Before starting to write your code, you need to add Pcap4J and its dependencies to your classpath. The easiest way to do that is to use a build tool such as Gradle and Maven.

• Gradle

  compile 'org.pcap4j:pcap4j-core:1.+'
  compile 'org.pcap4j:pcap4j-packetfactory-static:1.+'
  

• Maven

  <dependency>
    <groupId>org.pcap4j</groupId>
    <artifactId>pcap4j-core</artifactId>
    <version>[1.0, 2.0)</version>
  </dependency>
  <dependency>
    <groupId>org.pcap4j</groupId>
    <artifactId>pcap4j-packetfactory-static</artifactId>
    <version>[1.0, 2.0)</version>
  </dependency>
  

It’s time to write your awesome application. Firstly, you probably want to find a network interface on which you want to capture packets.

InetAddress addr = InetAddress.getByName("192.168.10.100");
PcapNetworkInterface nif = Pcaps.getDevByAddress(addr);

Then, you can open a pcap handle from the network interface. A pcap handle provides you APIs to capture packets, send packets, and so on.

int snapLen = 65536;
PromiscuousMode mode = PromiscuousMode.PROMISCUOUS;
int timeout = 10;
PcapHandle handle = nif.openLive(snapLen, mode, timeout);

Now you’ve got an ability to capture packets. Let’s get a packet using the pcap handle.

Packet packet = handle.getNextPacketEx();
handle.close();

The packet you captured consists of headers and payloads of some protocols such as Ethernet, IPv4, and TCP. The Packet API of Pcap4J enables you to get information from the protocol headers.

IpV4Packet ipV4Packet = packet.get(IpV4Packet.class);
Inet4Address srcAddr = ipV4Packet.getHeader().getSrcAddr();
System.out.println(srcAddr);