Servlet is server side program .
CGI is written by Pearl .
Servlet is create new thread for every request.

Write servlet need to import below packages
servlet javax.servlet.* and javax.servlet.Http.*

Servlet class has to be public class and it extends from HttpServlet

Servlet has servlet life cycle
init() destroy() - Executed once in life cycle of servlet.
services() - Executed multiple time in life cycle of servlet.
Services Method is executed for every client request.
That means services method has logic for process the client every client request and responses.