java * Windows 10，版本1703 * over * lo上的Java多播消息示例（软件环回接口1）*

Posted 2021-05-08

# out
---
```
is up: true
support multicast: true
is loopback: true
is point 2 point: false
java.net.SocketException: Network is unreachable: Datagram send failed
	at java.net.TwoStacksPlainDatagramSocketImpl.send(Native Method)
	at java.net.DatagramSocket.send(DatagramSocket.java:693)
	at de.dailab.jiactng.MulticastExample.main(MulticastExample.java:42)
```  
----  

import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import java.net.NetworkInterface;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.Date;
import java.util.Enumeration;
import java.util.Optional;

import static java.lang.String.format;

public class MulticastExample {
    public static void main(String[] args) {

        MulticastSocket socket = null;
        String address = "226.6.6.7";
        int multicastPort = 9999;
        InetAddress group = null;
        Enumeration<NetworkInterface> networkInterfaces = null;
        Optional<NetworkInterface> optLoInterface = Optional.empty();

        try {
             group = InetAddress.getByName(address);
             socket = new MulticastSocket(multicastPort);
             socket.setTimeToLive(1);
             networkInterfaces = NetworkInterface.getNetworkInterfaces();
             socket.joinGroup(group);

            if (networkInterfaces.hasMoreElements()) {
                optLoInterface = Collections.list(networkInterfaces).stream().filter(ni -> ni.getName().equals("lo")).findFirst();
            }
            if (optLoInterface.isPresent()) {
                final NetworkInterface lo = optLoInterface.get();
                System.out.println(format("is up: %b", lo.isUp()));
                System.out.println(format("support multicast: %b", lo.supportsMulticast()));
                System.out.println(format("is loopback: %b", lo.isLoopback()));
                System.out.println(format("is point 2 point: %b", lo.isPointToPoint()));
                socket.setNetworkInterface(lo);
                byte[] buffer = new Date().toString().getBytes(StandardCharsets.UTF_8);
                final DatagramPacket dp = new DatagramPacket(buffer, buffer.length, group, multicastPort);
                socket.send(dp);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}