PHP Tutorial Tutorials - PHP OOP Autoloading

Autoloading allows you to load class and interface files automatically whenever you try to create an object from a none-existent class in the context of the current script file.

Why Autoloading?

We recommend one PHP source file contain a class definition.But the problem is having to write a long list of needed includes at the beginning of each script (one for each class).

<?php
include 'ClassName1.php';
include 'ClassName2.php';
include 'Namespace1\ClassName3.php';
include 'Namespace2\ClassName4.php';

Register autoloaders

In PHP 5, By registering autoloaders, PHP is given a last chance to load the class or interface before it fails with an error.

We can use the spl_autoload_register() function to register any number of autoloaders, enabling for classes and interfaces to be automatically loaded if they are currently not defined.

test.php

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

$obj  = new ClassName1();
$obj2 = new ClassName2();
$obj3 = new Namespace1\ClassName3();
$obj4 = new Namespace2\ClassName4();
?>

Whenever you create an object from a non-existent class, PHP looks into the current folder and load the corresponding class file using the include() function.

Autoloading with namespace

In the namespaces chapter, we create a project which map namespace classes with the folder structure.
but the source codes are under lib folder:

project/
  |---index.php
  |---autoload.php
  |---lib/ (or vender)
       |---Lau/
            |---BaseLau.php  (namespace lau;class BaseLau{})
            |---web/
                 |---App.php (namespace lau\web;class App{})
       |---XXSoft/ (vender name)
            |---Helper.php  (namespace xxsoft;class Helper{})

So, we need to modify it in spl_autoload_register;
Create a new file autoload.php in project directory.
autoload.php

<?php
spl_autoload_register(function ($class_name) {
    echo $class_name;
    $file = __DIR__ . '\\lib\\' . $class_name . '.php';
    $file = str_replace('\\', DIRECTORY_SEPARATOR, $file);
    if (file_exists($file)) {
        include $file;
    }
});

The value of __DIR__ is the folder path where autoload.php is in.
in the file index.php,we can just include and use it:

<?php
include 'autoload.php';

Autoloading with exception handling

We can throws a customize exception when the class name is fail to load.

<?php
spl_autoload_register(function ($class_name) {
    echo "Want to load $class_name.\n";
    $file = $class_name . '.php';
    if (file_exists($file)) {
        include $file;
    }
    else{
        throw new Exception("Unable to load $class_name.");
    }
});

try {
    $obj = new NonExistClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
?>