source file name: SessionServlet.java 


import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

@WebServlet(urlPatterns = {"/SessionServlet"})

public class SessionServlet extends HttpServlet 

{

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        response.setContentType("text/html;charset=UTF-8");

        try (PrintWriter out = response.getWriter()) {

           HttpSession hs=request.getSession();

           Integer cnt=(Integer)hs.getAttribute("count");

if(cnt==null)

cnt=new Integer(1);

else

cnt=new Integer(cnt.intValue()+1);

hs.setAttribute("count", cnt);

 out.println("<h1> Counter :  "+cnt);

 

            out.println("<html>");

            out.println("<head>");

            out.println("<title> Session Servlet program </title>");            

            out.println("</head>");

            out.println("<body>");

            

            out.println("<form action=http://localhost:8080/ServletPrgs/SessionServlet method=get >");

            out.println("<input type=submit value=click >");

            out.println("</form>");

              out.println("</body>");

            out.println("</html>");

        }

    }

    @Override

    protected void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        processRequest(request, response);

    }

    @Override

    protected void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        processRequest(request, response);

    }

    @Override

    public String getServletInfo() {

        return "Short description";

    }// </editor-fold>


}

output: