Confused what exactly Java Servlets are?

Question

Hi,
I(JSP Biginner) have gone through some tutorials about JSP, Servlet and Java bean.
I'm really confused by the term SERVLET.
There are a lot of the definitions:
1.) Is a Java Class that provides special Server Side Specification.
2.) A servlet is a dynamically loaded module that services requests from a Web server.
From above mentioned definition, my understanding is, SerVlet is like an engine which is provided server service. Is the SERVLET that I mentioned same as the JSP Servlet Engine which parse the JSP file, generate and compile the servlet source code and then send it to the browser?????
3.)What about the SERVLET that created by developer and use in the JSP page? what are the differents between the servlet 1,2 and 3.
Please advice!

Answer 1

thanks so much...
guess I have better understand of what java servlet is when I read the article from
http://www.novocode.com/doc/servlet-essentials/
from my understanding:
1.) we said that SerVlet Provides Request and Response services is because the purpose of we creating our servlet is used to Read (Request) the data from Client and Send back (Response) the data to the Client. Of course all this can be done by code in the JSP page, but because of SerVlet technology, instead of we write the long code in the JSP page, we can modularise our code by creating servlet, why?? as servlets are web components, they can be reused easily. Moreover, java servlet is platform independent. After that at our JSP page, we just call the servlet we have created.
2.)As we can see from all the example, a SerVlet sure has
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
Are all of them only available when we installed our Web Server (i.e tomcat)???
3.)Can I say that we create servlets by Inherit all the routines and structure in those classes (q.2), as well as use their Built-In functions to create our servlets???
4.) Can I say that we create servlet by create an instance of a BIG SERVLET which served as a base (Which has all the classes we needes for creating our own servlets)
I don't know how much you can understand what I'm writting. Anyway, hope u can help.
Thanks so much.