Java UDP 多播 - 奇怪的异常

Question

我正在使用以下代码通过 Java 将 Hello, world! 发送到多播组。

InetSocketAddress sa = new InetSocketAddress("239.0.0.1", 12345);
MulticastSocket s = new MulticastSocket(sa);
s.setTimeToLive(255);
s.joinGroup(sa.getAddress());

byte[] sbuf = "Hello, world!".getBytes();
DatagramPacket sp = new DatagramPacket(sbuf, sbuf.length, sa);
s.send(sp);

byte[] rbuf = new byte[1024];
DatagramPacket rp = new DatagramPacket(rbuf, rbuf.length);
s.receive(rp);

System.out.format("Received \"%s\".\n", new String(rbuf));

s.leaveGroup(sa.getAddress());
s.close();

由于某些原因，代码总是抛出这样的异常:

java.io.Exception: Invalid argument
    at java.net.PlainDatagramSocketImpl.send(Native Method)
    at java.net.DatagramSocket.send(...)
    at ...

这是为什么？我该如何解决？

Answer 1

获取数据:

            InetAddress group;
            int port;
            group = InetAddress.getByName("239.0.0.1");
            port = Integer.parseInt("12345");

            //create Multicast socket to to pretending group
            MulticastSocket s = new MulticastSocket(port);
            s.joinGroup(group);

while(running){

            s.receive(pkt);

            System.out.println();

            String msg_rec;

            msg_rec = new String(pkt.getData(), 0, pkt.getLength());


            System.out.println("(FROM:" + pkt.getAddress()+ ") "+ msg_rec);

            System.out.println();

        }

发送数据:

String msgToSend = "Hello, world!";

            dgram = new DatagramPacket(msgToSend.getBytes(), msgToSend.length(), group ,port);
            s.send(dgram);