Q)What are the system  requirements to develop and run a Java
web application?
=>Install a Web Container. For eg, Tomcat

Q)What is the hierarchy of servlet classes?
   
   DIAGRAM

   =>javax.servlet.Servlet is a library interface of Servlet API. 
   =>javax.servlet.GenericServlet is the child class of Servlet interface.
   =>javax.servlet.http.HttpServlet is the child class of GenericServlet.
   =>A user defined servlet class never directly implements Servlet interface.
   =>GenericServlet is an abstract class. In this class service() method
   is absract.
   =>HttpServlet also is an abstract class. But no method is abstract in this class.

Q)Develop a Java web application in which, a servlet  produces a web page
that displays "Hello Web World" to the the end-user.

Step 1:- create a structured hierarchy of directories.

                        hellowolrdapplication
			       WEB-INF
			            classes
				    src
				    lib

Step 2:- Develop the web resources 
Note:- In this application, we have only one web resource. I.e. a servlet.
//HelloWorldServlet.java
import javax.servlet.*;
import java.io.IOException;
public class  HelloWorldServlet extends  GenericServlet
{
	public void service(ServletRequest request,ServletResponse response)throws ServletException,IOException
	{
             System.out.println("Hello ! Web world");
	}
}
Note:- Place servlet-api.jar file in class path before compiling this servlet.

Step 3:- web.xml development
<web-app>
     <servlet>
          <servlet-name>one</servlet-name>
	  <servlet-class>HelloWorldServlet</servlet-class>
    </servlet>
    <servlet-mapping>
          <servlet-name>one</servlet-name>
	  <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

Step 4:- configure the application files.
  =>Copy web.xml into WEB-INF
  =>Compile HelloWorldServlet.java and copy the .class file
  into classes folder.

Q)How to deploy the above web application into Tomcat?

Step 1:- Copy the entire directory structure(along with files) into
"webapps" folder  of Tomcat installation folder.

Step 2:- start Tomcat web container

Q)How to run the above servlet?
=>Open the browser and specify the following URL.

  http://localhost:8081/helloworldapplication/hello