There are 2 different Servlets Generic Servlet & HTTP Servlet, whic is the derivation of other. Like this can we derive FTP Servlet from any Basic servlets.

Or

Can we create an FTP Servlet? If Yes, How? and what are the other types of servlet can we create

Because you've posted this question in the servlets forum, it is already assumed that your question is about servlets. Therefore the subject "Servlets" tells us exactly nothing.