Login form program

This is a login form program in Java. In this program, you will learn how to write Java code to create a login form, and register form.  Once an account is created, it can be used to login to the program. An account information contains user name and password. The password is encrypted before it is stored in the accounts.txt file. A strong password should contain both numbers and alphabetical characters and more than eight characters. All accounts  are stored in the accounts.txt file in the form: username-password. A duplicate account is not allowed to save in the file.

LoginForm source code:

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.event.*;

import java.io.*;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

class  LoginForm extends JFrame implements ActionListener{

            JPanel panel;

            JLabel lblname;

            JLabel lblpassword;

            JLabel lblmess;

            JTextField txtname;

            JPasswordField txtpassword;

            JButton btlogin;

           

            JPanel panelreg;

            JLabel lblnamereg;

            JLabel lblpasswordreg;

            JLabel lblmessreg;

            JTextField txtnamereg;

            JPasswordField txtpasswordreg;

            JButton btsubmit;    

           

            LoginForm(){

                       

1                      setTitle("Member login and Registration");

2                      setSize(630,250);

3                      setResizable(false);

4                      setDefaultCloseOperation(EXIT_ON_CLOSE);

5                      Container content=getContentPane();

6                      JDesktopPane des=new JDesktopPane();

                        //Login form

7                      JInternalFrame flog=new JInternalFrame();

8                      flog.setSize(300,200);

9                      flog.setLocation(10,2);

10                    flog.setTitle("Member Login");

11                    lblname=new JLabel("User Name:");

12                    lblpassword=new JLabel("Password:");

13                    lblmess=new JLabel("");

14                    btlogin=new JButton("Login");

15                    btlogin.addActionListener(this);               

17                    txtname=new JTextField(20);

18                    txtpassword=new JPasswordField(20);

19                    panel=new JPanel();

20                    panel.add(lblname);

21                    panel.add(txtname);

22                    panel.add(lblpassword);

23                    panel.add(txtpassword);

24                    panel.add(btlogin);

25                    panel.add(lblmess);

26                    flog.add(panel);

27                    flog.setVisible(true);                       

                       

                        //Registration form

28                    JInternalFrame freg=new JInternalFrame();

29                    freg.setSize(300,200);

30                    freg.setLocation(315,2);

31                    freg.setTitle("Member Registration");

32                    lblnamereg=new JLabel("User Name:");

33                    lblpasswordreg=new JLabel("Password:");

34                    lblmessreg=new JLabel("");

35                    btsubmit=new JButton("Submit");

36                    btsubmit.addActionListener(this);

37                    btlogin.addActionListener(this);

38                    txtnamereg=new JTextField(20);

39                    txtpasswordreg=new JPasswordField(20);

40                    txtpasswordreg.addKeyListener(new KeyList());

41                    panelreg=new JPanel();

42                    panelreg.add(lblnamereg);

43                    panelreg.add(txtnamereg);

44                    panelreg.add(lblpasswordreg);

45                    panelreg.add(txtpasswordreg);

46                    panelreg.add(btsubmit);

47                    panelreg.add(lblmessreg);            

48                    freg.add(panelreg);

49                    freg.setVisible(true);                       

50                    des.add(flog);

51                    des.add(freg);

52                    content.add(des, BorderLayout.CENTER);

53                    setVisible(true);                   

54                    txtname.requestFocus();                

                       

            }

55 public void actionPerformed(ActionEvent e){

           

            if(e.getSource()==btsubmit){

                        String uname=txtnamereg.getText();

                        String passw=new String(txtpasswordreg.getPassword());

                        if(!checkBlank(uname,passw, lblnamereg,lblpasswordreg)){

                                    if(!checkExist("accounts.txt",uname)){

                                                passw=new String(encrypt(passw));                   

                                                String accinfo=uname+"-"+passw;

                                                saveToFile("accounts.txt",accinfo);

                                           }

                                    }          

                                   

                        }

            else if(e.getSource()==btlogin){

                        String uname=txtname.getText();

                        String passw=new String(txtpassword.getPassword());

                        if(!checkBlank(uname,passw,lblname,lblpassword))

                                    validateUser("accounts.txt",uname,passw);

