在局域网中发现 Java 服务器：UDP 广播实现

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

public class Server {

    public static void main(String[] args) {
        try {
            // 监听的端口
            int port = 8888;
            DatagramSocket socket = new DatagramSocket(port);
            byte[] buffer = new byte[256];

            while (true) {
                DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
                socket.receive(packet);

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

                String received = new String(packet.getData(), 0, packet.getLength());
                System.out.println("Received from " + address.getHostAddress() + ":" + clientPort + " - " + received);

                // 如果收到广播消息，则发送响应
                if (received.equals("DISCOVER_REQUEST")) {
                    String response = "SERVER_ADDRESS:" + InetAddress.getLocalHost().getHostAddress() + ":" + port;
                    byte[] responseBytes = response.getBytes();
                    DatagramPacket responsePacket = new DatagramPacket(responseBytes, responseBytes.length, address, clientPort);
                    socket.send(responsePacket);
                    System.out.println("Sent response to " + address.getHostAddress() + ":" + clientPort);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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

public class Client {

    public static void main(String[] args) {
        try {
            // 广播地址和端口
            String broadcastAddress = "192.168.1.255"; // 替换为你的广播地址
            int port = 8888;

            DatagramSocket socket = new DatagramSocket();
            socket.setBroadcast(true); // 允许广播

            // 发送广播消息
            String message = "DISCOVER_REQUEST";
            byte[] buffer = message.getBytes();
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, InetAddress.getByName(broadcastAddress), port);
            socket.send(packet);
            System.out.println("Sent broadcast message to " + broadcastAddress + ":" + port);

            // 接收服务器响应
            socket.setSoTimeout(5000); // 设置超时时间，避免无限等待
            byte[] receiveBuffer = new byte[256];
            DatagramPacket receivePacket = new DatagramPacket(receiveBuffer, receiveBuffer.length);

            try {
                socket.receive(receivePacket);
                String received = new String(receivePacket.getData(), 0, receivePacket.getLength());
                System.out.println("Received response: " + received);

                // 解析服务器地址和端口
                String[] parts = received.split(":");
                if (parts.length == 3 && parts[0].equals("SERVER_ADDRESS")) {
                    String serverAddress = parts[1];
                    int serverPort = Integer.parseInt(parts[2]);
                    System.out.println("Server found at " + serverAddress + ":" + serverPort);
                }
            } catch (SocketTimeoutException e) {
                System.out.println("No server found within timeout.");
            }


            socket.close();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}