You can wrap a HTTPClient with the LoggingHttpClient to log all requests generated. This can be accomplished by:

HTTPClient client = HTTPFactoryFinder.createClient(new Hints(Hints.HTTP_LOGGING,

Or as a system propety:

java -Dorg.geotools.http.logging=True ....

All messages goes through the regular channel, and you will get the url requested. And if you turn on FINEST you can get the content sent in a POST or the content of the response.