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1.简介

使用java 实现多网卡下组播的监听与发送消息。只查询到只有监听多网卡例子，补充下多网卡下的发送。

2.参考

https://blog.csdn.net/u012134942/article/details/109231666
https://blog.csdn.net/lizefeng1998/article/details/121201524

3.环境

C:\Users\Administrator>java -version
openjdk version "11.0.4" 2019-07-16
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.4+11)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.4+11, mixed mode)

4.组播IP地址

224.0.0.0～239.255.255.255 所有组播地址
224.0.0.0～224.0.0.255 有特殊用途的组播地址（不能被路由）
224.0.0.1 同一网段所有主机
224.0.0.2 同一网段所有组播路由器
224.0.1.0～238.255.255.255 公网组播地址
239.0.0.0～239.255.255.255 私网组播地址

5.验证网卡是否加入组播

windows: 执行 netsh interface ipv4 show joins

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Linux：执行 netstat -g

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6.实现

import java.io.IOException;
import java.net.*;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;

/**
 * @ClassName
 * @Description
 * @Author dyf
 * @Date 2022/5/20
 * @Version 1.0
 */
public class MulticastDemo {
    private static int PORT = 5555;
    private static InetSocketAddress MULTICAST_ADDRESS = new InetSocketAddress("239.0.0.1", 0);

    public static void main(String[] args) throws IOException {
        System.out.println("#1 获取本机有效网卡");
        Iterator<NetworkInterface> iterator = NetworkInterface.getNetworkInterfaces().asIterator();
        Set<NetworkInterface> niSet = StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false).filter(ni -> {
            try {
                boolean filter = ni.isUp() && !ni.isLoopback();
                if (filter) System.out.printf("\t##1获取网卡:[%s] ip:%s \n", ni.getName(), ni.getInterfaceAddresses());
                return filter;
            } catch (SocketException e) {
                e.printStackTrace();
                return false;
            }
        }).collect(Collectors.toSet());

        System.out.println("#2 监听所有网卡组播消息");
        MulticastSocket server = new MulticastSocket(PORT);
        for (NetworkInterface networkInterface : niSet) {
            System.out.printf("\t##2监听网卡:%s \n", networkInterface.getName());
            //joinGroup 这个方法只用到了 ip属性 并没有使用 port 属性，这个port 对于 socket 可以任意指定
            server.joinGroup(MULTICAST_ADDRESS, networkInterface);
        }
        new Thread(() -> {
            final byte[] buf = new byte[256];
            while (true) {
                try {
                    DatagramPacket packet = new DatagramPacket(buf, buf.length);
                    server.receive(packet);
                    String msg = new String(packet.getData(), packet.getOffset(), packet.getLength());
                    System.out.printf("\t##2监听网卡数据 客户端:[%s] 数据:[%s] \n", packet.getSocketAddress(), msg);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        System.out.println("#3 发送所有网卡组播消息");
        MulticastSocket socket = new MulticastSocket();
        for (NetworkInterface networkInterface : niSet) {
            String msg = "msg" + networkInterface.getName();
            byte[] bytes = msg.getBytes();
            System.out.printf("##3发送消息 使用网卡:[%s] 消息:[%s] \n", networkInterface.getName(), msg);
            //socket 会使用赋值网卡进行发送消息，不指定的话默认使用本机某张网卡
            socket.setNetworkInterface(networkInterface);
            socket.send(new DatagramPacket(bytes, bytes.length, MULTICAST_ADDRESS.getAddress(), PORT));
        }
    }
}

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