It depends if you want it to run as a servlet or just another class. If you want it to run as a servl;et, you'll want to put it in a container and call it via a url connection. Otherwise, just create a fake implementation of the request and response interfaces and go for it!
Note that if you open a URLConnection with a URL that starts "http://" what you get is actually a HttpURLConnection (in the java.net package). There is where you find methods such as setRequestMethod() which are probably going to be useful when talking to your servlet. Bill