This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Why would you want to? It's much easier to use the provided methods.
The service() method is defined in GenericServlet, which was intended to be able to support different protocols. In practice you're always going to be using HTTP. The service() method is implemented in HttpServlet in a way that makes life simpler - it does all the mapping of HTTP requests for you, so all you need to do is implement the ones you want to use.