PHP's automatic loading mechanism_PHP tutorial

1. How to implement automatic loading in php

Use require, include, require_once, include_once to load manually.

Use __autoload for automatic loading
Use spl’s autoload to implement automatic loading
Implementation of manual loading:

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

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

require_once 'a.php';
require_once 'b.php';
require_once 'c.php';
But is this okay when there are a lot of files to load? 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.

__autoload implementation:

We create an in.php file in the test directory with the following content.

[php]
echo 'I am in.php under test
';

echo 'I am in.php under test
'; Then create a loader.php in the test directory with the following content.

[php]
// 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 in.php under test

// 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(); // The output will be output when executed here. I am in.php under test, no problem, successful! 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.

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

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

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 items in the mapping need to be modified.

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.

Autoload loading implementation of spl:

SPL's autoload series of functions use an autoload call stack. You can use spl_autoload_register to register multiple customized autoload functions, with a wide range of application scenarios

Automatically loaded related 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: Create in.php in the test directory with the following content

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

class in {
public function index() {
echo 'I am in.php under test';
}
}
?> Create loader.php in the test directory with the following content
[html]
set_include_path("/var/www/test/"); //You need to put the path into include
spl_autoload("in"); //Looking for /var/www/test/in.php
$in = new in();
$in->index();

set_include_path("/var/www/test/"); //Here you need to put the path into include
spl_autoload("in"); //Find /var/www/test/in.php
$in = new in();
$in->index();
spl_autoload_register registers the function into the SPL __autoload function stack and modifies loader.php
[php]
function AutoLoad($class){
If($class == 'in'){
​​​​ require_once("/var/www/test/in.php");
}  
}
spl_autoload_register('AutoLoad');
$a = new in();
$a->index();

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 applications with multiple custom autoload functions
First create the mods folder in the test directory and create inmod.mod.php with the following content:
[php]
class inmod
{
Function __construct()
{
echo 'I am in under mods';
}  
}

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:
[php]
class inlib
{
Function __construct()
{
echo 'I am in under libs';
}  
}

class inlib
{
function __construct()
{
echo 'I am in under libs';
}
}               Finally, create loader.php in the test directory with the following content
[php]
class Loader {
/**
* Automatic loading 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 under mods in
new inlib();//outputI am under libs in

class Loader {
/**
* Automatic loading 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();//Output I am in under mods
new inlib();//Output I am in under libs

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