Question

经过几次尝试让一个简单的UDP多播接收器正常工作后，我才开始兴奋不已。在我自己的代码没有按预期工作后，我尝试了vertx文档中发布的确切示例：

DatagramSocket socket = vertx.createDatagramSocket(new DatagramSocketOptions());
socket.listen(1234, "0.0.0.0", asyncResult -> {
  if (asyncResult.succeeded()) {
    socket.handler(packet -> {
      // Do something with the packet
    });

    // join the multicast group
    socket.listenMulticastGroup("230.0.0.1", asyncResult2 -> {
        System.out.println("Listen succeeded? " + asyncResult2.succeeded());
    });
  } else {
    System.out.println("Listen failed" + asyncResult.cause());
  }
});

执行后，我得到以下异常：

java.lang.NullPointerException: networkInterface
    at io.netty.channel.socket.nio.NioDatagramChannel.joinGroup(NioDatagramChannel.java:409)
    at io.netty.channel.socket.nio.NioDatagramChannel.joinGroup(NioDatagramChannel.java:368)
    at io.netty.channel.socket.nio.NioDatagramChannel.joinGroup(NioDatagramChannel.java:362)
    at io.vertx.core.datagram.impl.DatagramSocketImpl.listenMulticastGroup(DatagramSocketImpl.java:90)

我可以在提供网络接口的正确IP地址（例如192.168.178.52）而不是0.0.0.0时使用它。但是，这意味着遍历所有网络接口并为每个接口添加套接字。

有什么想法吗？谢谢！

Answer 1

UDP多播侦听非常容易出错，尤其是在虚拟机中。

这是我的生产代码。首先，获得有效的界面：

static NetworkInterface mainInterface() throws SocketException {
    final ArrayList<NetworkInterface> interfaces = Collections.list(NetworkInterface.getNetworkInterfaces());
    final NetworkInterface networkInterface = interfaces.stream().filter(ni -> {
        boolean isLoopback = false;
        boolean supportsMulticast = false;
        boolean isVirtualbox = false;
        try {
            isLoopback = ni.isLoopback();
            supportsMulticast = ni.supportsMulticast();
            isVirtualbox = ni.getDisplayName().contains("VirtualBox") || ni.getDisplayName().contains("Host-Only");
        } catch (IOException loopbackTestFailure) {
        }
        final boolean hasIPv4 = ni.getInterfaceAddresses().stream().anyMatch(ia -> ia.getAddress() instanceof Inet4Address);
        return supportsMulticast && !isLoopback && !ni.isVirtual() && hasIPv4 && !isVirtualbox;
    }).sorted(Comparator.comparing(NetworkInterface::getName)).findFirst().orElse(null);
    return networkInterface;
}

然后，创建最防弹的数据报套接字：

String multicastAddress = "230.0.0.1";
NetworkInterface networkInterface = mainInterface();
Future isListening = Future.future();
vertx.createDatagramSocket(new DatagramSocketOptions()
            .setReuseAddress(true)
            .setReusePort(true))
            .listen(6112, "0.0.0.0", next -> {
                next.result().listenMulticastGroup(multicastAddress, networkInterface.getName(), null, listener -> {
                    final DatagramSocket socket = listener.result();
                    socket.handler(packet -> {
                        // Your handler here
                    });

                    isListening.complete();
                });
            });

观察我选择的高于1024的端口，重用标志和VirtualBox的特殊外壳。

尝试接收UDP多播时出现Nullpointer异常

1 个答案: