A servlet can be run from a browser on a remote computer, whereas an application cannot.
A2:
A servlet container is a program that runs on a server that is capable of running servlets. Often, the servlet container is installed automatically with the Web server software.
A3:
The HTTPServlet class can only process HTTP requests. If you are using another protocol, you must use the GenericServlet class.
A4:
A session object stores the values of a servlet's variables on the server. This enables the state of the user's session to be maintained for a period of time.
A5:
A cookie stores the state information in the user's browser. The Session object stores the same information, but on the server itself.