package moreservlets.listeners;

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

/** Listener that keeps track of the number of sessions
 *  that the Web application is currently using and has
 *  ever used in its life cycle.
 *  <P>
 *  Taken from More Servlets and JavaServer Pages
 *  from Prentice Hall and Sun Microsystems Press,
 *  http://www.moreservlets.com/.
 *  &copy; 2002 Marty Hall; may be freely used or adapted.
 */

public class SessionCounter implements HttpSessionListener {
  private int totalSessionCount = 0;
  private int currentSessionCount = 0;
  private int maxSessionCount = 0;
  private ServletContext context = null;
  
  public void sessionCreated(HttpSessionEvent event) {
    totalSessionCount++;
    currentSessionCount++;
    if (currentSessionCount > maxSessionCount) {
      maxSessionCount = currentSessionCount;
    }
    if (context == null) {
      storeInServletContext(event);
    }
  }

  public void sessionDestroyed(HttpSessionEvent event) {
    currentSessionCount--;
  }

  /** The total number of sessions created. */
  
  public int getTotalSessionCount() {
    return(totalSessionCount);
  }

  /** The number of sessions currently in memory. */
  
  public int getCurrentSessionCount() {
    return(currentSessionCount);
  }

  /** The largest number of sessions ever in memory
   *  at any one time.
   */

  public int getMaxSessionCount() {
    return(maxSessionCount);
  }

  // Register self in the servlet context so that
  // servlets and JSP pages can access the session counts.
  
  private void storeInServletContext(HttpSessionEvent event) {
    HttpSession session = event.getSession();
    context = session.getServletContext();
    context.setAttribute("sessionCounter", this);
  }
}