AndroidUDP使用Demo

以下是一个使用 Android UDP 的简单示例：

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private static final int PORT = 8888; // 定义端口号
    private DatagramSocket socket;
    private DatagramPacket packet;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    // 创建UDP套接字，指定端口号
                    socket = new DatagramSocket(PORT);
                    byte[] buf = new byte[1024];
                    packet = new DatagramPacket(buf, buf.length);

                    while (true) {
                        Log.d(TAG, "Waiting for packet...");
                        // 接收数据包
                        socket.receive(packet);
                        String message = new String(packet.getData(), 0, packet.getLength());
                        Log.d(TAG, "Received message: " + message);

                        // 发送响应
                        byte[] response = "Response from server".getBytes();
                        DatagramPacket responsePacket = new DatagramPacket(response, response.length, packet.getAddress(), packet.getPort());
                        socket.send(responsePacket);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    if (socket != null) {
                        socket.close();
                    }
                }
            }
        }).start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    // 创建UDP套接字
                    DatagramSocket socket = new DatagramSocket();
                    InetAddress address = InetAddress.getByName("localhost");

                    // 发送数据包
                    String message = "Hello, server!";
                    byte[] buf = message.getBytes();
                    DatagramPacket packet = new DatagramPacket(buf, buf.length, address, PORT);
                    socket.send(packet);

                    // 接收响应
                    byte[] responseBuf = new byte[1024];
                    DatagramPacket responsePacket = new DatagramPacket(responseBuf, responseBuf.length);
                    socket.receive(responsePacket);
                    String response = new String(responsePacket.getData(), 0, responsePacket.getLength());
                    Log.d(TAG, "Received response: " + response);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}

这个示例中，我们创建了两个线程，一个用于接收数据包和发送响应，另一个用于发送数据包和接收响应。请注意，我们在接收数据包时使用了 `socket.receive(packet)` 方法，该方法会一直阻塞，直到收到数据包。在发送数据包时，我们需要指定目标地址和端口号。最后，在每次发送和接收数据包之后，我们需要关闭套接字。