In-depth analysis of PHP automatic loading mechanism

In-depth analysis of PHP automatic loading mechanism_PHP tutorial

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Release： 2016-07-21 15:07:24

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1. How to implement automatic loading in php
1. Use require, include, require_once, and include_once to load manually.
2. Use __autoload for automatic loading
3. Use spl’s autoload to realize automatic loading
Manual loading implementation:

We can use the first one when there are few files to load. It's easy and no problem to do so.

Copy code The code is as follows:

require_once 'a.php';
require_once 'b.php';
require_once 'c.php';

But is this okay when there are a lot of files to be loaded? What should we do when we need to write ten, twenty require_once or more?

At this time we can use the __autoload method to simplify our code.

Implementation of __autoload loading:
We create an in.php file in the test directory with the following content.

Copy code The code is as follows:

echo 'I am in.php under test
';

Then create a loader.php in the test directory with the following content.

Copy code The code is as follows:

// You need to overload the __autoload method and customize the path containing the class file 
function __autoload($classname) 
{ 
 $class_file = strtolower($classname).".php"; 
 if (file_exists($class_file)){ 
 require_once($class_file); 
 } 
}
@$test = new in(); // When executed here, it will outputI am under test in.php

No problem, it worked! We can also create other files for loading, but what should we do when there are many files that need to be divided into directories?

At this time we need to modify loader.php to use mapping to find the file to be loaded.

Copy code The code is as follows:

function __autoload($class_name) {
$map = array(
'index' => './include/index.php',
'in' => './in.php'
);

if (file_exists($map[$class_name]) && isset($map[$class_name])) {
require_once $map[$class_name];
}
}
new index ();

The advantage of this method is that the class name and file path are only maintained with a mapping, so when the file structure changes, there is no need to modify the class name, only the corresponding Just modify it.

But __autoload can only be used once in a project. When your project references a project of others, there is an __autoload in your project, and there is also an __autoload in other people's projects, so the two __autoloads conflict. The solution is to modify __autoload to become one. This is undoubtedly very cumbersome and has a single application scenario.

SPL's autoload loading implementation:
SPL's autoload series of functions use an autoload call stack. You can use spl_autoload_register to register multiple custom autoload functions and application scenarios. Extensive

•Create in.php in the test directory with the following content

Copy the code The code is as follows:

 
class in {
 public function index() {
 echo 'I am in.php under test';
 }
}
?> ;

Create loader.php in the test directory with the following content

Copy the code The code is as follows:

 
set_include_path("/var/www/test/"); //Here you need to put the path into include
spl_autoload("in"); //Look for /var/www/ test/in.php
$in = new in();
$in->index();

•spl_autoload_register registers the function into the SPL __autoload function stack, modify loader.php

Copy code The code is as follows:

function AutoLoad($class){
 if($class == 'in'){
 require_once("/var/www/test/in.php");
 } 
}
spl_autoload_register('AutoLoad');
$a = new in();
$a->index();

•spl_autoload_register registers more To apply a custom autoload function
first create the mods folder in the test directory and create inmod.mod.php with the following content:

Copy code The code is as follows:

class inmod
{
 function __construct()
 {
 echo 'I am in under mods';
 }
}

Then create the libs folder in the test directory and create inlib.lib.php with the following content:

Copy code The code is as follows:

class inlib
{
 function __construct()
 {
 echo 'I am under libs in';
}
}

Finally create loader.php in the test directory with the following content

Copy code The code is as follows:

class Loader {
 /**
 * Automatically load class
 * @param $class class name
*/
 public static function mods($class) {
 if($class){
 set_include_path( "/var/www/test/mods/" );
 spl_autoload_extensions( ".mod.php" );
 spl_autoload( strtolower($class) );
 }
 }
 public static function libs($class) {
 if($class){
 set_include_path( "/var/www/test/libs/" );
 spl_autoload_extensions ( ".lib.php" );
 spl_autoload( strtolower($class) );
 }
 }
}
spl_autoload_register(array('Loader', 'mods')); 
spl_autoload_register(array('Loader', 'libs'));
new inmod();//OutputI am in under mods
new inlib();//Output< SPAN style="FONT-FAMILY: 'Times New Roman'; FONT-SIZE: 14px">I am under libs in