Struts 2 SessionMap not synchronized

Question

I have a long action with some insterts in a SessionMap and a very short action that read my SessionMap. They are like that:

public class LongAction extends ActionSupport implements SessionAware {
    private SessionMap session;
    public String index() {
        for(int i = 0 ; i < 50 ; ++i) {

            /*
             * long treatment
             */

            synchronized(session) {
                session.put("TEST", "TEST_OBJECT");
            }
         }
         return SUCCESS;
    }
    @Override
    public void setSession(Map<String, Object> arg0) {
        this.session = (SessionMap<String, Object>) arg0;
    }
}

And this is my shorter action:

public class LongAction extends ActionSupport implements SessionAware {
    private SessionMap session;
    public String index() {
        synchronized (session) { 
            for(Entry<String, Object> e : session.entrySet()) {
                System.out.println(e.getKey() + " --> " + e.getValue());
            }
        }
        return SUCCESS;
    }
    @Override
    public void setSession(Map<String, Object> arg0) {
        this.session = (SessionMap<String, Object>) arg0;
    }
}

But the entry "TEST" does not appear if I execute the second action while the first is still running.

I tried removing synchronized blocs because I saw here that SessionMap are made for safe-threading. The problem is the same.

PS: I am using JBoss 7.1.1

EDIT:

I have noticed something weird:

I execute my big action (it inserts a string in my session);
I execute my small action: it does not read my string in the session;
I execute my big action one more time while the first is still running (it change the string in my session)
I execute my small action one more time: it DOES read the new string in the session;

Trace:

[stdout] (http-localhost/127.0.0.1:8781-1) 687da6e5-bd4d-474d-be60-c2d2fdc4892a
[stdout] (http-localhost/127.0.0.1:8781-2) null

[stdout] (http-localhost/127.0.0.1:8781-1) 82e6d9b7-558f-46f5-a457-b5332bb4f54e
[stdout] (http-localhost/127.0.0.1:8781-2) 82e6d9b7-558f-46f5-a457-b5332bb4f54e

Moreover, the first time, session id is not the same for both actions; but the the second time, it is the same. Example:

[stdout] (http-localhost/127.0.0.1:8781-1) SessionId: j9vJzYzofPvImdrlLKKIWOGW.undefined
[stdout] (http-localhost/127.0.0.1:8781-2) SessionId: vsXtGHmJAtaJxZcd4w9+Og6B.undefined

[stdout] (http-localhost/127.0.0.1:8781-1) SessionId: vsXtGHmJAtaJxZcd4w9+Og6B.undefined
[stdout] (http-localhost/127.0.0.1:8781-2) SessionId: vsXtGHmJAtaJxZcd4w9+Og6B.undefined

But, if I execute a small action before the big one, everything works well. So, I think the session needs to be initialized before because it need an action to be ended. But I do not know how.

If the long-running part happens before your `synchronize` part, why is this unexpected? — Dave Newton, Jul 23 '13 at 14:04
in fact, if I wait until the first loop ends and execute the second action, the problem still occurs. — Florent06, Jul 23 '13 at 14:36
Sounds like a different issue, then; the session is the session. — Dave Newton, Jul 23 '13 at 14:41
I follow this [solution](http://stackoverflow.com/a/16433488/1479829) but it does not work. — Florent06, Jul 23 '13 at 15:27
Unless you're doing session replication across machines that's irrelevant. Are you? If so, you should mention that, as it's a critical point. — Dave Newton, Jul 23 '13 at 16:38
No I'm not. I just use it in local environment to do the development. — Florent06, Jul 24 '13 at 09:07
I have found a solution so far: response.flushBuffer(); after each session insert. — Florent06, Jul 24 '13 at 12:31

Struts 2 SessionMap not synchronized

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