刚开始接触laravel，一天时间走马观花的看了一些官方文档之后便开始了laravel的学习。这里谈到的都是最基础的东西，各路大神，可直接略过。
composer概述
一开始，最吸引我的当属 Composer 了，因为之前从没用过 Composer 。
Composer 是PHP中用来管理依赖关系的工具，你只需在自己的项目中声明所依赖的外部工具库，Composer就会帮你安装这些依赖的库文件。运行 Composer 需要 PHP 5.3.2+ 以上版本。
使用composer
第一步,声明依赖关系。比方说，你正在创建的一个项目需要一个库来做日志记录。你决定使用 monolog。为了将它添加到你的项目中，你所需要做的就是创建一个 composer.json 文件，其中描述了项目的依赖关系。
<span>{
</span><span>"</span><span>require</span><span>"</span><span>: {
</span><span>"</span><span>monolog/monolog</span><span>"</span>: <span>"</span><span>1.2.*</span><span>"</span><span>
}
}</span>第二步，使用composer。在项目根目录，执行安装命令，执行完毕后，monolog就会被下载到vendor/monolog/monolog 目录。
$ php composer.phar install
第三步，类的自动加载。除了库的下载，Composer 还准备了一个自动加载文件，它可以加载 Composer 下载的库中所有的类文件。使用它，你只需要将下面这行代码添加到你项目的引导文件中：
require <span>'</span><span>vendor/autoload.php</span><span>'</span>;
这使得你可以很容易的使用第三方代码。例如：如果你的项目依赖 monolog，你就可以像这样开始使用这个类库，并且他们将被自动加载。
<span>$log</span> = <span>new</span> Monolog\Logger('name'<span>);
</span><span>$log</span>->pushHandler(<span>new</span> Monolog\Handler\StreamHandler('app.log', Monolog\Logger::<span>WARNING));
</span><span>$log</span>->addWarning('Foo');
Composer 自动加载探秘
在现实世界中使用工具时，如果理解了工具的工作原理，使用起来就会更加有底气。对于一个第一次接触laravel，且是第一次接触 composer 的新手来说，如果理解Composer 是如何工作的，使用起来将会更加自如。
我的理解是，composer 根据声明的依赖关系，从相关库的 源 下载代码文件，并根据依赖关系在 Composer 目录下生成供类自动加载的 PHP 脚本，使用的时候，项目开始处引入 “/vendor/autoload.php” 文件，就可以直接实例化这些第三方类库中的类了。那么，Composer 是如何实现类的自动加载的呢？接下来，我们从 laravel 的入口文件开始顺藤摸瓜往里跟进，来一睹 Composer 自动加载的奥妙。
1.代码清单 laravel/public/index.php
<span>#laravel/public/index.php<br /><br />require</span> __DIR__.'/../bootstrap/autoload.php'<span>; </span><span>$app</span> = <span>require_once</span> __DIR__.'/../bootstrap/start.php'<span>; </span><span>$app</span>->run();
第一行先是引入了 laravel/bootstrap/autoload.php，不做解释，打开该文件。
2.代码清单 laravel/bootstrap/autoload.php
<span>define</span>('LARAVEL_START', <span>microtime</span>(<span>true</span><span>));
</span><span>require</span> __DIR__.'/../vendor/autoload.php'<span>;
</span><span>if</span> (<span>file_exists</span>(<span>$compiled</span> = __DIR__.'/compiled.php'<span>))
{
</span><span>require</span> <span>$compiled</span><span>;
}
Patchwork\Utf8\Bootup</span>::<span>initMbstring();<br /></span>第一行定义了程序开始执行的时间点。紧接着第二行，引入了 laravel/vendor/autoload.php。
第七行，前面说过，引入Composer的autoload.php之后就可以直接使用第三方类库中的类了，这里就是直接使用的 Bootup 类。下面来看看 /vendor/autoload.php 到底做了什么。
3.代码清单 laravel/vendor/autoload.php
<span>1</span> <span>//</span><span> autoload.php @generated by Composer</span> <span>2</span> <span>3</span> <span>require_once</span> __DIR__ . '/composer' . '/autoload_real.php'<span>; </span><span>4</span> <span>5</span> <span>return</span> ComposerAutoloaderInit9b2a1b1cf01c9a870ab98748dc5f1256::getLoader();
到这里，马上就进入自动加在的大门了。
这个文件很简单，第5行的函数名是不是看的一头雾水？别被吓到了,他就是个类名而已。这个类是在第3行引入的文件 laravel/vendor/composer/autoload_real.php 里头声明的，接下来打开该文件看 getLoader();
4.代码清单laravel/vendor/composer/autoload_real.php
<span> 1</span> <?<span>php
</span><span> 2</span>
<span> 3</span> <span>//</span><span> autoload_real.php @generated by Composer</span>
<span> 4</span>
<span> 5</span> <span>class</span><span> ComposerAutoloaderInit9b2a1b1cf01c9a870ab98748dc5f1256
</span><span> 6</span> <span>{
</span><span> 7</span> <span>private</span> <span>static</span> <span>$loader</span><span>;
</span><span> 8</span>
<span> 9</span> <span>public</span> <span>static</span> <span>function</span> loadClassLoader(<span>$class</span><span>)
</span><span>10</span> <span> {
</span><span>11</span> <span>if</span> ('Composer\Autoload\ClassLoader' === <span>$class</span><span>) {
</span><span>12</span> <span>require</span> __DIR__ . '/ClassLoader.php'<span>;
</span><span>13</span> <span> }
</span><span>14</span> <span> }
</span><span>15</span>
<span>16</span>
<span>17</span> <span>public</span> <span>static</span> <span>function</span><span> getLoader()
</span><span>18</span> <span> {
</span><span>19</span> <span>if</span> (<span>null</span> !== self::<span>$loader</span><span>) {
</span><span>20</span> <span>return</span> self::<span>$loader</span><span>;
</span><span>21</span> <span> }
