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php自动加载方式集合,php加载方式集合
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PHP automatic loading method collection, PHP loading method collection_PHP tutorial

Jul 12, 2016 am 08:55 AM
php autoload

php自动加载方式集合,php加载方式集合

php加载文件方式:
1、include,include_once,requice,requice_one常规加载
2、__autoload()
3、spl_autoload_register()

常规加载方式
假设我们有一个类文件A.php,里面定义了一个名字为A的类:

<&#63;php  
class A {  
  public function __construct() {  
    echo 'Got it.';  
  }  
}
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然后我们有一个index.php需要用到这个类A,常规的写法就是

<&#63;php  
  require('A.php');  
  $a = new A();
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但是有一个问题就是,假如我们的index.php需要包含的不只是类A,而是需要很多类,这样子就必须写很多行require语句,有时候也会让人觉得不爽。

__autoload()自动加载
不过在php5之后的版本,我们就不再需要这样做了。
在php5中,试图使用尚未定义的类时会自动调用__autoload函数,所以我们可以通过编写__autoload函数来让php自动加载类,而不必写一个长长的包含文件列表。

例如在上面那个例子中,index.php可以这样写:

<&#63;php  
function __autoload($class){  
  $file = $class . '.php';  
  if (is_file($file)) {  
    require_once($file);  
  }  
}  
$a = new A();
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当然上面只是最简单的示范,__autoload只是去include_path寻找类文件并加载,我们可以根据自己的需要定义__autoload加载类的规则。注意:由于__autoload()是个函数,只能存在一次。

spl_autoload_register()自动加载
但现在问题来了,如果在一个系统的实现中,如果需要使用很多其它的类库,这些类库可能是由不同的开发人员编写的,其类名与实际的磁盘文件的映射规则不尽相同。这时如果要实现类库文件的自动加载,就必须在__autoload()函数中将所有的映射规则全部实现,这样的话__autoload()函数有可能 会非常复杂,甚至无法实现。最后可能会导致__autoload()函数十分臃肿,这时即便能够实现,也会给将来的维护和系统效率带来很大的负面影响。在这种情况下,难道就没有更简单清晰的解决办法了吧?答案当然是:NO!

spl_autoload_register() 满足了此类需求。 它实际上创建了 autoload 函数的队列,按定义时的顺序逐个执行。相比之下, __autoload() 只可以定义一次。

bool spl_autoload_register ([ callable $autoload_function [, bool $throw = true [, bool $prepend = false ]]] )
我们继续改写上面那个例子:

<&#63;php  
function loader($class){  
  $file = $class . '.php';  
  if (is_file($file)) {  
    require_once($file);  
  }  
}  
spl_autoload_register('loader');  
$a = new A();
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或者直接使用匿名函数:

<&#63;php  
 
spl_autoload_register(function($file){
  $file = $class . '.php';  
  if (is_file($file)) {  
    require_once($file);  
  }
});  
$a = new A();
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这样子也是可以正常运行的,这时候php在寻找类的时候就没有调用__autoload而是调用我们自己定义的函数loader了。同样的道理,下面这种写法也是可以的:

<&#63;php  
class Loader {  
  public static function loadClass($class){  
    $file = $class . '.php';  
    if (is_file($file)) {  
      require_once($file);  
    }  
  }  
}  
spl_autoload_register(array('Loader', 'loadClass')); 
//spl_autoload_register(array(__CLASS__, 'loadClass')); 
//spl_autoload_register(array($this, 'loadClass')); 
$a = new A();
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更多示例
autoload.php

<&#63;php

define('SDK_PATH', __DIR__);

require_once SDK_PATH . '/common/functions.php';
require_once SDK_PATH . '/common/config.php';

spl_autoload_register(function ($class) {
  if (false !== stripos($class, 'YJC\Wechat')) {
    require_once __DIR__ . '/' . str_replace('\\', DIRECTORY_SEPARATOR, substr($class, 10)) . '.php';
  }
});


/*
function __autoload($class){
  if (false !== stripos($class, 'YJC\Wechat')) {
    require_once __DIR__ . '/' . str_replace('\\', DIRECTORY_SEPARATOR, substr($class, 10)) . '.php';
  }
}
*/

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建议入口文件里养成定义绝对地址SDK_PATH的习惯,这样require不会出错。
以上就是本文的全部内容,希望对大家的学习有所帮助。

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