Table of Contents
如何在composer.json文件中配置类和命名空间 ?
PSR-4
Classmap方式
Files
composer是如何实现自动加载的 ?
ClassLoader类中值得注意的方法:
Home Backend Development PHP Tutorial Composer automatically loads instance analysis

Composer automatically loads instance analysis

Feb 26, 2018 am 10:37 AM
composer Case Analysis automatic

通过在composer.json文件中配置需要加载的类、命名空间,通过执行composer install 命令自动生成类名和对应的类文件的映射,而后通过注册loadClass方法,实现对composer管理的诸多类的自动加载;

如何在composer.json文件中配置类和命名空间 ?

共有四种方式:
PSR-0(网上查到的例子和PSR-4没有看出太大区别,且已不推荐使用);
PSR-4;
Class-map;
Files;
在composer.json文件中添加以下代码块:

"autoload": {
    "psr-4": {
        "src\\darren\\": "src/",
        "project\\darren\\": "project"
        },
    "files": ["common/Darren.php", "common/Since.php"],
    "classmamp": [lib]
}
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测试代码目录结构如下:

common
    Darren.php
    Since.php
lib
    Darren.php
    Since.php
project
    Darren.php
src
    Darren.php
vendor
composer.json
index.php
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代码中的命名空间习惯为:目录名/Darren
当我们配置好composer.json文件,并执行compoer install命令后,在vendor/composer目录下会自动生成一些php文件,这些文件实际上记录了类、命名空间和对应的类文件的映射,下面一一举例说明;

PSR-4

如上所述,通过psr-4方式配置了两个命名空间的自动加载,分别是src\daren和projecr\darren;vendor/composer目录下自动生成了autoload_psr4.php文件,具体代码如下所示:

<?php

// autoload_psr4.php @generated by Composer

$vendorDir = dirname(dirname(__FILE__));
$baseDir = dirname($vendorDir);

return array(
&#39;src\\darren\\&#39; => array($baseDir . &#39;/src&#39;),
&#39;project\\darren\\&#39; => array($baseDir . &#39;/project&#39;),
);
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Classmap方式

classmap方式只需要我们配置需要自动加载的目录,compoer会自动扫描目录下的的.php文件或.inc文件中的class,并自动生成这些类和其对应的类文件的映射关系,保存在vendor/composer目录下的autoload_classmap.php文件中,具体代码如下:

<?php

// autoload_classmap.php @generated by Composer

$vendorDir = dirname(dirname(__FILE__));
$baseDir = dirname($vendorDir);

return array(
&#39;lib\\darren\\Darren&#39; => $baseDir . &#39;/lib/Darren.php&#39;,
&#39;lib\\since\\Since&#39; => $baseDir . &#39;/lib/Since.php&#39;,
);
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其中lib\darren为命名空间,Darren为类名;

Files

files方式其实就是手动指定要加载的文件,这通常适用于一些全局的functions,可以将这些functions统一放在一个文件里,然后直接进行加载;
上述的配置文件通过files方式加载了两个文件common/Darren.php和common/Since.php,vendor/composer目录下自动生成了autoload_files.php文件,具体代码如下所示:

<?php

// autoload_files.php @generated by Composer

$vendorDir = dirname(dirname(__FILE__));
$baseDir = dirname($vendorDir);

return array(
&#39;b704865b506bf33e8097e6f62604fc7f&#39; => $baseDir . &#39;/common/Darren.php&#39;,
&#39;603921ee67f9053beb44a88f05b115d2&#39; => $baseDir . &#39;/common/Since.php&#39;,
);
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composer是如何实现自动加载的 ?

配置完compoer.json文件,跑完了composer install命令,在文件的开始引用vendor/autolaod.php即可实现类的自动加载,那么composer是如何实现自动加载的呢?


