Creating Attribute at Request ,Session and Application in Servlet class

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import education.Student;

public class SessionApplicationDemo extends HttpServlet {

  public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException

  {
    response.setContentType("text/html");

PrintWriter out = response.getWriter();
out.println("<html> <head> <title> First Servlet ... </title></head>");
out.println("<body> <h1> Welcome to JAVA  </h1>");
out.println("Hello World <br>" );

Student student1 = new Student();
student1.setSid(2020);
student1.setSname("Hitesh");

Student student2 = new Student();
student2.setSid(3020);
student2.setSname("Nayan");
//access ServletContext

ServletContext application = request.getServletContext();

application.setAttribute("s2",student1);
//accessing application attribute
Student st1 = (Student) application.getAttribute("s2");

out.println(st1.getSid() +"<br/>");
out.println(st1.getSname());



//creating session

HttpSession session = request.getSession();

session.setAttribute("s3",student2);

/*request.setAttribute("s2",student1);
//accessing request attribute
Student st1 = (Student) request.getAttribute("s2");

out.println(st1.getSid() +"<br/>");
out.println(st1.getSname());
*/
//access session attribute
Student st2 = (Student) session.getAttribute("s3");

out.println(st2.getSid() +"<br/>");
out.println(st2.getSname());

out.println("</body></html>" );
 
  }  //end of method
 public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException

  {
doPost(request, response);
  }


}