编写Java程序，用Socket通信机制在服务器端和客户端之间传输文件。把代码敲出来

对于编写Java程序，用Socket通信机制在服务器端和客户端之间传输文件，以下是通用的示例代码：

Server代码：

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(9999);
        // 开始监听端口
        System.out.println("Server listening on port 9999");
        while(true) {
            Socket clientSocket = serverSocket.accept();
            System.out.println("Client connected: " + clientSocket.getInetAddress().getHostAddress() + ":" + clientSocket.getPort());
            new Thread(new ClientHandler(clientSocket)).start();
        }
    }
    // 处理Client连接的单独线程
    private static class ClientHandler implements Runnable {
        private Socket clientSocket;
        public ClientHandler(Socket clientSocket) {
            this.clientSocket = clientSocket;
        }
        public void run() {
            DataInputStream dis = null;
            try {
                dis = new DataInputStream(clientSocket.getInputStream());
                String fileName = dis.readUTF();
                long fileSize = dis.readLong();
                Path filePath = Paths.get(fileName);
                System.out.println("Receiving file: " + fileName + ", size: " + fileSize + " bytes");
                byte[] buffer = new byte[1024];
                int readBytes = 0;
                // 创建输出的文件
                File outputFile = new File("output_" + fileName);
                while (fileSize > 0 && (readBytes = dis.read(buffer, 0, (int)Math.min(buffer.length, fileSize))) != -1) {
                    Files.write(outputFile.toPath(), buffer, 0, readBytes);
                    fileSize -= readBytes;
                }
                System.out.println("File saved to: " + outputFile.getAbsolutePath());
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (dis != null) dis.close();
                    if (clientSocket != null) clientSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

Client代码：

import java.io.BufferedInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.Socket;
import java.net.UnknownHostException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class Client {
    public static void main(String[] args) throws UnknownHostException, IOException {
        final String fileName = "example.txt";
        final String serverHost = "localhost";
        final int serverPort = 9999;
        Socket clientSocket = null;
        BufferedInputStream bis = null;
        DataOutputStream dos = null;
        try {
            clientSocket = new Socket(serverHost, serverPort);
            bis = new BufferedInputStream(new FileInputStream(fileName));
            dos = new DataOutputStream(clientSocket.getOutputStream());

            dos.writeUTF(fileName);
            dos.writeLong(new File(fileName).length());

            byte[] buffer = new byte[1024];
            int readBytes;
            while ((readBytes = bis.read(buffer)) != -1) {
                dos.write(buffer, 0, readBytes);
            }
        } finally {
            // 关闭连接和文件流
            try {
                if (bis != null) bis.close();
                if (dos != null) dos.close();
                if (clientSocket != null) clientSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

使用以上代码可以在服务端和客户端间通过Socket传输文件。编译运行前先在服务器运行Server.java，然后在客户端运行Client.java即可。