window.onunload not called on closing the browser

[Kunal Lakhani]

I am using Google Chrome.

Following code is in my Jsp

window.onunload = doUnload;
function doUnload(){
alert('in doUnload');
var left = window.screenLeft;
var top = window.screenTop;
alert(left);
alert(top);
if((left == 10004) && (top == 10144)){
alert('Signing out');
window.location = "./signOut"; //calls a servlet 
}
}

On closing the window, this code is not called up (alert is not executed)
While i did the same check using firefox with little change in code as "window.screenX" and "window.screenY", the code is called up only when i close the tab , and not the whole browser
What is the problem?
(I have also checked similar topics in this forum, but, couldn't find the solution)

[Rob Crowther]

There's a long discussion of the issues with unload in the blog post WebKit Page Cache II – The unload Event, for more modern browsers try pageshow and pagehide.

[Eric Pascarello]

When the page unloads you have no control over it. You can not redirect to another page when it is exiting. Session end event on the server should end the session.

[Kunal Lakhani]

There is a requirement in my application, where only one user with a particular username can log in at a time. Also, if he is logged in, the status in db changes to LOGGED IN. When he logs out, status chnages to LOGGED OUT.
Suppose, i set the time out to 15mins, or session inactiave to 5mins. The user accidently closes the browser. Then, status remains LOGGED IN, unless and until, that time period of 5mins/15mins is over.
That's the reason why, i need to invalidate the session as soon as browser closes (or PC shuts down)

[Bear Bibeault]

Requirements that cannot be met need to be changed.

[Kunal Lakhani]

I wish i could. But, all depends on my seniors. I was just said to implement this

[Bear Bibeault]

Well, as there is no way for this to be accomplished, you have a problem. You can either:

Let whoever is setting the requirement know that the session timeout is the only way to know if a browser has been adandoned

Or, continue to waste time trying to find a way to do this when it cannot be accomplished.

Bottom line: you can not get any reliable indication that a browser has been abandoned, or that a PC has been shut down, or has crashed. In these cases, you need to rely upon the session timeout.

[Kunal Lakhani]

Thanks Bear,Eric Pascarello,Rob Crowther for your replies

[Kunal Lakhani]

Hello
I have got another situation, which is causing problem.
My servlet class has following lines in the beginning :

HttpSession session = req.getSession();
		String nextPage = "";
		String username = (String) session.getAttribute("Username");
		if ((session.isNew()) || (username == null)) {
			nextPage = "login.html";
		} else {
                some codes that changes the db by calling dao class
               }

Suppose the user closes the browser, and session still is active (some mins remaining to make it inactive)
If some user, without login in, types any url specified in the web.xml, which calls any servlet. Then, that will change the db details, since it will satisfy the condition stated above in if block
That's the reason why i want to invalidate the session on closing of browser

[Bear Bibeault]

Again, it does not matter why you want to do it. It is the responsibility of the user of the application to log out of the application, and for you to set the session timeout to an appropriate value.

P.S. Why the check for isNew()? It's superfluous.

[Kunal Lakhani]

P.S. Why the check for isNew()? It's superfluous.

Will username == null alone do?

[Jayesh A Lalwani]

Hmm if user closes the browser, and another user logs in, the second user should get a different http session

[Bear Bibeault]

Kunal Lakhani wrote:

P.S. Why the check for isNew()? It's superfluous.

Will username == null alone do?

Think about it. Will there ever be a new session with a username in it?

[Kunal Lakhani]

Think about it. Will there ever be a new session with a username in it?

No. Not at all.

[Bear Bibeault]

Right. So why check for it?

[Kunal Lakhani]

Right

Thanks Bear Bibeault, Jayesh A Lalwani, Eric Pascarello, Rob Crowther