One time initialization for Application

Question

I have a Java background. So please bear with me.

In a Java application, one way to perform one time initialization is to have an "Initializer Servlet" whose init() method can have one time initialization code. Another more general purpose mechanism is to have a Singleton that initializes on first use - and this mechanism will work in various languages / platforms. What I need to know is how to do it for my PHP webapp.

Should I use the Singleton Pattern? Is there another / better / PHP specific way? Essentially I want have a "Registry" - a single instance of it - which I can then use to create instances of other objects (themselves Singleton or not depends on situation at hand).

The ultimate goal is - I need certain things initialized BEFORE any web request is served by my PHP web application - something an "Initializer Servlet" in Java guarantees me. Maybe there is an "Initializer PHP Page" or something like that?

Thanks in advance

Answer 1

The source PHP, in the regular sense, does not generate an executable program. It is a scripting language. However, you are able to create a singleton.

Answer 2

PHP's nature will not allow you to have a initialization like servlets. In PHP everything will be inside a web request. As you mentioned, the Registry design pattern can help you to have a place to put your objects, however, they will be recreated on every request.

Answer 3

I do not have a Java background, but a singleton that on construction initiates and returns (or holds as static) other singletons/factories is a common pattern. Because the only defined "entry point" of a PHP application is the file that gets passed to the parser, many PHP applications go to great lengths to redirect to a "bootstrap" script, which prepares the environment and instantiates any singleton and static objects needed by the application. This is then included at the entry point to assure it is available to the entire application.

<?php // this file is bootstrap.php
// ... 
class MySingleton {
    private static $instance;

    private function __construct() {
        $this->myFactory1 = new MyFactory1();
        $this->myFactory2 = new MyFactory2();
        $this->myOtherSingleton = MyOtherSingleton::get();
    }

    public static function get() {
        if (!isset(self::$instance)) {
            $c = __CLASS__;
            self::$instance = new $c;
        }
        return self::$instance;
    }

    public function __clone() {
        trigger_error('Clone is not allowed.', E_USER_ERROR);
    }
}

// Before we leave, we'll get an instance!
$myBootstrapUtility = MySingleton::get();
// end of bootstrap.php ?>

one would then make sure to require_once('bootstrap.php'); before the rest of application logic.

Of course the actual details are entirely up to you, but this is certainly not an uncommon way of doing what you're after.