Java Socket套接字如何实现文件传输

在Java中，使用Socket套接字实现文件传输主要涉及两个步骤：服务器端接收文件和客户端发送文件。下面是一个简单的示例，展示了如何使用Java Socket套接字实现文件传输。

1. 首先，创建一个服务器端程序，监听指定端口，等待客户端连接。

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

public class FileServer {
    public static void main(String[] args) {
        int port = 12345;
        try (ServerSocket serverSocket = new ServerSocket(port)) {
            System.out.println("Server is listening on port " + port);
            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("New client connected");
                new FileTransferHandler(socket).start();
            }
        } catch (IOException e) {
            System.out.println("Server exception: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

2. 创建一个处理文件传输的线程类。

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

public class FileTransferHandler extends Thread {
    private Socket socket;

    public FileTransferHandler(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try {
            InputStream input = socket.getInputStream();
            DataInputStream dataInput = new DataInputStream(input);

            String fileName = dataInput.readUTF();
            long fileSize = dataInput.readLong();
            System.out.println("Receiving file: " + fileName + ", size: " + fileSize);

            FileOutputStream output = new FileOutputStream(fileName);
            BufferedOutputStream bufferedOutput = new BufferedOutputStream(output);

            byte[] buffer = new byte[4096];
            int bytesRead;
            long totalBytesRead = 0;

            while (totalBytesRead < fileSize && (bytesRead = dataInput.read(buffer, 0, (int) Math.min(buffer.length, fileSize - totalBytesRead))) != -1) {
                bufferedOutput.write(buffer, 0, bytesRead);
                totalBytesRead += bytesRead;
            }

            bufferedOutput.close();
            output.close();
            System.out.println("File received: " + fileName);

            socket.close();
        } catch (IOException e) {
            System.out.println("File transfer error: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

3. 创建一个客户端程序，连接到服务器并发送文件。

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

public class FileClient {
    public static void main(String[] args) {
        String serverAddress = "localhost";
        int port = 12345;
        String filePath = "example.txt";

        try (Socket socket = new Socket(serverAddress, port)) {
            System.out.println("Connected to server");

            FileInputStream fileInput = new FileInputStream(filePath);
            DataOutputStream dataOutput = new DataOutputStream(socket.getOutputStream());

            File file = new File(filePath);
            String fileName = file.getName();
            long fileSize = file.length();

            dataOutput.writeUTF(fileName);
            dataOutput.writeLong(fileSize);

            byte[] buffer = new byte[4096];
            int bytesRead;

            while ((bytesRead = fileInput.read(buffer)) != -1) {
                dataOutput.write(buffer, 0, bytesRead);
            }

            dataOutput.flush();
            System.out.println("File sent: " + fileName);

            fileInput.close();
            socket.close();
        } catch (IOException e) {
            System.out.println("File transfer error: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

在这个示例中，服务器端监听指定端口，等待客户端连接。当客户端连接时，服务器端创建一个FileTransferHandler线程来处理文件传输。客户端连接到服务器，发送文件名和文件大小，然后将文件内容发送给服务器。

注意：这个示例仅用于演示目的，实际应用中可能需要考虑更多的错误处理和优化。