Session Monitor

asked 2013-01-24 10:34:16 +0800

gquintana
33 ● 3

Hello,

I'd like to monitor (via JMX) how many users are connected to my application.

I discovered the org.zkoss.zk.ui.util.Statistics class. After some testing (WebLogic 10.3 + ZK 5.0) and many Session timeouts, the activeSessionCount becomes negative. This may be possible since Statistics is not thread-safe.

So I developped my own Monitor implementation replacing ints by AtomicInts:

public class ZkMetrics implements Monitor {
    private final AtomicInteger activeSessionCount = new AtomicInteger();
    public int getActiveSessionCount() {
        return activeSessionCount.get();
    }
    public void sessionCreated(Session sess) {
        activeSessionCount.incrementAndGet();
    }
    public void sessionDestroyed(Session sess) {
        activeSessionCount.decrementAndGet();
    }
    ...
}

Even with that change, sessionCount was still becoming negative after some time. Obviously sessionDestroyed is called more than sessionCreated: so I have to maintain a sessionId set:

public class ZkMetrics implements Monitor {
    private final Set<String> activeSessionIds = Collections.synchronizedSet(new HashSet<String>());
    public int getActiveSessionCount() {
        return activeSessionIds.size();
    }
    private static String getSessionId(Session session) {
        return ((HttpSession) session.getNativeSession()).getId();
    }
    public void sessionCreated(Session sess) {
        activeSessionIds.add(getSessionId(sess));
    }
    public void sessionDestroyed(Session sess) {
        activeSessionIds.remove(getSessionId(sess));
    }

I can't tell whether the problem is related to ZK or WebLogic, did some of you experiment similar thing?

How is the ZK listener related to JavaEE HttpSessionListener?

Thanks for advice