1.  Servlet interface, Generic Servlet class, HttpServlet class
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public interface Servlet
{
	public void init(ServletConfig sc);
	public void destroy();
	public void service(ServletRequest req,ServletResponse res)throws ServletException;
	public ServletConfig getServletConfig ();
	public ServletContext getServletContext();
}
==================================================================================================================================================================================
public abstract class GenericServlet implements Servlet
{
	public void init(ServletConfig sc)
	{}
	public void destroy()
	{}	
	public ServletConfig getServletConfig ()
	{
		return null;
	}
	public ServletContext getServletContext()
	{
		return null;
	}
}
==================================================================================================================================================================================
public class HttpServlet extends GenericServlet
{
	public void service(ServletRequest req,ServletResponse res) throws ServletException
	{
		...
		...
	}
	protected void service(HttpServletRequest req,HttpServletResponse res) throws ServletException
	{
		...
		...
	}
	public void doGet(HttpServletRequest req,HttpServletResponse res) throws ServletException
	{}
	public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException
	{}
	public void doDelete(HttpServletRequest req,HttpServletResponse res) throws ServletException
	{}
	public void doPut(HttpServletRequest req,HttpServletResponse res) throws ServletException
	{}
}
endAns
How to create a servlet
	define a public class
	inherit class from Servlet interface (directly / indirectly)
		Servlet interface ==> GenericServlet class ==> HttpServlet class
	override / define required/useful methods
=============================================================================================
Method : 1 : inherit class from Servlet interface	
=============================================================================================
public class FirstServlet implements Servlet
{
	public void init(ServletConfig sc)
	{
		System.out.println("init");
	}
	public void destroy()
	{
		System.out.println("destroy");		
	}
	public void service(ServletRequest req,ServletResponse res)throws ServletException
	{
		System.out.println("service");
	}
	public ServletConfig getServletConfig ()
	{
		System.out.println("getServletConfig");
		return null;
	}
	public ServletContext getServletContext()
	{
		System.out.println("getServletContext");
		return null;
	}
}
=============================================================================================	
Method : 2 : inherit class from GenericServlet class
=============================================================================================	
public class FirstServlet extends GenericServlet
{
	public void service(ServletRequest req,ServletResponse res)throws ServletException
	{
		System.out.println("service");
	}
}
=============================================================================================	
Method : 3 : inherit class from HttpServlet class
=============================================================================================	
public class FirstServlet extends HttpServlet
{
	
}
=============================================================================================	
endAns
1.  open apache tomcat folder
	    in webapps create a new folder (myapp)
		    in myapp create a new folder (WEB-INF)
			    in WEB-INF create a new folder (classes)
			    
    apache tomcat ==> webapps ==> website_name(myapp) ==> WEB-INF ==> classes
	
2.  define a servlet class

3.  compile a servlet class and paste class file into classes folder

4.  create one xml file : web.xml in WEB-INF : mapper file : url ==> servlet
	
	
		
			a
			firstservlet
		
		
			a
			/text
		
	
5. 	
	start server
		apache-tomcat ==> bin ==> startup.bat
		
6.
	open browser ==> make a request
endAns