Java-xmpp-collecta is a project mainly written in ..., it's free.
A library for using Collecta XMPP API. This uses the Smack Library
This is an example of how to subscribe to a collecta search using the Smack XMPP library [http://www.igniterealtime.org/projects/smack/]
You need to have Smack API in your class path to compile and run this.