Is it possible to implement HttpSessionListener this way?

I am trying to keep track of valid user IDs in my Java Servlet, can I implement HttpSessionListener this way?

public class my_Servlet extends HttpServlet implements HttpSessionListener
{
  String User_Id;
  static Vector<String> Valid_User_Id_Vector=new Vector<String>();
  private static int activeSessions=0;

  public void sessionCreated(HttpSessionEvent se)
  {
// associate User_Id with session Id;
// add User_Id to Valid_User_Id_Vector
    Out(" sessionCreated : "+se.getSession().getId());
    activeSessions++;
  }

  public void sessionDestroyed(HttpSessionEvent se)
  {
    if (activeSessions>0)
    {
// remove User_Id from Valid_User_Id_Vector by identifing it session Id
      Out(" sessionDestroyed : "+se.getSession().getId());
      activeSessions--;
    }
  }

  public static int getActiveSessions()
  {
    return activeSessions;
  }

  public void init(ServletConfig config) throws ServletException
  {
  }

  public void destroy()
  {

  }

  protected void processRequest(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException
  {
    User_Id=request.getParameter("User_Id");
  }

  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
  {
    processRequest(request, response);
  }

  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
  {
    processRequest(request, response);
  }

  public String getServletInfo()
  {
    return "Short description";
  }
}

      

        
        
        
      

    

How do I get a listener notification when the session ends? I am trying to bypass "/WEB-INF.web.xml" all together, is this doable? Or does it make sense?