java session 监听

相应的在web.xml配置

<listener>
	   <listener-class>....essionHandler</listener-class>
	</listener>

public class SessionHandler implements HttpSessionListener {

    private final static String COUNT = "count";

    @Override
    public void sessionCreated(HttpSessionEvent event) {
        ServletContext ctx = event.getSession().getServletContext();
        Integer numSessions = (Integer) ctx.getAttribute(COUNT);
        if (numSessions == null) {
            numSessions = new Integer(1);
        } else {
            int count = numSessions.intValue();
            numSessions = new Integer(count + 1);
        }
        ctx.setAttribute(COUNT, numSessions);
        System.out.println("create count : " + numSessions);
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        ServletContext ctx = event.getSession().getServletContext();
        Integer numSessions = (Integer) ctx.getAttribute(COUNT);
        if (numSessions == null) {
            numSessions = new Integer(0);
        } else {
            int count = numSessions.intValue();
            numSessions = new Integer(count - 1);
        }
        ctx.setAttribute(COUNT, numSessions);
        System.out.println("destroy count : " + numSessions);
    }
}