用JavaSocket编程实现白板程序

实现白板程序需要使用Java Socket编程和图形用户界面（GUI）开发。下面是一个简单的示例：

1. 创建服务器端

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class WhiteboardServer {
    private ServerSocket serverSocket;
    private Socket clientSocket;

    public void start(int port) {
        try {
            serverSocket = new ServerSocket(port);
            System.out.println("Server started on port " + port);

            while (true) {
                clientSocket = serverSocket.accept();
                System.out.println("New client connected: " + clientSocket.getInetAddress().getHostName());

                // 处理客户端连接
                Thread clientThread = new Thread(new WhiteboardClientHandler(clientSocket));
                clientThread.start();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        WhiteboardServer server = new WhiteboardServer();
        server.start(8888);
    }
}

2. 创建客户端处理程序

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;

public class WhiteboardClientHandler implements Runnable {
    private Socket clientSocket;
    private ObjectInputStream inputStream;
    private ObjectOutputStream outputStream;
    private List<Point> points = new ArrayList<>();

    public WhiteboardClientHandler(Socket clientSocket) {
        this.clientSocket = clientSocket;
    }

    @Override
    public void run() {
        try {
            // 获取输入和输出流
            outputStream = new ObjectOutputStream(clientSocket.getOutputStream());
            inputStream = new ObjectInputStream(clientSocket.getInputStream());

            // 处理客户端请求
            while (true) {
                Object inputObject = inputStream.readObject();
                if (inputObject instanceof String) {
                    String command = (String) inputObject;

                    // 清空画板
                    if (command.equals("clear")) {
                        points.clear();
                    }
                } else if (inputObject instanceof Point) {
                    Point point = (Point) inputObject;

                    // 绘制线条
                    if (!points.isEmpty()) {
                        Point lastPoint = points.get(points.size() - 1);
                        Graphics graphics = WhiteboardApp.getWhiteboardPanel().getGraphics();
                        graphics.setColor(Color.BLACK);
                        graphics.drawLine(lastPoint.x, lastPoint.y, point.x, point.y);
                    }
                    points.add(point);
                }
            }

        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

3. 创建客户端

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;

public class WhiteboardApp {
    private static JPanel whiteboardPanel;
    private static ObjectOutputStream outputStream;
    private static ObjectInputStream inputStream;

    public static void main(String[] args) {
        JFrame frame = new JFrame("Whiteboard");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // 创建画板面板
        whiteboardPanel = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.WHITE);
                g.fillRect(0, 0, getWidth(), getHeight());
            }
        };
        whiteboardPanel.setPreferredSize(new Dimension(800, 600));
        whiteboardPanel.addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                try {
                    outputStream.writeObject(e.getPoint());
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });
        whiteboardPanel.addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                try {
                    outputStream.writeObject(e.getPoint());
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });

        // 创建清空按钮
        JButton clearButton = new JButton("Clear");
        clearButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    outputStream.writeObject("clear");
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });

        // 将画板面板和清空按钮添加到面板中
        JPanel contentPanel = new JPanel(new BorderLayout());
        contentPanel.add(whiteboardPanel, BorderLayout.CENTER);
        contentPanel.add(clearButton, BorderLayout.SOUTH);

        // 创建客户端连接
        try {
            Socket clientSocket = new Socket("localhost", 8888);
            outputStream = new ObjectOutputStream(clientSocket.getOutputStream());
            inputStream = new ObjectInputStream(clientSocket.getInputStream());
        } catch (IOException e) {
            e.printStackTrace();
        }

        // 启动线程处理服务器响应
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    while (true) {
                        Object inputObject = inputStream.readObject();
                        if (inputObject instanceof Point) {
                            Point point = (Point) inputObject;

                            // 绘制线条
                            Graphics graphics = whiteboardPanel.getGraphics();
                            graphics.setColor(Color.BLACK);
                            graphics.drawLine(point.x, point.y, point.x + 1, point.y + 1);
                        } else if (inputObject instanceof String) {
                            String command = (String) inputObject;

                            // 清空画板
                            if (command.equals("clear")) {
                                whiteboardPanel.repaint();
                            }
                        }
                    }
                } catch (IOException | ClassNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        // 设置面板内容和显示窗口
        frame.getContentPane().add(contentPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static JPanel getWhiteboardPanel() {
        return whiteboardPanel;
    }
}

这个示例程序中，服务器端监听客户端连接，并启动一个新线程处理每个客户端的请求。客户端与服务器端通过套接字连接，并使用对象输入输出流来传输绘图命令和数据。客户端使用鼠标事件来捕获用户的绘图动作，并将数据发送到服务器端。服务器端接收到数据后，将绘图命令和数据转发给所有客户端。客户端接收到服务器响应后，将绘图结果显示在画板上。