Simple example of how to use pkts.io to load a pcap file and print the content of all UDP packets.

PktsIOCoreExample001.java

import io.pkts.PacketHandler;
import io.pkts.Pcap;
import io.pkts.packet.Packet;
import io.pkts.protocol.Protocol;

import java.io.IOException;

// Step 1 - obtain a new Pcap instance by supplying an InputStream that points
//          to a source that contains your captured traffic. Typically you may
//          have stored that traffic in a file so there are a few convenience
//          methods for those cases, such as just supplying the name of the
//          file as shown below.
final Pcap pcap = Pcap.openStream("my_traffic.pcap");

// Step 2 - Once you have obtained an instance, you want to start
//          looping over the content of the pcap. Do this by calling
//          the loop function and supply a PacketHandler, which is a
//          simple interface with only a single method - nextPacket
pcap.loop(new PacketHandler() {
    @Override
    public void nextPacket(final Packet packet) throws IOException {

        // Step 3 - For every new packet the PacketHandler will be
        //          called and you can examine this packet in a few
        //          different ways. You can e.g. check whether the
        //          packet contains a particular protocol, such as UDP.
        if (packet.hasProtocol(Protocol.UDP)) {

            // Step 4 - Now that we know that the packet contains
            //          a UDP packet we get ask to get the UDP packet
            //          and once we have it we can just get its
            //          payload and print it, which is what we are
            //          doing below.
            System.out.println(packet.getPacket(Protocol.UDP).getPayload());
        }
    }
});