In exchange for some RFID-enabled material (a reader and some tags), I have created such a libary for Mediamatic and the general public to use. The libarry constists of a set of Java classes which are used in the Processing application to directly communicate with one (or even more than one) reader.
More information and a download link can be found at the following address:
www.on-signal.org/projects/RFID_Processing