How does Java network programming use UDP for connectionless communication?

UDP (User Datagram Protocol) is a lightweight connectionless network protocol commonly used in time-sensitive applications. It allows applications to send and receive data without establishing a TCP connection. Sample Java code can be used to create a UDP server and client, with the server listening for incoming datagrams and responding, and the client sending messages and receiving responses. This code can be used to build real-world use cases such as chat applications or data collection systems.

Java Network Programming: Connectionless Communication Using UDP

Introduction

UDP (User Datagram Protocol) is a lightweight, connectionless network protocol commonly used in time-sensitive applications. It allows applications to send and receive data without establishing a TCP connection.

Usage

The following is an example of creating a UDP server and client using Java:

Server code:

import java.net.*;

public class UDPServer {

    public static void main(String[] args) throws Exception {
        // 创建一个DatagramSocket，监听6789端口
        DatagramSocket serverSocket = new DatagramSocket(6789);

        // 持续监听传入的数据报
        while (true) {
            // 创建一个数据报对象来接收数据
            DatagramPacket receivePacket = new DatagramPacket(new byte[1024], 1024);

            // 接收数据报
            serverSocket.receive(receivePacket);

            // 获取客户端地址和端口
            InetAddress clientAddress = receivePacket.getAddress();
            int clientPort = receivePacket.getPort();

            // 将数据报转换为字符串
            String message = new String(receivePacket.getData(), 0, receivePacket.getLength());

            System.out.println("收到来自 " + clientAddress + ":" + clientPort + " 的消息：" + message);

            // 创建一个数据报对象来响应客户端
            DatagramPacket responsePacket = new DatagramPacket(
                    ("响应：" + message).getBytes(),
                    ("响应：" + message).getBytes().length,
                    clientAddress,
                    clientPort
            );

            // 发送响应
            serverSocket.send(responsePacket);
        }

        // 关闭服务器套接字
        serverSocket.close();
    }
}

Client code:

import java.net.*;

public class UDPClient {

    public static void main(String[] args) throws Exception {
        // 创建一个DatagramSocket
        DatagramSocket clientSocket = new DatagramSocket();

        // 获取要发送的消息
        String message = "你好，世界！";

        // 将消息转换为字节数组
        byte[] messageBytes = message.getBytes();

        // 创建一个数据报对象，将消息发送到服务器的6789端口
        DatagramPacket sendPacket = new DatagramPacket(
                messageBytes,
                messageBytes.length,
                InetAddress.getByName("localhost"), // 服务器地址
                6789 // 服务器端口
        );

        // 发送数据报
        clientSocket.send(sendPacket);

        // 创建一个数据报对象来接收服务器的响应
        DatagramPacket receivePacket = new DatagramPacket(new byte[1024], 1024);

        // 接收响应
        clientSocket.receive(receivePacket);

        // 将响应转换为字符串
        String response = new String(receivePacket.getData(), 0, receivePacket.getLength());

        // 打印响应
        System.out.println("收到服务器的响应：" + response);

        // 关闭客户端套接字
        clientSocket.close();
    }
}

Practical case

This code can be used to build a simple chat application or data collection system. For example, you can use client code to send a message to the server, and then use server code to respond to the message.

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