composer實現自動加載原理【詳解】

下面由composer教程欄目給大家介紹composer實現自動加載原理，希望對需要的朋友有所幫助！

簡介

一般在框架中都會用到composer工具,用它來管理依賴。其中composer有類的自動加載機制，可以加載composer下載的庫中的所有的類文件。那么composer的自動加載機制是怎么實現的呢？

composer 自動加載原理

以在Laravel框架中為例：

1. 首先在入口文件（/public/index.php）中引入了autoload.php

   require?__DIR__.'/../vendor/autoload.php';

2. 我們看看autoload.php的內容

   require_once?__DIR__?.?'/composer/autoload_real.php'; return?ComposerAutoloaderInit1215780529014c2b50a6fca7ce889273::getLoader();

3. 我們再看看 autoload_real.php的內容

   <?php // autoload_real.php @generated by Composer  class ComposerAutoloaderInit1215780529014c2b50a6fca7ce889273 {     private static $loader;      public static function loadClassLoader($class)     {         if (&#39;ComposerAutoloadClassLoader&#39; === $class) {             require __DIR__ . &#39;/ClassLoader.php&#39;;         }     }      public static function getLoader()     {         if (null !== self::$loader) {             return self::$loader;         }         spl_autoload_register(array(&#39;ComposerAutoloaderInit1215780529014c2b50a6fca7ce889273&#39;, &#39;loadClassLoader&#39;), true, true);         self::$loader = $loader = new ComposerAutoloadClassLoader();         spl_autoload_unregister(array(&#39;ComposerAutoloaderInit1215780529014c2b50a6fca7ce889273&#39;, &#39;loadClassLoader&#39;));          $useStaticLoader = PHP_VERSION_ID >=?50600?&amp;&amp;?!defined('HHVM_VERSION')?&amp;&amp;?(!function_exists('zend_loader_file_encoded')?||?!zend_loader_file_encoded()); ????????if?($useStaticLoader)?{ ????????????require_once?__DIR__?.?'/autoload_static.php';  ????????????call_user_func(ComposerAutoloadComposerStaticInit1215780529014c2b50a6fca7ce889273::getInitializer($loader)); ????????}?else?{ ????????????$map?=?require?__DIR__?.?'/autoload_namespaces.php'; ????????????foreach?($map?as?$namespace?=&gt;?$path)?{ ????????????????$loader-&gt;set($namespace,?$path); ????????????}  ????????????$map?=?require?__DIR__?.?'/autoload_psr4.php'; ????????????foreach?($map?as?$namespace?=&gt;?$path)?{ ????????????????$loader-&gt;setPsr4($namespace,?$path); ????????????}  ????????????$classMap?=?require?__DIR__?.?'/autoload_classmap.php'; ????????????if?($classMap)?{ ????????????????$loader-&gt;addClassMap($classMap); ????????????} ????????}  ????????$loader-&gt;register(true);  ????????if?($useStaticLoader)?{ ????????????$includeFiles?=?ComposerAutoloadComposerStaticInit1215780529014c2b50a6fca7ce889273::$files; ????????}?else?{ ????????????$includeFiles?=?require?__DIR__?.?'/autoload_files.php'; ????????} ????????foreach?($includeFiles?as?$fileIdentifier?=&gt;?$file)?{ ????????????composerRequire1215780529014c2b50a6fca7ce889273($fileIdentifier,?$file); ????????}  ????????return?$loader; ????} }  function?composerRequire1215780529014c2b50a6fca7ce889273($fileIdentifier,?$file) { ????if?(empty($GLOBALS['__composer_autoload_files'][$fileIdentifier]))?{ ????????require?$file;  ????????$GLOBALS['__composer_autoload_files'][$fileIdentifier]?=?true; ????} }

可以看出這一段是composer自動加載的重點，首先在 autoload.php中調用ComposerAutoloaderInit1215780529014c2b50a6fca7ce889273::getLoader()方法，getLoader()首先判斷當前(loader是不是null，如果不為null就直接返回，否則就初始化一個ClassLoader類給賦值給)loader，接著將autoload_namespaces.php、autoload_psr4.php、autoload_classmap.php文件中的內容加入到$loader中對應的數組中,然后給注冊loadClass函數，將autoload_files.php中的所有路徑所示的文件都包含進來，當在new一個類的時候如果沒有找到相關的類就會觸發這個loadClass函數，在loadClass()又調用了findFile()去查找相應的文件，找到相應文件后就會返回該文件，然后loadClass調用includeFile()方法將該文件include進去，否則findFile返回false，這樣就完成了自動加載

4. 下面來看一下 findFile()

