package test;
import javax.servlet.*;
import javax.servlet.http.*;

public class SessionCounterListener implements HttpSessionListener{
	private static final String COUNTER_ATTR="session_counter";
	public void sessionCreated(HttpSessionEvent hse){
		int[] counter=getCounter(hse);
		counter[0]++;
	}

	public void sessionDestroyed(HttpSessionEvent hse){
		int[] counter = getCounter(hse);
		counter[0]--;
	}

	private int[] getCounter(HttpSessionEvent hse){
		HttpSession session = hse.getSession();
		ServletContext context=session.getServletContext();
		int[] counter = (int[]) context.getAttribute(COUNTER_ATTR);
		if(counter==null){
			counter = new int[1];
			context.setAttribute(COUNTER_ATTR,counter);
		}
		return counter;
	}
}