Yii2 的自动加载分两部分,一部分是 Composer 的自动加载机制,另一部分是 Yii2 框架自身的自动加载机制。
Composer自动加载
对于库的自动加载信息,Composer 生成了一个 vendor/autoload.php
文件。你可以简单的引入这个文件,你会得到一个自动加载的支持。
在之前的文章,入口文件的介绍中,我们可以看到如下内容:
<span>//</span><span> 引入 vendor 中的 autoload.php 文件,会基于 composer 的机制自动加载类</span><span><strong>require</strong></span>(__DIR__ . '/../vendor/autoload.php');
因为这个系列主要是关于 Yii2 的,所以有关 Composer 自动加载机制就不在这里详细说明了。
可查阅资料:
- Composer 自动加载
- Composer 自动加载-参考
- Composer 中文官网
Yii2 框架的自动加载机制
Yii2 框架的自动加载是通过 spl_autoload_register 方法实现的。
在之前的文章,入口文件的介绍中,我们可以看到如下内容:
<span>//</span><span> 引入 Yii 框架的文件 Yii.php</span><span><strong>require</strong></span>(__DIR__ . '/../vendor/yiisoft/yii2/Yii.php');
Yii.php 里究竟是什么内容?如何实现了自动加载?
下面我们来看一下,Yii.php 的内容如下:
<span>php </span><span>/*</span><span>* * Yii bootstrap file. * * @link http://www.yiiframework.com/ * @copyright Copyright (c) 2008 Yii Software LLC * @license http://www.yiiframework.com/license/ </span><span>*/</span><span><strong>require</strong></span>(__DIR__ . '/BaseYii.php'<span>); </span><span>/*</span><span>* * Yii is a helper class serving common framework functionalities. * * It extends from [[\yii\BaseYii]] which provides the actual implementation. * By writing your own Yii class, you can customize some functionalities of [[\yii\BaseYii]]. * * @author Qiang Xue <qiang.xue> * @since 2.0 </qiang.xue></span><span>*/</span><span>class</span> Yii <span>extends</span><span> \yii\BaseYii { } </span><span>/*</span><span>* * spl_autoload_register — 注册给定的函数作为 __autoload 的实现 * * bool spl_autoload_register ([ callable $autoload_function [, bool $throw = true [, bool $prepend = false ]]] ) * * 将函数注册到SPL __autoload函数<strong>队列</strong>中。如果该<strong>队列</strong>中的函数尚未激活,则激活它们。 * 如果在你的程序中已经实现了__autoload()函数,它必须显式注册到__autoload()<strong>队列</strong>中。 * 因为 spl_autoload_register()函数会将Zend Engine中的__autoload()函数取代为spl_autoload()或spl_autoload_call()。 * 如果需要多条 autoload 函数,spl_autoload_register() 满足了此类需求。 * 它实际上创建了 autoload 函数的<strong>队列</strong>,按定义时的顺序逐个执行。 * 相比之下, __autoload() 只可以定义一次。 * * autoload_function * 欲注册的自动装载函数。如果没有提供任何参数,则自动注册 autoload 的默认实现函数spl_autoload()。 * * throw * 此参数设置了 autoload_function 无法成功注册时, spl_autoload_register()是否抛出异常。 * * prepend * 如果是 true,spl_autoload_register() 会添加函数到<strong>队列</strong>之首,而不是<strong>队列</strong>尾部。 * * Yii 注册了 Yii 的 autoload 函数,实现自动加载, 其实现在 \yii\BaseYii 中 </span><span>*/</span><span>spl_autoload_register([</span>'Yii', 'autoload'], <span>true</span>, <span>true</span><span>); </span><span>//</span><span> 定义 Yii 核心的 class 的类名与文件地址的 Map</span>Yii::<span>$classMap</span> = <span><strong>require</strong></span>(__DIR__ . '/classes.php'<span>); </span><span>//</span><span> 创建 Yii 的依赖注入的容器</span>Yii::<span>$container</span> = <span>new</span> yii\di\Container();
其主要内容就是引入了 BaseYii.php 文件,然后声明了类 Yii,继承了 BaseYii,然后注册了 Yii (其实是 BaseYii)的 autoload 方法,去实现自动加载。之后又引入了Yii 核心类名与文件地址一一对应的 Map,存储到 Yii::$classMap 中。最后创建了一个 yii\di\Container 的实例,存储到 Yii::$container 中。
可以看出实现自动加载的关键代码是:
spl_autoload_register(['Yii', 'autoload'], <span>true</span>, <span>true</span>);
下面我们来看一下 BaseYii 中 autoload 方法的实现,其内容如下:
