Java：无法接收多播数据

Question

我正在尝试测试多播客户端服务器应用程序，但是客户端无法接收任何数据。 我通读了教程，找不到任何方法。 你能帮我吗

客户代码

MulticastSocket socket = new MulticastSocket("9000");
socket.setInterface(InetAddress.getLocalHost());
socket.joinGroup("237.0.0.1");

while(true)
{
    byte ab[] = new byte[100];
    DatagramPacket packet = new DatagramPacket(ab, ab.length);
    socket.receive(packet);
    System.out.println("Got packet " + Arrays.toString(ab));
}

服务器代码

MulticastSocket socket = new MulticastSocket("9000");
socket.setInterface(InetAddress.getLocalHost());

socket.joinGroup("237.0.0.1");

byte index = 0;
while(true)
{
    byte[] bt = new byte[100];
    Arrays.fill(bt, (byte)index++);
    DatagramPacket packet = new DatagramPacket(bt, 100,"237.0.0.1", "9000");
    socket.send(packet);
    System.out.println("sent 100 bytes");
    Thread.sleep(10*1000);
}

---

我认为问题出在我设置界面的方式上。

有人可以在这里帮助我，清除我想了解的内容。

Answer 1

您的代码无法在我的系统上编译，但是当我进行以下更改（如下所示）时，它可以按预期工作：

• 端口号应为int

   MulticastSocket socket = new MulticastSocket(9000); 

• 应当使用以下命令将IP地址指定为InetAddress ：

   InetAddress.getByName("237.0.0.1") 

除此之外，请检查防火墙是否阻止了流量 。

---

完整示例（带有上面的编译修补程序）：

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

    final InetAddress group = InetAddress.getByName("237.0.0.1");
    final int port = 9000;

    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                MulticastSocket socket = new MulticastSocket(port);
                socket.setInterface(InetAddress.getLocalHost());
                socket.joinGroup(group);

                DatagramPacket packet = new DatagramPacket(new byte[100], 100);
                while(true) {
                    socket.receive(packet);
                    System.out.println("Got packet " + 
                            Arrays.toString(packet.getData()));
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();

    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                MulticastSocket socket = new MulticastSocket(port);
                socket.setInterface(InetAddress.getLocalHost());
                socket.joinGroup(group);

                byte[] bt = new byte[100];
                byte index = 0;
                while(true) {
                    Arrays.fill(bt, (byte) index++);
                    socket.send(new DatagramPacket(bt, 100, group, port));
                    System.out.println("sent 100 bytes");
                    Thread.sleep(1*1000);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();
}

输出：

sent 100 bytes
Got packet [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
sent 100 bytes
Got packet [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]
sent 100 bytes
Got packet [2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2]
sent 100 bytes
Got packet [3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3]
sent 100 bytes
Got packet [4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4]
sent 100 bytes
Got packet [5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5]
sent 100 bytes
Got packet [6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6]
^C