PHP: persistent variable value

Question

I have to read a file and do some computation, than save the result of this computation inside a variable.

I just need to do this once. In Java + Servlet I can do this using a servlet container and, for instance, the singleton pattern.

I know that in PHP I can't act like this. Which is the better way to do this? Save the computation (or transfer the data) on DB?

@JaredFarrish because the variable will not persist between multiple requests — Antonio
– Antonio, Commented Dec 28, 2012 at 19:59
@Antonio That's what sessions are for us1.php.net/manual/en/book.session.php, or do you mean you need a global state for all users? — Michael Berkowski
– Michael Berkowski, Commented Dec 28, 2012 at 19:59
@MichaelBerkowski sessions are relative to a single user, am I wrong? edit: yes, I need some global state, sorry you edited :) — Antonio
– Antonio, Commented Dec 28, 2012 at 20:00

hek2mgl · Accepted Answer · 2012-12-28 22:00:18Z

9

No, it won't work like with Java Servlets. You'll have to find a workaround.

First, I assume that using $_SESSION, $_COOKIE or $_REQUEST in general isn't practicable to you as you want to save the state per server (or per application) and not per 'User Session'.

Using a database sounds practicable in your case. In a regular application design it will be the most common solution.

Also you can do something like this, using the serialization capabilities of PHP:

<?php

$resultfile = 'result.dat';
if(!file_exists($resultfile)) {
    $result = compute_result('foo bar');
    file_put_contents($resultfile, serialize($result));
} else {
    $result = unserialize(file_get_contents($resultfile));
}

Using PHP's serialize() attempt is especially practicable when

You are in a PHP only environment
$result is a complex datatype but you don't want to create a database structure and map $result too it

If you are not in a PHP only environment you might prefer other serialization formats as JSON or XML.

Also the serialization result can be stored as a string in a database instead of a file. Saving it to a database instead of a file would make the application more scalable as the result would be available to all servers that access the same database (cluster).

In short: I would suggest using a database maybe combined with serialization.

edited Dec 28, 2012 at 22:00

answered Dec 28, 2012 at 21:05

hek2mgl

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2 Comments

Carsten Over a year ago

Just as an additional suggestion: if you need to access this global state using another language (maybe Java), using a format like JSON might be easier.

hek2mgl Over a year ago

Yes, thats right. I updated the answer according to your comment.

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