Analysis of PHP's autoload automatic loading mechanism

This article mainly introduces the PHP autoload automatic loading mechanism analysis, has a certain reference value, now share to everyone, the need for friends can refer to

PHP's autoload can be used in roughly two ways: __autoload and SPL methods. There are different ways of using these two methods

How to use __autoload 1:
The most common use of this method, according to the class name, find the class file, and then Require_one

function __autoload ($class _name) {$path = Str_replace (' _ ', '/', $class _name); require_once $path. '. php '; }//This will automatically load the http/file/interface.php file $a = new Http_file_interface ();

The benefits of this approach are simple and easy to use. Of course there are shortcomings, the disadvantage is that the class name and file path is forced to make a convention, when the file structure is modified, it is bound to modify the class name.

How to use __autoload 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];}//This will automatically load c:/php/h ttp/file/interface.php file $a = new Http_file_interface ();

The advantage of this approach is that the class name and file path are only maintained with a single map, so when the file structure changes, you do not need to modify the class name, just modify the corresponding item in the map.
The disadvantage of this approach compared to the previous method is that when the file is much more difficult to maintain, perhaps you will consider using JSON or a single file for maintenance. Perhaps you would have thought of using a framework to maintain or build such a mapping.
Spl_autoload
The biggest flaw in __autoload is the inability to have multiple autoload methods
Well, think of the following scenario, your project refers to someone else's project, your project has a __autoload, other people's project also has a __autoload, so that two __autoload conflict. The solution is to modify the __autoload to become one, which is undoubtedly very cumbersome.
So we urgently need to use a autoload call stack so that SPL's AutoLoad series functions 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 the Spl_autoload
Learn some of the functions of SPL first:


Spl_autoload is the default implementation of _autoload (), which will go to include_path for $class_name (. php/.inc)
Spl_autoload for automatic loading:

/*http.php*/<?php class HTTP {public Function callname () {echo ' this is HTTP ';}}/*test.php*/<?php Set_include_ Path ("/home/yejianfeng/handcode/"); Here you need to put the path in include Spl_autoload ("http"); Looking for/home/yejianfeng/handcode/http.php $a = new http (); $a->callname ();

Spl_autoload_register

Register the function in the SPL __autoload function stack and look directly at an example:

/*http.php*/<?php class HTTP {public Function callname () {echo ' this is HTTP ';}}/*test.php*/<?php spl_autoload _register (function ($class) {if ($class = = ' http ') {require_once ("/home/yejianfeng/handcode/http.php");}}); $a = new http (); $a->callname (); Spl_autoload_call

Call the call function registered in Spl_autoload_register to see 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 = = ' http ') {require_once ("/home/yejianfeng/ Handcode/http.php "); } if ($class = = ' HTTP2 ') {require_once ("/home/yejianfeng/handcode/http2.php");}}); Spl_auto_call (' HTTP2 '); $a = new http (); $a->callname (); This time it will output "This is HTTP2"

Spl_auto_register This function makes it possible to use a custom function for automatic loading without using __autoload. This method is now used frequently.
This method is used by the Zend Autoloader module. Extract the corresponding code

Spl_autoload_register (Array (__class__, ' autoload ')); public static function AutoLoad ($class) {...}

The above is the whole content of this article, I hope that everyone's learning has helped, more relevant content please pay attention to topic.alibabacloud.com!