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在Android中，UDP广播和监听可以通过DatagramSocket和DatagramPacket来实现。UDP广播允许你将数据包发送到网络中的所有设备，而监听则允许你接收这些广播数据包。

1. 发送UDP广播
要发送UDP广播，你需要创建一个DatagramSocket，并使用DatagramPacket来封装要发送的数据。广播地址通常是255.255.255.255，或者子网广播地址（如192.168.1.255）。

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class UdpBroadcastSender {private static final ExecutorService executorService = Executors.newCachedThreadPool();public static void sendBroadcast(String message, int port) {executorService.execute(() -> {DatagramSocket socket = null;try {// 创建DatagramSocketsocket = new DatagramSocket();socket.setBroadcast(true);// 将消息转换为字节数组byte[] sendData = message.getBytes();// 创建DatagramPacket，指定广播地址和端口DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, InetAddress.getByName("255.255.255.255"), port);// 发送数据包socket.send(sendPacket);System.out.println("Broadcast message sent to: 255.255.255.255:" + port);} catch (Exception e) {System.err.println("Failed to send broadcast: " + e.getMessage());} finally {// 确保socket关闭if (socket != null && !socket.isClosed()) {socket.close();}}});}public static void shutdown() {executorService.shutdown();}
}

2. 监听UDP广播
要监听UDP广播，你需要创建一个DatagramSocket并绑定到指定的端口。然后使用DatagramPacket来接收数据。

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class UdpBroadcastReceiver {private static final ExecutorService executorService = Executors.newCachedThreadPool();private DatagramSocket socket;private boolean isListening = false;public void startListening(int port, BroadcastListener listener) {executorService.execute(() -> {try {// 创建DatagramSocket并绑定到指定端口socket = new DatagramSocket(port);byte[] receiveData = new byte[1024];DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);isListening = true;while (isListening) {// 接收数据包socket.receive(receivePacket);// 将接收到的数据转换为字符串String message = new String(receivePacket.getData(), 0, receivePacket.getLength());// 回调监听器if (listener != null) {String senderIp = receivePacket.getAddress().getHostAddress();listener.onBroadcastReceived(message, senderIp);}}} catch (Exception e) {System.err.println("UDP listening error: " + e.getMessage());} finally {stopListening();}});}public void stopListening() {isListening = false;if (socket != null && !socket.isClosed()) {socket.close();}}public static void shutdown() {executorService.shutdown();}// 定义回调接口public interface BroadcastListener {void onBroadcastReceived(String message, String senderIp);}
}

3. 在Android中使用

import android.os.Bundle;
import android.util.Log;
import androidx.appcompat.app.AppCompatActivity;public class MainActivity extends AppCompatActivity implements UdpBroadcastReceiver.BroadcastListener {private static final int UDP_PORT = 8888; // 自定义端口private UdpBroadcastReceiver receiver;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);// 初始化UDP广播接收器receiver = new UdpBroadcastReceiver();// 开始监听广播receiver.startListening(UDP_PORT, this);// 发送广播UdpBroadcastSender.sendBroadcast("Hello from Android!", UDP_PORT);}@Overridepublic void onBroadcastReceived(String message, String senderIp) {// 在主线程中更新UIrunOnUiThread(() -> {Log.d("UDP_BROADCAST", "Received: " + message + " from " + senderIp);});}@Overrideprotected void onDestroy() {super.onDestroy();// 停止监听并关闭线程池receiver.stopListening();UdpBroadcastSender.shutdown();UdpBroadcastReceiver.shutdown();}
}

总结：
线程池管理：

使用ExecutorService管理线程，避免频繁创建和销毁线程。

通过shutdown()方法优雅地关闭线程池。

资源释放：

在finally块中确保DatagramSocket关闭，避免资源泄漏。

回调机制：

通过BroadcastListener接口实现回调，解耦接收逻辑和UI更新。

动态停止监听：

提供stopListening()方法，支持动态停止UDP监听。

异常处理：

捕获并记录异常，确保程序在出现错误时不会崩溃。