Pcap4J is hosted on Github. Click on the link below to see the detail.
https://github.com/kaitoy/pcap4j

Pcap4J is distributed under the MIT license. It's been available on the Maven Central Repository since version 0.9.14:
http://search.maven.org/#search|ga|1|g%3A%22org.pcap4j%22

Extra

SNeO: An SNMP Network Simulator using Pcap4J is available at the link below. The documents will come someday. You can use SNeO in both personal and commercial for free. You can also copy and redistribute it with no restriction.

SNeO is also hosted on Github: https://github.com/kaitoy/sneo