这里先插叙一点php的特性:当调用不存在的类时,系统会自动调用__autoload( )方法来加载相应的类;

举例子说明如下:
我们在index.php文件中调用Darren类中的testAutoload( )方法【Darren类与index.php文件在同级目录】,这里我们没有在index.php文件中引入Darren类,那么肯定是会报错的;但是我们可以重写__autoload( )方法实现Darren类的加载,具体代码如下:

//当调用不存在的类时,系统自动调用__autolaod()查找
function __autolaod($class)
{
    $file = $class . &#39;.php&#39;;
    if (is_file($file)) {
        require_once($file);
    }
}
Darren::testAutoload();
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我们也可以通过spl_autoload_register( )方法来注册一个其它方法来替代__autoload( );

举例如下:

function loader($class)
{
    $file = $class . &#39;.php&#39;;
    if (is_file($file)) {
        require_once($file);
    }
}
spl_autoload_register(&#39;loader&#39;);
Darren::testAutoload();
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这样,loader方法就取代了__autoload;


接下来我们继续研究composer背后的加载机制,autoload.php中引入了autoload_real.php然后调用了getLoader( )方法,getLoader( )方法具体代码如下:

public static function getLoader()
{
    if (null !== self::$loader) {
        return self::$loader;
    }

    spl_autoload_register(array(&#39;ComposerAutoloaderInit0a8197b9e4da93df051721eff8ed7b28&#39;, &#39;loadClassLoader&#39;), true, true);
    self::$loader = $loader = new \Composer\Autoload\ClassLoader();
    spl_autoload_unregister(array(&#39;ComposerAutoloaderInit0a8197b9e4da93df051721eff8ed7b28&#39;, &#39;loadClassLoader&#39;));

    $map = require __DIR__ . &#39;/autoload_namespaces.php&#39;;
    foreach ($map as $namespace => $path) {
        $loader->set($namespace, $path);
    }

    //整理通过psr-4方式配置的类
    $map = require __DIR__ . &#39;/autoload_psr4.php&#39;;
    foreach ($map as $namespace => $path) {
        $loader->setPsr4($namespace, $path);
    }

    //整理通过classmap方式配置的类
    $classMap = require __DIR__ . &#39;/autoload_classmap.php&#39;;
    if ($classMap) {
        $loader->addClassMap($classMap);
    }

    //注册实现自动加载的方法
    $loader->register(true);

    //直接引入通过files配置的类
    $includeFiles = require __DIR__ . &#39;/autoload_files.php&#39;;
    foreach ($includeFiles as $fileIdentifier => $file) {
        composerRequire0a8197b9e4da93df051721eff8ed7b28($fileIdentifier, $file);
    }

    return $loader;
}
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该方法先是创建了一个ClassLoader类的对象,然后加载composer自动生成的那些记录类、命名空间与文件映射关系的文件,调用ClassLoader中的方法对这些文件整理,并将映射关系通过数组保存,数组的键为类名或者命名空间加类名,数组的值为类对应的类文件地址;这里值得注意的一点是,我们通过files配置的那些需要自动加载的类,是直接将类文件引入进来,并不是在调用时才去加载,代码如下:

function composerRequire0a8197b9e4da93df051721eff8ed7b28($fileIdentifier, $file)
{
    if (empty($GLOBALS[&#39;__composer_autoload_files&#39;][$fileIdentifier])) {
        require $file;//直接引入类文件
        $GLOBALS[&#39;__composer_autoload_files&#39;][$fileIdentifier] = true;
     }
}
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ClassLoader类中值得注意的方法:

通过register方法注册loadClass方法,取代__autoload( )方法,实现类的加载

public function register($prepend = false)
{
    spl_autoload_register(array($this, &#39;loadClass&#39;), true, $prepend);
}
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loadClass方法查找类对应的文件,并引入:

public function loadClass($class)
{
    if ($file = $this->findFile($class)) {
        includeFile($file);
        return true;
    }
}
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具体如何查找数组从而得到该类对应的类文件,可以通过xdebug跟一遍代码,并不难理解;

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