Demonstration of JRuby and jnetpcap This was test on Windows with pcap installed

dumper.rb

require 'java'
require 'jnetpcap.jar'
require 'ipaddr'
require 'json'


class PacketHandler
  include Java::org::jnetpcap::packet::PcapPacketHandler
  def initialize
    @tcp_header = Java::org::jnetpcap::protocol::tcpip::Tcp.new
    @ip_header = Java::org::jnetpcap::protocol::network::Ip4.new
  end
  def nextPacket(packet,user)
    pkt_info = my_decode packet
    if pkt_info
      if use? pkt_info
        puts pkt_info.to_json
        if false
          puts "#{pkt_info[:source_address]} #{pkt_info[:source_port]} => #{pkt_info[:destination_address]} #{pkt_info[:destination_port]} seq #{pkt_info[:seq]} payload size #{pkt_info[:payload].length}"
        end
      end
    end
  end
  def my_decode(packet)
    info = nil
    if packet.hasHeader @tcp_header
      if packet.hasHeader @ip_header
        info = {}
        info[:source_address] = addressToString @ip_header.sourceToInt
        info[:source_port] = @tcp_header.source
        info[:destination_address] = addressToString @ip_header.destinationToInt
        info[:destination_port] = @tcp_header.destination
        info[:seq] = @tcp_header.seq
        payload = @tcp_header.getPayload
        info[:payload] = payload.to_a
        info[:payload_chars] = info[:payload].map { |x| ((x >= 0) && (x < 127)) ? x.chr : '.' }
      end
    end
    info
  end
  def addressToString(addr)
    b1 = addr & 255
    b2 = (addr >> 8) & 255
    b3 = (addr >> 16) & 255
    b4 = (addr >> 24) & 255
    "#{b4}.#{b3}.#{b2}.#{b1}"
  end
  def use?(pkt_info)
    use_it = false
    if pkt_info[:payload].length > 0
      if (pkt_info[:source_address] == '192.168.100.1') && (pkt_info[:source_port] == 9999)
        use_it = true
      elsif (pkt_info[:destination_address] == '192.168.100.1') && (pkt_info[:destination_port] == 9999)
        use_it = true
      end
    end
    use_it
  end
end
my_handler = PacketHandler.new

devices = []
errs = java.lang.StringBuilder.new
pcap = Java::org::jnetpcap::Pcap
r = pcap.findAllDevs devices,errs
my_dev = devices[2]

if false
  puts "my_dev #{my_dev.getName} #{my_dev.getAddresses}"
end

pcap_live = pcap.openLive my_dev.getName, (64 * 1024), Java::org::jnetpcap::Pcap::MODE_PROMISCUOUS, (30 * 1000), errs
pcap_live.loop -1, my_handler, 'JRuby Rocks'
pcap_live.close