TCP/IP 和 UDP 概述

TCP/IP (Transmission Control Protocol/Internet Protocol)UDP (User Datagram Protocol) 是两种常用的传输层协议,用于在网络上发送和接收数据。

TCP/IP (传输控制协议/互联网协议)
  • 特点

    • 面向连接:在数据传输之前需要建立连接。
    • 可靠传输:通过确认机制、重传机制、流量控制和拥塞控制来确保数据的可靠传输。
    • 有序传输:数据包按顺序到达接收端。
    • 流量控制:防止发送方发送过快导致接收方无法处理。
    • 拥塞控制:避免网络拥塞。
  • 应用场景:适用于需要高可靠性的应用,如文件传输、电子邮件、网页浏览等。

UDP (用户数据报协议)
  • 特点

    • 无连接:不需要预先建立连接,发送数据前不需要握手。
    • 不可靠传输:没有确认机制,数据包可能丢失或乱序到达。
    • 低延迟:由于没有复杂的控制机制,传输速度更快。
    • 简单高效:协议开销小,适合实时应用。
  • 应用场景:适用于对实时性要求较高且可以容忍一定数据丢失的应用,如视频会议、在线游戏、VoIP等。

Java代码示例

TCP/IP 示例
服务器端代码
import java.io.*;
import java.net.*;

public class TCPServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        System.out.println("TCP Server started on port 8080");

        while (true) {
            Socket clientSocket = serverSocket.accept();
            System.out.println("New client connected");

            // 创建新线程处理每个客户端连接
            new Thread(new ClientHandler(clientSocket)).start();
        }
    }

    static class ClientHandler implements Runnable {
        private final Socket clientSocket;

        public ClientHandler(Socket socket) {
            this.clientSocket = socket;
        }

        @Override
        public void run() {
            try (
                PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
                BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()))
            ) {
                String inputLine;
                while ((inputLine = in.readLine()) != null) {
                    System.out.println("Received from client: " + inputLine);
                    out.println("Echo: " + inputLine);
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    clientSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}
客户端代码
import java.io.*;
import java.net.*;

public class TCPClient {
    public static void main(String[] args) throws IOException {
        String host = "localhost";
        int port = 8080;
        Socket socket = new Socket(host, port);
        System.out.println("Connected to TCP Server");

        try (
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in))
        ) {
            String userInput;
            while ((userInput = stdIn.readLine()) != null) {
                out.println(userInput);
                System.out.println("Server response: " + in.readLine());
            }
        } finally {
            socket.close();
        }
    }
}

UDP 示例

服务器端代码
import java.io.*;
import java.net.*;

public class UDPServer {
    public static void main(String[] args) throws IOException {
        DatagramSocket serverSocket = new DatagramSocket(9090);
        byte[] receiveData = new byte[1024];
        System.out.println("UDP Server started on port 9090");

        while (true) {
            DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
            serverSocket.receive(receivePacket);
            String receivedData = new String(receivePacket.getData(), 0, receivePacket.getLength());
            System.out.println("Received from client: " + receivedData);

            // 回复客户端
            byte[] sendData = ("Echo: " + receivedData).getBytes();
            InetAddress clientAddress = receivePacket.getAddress();
            int clientPort = receivePacket.getPort();
            DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, clientAddress, clientPort);
            serverSocket.send(sendPacket);
        }
    }
}
客户端代码
import java.io.*;
import java.net.*;

public class UDPClient {
    public static void main(String[] args) throws IOException {
        String host = "localhost";
        int port = 9090;
        DatagramSocket clientSocket = new DatagramSocket();
        InetAddress serverAddress = InetAddress.getByName(host);
        System.out.println("Connected to UDP Server");

        try (
            BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in))
        ) {
            String userInput;
            while ((userInput = stdIn.readLine()) != null) {
                // 发送数据到服务器
                byte[] sendData = userInput.getBytes();
                DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, serverAddress, port);
                clientSocket.send(sendPacket);

                // 接收服务器的回复
                byte[] receiveData = new byte[1024];
                DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
                clientSocket.receive(receivePacket);
                String receivedData = new String(receivePacket.getData(), 0, receivePacket.getLength());
                System.out.println("Server response: " + receivedData);
            }
        } finally {
            clientSocket.close();
        }
    }
}

解释

  1. TCP/IP 示例

    • 服务器端:使用ServerSocket监听指定端口,接受客户端连接,并为每个连接创建一个新线程来处理请求。
    • 客户端:连接到服务器,发送数据并接收服务器的回复。
  2. UDP 示例

    • 服务器端:使用DatagramSocket监听指定端口,接收客户端的数据包,并回复客户端。
    • 客户端:发送数据包到服务器,并接收服务器的回复。

这两个示例分别展示了如何在Java中使用TCP/IP和UDP进行网络通信。TCP/IP适用于需要可靠传输的场景,而UDP适用于对实时性要求较高的场景。

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