如何使用 BufferedReader 登录 function？

Question

I am a first-year programming student and I was tasked to make a Login and Register program using Java Swing (Application Window) and BufferedReader+Writer. I am now able to write a username and password into a text file via BWriter, however I have no idea how to make the Login read the text file and only Login when the inputted username and password in their respected TextField matches the one I wrote into the text file. (For reference the text file looks like this after I wrote the supposed username and password from the Register portion: Redman, 1234)

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.SwingConstants;

import java.awt.Font;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.Reader;
import java.awt.event.ActionEvent;

public class Register {

    private JFrame frame;
    private JTextField tfNewUser;
    private JTextField tfNewPass;
    
    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Register window = new Register();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public Register() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setTitle("Register");
        frame.setBounds(100, 100, 286, 324);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);
        
        JLabel lblNewLabel = new JLabel("REGISTER ");
        lblNewLabel.setBounds(10, 11, 250, 26);
        lblNewLabel.setFont(new Font("Tahoma", Font.BOLD, 12));
        lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
        frame.getContentPane().add(lblNewLabel);
        
        tfNewUser = new JTextField();
        tfNewUser.setBounds(117, 48, 143, 20);
        frame.getContentPane().add(tfNewUser);
        tfNewUser.setColumns(10);
        
        tfNewPass = new JTextField();
        tfNewPass.setBounds(117, 79, 143, 20);
        tfNewPass.setColumns(10);
        frame.getContentPane().add(tfNewPass);
        
        JButton btnReg = new JButton("REGISTER");
        btnReg.setBounds(10, 110, 250, 23);
        btnReg.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
            String regUser = tfNewUser.getText().toString();
            String regPass = tfNewPass.getText().toString();
            addReg(regUser, regPass);
            }
        });
        frame.getContentPane().add(btnReg);
        
        JButton btnUpdate = new JButton("UPDATE CREDENTIALS");
        btnUpdate.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                UpdateCreds newformu = new UpdateCreds();
                newformu.main(null);
                frame.setVisible(false);
            }
        });
        btnUpdate.setBounds(10, 213, 250, 23);
        frame.getContentPane().add(btnUpdate);
        
        JButton btnReturn = new JButton("RETURN TO LOGIN");
        btnReturn.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                Login newform = new Login();
                newform.main(null);
                frame.setVisible(false);
            }
        });
        btnReturn.setBounds(10, 142, 250, 23);
        frame.getContentPane().add(btnReturn);
        
        JLabel lblNewLabel_1 = new JLabel("New Username: ");
        lblNewLabel_1.setBounds(10, 48, 97, 14);
        frame.getContentPane().add(lblNewLabel_1);
        
        JLabel lblNewLabel_1_1 = new JLabel("New Password: ");
        lblNewLabel_1_1.setBounds(10, 82, 97, 14);
        frame.getContentPane().add(lblNewLabel_1_1);
        
        JButton btnDeleteAcc = new JButton("DELETE ACCOUNT");
        btnDeleteAcc.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
            deleteAcc();
            }
        });
        btnDeleteAcc.setBounds(10, 247, 250, 23);
        frame.getContentPane().add(btnDeleteAcc);
        
        JLabel lblAccountSettings = new JLabel("ACCOUNT SETTINGS");
        lblAccountSettings.setBounds(10, 176, 250, 26);
        lblAccountSettings.setHorizontalAlignment(SwingConstants.CENTER);
        lblAccountSettings.setFont(new Font("Tahoma", Font.BOLD, 12));
        frame.getContentPane().add(lblAccountSettings);
    }
    
    public void errorPane (String msg, String status) {
        JOptionPane.showMessageDialog(frame, msg, status, JOptionPane.ERROR_MESSAGE);
    }
    public void succMess (String smsg, String status2) {
        JOptionPane.showMessageDialog(frame, smsg, status2, JOptionPane.INFORMATION_MESSAGE);
    }
    public void clearTF() {
        tfNewUser.setText("");
        tfNewPass.setText("");
    }
    public void addReg(String regUser, String regPass) {
        try {
        BufferedWriter bw = new BufferedWriter(new FileWriter("Creds", true));
        bw.write(regUser+", "+regPass);
        bw.flush();
        bw.newLine();
        bw.close();
        succMess ("Account registered!", "SUCCESS");
        clearTF();
        }
        catch (Exception e) {
            errorPane("There is a problem with the data. Please input new data.", "ERROR" );
        }
        }
    public void deleteAcc() {
        try {
        String record;
        String regUser = tfNewUser.getText().toString();
        File tempCred = new File("Creds_temp");
        File cred = new File ("Creds");
        BufferedReader br = new BufferedReader(new FileReader(cred));
        BufferedWriter bw = new BufferedWriter(new FileWriter(tempCred));
        
        while((record = br.readLine())!=null) {
            if(record.contains(regUser))
                continue;
            
            bw.write(record);
            bw.flush();
            bw.newLine();
                
        }
        br.close();
        bw.close();
        
        cred.delete();
        tempCred.renameTo(cred);
        succMess ("Account Deleted!", "SUCCESS");
        }
        catch (Exception e) {
            errorPane("Cannot find account. Please register an account first.", "ERROR" );
        }
    }       
}

Answer 1

So assuming that the login file only deals with the authentication...

1. Read the .txt file line by line (I'm using Java Scanner for convenience, but you could use FileReader or anything else as well)
2. Split each line by comma delimiters and store the data in a hash map
3. Compare whether the user input matches one

---

In Login.java :

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.HashMap;

public class Login {
  private HashMap<String, String> userData = new HashMap<String, String>();
  private String name;
  private String password;
  void readFile() {
    try {
      // read file
      File file = new File("passwords.txt"); // replace with file name!!
      Scanner reader = new Scanner(file);
      // loop through each line inside the file being read
      while (reader.hasNextLine()) {
        String str = reader.nextLine();
        String[] user = str.split(", "); // user[0] = anything before ", " and user[1] = anything after ", "
        userData.put(user[0], user[1]); // store username and password
      }
      reader.close(); // remember to close the reader
    } catch (FileNotFoundException e) {
      System.out.println("Something happened...");
      e.printStackTrace();
    }
  }
  public boolean loggedIn() {
    return password.equals(userData.get(name));
  }
  
  // constructor to execute on instance creation
  public Login(String name, String password) {
    // initialize data
    this.name = name;
    this.password = password;
    readFile();
  }
}

And pretend your user data file ( passwords.txt ) looks something like:

Redman, 1234
Bob, $up3r-$ecur3
Rob, pls don't hack

Using the class is pretty easy:

Login attempt = new Login(username, password); // replace with requested variables as string
boolean success = attempt.loggedIn();

if(success) {
  // logged in successfully
} else {
  // incorrect username or password!
}

Working (only login) example.

Hope that helps you get somewhere.