Check whether a session is new in PHP

问题:

I have a website that needs to perform a certain backend function once per user session. I therefore want to be able to determine whether any given page view is the first within a given session.

According to the PHP docs:

session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.

So is there any way to know whether the session is being created or resumed?

Or is this a situation where I have to check the current session ID against a list I maintain on the server, to check if it's been registered before? If so, does this necessitate writing to a database, or is there a less cumbersome, in-memory way of doing this?

回答1:

<?php
session_start();
if(empty($_SESSION['exists'])){
    //handle completely new session here
}
$_SESSION['exists'] = true;
.... //continue on with normal request

回答2:

All documented ways of checking for session "newness" have failed me in the past, so I tend to do

$_SESSION['existing']=true;

when starting a session, and then just testing

if (isset($_SESSION['existing'])) ...

回答3:

Check if $_COOKIE['PHPSESSID'] is defined (or whatever the cookie name is if you changed it from default.

If the cookie doesn't exist, then the session has just been created.