在Java中，使用多播套接字，我试图从另一台计算机获取输出，但是失败。 吗

Question

I am trying to get some data (in this particular case, and in the code I'm going to send, the Date object, with .toString() ) from another computer. The set up is simply like below in steps;

1. I create a server thread on my computer.
2. I open a client program (not a thread) on another computer.

What I expect is to get 5 date objects from server to client, but when I open a client on a different computer, I fail to receive such data. I will share what I wrote so far, but if you feel not sated, you can check the example at here .

My code is below.

ServerThread:

public class MulticastServerThread extends QuoteServerThread {

    private long FIVE_SECONDS = 5000;

    public MulticastServerThread() throws IOException {
        super("MulticastServerThread");
    }

    public void run() {
        while (moreQuotes) {
            try {
                byte[] buf = new byte[256];

                    // construct quote
                String dString = null;
                if (in == null)
                    dString = new Date().toString();
                else
                    dString = getNextQuote();
                buf = dString.getBytes();

                InetAddress group = InetAddress.getByName("255.255.255.255");
                DatagramPacket packet = new DatagramPacket(buf, buf.length, group, 4446);
                socket.send(packet);


                try {
                    sleep((long)(Math.random() * FIVE_SECONDS));
                } catch (InterruptedException e) { }
            } catch (IOException e) {
                e.printStackTrace();
                moreQuotes = false;
            }
        }
        socket.close();
    }
}

And the client class:

public class MulticastClient {

    public static void main(String[] args) throws IOException {

        MulticastSocket socket = new MulticastSocket(4446);
        InetAddress address = InetAddress.getByName("224.0.0.252");
        socket.joinGroup(address);

        DatagramPacket packet;

            // get a few quotes
        for (int i = 0; i < 5; i++) {

            byte[] buf = new byte[256];
            packet = new DatagramPacket(buf, buf.length);
            socket.receive(packet);

            String received = new String(packet.getData(), 0, packet.getLength());
            System.out.println("Quote of the Moment: " + received);
        }

        socket.leaveGroup(address);
        socket.close();
    }

}

Answer 1

You need to have your server cast the information to the same group that the client has joined. Make your server group this: InetAddress group = InetAddress.getByName("224.0.0.252");

public class MulticastServerThread extends QuoteServerThread {

private long FIVE_SECONDS = 5000;

public MulticastServerThread() throws IOException {
    super("MulticastServerThread");
}

public void run() {
    while (moreQuotes) {
        try {
            byte[] buf = new byte[256];

                // construct quote
            String dString = null;
            if (in == null)
                dString = new Date().toString();
            else
                dString = getNextQuote();
            buf = dString.getBytes();

            InetAddress group = InetAddress.getByName("255.255.255.255"); //Keep this as the same multicast ip as in your client
            DatagramPacket packet = new DatagramPacket(buf, buf.length, group, 4446);
            socket.send(packet);


            try {
                sleep((long)(Math.random() * FIVE_SECONDS));
            } catch (InterruptedException e) { }
        } catch (IOException e) {
            e.printStackTrace();
            moreQuotes = false;
        }
    }
    socket.close();
}

}

Answer 2

Try this code.

public class Server3 {

public static void main(String[] args) throws IOException {
    MulticastSocket multiSocket = new MulticastSocket(3575);
    InetAddress groupMulticast = InetAddress.getByName("224.0.0.1");
    multiSocket.setBroadcast(true);
    multiSocket.joinGroup(groupMulticast);

    while (true) {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        System.out.println("Sending...");
        String msg = "Hai";
        byte[] bufSend = msg.getBytes();

        DatagramPacket packetSend = new DatagramPacket(bufSend, bufSend.length, groupMulticast, 3575);
        try {
            multiSocket.send(packetSend);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
}
public class Client3 {
public static void main(String[] args) throws IOException {
    MulticastSocket multiSocket = new MulticastSocket(3575);
    InetAddress groupMulticast = InetAddress.getByName("224.0.0.1");
    multiSocket.setBroadcast(true);
    multiSocket.joinGroup(groupMulticast);
    byte[] bufReceive = new byte[1024];
    while (true) {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
        System.out.println("Receiving...");
        DatagramPacket packetReceive = new DatagramPacket(bufReceive, bufReceive.length);
        try {
            multiSocket.receive(packetReceive);
            System.out.println("msg...");
            System.out.println(new String(bufReceive));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
}