How to keep alive a user's session while they

问题:

I have a site with a session timeout of 15 minutes. On some pages a user occasionally spends longer than 15 minutes filling in a reply. What is the best solution to keep alive the session in this case?

I already use JQuery on these pages, so possibly pinging a server, but on what events?

The backend is a Struts on Tomcat.

回答1:

Given you don't want to change the site's session timeout..

Set a timeout/interval (< 15min) event in javascript and decide what to do when the event triggers. If you want the session to be active as long as the page is open, then fine, keep pinging every < 15 min. But that's probably not what you want as a user leaving a public computer should get logged out at some point.

You could maintain a variable lastActivity, which is updated on each document mousemove or document keydown. If there's been any activity since last ping, ping again.

To get more sophisticated, you could count the events and ping the server only if number of events > threshold at timeout.

The basic example:

setInterval(function(){
   $.get('/ImStillAlive.action');
}, 840000); // 14 mins * 60 * 1000

With basic check for typing activity:

$(function(){
    var lastUpdate = 0;
    var checkInterval = setInterval(function(){
       if(new Date().getTime() - lastUpdate > 840000){
           clearInterval(checkInterval);
       }else{   
            $.get('/ImStillAlive.action');
       }
    }, 840000); // 14 mins * 60 * 1000

    $(document).keydown(function(){
         lastUpdate = new Date().getTime();
    });
});

回答2:

I'm thinking that you really don't want this for ALL pages though. If you were to do this on every page, even the ones that really don't depend on session variables, you'd consume a lot of memory.

I'd suggest throwing in a conditional to do it only on certain pages where it's necessary, i.e.

if (location.href.indexOf('/checkout') !== -1) {
setInterval(function(){
    $.get('/keepalive.action');
}, 840000); // 14 mins
}

回答3:

You could set an interval ever 5 minutes:

setInterval(function() {
    // check if a reply textarea is present on the page and focussed
    // assuming it's e.g. a textarea with the id "reply"
    if ($('#reply:focussed').length) {
        // user is still on the reply page
        // call on a script on the server that renews the session
    }
}, 300000);

Or check whether he/she is still typing something:

<textarea id="reply"></textarea>
<input type="hidden" id="reply_length" name="length" />

setInterval(function() {
    // get length of text in textarea
    var len = $('#reply').val().length;

    // get previous length
    var prev = $('#reply_length').val().length;

    // if they don't match, assume they're doing something
    if (len != prev) {
        // renew session
    }

    // update previous length
    $('#reply_length').val(len);
}, 300000);