public class SessionListener implements HttpSessionListener {
	
	static Logger log = Logger.getLogger(
			SessionListener.class.getName());
    private static Map<String, HttpSession> map = new   
            HashMap<String, HttpSession>();  
	static private int sessionCount = 0;
	    public void sessionCreated(HttpSessionEvent event) {
	        String id = event.getSession().getId();  
            log.debug("session created : " + id);  
	        synchronized (this) {
	            sessionCount++;
	            map.put(id, event.getSession());
	        }
	 
	       log.info("Session Created: " + event.getSession().getId());
	       log.info("Total Sessions: " + sessionCount);
	    }
	 
	    public void sessionDestroyed(HttpSessionEvent event) {
	        synchronized (this) {
	            sessionCount--;
	        }
	        log.info("Session Destroyed: " + event.getSession().getId());
	        log.info("Total Sessions: " + sessionCount);
	    }
	    public static HttpSession getHttpSession(String sessionID)  
	    {  
	        return map.get(sessionID);  
	    }
}

in web.xml

 <listener>
		<listener-class>com.ipcs.listener.SessionListener</listener-class>
	  </listener>

Java web Session 监听类。