println("Passwords do not match, please try again.");
                            RequestDispatcher rd = request.getRequestDispatcher("changePassAdmin.html");
                            rd.include(request, response);
                        }
                        else if(newpass < 8 ) {
                            out.println("New Password must be atleast 8 characters in length.");
                            RequestDispatcher rd = request.getRequestDispatcher("changePassAdmin.html");
                            rd.include(request, response);
                        }



                    }
                }catch(Exception e)
                 {
                     e.printStackTrace();
                 }
               out.close();
       }
   }

Answer 1

You can use ajax and js to deal with the error.Use ajax to communicate with the server and when get the error,use js function to show a dialog.This is just a solution.You can try this.

Answer 2

You can use spring-form tags with bean validation.

For instance, in jsp you can show error for specific field:

<form:form method="post" action="/change-password" modelAttribute="passwordChangeForm">
       <form:label path="password">New password</form:label>
       <form:input path="password"/>
       <form:errors path="password"/>
</form:form>

Answer 3

You can use a logging framework like log4j. For example, in Log4j, there are logger, appenders and layout. With the help of a layout, you can design the format of your own error messages.

A short introduction to Log4j