import javax.servlet.*;
import javax.servlet.http.*;

public class SessionMonitor 
    implements HttpSessionListener, ServletContextListener {
  private int active = 0, max = 0;

  public void contextInitialized(ServletContextEvent sce) {
    store(sce.getServletContext());
  }

  public void contextDestroyed(ServletContextEvent sce) {}

  public void sessionCreated(HttpSessionEvent se) {
    active++;
    if (active>max)
      max = active;
    store(se.getSession().getServletContext());
  }

  public void sessionDestroyed(HttpSessionEvent se) {
    active--;
    store(se.getSession().getServletContext());
  }

  private void store(ServletContext c) {
    c.setAttribute("sessions_active", new Integer(active));
    c.setAttribute("sessions_max", new Integer(max));
  }
}