docker中的多播问题

public static void main(String[] args) throws IOException {
        int port = 6789;  
        String sendMessage="hello";  
       InetAddress inetAddress = InetAddress.getByName("228.5.6.7");  
       DatagramPacket datagramPacket = new DatagramPacket(sendMessage.getBytes(), sendMessage.length(), inetAddress, port);  
       MulticastSocket multicastSocket = new MulticastSocket();  
       multicastSocket.send(datagramPacket);  
	}

public static void main(String[] args) throws IOException {
	    InetAddress group = InetAddress.getByName("228.5.6.7");  
        MulticastSocket s = new MulticastSocket(6789);   
        byte[] arb = new byte[1024];  
        s.joinGroup(group);//加入该组  

        while(true){  
             DatagramPacket datagramPacket =new DatagramPacket(arb,arb.length);  
             s.receive(datagramPacket);  
             System.out.println(arb.length);  
             System.out.println(new String(arb));   
        }  
	}