用JavaSocket编程实现白板程序 要求：1. 编写图形用户界面，教师为服务器端，学生为客户端，一个服务端可以接受多个客户端连接。 2. 要求完成教师白板的建立,实现教师在白板上画图，学生端能够实时刷新。 3. 教师可以传输文件给学生。 4. 学生可以向教师提问，问答内容所有学生都能看到。

这是一个比较复杂的项目，需要考虑多个方面的实现，包括图形用户界面、服务器端和客户端的通信、文件传输和问答功能的实现。下面是一个简单的实现过程，仅供参考。

1. 图形用户界面

可以使用Java Swing或JavaFX来实现图形用户界面，需要包括以下几个部分：

- 教师白板画面，用来展示教师在白板上画的图形。
- 学生白板画面，用来展示教师在白板上画的图形，并且允许学生在上面进行标注和操作。
- 文件传输界面，用来展示文件传输的进度和状态。
- 问答界面，用来展示学生提问和教师回答的内容。

2. 服务器端

服务器端需要维护多个客户端的Socket连接，用来实现客户端之间的通信。具体实现过程如下：

- 服务器端需要监听多个客户端的连接请求，并且保存每个客户端的Socket连接对象。
- 教师可以在白板上画图，并且将画图信息发送给所有连接的客户端。
- 学生可以向教师提问，问答内容将广播给所有连接的客户端。
- 教师可以向学生发送文件，学生可以在文件传输界面中看到文件传输的进度和状态。

具体实现过程如下：

public class WhiteboardServer {
    private Map<String, Socket> clientMap = new ConcurrentHashMap<>();
    private WhiteboardServerGui gui;

    public WhiteboardServer() {
        gui = new WhiteboardServerGui(this);
        gui.setVisible(true);
    }

    public void start(int port) {
        try (ServerSocket serverSocket = new ServerSocket(port)) {
            gui.log("Server started on port " + port);
            while (true) {
                Socket clientSocket = serverSocket.accept();
                new Thread(() -> handleClient(clientSocket)).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void handleClient(Socket clientSocket) {
        try {
            InputStream inputStream = clientSocket.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String message;
            while ((message = bufferedReader.readLine()) != null) {
                String[] msgArray = message.split(":");
                String cmd = msgArray[0];
                String[] params = msgArray[1].split(",");
                String clientAddress = clientSocket.getInetAddress().getHostAddress() + ":" + params[0];
                switch (cmd) {
                    case "connect":
                        clientMap.put(clientAddress, clientSocket);
                        broadcast(clientAddress + " joined the whiteboard");
                        break;
                    case "draw":
                        broadcast("draw:" + params[1]);
                        break;
                    case "question":
                        broadcast("question:" + params[1]);
                        break;
                    case "answer":
                        broadcast("answer:" + params[1]);
                        break;
                    case "file":
                        int fileSize = Integer.parseInt(params[1]);
                        String fileName = params[2];
                        receiveFile(clientSocket, fileSize, fileName);
                        break;
                    default:
                        break;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                clientSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void broadcast(String message) {
        for (Socket clientSocket : clientMap.values()) {
            try {
                OutputStream outputStream = clientSocket.getOutputStream();
                PrintWriter printWriter = new PrintWriter(outputStream, true);
                printWriter.println(message);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void receiveFile(Socket clientSocket, int fileSize, String fileName) {
        try (OutputStream outputStream = new FileOutputStream(fileName)) {
            InputStream inputStream = clientSocket.getInputStream();
            byte[] buffer = new byte[1024];
            int bytesRead;
            int totalBytesRead = 0;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                totalBytesRead += bytesRead;
                outputStream.write(buffer, 0, bytesRead);
                gui.updateFileProgress(totalBytesRead * 1.0 / fileSize);
            }
            gui.log("File " + fileName + " received from " + clientSocket.getInetAddress().getHostAddress());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

3. 客户端

客户端需要连接指定的服务器端，并且接收和发送消息。具体实现过程如下：

- 客户端需要连接服务器端，并且向服务器发送自己的IP地址和端口号。
- 学生可以在白板上进行标注和操作，并且将操作信息发送给服务器端。
- 学生可以向教师提问，并且将问题发送给服务器端。
- 教师可以向学生发送文件，学生需要接收文件并显示在文件传输界面中。

具体实现过程如下：

public class WhiteboardClient {
    private Socket socket;
    private String serverHost;
    private int serverPort;
    private String clientHost;
    private int clientPort;
    private WhiteboardClientGui gui;

    public WhiteboardClient(String serverHost, int serverPort, String clientHost, int clientPort) {
        this.serverHost = serverHost;
        this.serverPort = serverPort;
        this.clientHost = clientHost;
        this.clientPort = clientPort;
        gui = new WhiteboardClientGui(this);
        gui.setVisible(true);
    }

    public void connect() {
        try {
            socket = new Socket(serverHost, serverPort);
            OutputStream outputStream = socket.getOutputStream();
            PrintWriter printWriter = new PrintWriter(outputStream, true);
            printWriter.println("connect:" + clientPort);
            gui.log("Connected to server " + serverHost + ":" + serverPort);
            new Thread(() -> handleServer()).start();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void sendDrawMessage(String message) {
        try {
            OutputStream outputStream = socket.getOutputStream();
            PrintWriter printWriter = new PrintWriter(outputStream, true);
            printWriter.println("draw:" + message);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void sendQuestion(String message) {
        try {
            OutputStream outputStream = socket.getOutputStream();
            PrintWriter printWriter = new PrintWriter(outputStream, true);
            printWriter.println("question:" + message);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void sendAnswer(String message) {
        try {
            OutputStream outputStream = socket.getOutputStream();
            PrintWriter printWriter = new PrintWriter(outputStream, true);
            printWriter.println("answer:" + message);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void sendFile(String filePath) {
        File file = new File(filePath);
        if (!file.exists() || !file.isFile()) {
            return;
        }
        try {
            OutputStream outputStream = socket.getOutputStream();
            PrintWriter printWriter = new PrintWriter(outputStream, true);
            printWriter.println("file:" + file.length() + "," + file.getName());
            InputStream inputStream = new FileInputStream(file);
            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            gui.log("File " + file.getName() + " sent to server " + serverHost);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void handleServer() {
        try {
            InputStream inputStream = socket.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String message;
            while ((message = bufferedReader.readLine()) != null) {
                String[] msgArray = message.split(":");
                String cmd = msgArray[0];
                String[] params = msgArray[1].split(",");
                switch (cmd) {
                    case "draw":
                        gui.draw(params[0]);
                        break;
                    case "question":
                        gui.showQuestion(params[0]);
                        break;
                    case "answer":
                        gui.showAnswer(params[0]);
                        break;
                    default:
                        break;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

以上是一个基于Java Socket编程实现的白板程序，可以根据具体需求进行优化和扩展。