Java DatagramSocket侦听广播地址

问题描述

我编写了一个简单的测试类，用于侦听Eth并接收所有 UDP 数据包，这些数据包转到端口 5001 ：

I have written the simple test class which is meant to listen on Eth and receive all UDP packets, which go to port 5001:

public class Main {

  public static void main(String[] args) throws SocketException, UnknownHostException, IOException {
    DatagramSocket socket = new DatagramSocket(5001, InetAddress.getByName("255.255.255.255"));
    socket.setBroadcast(true);
    System.out.println("Listen on " + socket.getLocalAddress() + " from " + socket.getInetAddress() + " port " + socket.getBroadcast());
    byte[] buf = new byte[512];
    DatagramPacket packet = new DatagramPacket(buf, buf.length);
    while (true) {
      System.out.println("Waiting for data");
      socket.receive(packet);
      System.out.println("Data received");
    }
  }
}

它不再起作用了。它打印出等待数据并且永远不会继续。 tcpdump告诉我，UDP广播包来了。我究竟做错了什么？非常感谢。

It does not work anymore. It prints out Waiting for data and never continue. tcpdump shows me, that UDP broadcast packets come. What am I doing wrong? Thank you much.

推荐答案

接收方无法收听广播地址。

Receiver can't listen on a broadcast address.

广播地址用于发送者 - 发送者可以发送一个255.255.255.255:5001作为目的地的数据包，并且监听子网中该端口的所有接收者都会收到它。但是没有办法创建一个可以接收所有UDP数据包的接收器。

Broadcast address is for senders - sender can send a packet with 255.255.255.255:5001 as a destination, and all receivers listening that port in a subnet would receive it. But there is no way to create a receiver that can receive "all UDP packets".

如果您已有广播发送者并希望收到其数据包，则需要收听通配符地址：

If you already have a broadcast sender and want to receive its packets, you need to listen on a wildcard address instead:

DatagramSocket socket = new DatagramSocket(5001, InetAddress.getByName("0.0.0.0"));

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