ICAP Server Implementation

Hi,
        I am  trying to play with ICAP recently. Is there any open source
implementation of ICAP server? 
        Since the performance is one of the most important issues of ICAP 
server, does anybody know how does the ICAP server hosting those services,
and mapping ICAP requests to them? If I have some services which are
implemented in Servlet, How can I benefit from ICAP? 
        Thanks. 

-Weisong