                        }

                       

            }

56 public class KeyList extends KeyAdapter{

            public void keyPressed(KeyEvent ke){

                        String passw=new String(txtpasswordreg.getPassword());

                        String mess=checkStrength(passw);

                        showMess(mess+" password",lblpasswordreg);

            }

    }

57 public boolean checkBlank(String name, String passw, JLabel namemess, JLabel passwmess){

            boolean hasBlank=false;

            if(name.length()<1){

                        showMess("User name is required.",namemess);

                        hasBlank=true;

                        }

            if(passw.length()<1){

                        showMess("Password is required.",passwmess);

                        hasBlank=true;

            }

            return hasBlank;

                                                                       

}

58 public void showMess(String mess, JLabel lbl){

                        lbl.setText(mess);

                        lbl.setForeground(Color.RED);                

            }

59 public String checkStrength(String passw){

            Pattern pat=Pattern.compile("([0-9][aA-zZ]|[aA-zZ][0-9])");

            Matcher mat=pat.matcher(passw);

            if(mat.find()) {

                        if(passw.length()>=8) return "Strong";

                        else return "Medium";

                        }

            else return "Weak";

           

}

60 public void reset(JLabel lblname,JLabel lblpassw ){

            lblname.setText("User Name:");

            lblname.setForeground(Color.BLACK);

            lblpassw.setText("Password:");

            lblpassw.setForeground(Color.BLACK);

            }

61 public void validateUser(String filename, String name, String password){

          FileReader fr;

          BufferedReader br;

          boolean valid=false;

          String accinfo;

             try{

                                                           

                                    fr=new FileReader(filename);

                                    br=new BufferedReader(fr);

                                    while ((accinfo=br.readLine())!=null){

           

                                    if(check(accinfo,name,password))

                                    {

                                                showMess("Valid login",lblmess);

                                                valid=true;

                                                break;

                                    }

                                   

             

                                     }

           

                         if(!valid) showMess("Invalid login",lblmess);

                                     reset(lblname,lblpassword);

           

                        br.close();

           fr.close();    

     } catch(Exception ie){System.out.println("Error!");}

  }

62 public boolean check(String accinfo, String name, String passw){

                        String[] info=accinfo.split("-");

                        String uname=info[0];

                        String pass=new String(decrypt(info[1]));

                        if(uname.equals(name) && pass.equals(passw))

                                    return true;

                        else return false;

                                   

            }

63 public boolean checkExist(String filename, String name){

          FileReader fr;

          BufferedReader br;

          String accinfo;

          boolean exist=false;

             try{          

                                   

                                    fr=new FileReader(filename);

                                    br=new BufferedReader(fr);

                                    while ((accinfo=br.readLine())!=null){

           

                                    if(check(accinfo,name))

                                    {

                                                showMess("The account already exists.",lblmessreg);

                                                exist=true;

                                                break;

                                    }

                                   

             

                                     }

           

                        br.close();

           fr.close();    

     } catch(Exception ie){System.out.println("Error!");}

            return exist;                          

}

64 public boolean check(String accinfo, String name){

                        String[] info=accinfo.split("-");

                        String uname=info[0];

                        if(uname.equals(name))

                                    return true;

                        else return false;

                                   

            }

65 public void saveToFile(String filename,String text){

            try{

                        FileWriter fw=new FileWriter(filename,true); 

                        BufferedWriter bw=new BufferedWriter(fw);

                        bw.write(text);

                        bw.newLine();

                        bw.flush();

                        bw.close();

                        showMess("The account is created.",lblmessreg);

                        reset(lblnamereg,lblpasswordreg);

             }catch(IOException ie){System.out.println("Error in writing to file...");}         

}

66 public byte[] encrypt(String passw){

                        byte[] sb=passw.getBytes();

                        int i;                

                        for(i=0;i<sb.length;i++)

                                    sb[i]=(byte)(sb[i]+1);

                       

                        return(sb);

            }

67 public byte[] decrypt(String passw){

                        byte[] sb=passw.getBytes();

                        int i;                

                        for(i=0;i<sb.length;i++)

                                    sb[i]=(byte)(sb[i]-1);

                       

                        return(sb);

            }

}

68 public class LoginProgram{

 

public static void main(String args[]){

     new LoginForm();

  

                }

}

Code Explanation:

1 Set the title of the program window (Member Login and Registration).

2 Specify the width and height of the program window when it opens.

3 Disable program window resizing.

4 Let the program window close when the user clicks the close button.

5 Create a container object to act as the controls placeholder.

6 Create a JDesktopPane des object . All JInternalFrame objects will be placed on this des object. In this program, we need two JInternalFrame objects, flog and freg. One JInternalFrame (flog) acts as a login form and another (freg) acts as registration form.

