yes, we can override service() in our servlet, but not 
preferable. if we want use these service from any protocol 
like ftp,telnet, then we have to override.

we can override service method in my servlet class if the 
request is not protocol dependent.
Bcoz we exdend HttpSrevlet class to handle Http GET and 
POST requests and we have to override some methods like 
doGet,doPost,doHead,doPut,doDelete.

But if u want to override service method then u have to 
extend genricServlet Class.Then only u can implement Service
() method.