java network

• jNetPcap is an open-source java library. It contains

    A Java wrapper for nearly all libpcap library native calls
    Decodes captured packets in real-time
    Provides a large library of network protocols (core protocols)
    Users can easily add their own protocol definitions using java SDK
    jNetPcap uses a mixture of native and java implementation for optimum packet decoding performance
http://jnetpcap.com/

• jpcap 

The jpcap network capture tool performs real-time decomposition and visualization of network traffic.
Screenshots of the capture console and visualization component in action
http://jpcap.sourceforge.net/