7-27 Create the login form interface. On the login form, there are two text boxes, three labels, and one button. The two text boxes are txtname and txtpassword. The txtname text box allows the user to enter the user name and txtpassword text box is used for password input. The three labels are lblname to display "User Name" text, lblpassword to display "Password", and lblmess to display "Valid login" or "Invalid login" text on the login form. The btlogin button is clicked to login to program.

28-49 Create the registration form interface. On the registration form, there are also two text boxes, three labels, and one button. The two text boxes are txtnamereg and txtpasswordreg. The txtnamereg text box is used to allow the user to enter the user name and txtpasswordreg text box is used for password input. The three labels are lblnamereg to display "User Name" text, lblpasswordreg to display "Password", and lblmessreg to display "The account is created." or "The account already exists." text on the registration form. The btsubmit button is clicked to save to account information to the text file.

50 Place the flog internal frame in the des object.

51 Place the freg internal frame in the des object.

52 Place the des object in the container.

53 Make sure the program window visible.

54 Set focus on the txtname text box of the login form.

55 The code in the actionPerformed method is written to enable the btlogin and btsubmit buttons to perform their tasks when the user clicks them. Once the btlogin is clicked,  the account information input by the user in the txtname, and txtpasswod text boxes are searched through the accounts. txt file. If it is found, the "Valid login" text is displayed. Otherwise, the "Invalid login" is displayed. If the btsubmit is clicked, firstly it checks whether the user name and password are not blank. Then the user name and password are searched through the accounts file to check account existing. If the account does not exist, it is saved to the file.

56 The KeyList class extends the KeyAdapter class to rewrite the keyPressed method of the KeyAdpater class. This method will enable the txtpasswordreg text to check its strength when the key is pressed by invoking the checkStrength method. 

57 The checkBlank method is implemented to determine whether the user does not enter the values in the 

txtpassword, txtname, txtpasswordreg, or txtnamereg text box.

58 The showMess method is invoked to show the text "The account is created." or "The account already exists." on the registration form or to show  the text "Valid login." or "Invalid login" on the login form.

59 The checkStrength method defines the code to check whether the input password is strong. A strong password should be the combination of numbers and alphabetical characters and more than eight characters long. To determine  whether  the password contains the combination of numbers and alphabetical characters, we use Java regular expression. The pattern to match this criteria is ([0-9][aA-zZ]|[aA-zZ][0-9]).   

60 The reset method resets text on lblname and lblpassword or lblnemreg and lblpasswordreg to their original text.

61 The validateUser is implemented to check whether the user name and password input are in the accounts.txt file. If they exist, it a valid login.

62 The check(String accoinfo,String name, String passw) mehtod is invoked by the valideUser method to compare the  user name and password input by the user with the account information read from the file.

63 The checkExist method checks whether the account info exists in the file. If it exists, saving is not allowed.

64 The check(String accoinfo,String name) mehtod is invoked by the checkExist method to compare the user name  input by the user with the user name read from the file. In Java, you can have many methods with the same name. However, those methods must be different from each other by return type, number of arguments, or argument type.

65 The saveToFile method is invoked to save the account informaton to the accounts.txt file. One account   (username-password) is written in a single line.

66 The encrypt method transforms a password to a different value before it is saved in the file . This is to ensure account security. The password is encrypted by changing all bytes of the orgical password value (add 1 to every byte).

67  The decrypt method transforms the encrypted password back to its orginal value before it is compared with the password input by the user to login. The password is decrypted by subtracting 1 from every byte of the encrypted password.

68 LoginProgram class has the main method to start the program.