Java - UDP 和组播检测

Question

在单个端口上，我想监听多播、UDP 和 TCP 流量。 (在我的局域网上)如果检测到某些内容，我还想通过 UDP 进行响应。

代码如下，但仅用于多播检测。 while(true) 循环肯定是在 main() 中执行此操作。

但是我在添加另一种协议(protocol)检测方法时遇到了困难。单个应用程序可以在多种协议(protocol)中打开多个套接字吗？我确信这是我对线程的了解有限，但也许有人可以在下面看到我的问题。

public class LANPortSniffer  {

  private static void autoSendResponse() throws IOException {

     String sentenceToSend = "I've detected your traffic";
     int PortNum = 1234;

     DatagramSocket clientSocket = new DatagramSocket();
     InetAddress IPAddress = InetAddress.getByName("192.168.1.121");
     byte[] sendData = new byte[1024];

     sendData = sentenceToSend.getBytes();
     DatagramPacket sendPacket = 
       new DatagramPacket(sendData, sendData.length, IPAddress, PortNum);
     clientSocket.send(sendPacket);
     clientSocket.close();


  }//eof autoSendResponse


  private static void MulticastListener() throws UnknownHostException {

     final InetAddress group = InetAddress.getByName("224.0.0.0");
     final int port = 1234;

     try {

       System.out.println("multi-cast listener is started......"); 
       MulticastSocket socket = new MulticastSocket(port);
       socket.setInterface(InetAddress.getLocalHost());
       socket.joinGroup(group);

       byte[] buffer = new byte[10*1024];

       DatagramPacket data = new DatagramPacket(buffer, buffer.length);

       while (true) {
          socket.receive(data);

           // auto-send response
           autoSendResponse();

       }


      } catch (IOException e) {
         System.out.println(e.toString());
      }

  }//eof MulticastListener

// this method is not even getting launched
private static void UDPListener() throws Exception {

    DatagramSocket serverSocket = new DatagramSocket(1234);
    byte[] receiveData = new byte[1024];

    System.out.println("UDP listener is started......"); 
    while(true)
       {
          DatagramPacket receivePacket = 
                new DatagramPacket(receiveData, receiveData.length);
          serverSocket.receive(receivePacket);
          String sentence = new String( receivePacket.getData());
          System.out.println("UDP RECEIVED: " + sentence);

       }    

}



    public static void main(String[] args) throws Exception {
            //Schedule a job for the event-dispatching thread:
            //creating and showing this application's GUI.
            javax.swing.SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    createAndShowGUI(); 
                }
             });


            try {
            MulticastListener();

        } catch (UnknownHostException e) {

            e.printStackTrace();
        }


           // this does not appear to be detected:
            try {
            UDPListener();

        } catch (Exception e) {

            e.printStackTrace();
        }


    }
}//eof LANPortSniffer

在 main() 中，我尝试添加第二个 try/catch，以实现简单的 UDPListener() 方法。
但当我在 Eclipse 中运行该应用程序时，它似乎被忽略了。

main()方法是否只允许一次try/catch？

简而言之，我想同时在单个端口上监听多播、UDP 和 TCP 数据包。这可能吗？

Answer 1

您在这里遇到了线程问题。我认为你需要加深对 Java 的理解。当您调用 MulticastListener() 时，它永远不会离开该 block ，直到连接失败。它有一个连续的 while 循环。您需要为每个 Activity 创建一个新线程。

Thread t = new Thread(new Runnable() { 
   public void run() {
         MulticastListener();
   }
}
t.start();

但是，我建议您在开始尝试实现线程程序之前，先阅读对程序流程的理解以及更多面向对象方法的使用。