用JavaSocket编程实现白板程序

实现一个基于Java Socket编程的白板程序可以分为以下步骤：

1.创建服务器端和客户端的Socket连接。

2.服务器端需要绑定一个端口号，等待客户端连接。客户端需要连接到服务器端的IP地址和端口号。

3.建立连接后，客户端可以向服务器端发送请求，服务器端可以接收并处理请求。

4.客户端可以通过鼠标事件监听器来获取用户的鼠标操作，然后将操作发送给服务器端。服务器端可以接收并处理这些操作，然后将这些操作广播给所有连接的客户端。

5.客户端接收到广播的操作后，需要将这些操作绘制在画板上。

6.当客户端关闭连接时，需要通知服务器端，服务器端需要将该客户端从连接列表中删除。

7.程序需要考虑多线程并发的情况，以保证程序的稳定性和性能。

具体实现可以参考以下代码：

服务器端：

import java.io.*;
import java.net.*;
import java.util.*;

public class Server {
    private static final int PORT = 8000;
    private static List<Socket> sockets = new ArrayList<Socket>();

    public static void main(String[] args) {
        try {
            ServerSocket ss = new ServerSocket(PORT);
            System.out.println("Server started.");

            while (true) {
                Socket s = ss.accept();
                sockets.add(s);
                System.out.println("New client connected.");

                new Thread(new ClientHandler(s)).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    static class ClientHandler implements Runnable {
        Socket s;
        String name;

        public ClientHandler(Socket s) {
            this.s = s;
        }

        public void run() {
            try {
                BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
                PrintWriter out = new PrintWriter(new OutputStreamWriter(s.getOutputStream()), true);

                out.println("Welcome to the whiteboard!");

                while (true) {
                    String line = in.readLine();
                    if (line == null) {
                        break;
                    }

                    if (name == null) { // the first line is the name
                        name = line;
                    } else {
                        broadcast(name + ": " + line);
                    }
                }

                System.out.println("Client disconnected.");
                sockets.remove(s);
                s.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        private void broadcast(String message) {
            for (Socket s : sockets) {
                try {
                    PrintWriter out = new PrintWriter(new OutputStreamWriter(s.getOutputStream()), true);
                    out.println(message);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

客户端：

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import javax.swing.*;

public class Client extends JFrame {
    private static final long serialVersionUID = 1L;
    private static final String SERVER_ADDRESS = "localhost";
    private static final int PORT = 8000;
    private static final int WIDTH = 800;
    private static final int HEIGHT = 600;

    private Socket s;
    private BufferedReader in;
    private PrintWriter out;
    private Whiteboard whiteboard;

    public Client() {
        super("Whiteboard");

        try {
            s = new Socket(SERVER_ADDRESS, PORT);
            in = new BufferedReader(new InputStreamReader(s.getInputStream()));
            out = new PrintWriter(new OutputStreamWriter(s.getOutputStream()), true);

            String welcomeMessage = in.readLine();
            System.out.println(welcomeMessage);

            String name = JOptionPane.showInputDialog("Enter your name:");
            out.println(name);

            whiteboard = new Whiteboard();
            add(whiteboard);

            new Thread(new Receiver()).start();

            setSize(WIDTH, HEIGHT);
            setLocationRelativeTo(null);
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setVisible(true);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private class Receiver implements Runnable {
        public void run() {
            try {
                while (true) {
                    String message = in.readLine();
                    whiteboard.append(message);
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    s.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private class Whiteboard extends JPanel implements MouseListener, MouseMotionListener {
        private static final long serialVersionUID = 1L;
        private StringBuilder sb = new StringBuilder();
        private int lastX, lastY;

        public Whiteboard() {
            setBackground(Color.WHITE);
            addMouseListener(this);
            addMouseMotionListener(this);
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.BLACK);
            g.drawString(sb.toString(), 20, 20);
        }

        public void append(String message) {
            sb.append(message + "\n");
            repaint();
        }

        public void mousePressed(MouseEvent e) {
            lastX = e.getX();
            lastY = e.getY();
        }

        public void mouseDragged(MouseEvent e) {
            int x = e.getX();
            int y = e.getY();
            out.println("LINE " + lastX + " " + lastY + " " + x + " " + y);
            lastX = x;
            lastY = y;
        }

        public void mouseClicked(MouseEvent e) {}
        public void mouseEntered(MouseEvent e) {}
        public void mouseExited(MouseEvent e) {}
        public void mouseReleased(MouseEvent e) {}
        public void mouseMoved(MouseEvent e) {}
    }

    public static void main(String[] args) {
        new Client();
    }
}