java - 从 GUI 读取文本文件

Question

我有一个 GUI 可以验证用户名和密码。作业的另一部分是读取包含用户名和密码的文件，并检查它是否与用户在文本字段中输入的内容相匹配。如果它确实匹配，那么它会隐藏登录页面，并且会出现另一个带有“欢迎”消息的页面。我对文本文件的经验为零，我应该把那段代码放在哪里？我假设它会进入 ActionListener 方法而不是主要方法，但我只是迷路了。我只需要朝正确的方向稍微插入一下。这是我到目前为止所拥有的。任何帮助将不胜感激。谢谢!

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.Color;
import java.awt.Font;
import java.awt.*;
import javax.swing.*;
import java.io.*;
/**
*/
public class PassWordFrame extends JFrame
{
   private static final int FIELD_WIDTH = 10;
   private static final int FRAME_WIDTH = 500;
   private static final int FRAME_HEIGHT = 300;
   private JLabel fileRead;
   private JLabel instruct;
   private JLabel username;
   private JLabel password;
   private JTextField usertext;
   private JTextField passtext;
   private JButton login;
   private ActionListener listener;
   //String text = "";

   public PassWordFrame()
   {
      createComponents();
      setSize(FRAME_WIDTH, FRAME_HEIGHT);
      listener = new ClickListener();
   }
   class ClickListener implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
          String inputFileName = ("users.txt");
          File userFile = new File(inputFileName);

      }
   }
   public void createComponents()
   {
      Color blue = new Color(0,128,155);
      Font font = new Font("Times New Roman", Font.BOLD, 14);

      instruct = new JLabel("Please enter your username and password.");
      instruct.setFont(font);

      username = new JLabel("Username: ");
      username.setFont(font);

      password = new JLabel("Password: ");
      password.setFont(font);

      usertext = new JTextField(FIELD_WIDTH);
      passtext = new JTextField(FIELD_WIDTH);

      login = new JButton("Login");
      login.setFont(font);

      instruct.setForeground(Color.BLACK);
      login.setForeground(Color.BLACK);
      username.setForeground(Color.BLACK);
      password.setForeground(Color.BLACK);

      login.addActionListener(listener);

      JPanel panel1 = new JPanel();
      JPanel panel2 = new JPanel();
      JPanel panel3 = new JPanel();
      JPanel panel4 = new JPanel();

      panel1.setBackground(blue);
      panel2.setBackground(blue);
      panel3.setBackground(blue);
      panel4.setBackground(blue);

      panel1.add(instruct);
      panel2.add(username);
      panel2.add(usertext);
      panel3.add(password);
      panel3.add(passtext);
      panel4.add(login);

      add(panel1, BorderLayout.NORTH);
      add(panel2, BorderLayout.WEST);
      add(panel3, BorderLayout.CENTER);
      add(panel4, BorderLayout.SOUTH);

      pack();
   }
}      

import javax.swing.*;
import java.awt.*;

/**

*/
public class PassWordFrameViewer
{
   public static void main(String[] args)
   {
      JFrame frame = new PassWordFrame();
      frame.setTitle("Password Verification");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);

   }
}      

Answer 1

首先，您在调用 #createComponents() 方法后初始化监听器 (listener = new ClickListener())，这意味着您将添加一个 null 登录按钮的监听器。所以你的构造函数应该是这样的:

    public PassWordFrame() {
      listener = new ClickListener();
      createComponents();
      setSize(FRAME_WIDTH, FRAME_HEIGHT);
    }

然后，因为您想用欢迎消息更改 GUI，您应该使用 SwingWorker ，一个旨在在后台线程中执行 GUI 交互任务的类。在 javadoc 中您可以找到很好的示例，但这里也是一个很好的教程:Worker Threads and SwingWorker .

下面我只写监听器实现(使用 swing worker):

    class ClickListener implements ActionListener {
      public void actionPerformed(ActionEvent event) {

        new SwingWorker<Boolean, Void>() {

          @Override
          protected Boolean doInBackground() throws Exception {

            String inputFileName = ("users.txt");
            File userFile = new File(inputFileName);

            BufferedReader reader = new BufferedReader(new FileReader(userFile));

            String user;
            String pass;

            try {
              user = reader.readLine();
              pass = reader.readLine();
            }

            catch (IOException e) {

              //
              // in case something is wrong with the file or his contents
              // consider login failed

              user = null;
              pass = null;

              //
              // log the exception

              e.printStackTrace();
            }

            finally {
              try {
                reader.close();
              } catch (IOException e) {
                // ignore, nothing to do any more
              }
            }

            if (usertext.getText().equals(user) && passtext.getText().equals(pass)) {
              return true;
            } else {
              return false;
            }
          }

          @Override
          protected void done() {

            boolean match;

            try {
              match = get();
            }

            //
            // this is a learning example so
            // mark as not matching
            // and print exception to the standard error stream

            catch (InterruptedException | ExecutionException e) {
              match = false;
              e.printStackTrace();
            }

            if (match) {
              // show another page with a "Welcome" message
            }
          }
        }.execute();
      }
    }

---

另一个提示:不要将组件添加到 JFrame，因此将其替换为:

    add(panel1, BorderLayout.NORTH);
    add(panel2, BorderLayout.WEST);
    add(panel3, BorderLayout.CENTER);
    add(panel4, BorderLayout.SOUTH);

与:

    JPanel contentPane = new JPanel(new BorderLayout());
    contentPane.add(panel1, BorderLayout.NORTH);
    contentPane.add(panel2, BorderLayout.WEST);
    contentPane.add(panel3, BorderLayout.CENTER);
    contentPane.add(panel4, BorderLayout.SOUTH);

    setContentPane(contentPane);