RBAC using XACML

Hello all,
   I'm trying to develop an simple RBAC service using Sun's XACML
implementation.The service it's actually a server , responding to
clients' requests.
  I'm having trouble sending/receving the RequestCtx/ResponseCtx over
the network.I know the Sun's XACML implementation doesn't have support
for this kind of operations, it only works with files(load and save
objects from .xml files).
I've tried using the "encode" and "getInstance" methods to send data
over stream obtained from a channel
(Channels.NewInput/OutputStream(channel)) but the "getInstance"
parsing method finishes only if the client closes the connection.I've
also tried reading the data first , and then create an InputStream
class over an nio.ByteBuffer with read/write methods instead of
put/get but I always get an parsing exception when I try to create an
Request object by calling getInstance.
 Does any of you know a standard way to send/receive this objects over
the network, or wat is the best way in doig that?
 Is there any "high-level" API to parse .xml format data from
socket/channel directly and returns a Node to the root element?
Best regards,
 Alex!