Let's start with our servlet that will load on the server's start up:

@WebServlet(name = "LoadOnStartupServlet", urlPatterns = {"/LoadOnStartupServlet"}, 
loadOnStartup = 1)
public class LoadOnStartupServlet extends HttpServlet {

    @Override
    public void init() throws ServletException {
        System.out.println("*******SERVLET LOADED 
                           WITH SERVER's STARTUP*******");
    }

}