How will I be able to printout the captured packets using pcap.loop() with a parameter of Pcap.LOOP_INFINITE into the JTextArea?

Question

I'm quite new to JNetPcap and I'm still finding my way around with it, I'm trying to build a Packet sniffer for my project, Lately I'm trying printout packet information into a JTextArea by appending the information from a pcap.loop() that I am using, but when I set the first parameter using a specific integer value let say 5 the pcap.loop() outputs 5 packets that had been captured, Now what I want is to continuously capture and output the packet until I press the button stop. The syntax below shows the Packet handler.

PcapPacketHandler<String> jpacketHandler = new PcapPacketHandler<String>() {  

  public void nextPacket(PcapPacket packet, String user) {  

   // System.out.printf is included to check if my code works in a non GUI fashion
   System.out.printf("Received packet at %s caplen=%-4d len=%-4d %s\n",  
                     new Date(packet.getCaptureHeader().timestampInMillis()),   
                     packet.getCaptureHeader().caplen(),  // Length actually captured  
                     packet.getCaptureHeader().wirelen(), // Original length   
                     user                                 // User supplied object  
                      );
                     Date a = new Date(packet.getCaptureHeader().timestampInMillis());
                      int b = packet.getCaptureHeader().caplen();
                      int c = packet.getCaptureHeader().wirelen();
                      String d = user;

                      pcktTextArea.append("Received packet at " + a + " caplen=" + Integer.toString(b) + " len=" + Integer.toString(b) + user + "\n" );
                      pcktTextArea.setForeground(Color.red);
                      pcktTextArea.setFont(font);
                    }  
                };

Now this bit here is my pcktTextArea which I use append to print out the information in the textarea:

   pcktTextArea.append("Received packet at " + a + " caplen=" + Integer.toString(b) + " len=" + Integer.toString(b) + user + "\n" );
   pcktTextArea.setForeground(Color.red);
   pcktTextArea.setFont(font);

And Finally the Pcap.loop which I am having trouble with, if I replace that i with let say 5 it does get printed in the JTextArea but when I put the Pcap.LOOP_INFINTE it only prints the information through console but not in GUI JTextArea:

   int i = Pcap.LOOP_INFINITE;

    pcap.loop(i , jpacketHandler, " ");  

    /*************************************************************************** 
     * Last thing to do is close the pcap handle 
     **************************************************************************/  
    pcap.close();

Is it because it has to finish the loop before printing the information out in the Textarea?

Are you using Threads? If you are not (you only have your main thread) it is normal that the GUI does not refresh until capture ends. Use a different thread to capture, so that you don't block the GUI Thread. — Salvatorelab, Feb 21 '13 at 11:37

score 1 · Answer 1 · answered Feb 21 '13 at 11:30

1

I assume you run the code in a thread. Use SwingUtilities.invokeAndWait to call the pcktTextArea.append() code

answered Feb 21 '13 at 11:30

StanislavL

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Thank you very much for your answer, I have not use threads before and I have to learn that as well but thanks for the answer now I know I have to use threads for this project. – Rojee Feb 22 '13 at 13:43

How will I be able to printout the captured packets using pcap.loop() with a parameter of Pcap.LOOP_INFINITE into the JTextArea?

1 Answers1