this is about abstraction level u prefer like writing a soket program using
assembly or
using java. They're in huge different levels of abstraction.

HttpServlet uses post,and get methods to process http request in high level
abstrated
way. It's to easy. Do u write any code about HTTP, do u know HTTP rfc
specification?

- service  method abstract, because they want u override this method whenever and
whereever u extend their class, an also u cannot process anything without
overriding this
method. Cause abtracted HTTP parser analizer workers(whatever u say) will call
your class' service method whenever a request came to your servlet  descriptor
that defined on
your web server. unless u override this method, there will be an internal server
error.