java session 监听

<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);
}
}