Basic structure of a Servlet.

gistfile1.java

import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/* The relative URL that this servlet will be handling. For instance, if we are running
Tomcat locally with an Eclipse project called "SomeProject", then by specifying "/Main"
below, Tomcat will use this servlet to handle requests for the URL
"http://localhost:8080/SomeProject/Main". */

@WebServlet("/Main")

public class MainPage extends HttpServlet {
  /* Boilerplate. */
  private static final long serialVersionUID = 1L;

  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException
  {
    /* Boilerplate. */
    response.setHeader("Cache-Control", "no-cache");
    response.setHeader("Pragma"       , "no-cache");

    /* Anything you print here will be visible in Eclipse's console, since servlets are run
    on the server side. */
    System.out.println("Got a request!");

    /* Get a parameter that was submitted through a form (if the request happened because a
    form was submitted). This example retrieves parameters submitted through the HTML form
    above. */
    String ageParam   = request.getParameter("ageParam"  );
    String colorParam = request.getParameter("colorParam");
    // Do something with the parameters here...

    /* Set some attributes; these will be available from the JSP file (e.g.
    "${someAttribute1}"). */
    request.setAttribute("someAttribute1", someObject1);
    request.setAttribute("someAttribute2", someObject2);
    request.setAttribute("someAttribute3", someObject3);

    /* Dispatch a particular JSP page to handle the request (now with attributes
    attached). */
    RequestDispatcher rd = getServletContext().getRequestDispatcher("/WEB-INF/SomePage.jsp");
    rd.forward(request, response);
  }
}