Automatisches Laden von Klassen

Viele Entwickler, die objektorientierte Anwendungen entwickeln, erzeugen für jede Klassendefinition eine eigene PHP-Quelldatei. Eines der größten Ärgernisse ist die Notwendigkeit, am Anfang eines jeden Skripts eine lange Liste von benötigten Include-Anweisungen (eine für jede Klasse) schreiben zu müssen.

Die Funktion spl_autoload_register() registriert eine beliebige Anzahl von Autoladern, die es ermöglichen, dass Klassen und Schnittstellen automatisch geladen werden, wenn sie derzeit nicht definiert sind. Durch das Registrieren von Autoladern erhält PHP einen letzten Versuch, die Klasse oder Schnittstelle zu laden, bevor es unter Ausgabe einer Fehlermeldung scheitert.

Jedes klassenähnliche Konstrukt kann auf die gleiche Weise automatisch geladen werden. Dazu gehören Klassen, Schnittstellen, Traits und Aufzählungen.

Achtung

Vor PHP 8.0.0 war es möglich, __autoload() zu verwenden, um Klassen und Schnittstellen automatisch zu laden. Dies ist jedoch eine weniger flexible Alternative zu spl_autoload_register(). __autoload() ist seit PHP 7.2.0 veraltet und wurde in PHP 8.0.0 entfernt.

Hinweis:

Die Funktion spl_autoload_register() kann mehrfach aufgerufen werden, um mehrere Autoloader zu registrieren. Wenn von einer Autoload-Funktion eine Exception ausgelöst wird, wird dieser Vorgang jedoch unterbrochen und es werden keine weiteren Autoload-Funktionen ausgeführt. Aus diesem Grund wird dringend davon abgeraten, von einer Autoload-Funktion aus eine Exception auszulösen.

Beispiel #1 Autoload-Beispiel

Dieses Beispiel versucht die Klassen MyClass1 und MyClass2 aus den entsprechenden Dateien MyClass1.php und MyClass2.php zu laden.

<?php
spl_autoload_register
(function ($class_name) {
    include 
$class_name '.php';
});

$obj  = new MyClass1();
$obj2 = new MyClass2();
?>

Beispiel #2 Weiteres Autoload-Beispiel

Dieses Beispiel versucht, das Interface ITest zu laden.

<?php

spl_autoload_register
(function ($name) {
    
var_dump($name);
});

class 
Foo implements ITest {
}

/*
string(5) "ITest"

Fatal error: Interface 'ITest' not found in ...
*/
?>

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User Contributed Notes 6 notes

up
96
jarret dot minkler at gmail dot com
13 years ago
You should not have to use require_once inside the autoloader, as if the class is not found it wouldn't be trying to look for it by using the autoloader.

Just use require(), which will be better on performance as well as it does not have to check if it is unique.
up
61
str at maphpia dot com
5 years ago
This is my autoloader for my PSR-4 clases. I prefer to use composer's autoloader, but this works for legacy projects that can't use composer.

<?php
/**
* Simple autoloader, so we don't need Composer just for this.
*/
class Autoloader
{
    public static function
register()
    {
       
spl_autoload_register(function ($class) {
           
$file = str_replace('\\', DIRECTORY_SEPARATOR, $class).'.php';
            if (
file_exists($file)) {
                require
$file;
                return
true;
            }
            return
false;
        });
    }
}
Autoloader::register();
up
17
toi]n[enkayt[attaat]gmaal.com
2 years ago
Autoloading plain functions is not supported by PHP at the time of writing. There is however a simple way to trick the autoloader to do this. The only thing that is needed is that the autoloader finds the searched class (or any other autoloadable piece of code) from the files it goes through and the whole file will be included to the runtime.

Let's say you have a namespaced file for functions you wish to autoload. Simply adding a class of the same name to that file with a single constant property is enough to trigger the autoloader to seek for the file. Autoloading can then be triggered by accessing the constant property.

The constant could be replaced by any static property or method or by default constructor. However, I personally find a constant named 'load' elegant and informative. After all this is a workaround. Another thing to keep in mind is that this introduces an unnecessary class to the runtime. The benefit of this is that there is no need to manually include or require files containing functions by path which in turn makes code maintaining easier. Such behaviour makes it easier to alter the project structure since manual includes need not to be fixed. Only the autoloader needs to be able to locate the moved files which can be automated.

A code file containing functions.
/Some/Namespace/Functions.php
<?php
namespace Some\Namespace;

class
Functions { const load = 1; }

function
a () {
}

function
b () {
}
?>

Triggering autoloading of the file containing functions.
main.php
<?php
\Some\Namespace\Functions::load;

a ();
b ();
?>
up
11
Anonymous
12 years ago
It's worth to mention, if your operating system is case-sensitive you need to name your file with same case as in source code eg. MyClass.php instead of myclass.php
up
3
kalkamar at web dot de
13 years ago
Because static classes have no constructor I use this to initialize such classes.
The function init will (if available) be called when you first use the class.
The class must not be included before, otherwise the init-function wont be called as autoloading is not used.

<?php
function __autoload($class_name)
{
    require_once(
CLASSES_PATH.$class_name.'.cls.php');
    if(
method_exists($class_name,'init'))
       
call_user_func(array($class_name,'init'));
    return
true;
}
?>

I use it for example to establish the mysql-connection on demand.

It is also possilbe do add a destructor by adding this lines to the function:
<?php
if(method_exists($class_name,'destruct'))
   
register_shutdown_function(array($class_name,'destruct'));
?>
up
1
info at atomosmaestoso dot com
1 month ago
Autoloading Classes with  spl_autoload_register() or spl_autoload() is the best and most modern way to securely code for API integration.

It restricts the various attacks that can be faced by using a "polyfill" or framework that is subject to data injection. Low level attacks, polyfill and framework vulnerabilities are some exploitations limited in using the core functionalities of your host programming language.

Your loop-holes and target endpoints are vastly removed to the level of programming experience of the developer - in not exposing the threats espoused to your programming language and its security protocols.

Each event you transfer data from one program to the next reveals another threat and another attack endpoint. When you are production, it is at this point composer and other tools that gather requirements specific secure integration should limit its use, such as PCI-DSS, HIPAA, or GDPR.

The use of a framework or polyfill gives an attacker hints at what point a function will access memory to produce intended results. Visiting the late L1-Cache Terminal Fault - attacks that use machine language to access memory and read what actually is happening will have all the details of what process is taking place and when.

Not to mention, when a product is open-source, the code is editable and easily compiled. Using access to machine level integrations a simply 10 second loss of time to process could well as infer the entire application has experienced an overhaul.

To deter this, and ensure maximum security for piece of mind and money-wise. The embedded resources of a programming language should be utilized at maximal capacity to prevent an overhaul on multiple endpoints. Visiting a system in use is not deletable or easily moved, removed or altered.
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