   ?public?function?findFile($class) ????{ ????????//?class?map?lookup ????????if?(isset($this->classMap[$class]))?{ ????????????return?$this->classMap[$class]; ????????} ????????if?($this->classMapAuthoritative?||?isset($this->missingClasses[$class]))?{ ????????????return?false; ????????} ????????if?(null?!==?$this->apcuPrefix)?{ ????????????$file?=?apcu_fetch($this->apcuPrefix.$class,?$hit); ????????????if?($hit)?{ ????????????????return?$file; ????????????} ????????}  ????????$file?=?$this->findFileWithExtension($class,?'.php');  ????????//?Search?for?Hack?files?if?we?are?running?on?HHVM ????????if?(false?===?$file?&&?defined('HHVM_VERSION'))?{ ????????????$file?=?$this->findFileWithExtension($class,?'.hh'); ????????}  ????????if?(null?!==?$this->apcuPrefix)?{ ????????????apcu_add($this->apcuPrefix.$class,?$file); ????????}  ????????if?(false?===?$file)?{ ????????????//?Remember?that?this?class?does?not?exist. ????????????$this->missingClasses[$class]?=?true; ????????}  ????????return?$file; ????}  ?????private?function?findFileWithExtension($class,?$ext) ????{ ????????//?PSR-4?lookup ????????$logicalPathPsr4?=?strtr($class,?'',?DIRECTORY_SEPARATOR)?.?$ext;  ????????$first?=?$class[0]; ????????if?(isset($this->prefixLengthsPsr4[$first]))?{ ????????????$subPath?=?$class; ????????????while?(false?!==?$lastPos?=?strrpos($subPath,?''))?{ ????????????????$subPath?=?substr($subPath,?0,?$lastPos); ????????????????$search?=?$subPath.''; ????????????????if?(isset($this->prefixDirsPsr4[$search]))?{ ????????????????????$pathEnd?=?DIRECTORY_SEPARATOR?.?substr($logicalPathPsr4,?$lastPos?+?1); ????????????????????foreach?($this->prefixDirsPsr4[$search]?as?$dir)?{ ????????????????????????if?(file_exists($file?=?$dir?.?$pathEnd))?{ ????????????????????????????return?$file; ????????????????????????} ????????????????????} ????????????????} ????????????} ????????}  ????????//?PSR-4?fallback?dirs ????????foreach?($this->fallbackDirsPsr4?as?$dir)?{ ????????????if?(file_exists($file?=?$dir?.?DIRECTORY_SEPARATOR?.?$logicalPathPsr4))?{ ????????????????return?$file; ????????????} ????????}  ????????//?PSR-0?lookup ????????if?(false?!==?$pos?=?strrpos($class,?''))?{ ????????????//?namespaced?class?name ????????????$logicalPathPsr0?=?substr($logicalPathPsr4,?0,?$pos?+?1) ????????????????.?strtr(substr($logicalPathPsr4,?$pos?+?1),?'_',?DIRECTORY_SEPARATOR); ????????}?else?{ ????????????//?PEAR-like?class?name ????????????$logicalPathPsr0?=?strtr($class,?'_',?DIRECTORY_SEPARATOR)?.?$ext; ????????}  ????????if?(isset($this->prefixesPsr0[$first]))?{ ????????????foreach?($this->prefixesPsr0[$first]?as?$prefix?=>?$dirs)?{ ????????????????if?(0?===?strpos($class,?$prefix))?{ ????????????????????foreach?($dirs?as?$dir)?{ ????????????????????????if?(file_exists($file?=?$dir?.?DIRECTORY_SEPARATOR?.?$logicalPathPsr0))?{ ????????????????????????????return?$file; ????????????????????????} ????????????????????} ????????????????} ????????????} ????????}  ????????//?PSR-0?fallback?dirs ????????foreach?($this->fallbackDirsPsr0?as?$dir)?{ ????????????if?(file_exists($file?=?$dir?.?DIRECTORY_SEPARATOR?.?$logicalPathPsr0))?{ ????????????????return?$file; ????????????} ????????}  ????????//?PSR-0?include?paths. ????????if?($this->useIncludePath?&&?$file?=?stream_resolve_include_path($logicalPathPsr0))?{ ????????????return?$file; ????????}  ????????return?false; ????}

   findFile()函數先在classMap中查找，如果找不到的話就會嘗試在apcu緩存中查找，如果還是找不到的話就會調用findFileWithExtension()函數查找，如果找到了就會將該文件加到apcu緩存，如果找不到的話就會在missingClasses數組中設一個標記表示識這個類找不到

   findFileWithExtension()方法根據之前通過(loader->set()namespace, (path)和)loader->setPsr4($namespace, $path)方法設置的信息找出類文件的路徑信息

5. 在上面有的地方用到了 spl_autoload_register和spl_autoload_unregister函數

   1. spl_autoload_register函數
      spl_autoload_register — 注冊給定的函數作為 __autoload 的實現，

      1. bool spl_autoload_register ([ callable $autoload_function [, bool $throw = true [, bool $prepend = false ]]] )

      2. prepend
         如果是 true，spl_autoload_register() 會添加函數到隊列之首，而不是隊列尾部。

      3. 如果在你的程序中已經實現了__autoload()函數，它必須顯式注冊到__autoload()隊列中。因為 spl_autoload_register()函數會將Zend Engine中的__autoload()函數取代為spl_autoload()或spl_autoload_call()
         例：

         function?__autoload($name) { ????require?'class/'.$name.'.php'; ????echo?'1'; } function?autoload_test($name) { ????echo?'2'; } spl_autoload_register('autoload_test'); spl_autoload_register('__autoload'); $ca=new?Ca();
   2. spl_autoload_unregister函數
      spl_autoload_unregister — 注銷已注冊的__autoload()函數，如果該函數隊列處于激活狀態，并且在給定函數注銷后該隊列變為空，則該函數隊列將會變為無效。如果該函數注銷后使得自動裝載函數隊列無效，即使存在有__autoload函數它也不會自動激活。
      1. bool spl_autoload_unregister ( mixed $autoload_function )

因本人水平有限，有些地方可能不對，歡迎留言。

以上就是