Analysis of PHP’s autoLoad automatic loading mechanism

This article mainly introduces the analysis of PHP's autoLoad automatic loading mechanism. It has a certain reference value. Now I share it with you. Friends in need can refer to it.

There are roughly two ways to use PHP's autoload. Methods: __autoload and spl methods. These two methods have different usage methods.

__autoload usage method 1:
The most commonly used method is to find the class based on the class name. file, and then require_one

function __autoload($class_name) { 
$path = str_replace('_', '/', $class_name); 
require_once $path . '.php'; 
} 
// 这里会自动加载Http/File/Interface.php 文件 
$a = new Http_File_Interface();

The advantage of this method is that it is simple and easy to use. Of course, there are also disadvantages. The disadvantage is that the class name and file path are forced to be agreed. When the file structure is modified, the class name must be modified.

__autoload usage method 2 (direct mapping method)

$map = array( 
'Http_File_Interface' => 'C:/PHP/HTTP/FILE/Interface.php' 
); 
function __autoload($class_name) { 
if (isset($map[$class_name])) { 
require_once $map[$class_name]; 
} 
} 
// 这里会自动加载C:/PHP/HTTP/FILE/Interface.php 文件 
$a = new Http_File_Interface();

The advantage of this method is that the class name and file path are only maintained with a mapping, so when the file structure When changing, you do not need to modify the class name, you only need to modify the corresponding item in the mapping.
The disadvantage of this method compared to the previous method is that it is very troublesome to maintain this mapping when there are too many files. Maybe at this time you will consider using json or a separate file for maintenance. Maybe you would think of using a framework to maintain or create such a mapping.
spl_autoload
__The biggest flaw of autoload is that it cannot have multiple autoload methods
Okay, think about the following scenario. Your project references a project of someone else. Your project There is an __autoload in the project, and other people's projects also have an __autoload, so the two __autoloads conflict. The solution is to modify __autoload to become one, which is undoubtedly very cumbersome.
So we urgently need to use an autoload call stack, so that the autoload series functions of spl appear. You can use spl_autoload_register to register multiple custom autoload functions
If your PHP version is greater than 5.1, you can use spl_autoload
First understand several functions of spl:


spl_autoload is the default implementation of _autoload(), it will look for $class_name(.php/.inc) in include_path
Spl_autoload implements automatic loading:

/*http.php*/ 
<?php 
class http 
{ 
public function callname(){ 
echo "this is http"; 
} 
} 
/*test.php*/ 
<?php 
set_include_path("/home/yejianfeng/handcode/"); //这里需要将路径放入include 
spl_autoload("http"); //寻找/home/yejianfeng/handcode/http.php 
$a = new http(); 
$a->callname();

Spl_autoload_register

will The function is registered in the SPL __autoload function stack. Let’s look at an example directly:

/*http.php*/ 
<?php 
class http 
{ 
public function callname(){ 
echo "this is http"; 
} 
} 

/*test.php*/ 
<?php 
spl_autoload_register(function($class){ 
if($class == &#39;http&#39;){ 
require_once("/home/yejianfeng/handcode/http.php"); 
} 
}); 

$a = new http(); 
$a->callname(); 


spl_autoload_call

Call the calling function registered in spl_autoload_register. Look at the following example

/*http.php*/ 
<?php 
class http 
{ 
public function callname(){ 
echo "this is http"; 
} 
} 
/*http2.php*/ 
<?php 
class http 
{ 
public function callname(){ 
echo "this is http2"; 
} 
} 

/*test.php*/ 
<?php 
spl_autoload_register(function($class){ 
if($class == &#39;http&#39;){ 
require_once("/home/yejianfeng/handcode/http.php"); 
} 
if($class == &#39;http2&#39;){ 
require_once("/home/yejianfeng/handcode/http2.php"); 
} 
}); 
spl_auto_call(&#39;http2&#39;); 
$a = new http(); 
$a->callname(); //这个时候会输出"this is http2"

spl_auto_register. This function allows us not to use __autoload. It is possible to use custom functions for automatic loading. This method is now commonly used.
Zend’s AutoLoader module uses this method. Extract the corresponding code

spl_autoload_register(array(__CLASS__, 'autoload')); 

public static function autoload($class) 
{ 
….. 

}

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