Java 树莓即席广播

我在Raspberry PI上编写了一些特别的应用程序。我将PI和我的笔记本电脑连接到ad-hoc网络，并编写一个小程序来测试这个网络。如果我通过ad-hoc网络在笔记本电脑和Raspberry PI之间发送一个单播数据包似乎是可行的，但当我将广播数据包从Raspberry PI发送到笔记本电脑时，我发现了一些奇怪的问题。数据包不是从Raspberry PI发送的（我使用wireshark捕获数据包），但是，如果我从笔记本电脑向Raspberry PI发送广播数据包，PI可以接收该数据包。此外，若我把一个广播包从PI发送到本地网络上的笔记本电脑上，那个么它工作得很好。我不知道为什么。你能给我一些建议吗

wlan0     IEEE 802.11bg  ESSID:"AdhocPI"  Nickname:"<WIFI@REALTEK>"
          Mode:Ad-Hoc  Frequency:2.412 GHz  Cell: 02:11:87:10:D7:41
          Bit Rate:54 Mb/s   Sensitivity:0/0
          Retry:off   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=2/100  Signal level=2/100  Noise level=0/100
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

lo        no wireless extensions.

eth0      no wireless extensions.

这是我的Java程序，用来监听数据包

public class UDPServer {
    public static void main(String args[]) {
        DatagramSocket aSocket = null;
        Message replyMsg =  new Message(999,"reply");
        System.out.println("UDPServer");
        try {
            aSocket = new DatagramSocket(6669);
            aSocket.setBroadcast(true);

            while (true) {
                byte[] buffer = new byte[1000];
                DatagramPacket request = new DatagramPacket(buffer,
                        buffer.length);
                aSocket.receive(request);
                Message msgReq = null;
                try {
                    msgReq = (Message)Serializer.deserialize(request.getData());
                } catch (ClassNotFoundException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                System.out.println("Send back to: "+request.getAddress()+ " port "+request.getPort());

                byte[]replyBytes = Serializer.serialize(replyMsg); 
                DatagramPacket reply = new DatagramPacket(replyBytes,
                        replyBytes.length, request.getAddress(),
                        request.getPort());
                aSocket.send(reply);

                System.out.println("Receive Msg : "+ msgReq.show());
            }
        } catch (SocketException e) {
            System.out.println("Socket: " + e.getMessage());
        } catch (IOException e) {
            System.out.println("IO: " + e.getMessage());
        } finally {
            if (aSocket != null)
                aSocket.close();
        }
    }
}

这是我发送广播数据包的Java程序

public class UDPClient {
    public static void main(String args[]) {
        DatagramSocket aSocket = null;
        try {
            //System.out.println("UDPClient " +getBroadcast().toString());
            aSocket = new DatagramSocket(5008);
            Message msgOb = new Message(1, "Hello");
            byte[] m = Serializer.serialize(msgOb);
            InetAddress aHost = InetAddress.getByName("192.168.1.255");

            int serverPort = 6669;
            System.out.println("Send data to: "+aHost.getHostAddress()+" Port "+serverPort);
            DatagramPacket request = new DatagramPacket(m, m.length,
                    aHost, serverPort);

            aSocket.setBroadcast(true);
            System.out.println("Broadcast: "+aSocket.getBroadcast());
            aSocket.send(request);

            byte[] buffer = new byte[3000];
            DatagramPacket reply = new DatagramPacket(buffer, buffer.length);
            aSocket.receive(reply);
            Message msgRep = null;
            try {
                msgRep = (Message)Serializer.deserialize(reply.getData());
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("Reply: " + msgRep.show());

        } catch (SocketException e) {
            System.out.println("Socket: " + e.getMessage());
        } catch (IOException e) {
            System.out.println("IO: " + e.getMessage());
        } finally {
            if (aSocket != null)aSocket.close();
        }

    }

---

问题出在Wifi适配器上。只需将带有驱动程序的wifi适配器更改为支持即席模式。它会很好地工作

public class UDPClient {
    public static void main(String args[]) {
        DatagramSocket aSocket = null;
        try {
            //System.out.println("UDPClient " +getBroadcast().toString());
            aSocket = new DatagramSocket(5008);
            Message msgOb = new Message(1, "Hello");
            byte[] m = Serializer.serialize(msgOb);
            InetAddress aHost = InetAddress.getByName("192.168.1.255");

            int serverPort = 6669;
            System.out.println("Send data to: "+aHost.getHostAddress()+" Port "+serverPort);
            DatagramPacket request = new DatagramPacket(m, m.length,
                    aHost, serverPort);

            aSocket.setBroadcast(true);
            System.out.println("Broadcast: "+aSocket.getBroadcast());
            aSocket.send(request);

            byte[] buffer = new byte[3000];
            DatagramPacket reply = new DatagramPacket(buffer, buffer.length);
            aSocket.receive(reply);
            Message msgRep = null;
            try {
                msgRep = (Message)Serializer.deserialize(reply.getData());
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("Reply: " + msgRep.show());

        } catch (SocketException e) {
            System.out.println("Socket: " + e.getMessage());
        } catch (IOException e) {
            System.out.println("IO: " + e.getMessage());
        } finally {
            if (aSocket != null)aSocket.close();
        }

    }