java - 实现一个持续向邻居广播的简单 UDP 网络

Question

1. 我有 3 个节点 A、B 和 C，它们具有各自的端口号。
2. 我正在尝试编写一个接受3 个参数 的 java 程序:它的节点名称和它的2个相邻节点的端口并向它们广播一个字符串"Hello I'm A"(所以A会广播给B和 C)。它将每 3 秒执行一次。
3. 该程序将在 3 个不同的实例中运行。
4. 收到字符串后，它将打印从“Received string” 接收到的节点(端口 B 的示例)。

我很难实现这个，不过我听说过使用 UDP 的叫做 multicasting 的东西。这是我到目前为止的工作，我做错了什么？

class UDP {
    public static void main(String[] args) throws Exception {
        String nodeName = args[0];
        int neighbourPort1 = Integer.valueOf(args[1]);
        int neighbourPort2 = Integer.valueOf(args[2]);

        while(true) {
            Thread.sleep(3000); //every 3 seconds
            //Continously broadcast and listen to neighbour1
            DatagramSocket socket1 = null;
            try {
                //CREATE SOCKET TO NEIGHBOUR1
                InetAddress host = InetAddress.getByName("localhost");
                socket1 = new DatagramSocket();
                socket1.connect(host, neighbour1);

                //CREATE DATAGRAMS FOR SENDING
                String message = "Hello I'm " + nodeName;
                byte[] sendData = message.getBytes();
                DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, host, port);
                socket1.send(sendPacket);

                //CREATE DATAGRAMS FOR RECEIVING
                byte[] receiveData = new byte[100]; //is there a way to determine the needed space?
                DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
                socket1.receive(receivePacket);
                System.out.println("Received string");

            } catch(Exception e) { }
            //Do the same for neighbour2, code is basically identical except for variables
            DatagramSocket socket2 = null;
            try {
                //CREATE SOCKET TO NEIGHBOUR2
                InetAddress host = InetAddress.getByName("localhost");
                socket2 = new DatagramSocket();
                socket2.connect(host, neighbour2);

                //FOR SENDING DATAGRAMS
                String message = "Hello I'm " + nodeName;
                byte[] sendData = message.getBytes();
                DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, host, port);
                socket2.send(sendPacket);

                //FOR RECEIVING DATAGRAMS
                byte[] receiveData = new byte[100]; //is there a way to determine the needed space?
                DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
                socket2.receive(receivePacket);
                System.out.println("Received string");

            } catch(Exception e) { }
        }

    }
}

我知道我已经接近解决方案了。我能够正常广播，但让我兴奋的是不断收听的部分。

Answer 1

我认为最好使用一个单独的线程来监听自己端口上的数据。

• A 将数据发送到 B 并阻塞，直到它从 B 收到数据包。
• B 将数据发送到 C 并阻塞，直到它从 C 收到数据包。
• C 将数据发送到 A 并阻塞，直到它从 A 收到数据包。

每个节点都在等待对方。只需发送数据包并等待 3 秒。另一个线程将只监听。

public class UDP {

    public static void main(String[] args) throws Exception {
        final String nodeName = args[0];
        final int ownPort = Integer.valueOf(args[1]);
        final int neighbourPort1 = Integer.valueOf(args[2]);
        final int neighbourPort2 = Integer.valueOf(args[3]);


        // Don't create a new socket every time
        DatagramSocket neighbour1 = new DatagramSocket();
        DatagramSocket neighbour2 = new DatagramSocket();

        neighbour1.connect(InetAddress.getLocalHost(), neighbourPort1);
        neighbour2.connect(InetAddress.getLocalHost(), neighbourPort2);

        // You have to LISTEN
        new Thread() {
            @Override
            public void run() {
                try {
                    DatagramSocket socket = new DatagramSocket(ownPort);

                    byte[] buffer = new byte[socket.getReceiveBufferSize()];
                    DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

                    while (true) {
                        // Blocks until it gets a packet
                        socket.receive(packet);

                        System.out.println("Received string");
                    }

                    // socket.close();
                } catch (final Exception e) {
                    e.printStackTrace();
                }
            }
        }.start();

        while (true) {
            Thread.sleep(3000);

            sendPacket(neighbour1, nodeName);
            sendPacket(neighbour2, nodeName);
        }

        // If you're not using an infinite loop:
        // neighbour1.close();
        // neighbour2.close();
    }

    private static void sendPacket(DatagramSocket to, String from) throws Exception {
        String message = "Hello I'm " + from;
        byte[] data = message.getBytes();

        DatagramPacket packet = new DatagramPacket(data, data.length);
        to.send(packet);
    }

}