Use the following code that basically works on TCP/IP protocol suit. Hope it will help you :-)

    import java.net.*;

07 import java.io.*;

08 import jpcap.JpcapCaptor;

09 import jpcap.JpcapSender;

10 import jpcap.NetworkInterface;

11 import jpcap.NetworkInterfaceAddress;

12 import jpcap.packet.*;

13
14 class Main { 15

16 /* variables */

17 JpcapCaptor captor;

18 NetworkInterface[] list;

19 String str,info;

20 int x, choice; 21

22 public static void main(String args[]) {

23 new Main(); 24 } 25

26 public Main() { 27
28 /* first fetch available interfaces to listen on */

29 list = JpcapCaptor.getDeviceList();

30 System.out.println("Available interfaces: "); 31

32 for(x=0; x

33 System.out.println(x+" -> "+list[x].description);

34 } 35
System.out.println("-------------------------\n");

36 choice = Integer.parseInt(getInput("Choose interface (0,1..): "));

37 System.out.println("Listening on interface -> "+list[choice].description);

38 System.out.println("-------------------------\n"); 39

40
41
42 /*Setup device listener */

43 try { 44 captor=JpcapCaptor.openDevice(list[choice], 65535, false, 20);

45 /* listen for TCP/IP only */

46 captor.setFilter("ip and tcp", true);

47 }

48 catch(IOException ioe) { ioe.printStackTrace(); }

49
50
51 /* start listening for packets */

52 while (true) { 53
54 Packet info =captor.getPacket();

55 if(info != null) 56 System.out.print(getPacketText(info));

57 } 58 } 59
60
61 /* get user input */

62 public static String getInput(String q) {

63 String input = "";

64 System.out.print(q);

65 BufferedReader bufferedreader = new BufferedReader(new InputStreamReader(System.in));

66 try {

67 input =bufferedreader.readLine();

68 }

69 catch(IOException ioexception) { }

70 return input;

71 } 72
73

74 /* return packet data in true text */

75 String getPacketText(Packet pack){

76 int i=0,j=0;

77 byte[] bytes=new byte[pack.header.length + pack.data.length];

78

79 System.arraycopy(pack.header, 0, bytes, 0, pack.header.length);

80 System.arraycopy(pack.data, 0, bytes, pack.header.length, pack.data.length);

81 StringBuffer buffer = new StringBuffer();

82
83 for(i=0; i

84 for(j=0;j<8 && i

85 String d = Integer.toHexString((int)(bytes [i] &0xff));

86 buffer.append((d.length() == 1 ? "0" + d:d ) + " "); 87

88 if(bytes[i]<32 || bytes[i]>126)

89 bytes[i] = 46; 90 }

91 }

92 return new String(bytes,i - j, j);

93 } 94 }

Can you please post the complete code....it's incomplete at line number 32...