Questions about implementing Jigsaw

Dear Sir/Madam,
  I'm interested in Jigsaw's implementation of extension API which
follows CGI's input & output's algorithm. Can you explain me the
following two questions, and point out which files in Jigsaw's source
code are related to these topics? Thank you!
1. How to re-locate the I/O?
  That's, as CGI program just read & write the standard I/O, how can we
change the System's I/O to the socket via Java? Do we have to use C
function?
2. How to run the extension API in the Java class which is written by
HTTP's administrators? Do we need an interface or so, and others just
extend the interface and implement their read/write function?

  Best wishes!

  zbchen