<span>/*</span><span>* * Class autoload loader. * This method is invoked automatically when PHP sees an unknown class. * The method will attempt to include the class file according to the following procedure: * * 1. Search in [[classMap]]; * 2. If the class is namespaced (e.g. `yii\base\Component`), it will attempt * to include the file associated with the corresponding path alias * (e.g. `@yii/base/Component.php`); * * This autoloader allows loading classes that follow the [PSR-4 standard](http://www.php-fig.org/psr/psr-4/) * and have its top-level namespace or sub-namespaces defined as path aliases. * * Example: When aliases `@yii` and `@yii/bootstrap` are defined, classes in the `yii\bootstrap` namespace * will be loaded using the `@yii/bootstrap` alias which points to the directory where bootstrap extension * files are installed and all classes from other `yii` namespaces will be loaded from the yii framework directory. * * Also the [guide section on autoloading](guide:concept-autoloading). * * @param string $className the fully qualified class name without a leading backslash "\" * @throws UnknownClass<strong>Exception</strong> if the class does not exist in the class file </span><span>*/</span><span>public</span><span>static</span><span>function</span> autoload(<span>$className</span><span>) { </span><span>//</span><span> 自动加载类</span><span>if</span> (<span>isset</span>(<span>static</span>::<span>$classMap</span>[<span>$className</span><span>])) { </span><span>//</span><span> 如果 $classMap 中存在该类,就直接使用</span><span>$classFile</span> = <span>static</span>::<span>$classMap</span>[<span>$className</span><span>]; </span><span>//</span><span> 如果第一个字符串为'@',就意味着对应的文件地址是别名,就将它转化成真实的文件地址</span><span>if</span> (<span>$classFile</span>[0] === '@'<span>) { </span><span>$classFile</span> = <span>static</span>::getAlias(<span>$classFile</span><span>); } } </span><span>elseif</span> (<span>strpos</span>(<span>$className</span>, '\\') !== <span>false</span><span>) { </span><span>//</span><span> 如果存在'\\',就意味着含有 namespace,可以拼成别名,再根据别名获取真实的文件地址</span><span>$classFile</span> = <span>static</span>::getAlias('@' . <span>str_replace</span>('\\', '/', <span>$className</span>) . '.php', <span>false</span><span>); </span><span>//</span><span> 没取到真是文件地址或者获取的地址不是一个文件,就返回空</span><span>if</span> (<span>$classFile</span> === <span>false</span> || !<span>is_file</span>(<span>$classFile</span><span>)) { </span><span>return</span><span>; } } </span><span>else</span><span> { </span><span>return</span><span>; } </span><span>//</span><span> 引入该类的文件</span><span>include</span>(<span>$classFile</span><span>); </span><span>//</span><span> 如果是调试模式,而且 $className 即不是类,不是接口,也不是 trait,就抛出异常</span><span>if</span> (YII_DEBUG && !<span>class_exists</span>(<span>$className</span>, <span>false</span>) && !<span>interface_exists</span>(<span>$className</span>, <span>false</span>) && !trait_exists(<span>$className</span>, <span>false</span><span>)) { </span><span>throw</span><span>new</span> UnknownClass<strong>Exception</strong>("Unable to find '<span>$className</span>' in file: <span>$classFile</span>. Namespace missing?"<span>); } }</span>
其中,大家可能不太清楚 getAlias 方法,这个方法其实就是将 Yii2 中的别名转化成真实的文件地址,关于该方法的具体内容,之后会详细讲解。
举几个例子,帮助大家理解一下。
如果 Yii::$classMap 的值如下:
Yii::<span>$classMap</span> =<span> [ </span>'app/test/Test' => '/var/www/basic/webtest/Test.php'<span>];</span>
当你使用 ‘app/test/Test’ 类时,就会自动引入 '/var/www/basic/webtest/Test.php' 文件,项目中的内容当然不是这个样子的,这只是个简单的例子,便于大家理解。
在继续上面的例子,如果你使用了‘yii\base\Component’ 类,它就会转变成 ‘@yii/base/Component.php’ 别名,然后在根据别名获取到它的文件地址,引入进来。
以上就是 Yii2 的自动加载机制的基本内容~~
对 Yii2 源码有兴趣的同学可以关注项目 yii2-2.0.3-annotated,现在在上面已经添加了不少关于 Yii2 源码的注释,之后还会继续添加~
有兴趣的同学也可以参与进来,提交 Yii2 源码的注释。
以上就介绍了Yii2的深入学习--自动加载机制,包括了require,队列,Exception方面的内容,希望对PHP教程有兴趣的朋友有所帮助。

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