</span><span>22</span>
<span>23</span> spl_autoload_register(<span>array</span>('ComposerAutoloaderInit9b2a1b1cf01c9a870ab98748dc5f1256', 'loadClassLoader'), <span>true</span>, <span>true</span><span>);
</span><span>24</span> self::<span>$loader</span> = <span>$loader</span> = <span>new</span><span> \Composer\Autoload\ClassLoader();
</span><span>25</span> spl_autoload_unregister(<span>array</span>('ComposerAutoloaderInit9b2a1b1cf01c9a870ab98748dc5f1256', 'loadClassLoader'<span>));
</span><span>26</span>
<span>27</span> <span>$vendorDir</span> = <span>dirname</span><span>(__DIR__);
</span><span>28</span> <span>$baseDir</span> = <span>dirname</span>(<span>$vendorDir</span><span>);
</span><span>29</span>
<span>30</span> <span>$includePaths</span> = <span>require</span> __DIR__ . '/include_paths.php'<span>;
</span><span>31</span>
<span>32</span> <span>array_push</span>(<span>$includePaths</span>, <span>get_include_path</span><span>());
</span><span>33</span> <span>set_include_path</span>(<span>join</span>(PATH_SEPARATOR, <span>$includePaths</span><span>));
</span><span>34</span>
<span>35</span>
<span>36</span> <span>$map</span> = <span>require</span> __DIR__ . '/autoload_namespaces.php'<span>;
</span><span>37</span> <span>foreach</span> (<span>$map</span> <span>as</span> <span>$namespace</span> => <span>$path</span><span>) {
</span><span>38</span> <span>$loader</span>->set(<span>$namespace</span>, <span>$path</span><span>);
</span><span>39</span> <span> }
</span><span>40</span>
<span>41</span> <span>$map</span> = <span>require</span> __DIR__ . '/autoload_psr4.php'<span>;
</span><span>42</span> <span>foreach</span> (<span>$map</span> <span>as</span> <span>$namespace</span> => <span>$path</span><span>) {
</span><span>43</span> <span>$loader</span>->setPsr4(<span>$namespace</span>, <span>$path</span><span>);
</span><span>44</span> <span> }
</span><span>45</span>
<span>46</span> <span>$classMap</span> = <span>require</span> __DIR__ . '/autoload_classmap.php'<span>;
</span><span>47</span> <span>if</span> (<span>$classMap</span><span>) {
</span><span>48</span> <span>$loader</span>->addClassMap(<span>$classMap</span><span>);
</span><span>49</span> <span> }
</span><span>50</span>
<span>51</span>
<span>52</span> <span>$loader</span>->register(<span>true</span><span>);
</span><span>53</span>
<span>54</span> <span>$includeFiles</span> = <span>require</span> __DIR__ . '/autoload_files.php'<span>;
</span><span>55</span> <span>foreach</span> (<span>$includeFiles</span> <span>as</span> <span>$file</span><span>) {
</span><span>56</span> composerRequire9b2a1b1cf01c9a870ab98748dc5f1256(<span>$file</span><span>);
</span><span>57</span> <span> }
</span><span>58</span>
<span>59</span> <span>return</span> <span>$loader</span><span>;
</span><span>60</span> <span> }
</span><span>61</span> <span>}
</span><span>62</span>
<span>63</span> <span>function</span> composerRequire9b2a1b1cf01c9a870ab98748dc5f1256(<span>$file</span><span>)及 $loader->addClassMap()
</span><span>64</span> <span>{
</span><span>65</span> <span>require</span> <span>$file</span><span>;
</span><span>66</span> }第17行，getLoader()中先是判断当前类中的 $loader 值，如果不是 null 就返回，这个可以略过。接着实例化了 ClassLoader 类给 $loader ，laravel/vendor/composer/ClassLoader.php
这里引入了几个文件，这些文件是由composer自动生成的，当依赖关系发生改变时不需要修改这些脚本，运行composer重新生成即可。
laravel/vendor/composer/autoloade_namespace.php
laravel/vendor/composer/autoloade_prs4.php
laravel/vendor/composer/autoloade_classmap.php
laravel/vendor/composer/autoloade_files.php
在设置完一堆的 path 信息后，执行了$loader->set()和 $loader->setPsr4()及$loader->addClassMap()，然后 进行了$loader->register(true);现在我们一个个来看。
5.代码清单laravel/vendor/composer/ClassLoader.php
$loader->set($namespace, $path);Psr0标准
设置命名空间对应的路径，以便于随后自动加载相关类文件。
$loader->setPsr4($namespace, $path);Psr4标准
设置命名空间对应的路径，以便于随后自动加载相关类文件。
$loader->addClassMap($classMap);
设置类文件路径与类名的对应关系，以便于随后自动加载相关类文件。
$loader->register(true);
<span>public</span> <span>function</span> register(<span>$prepend</span> = <span>false</span><span>)
{
spl_autoload_register(</span><span>array</span>(<span>$this</span>, 'loadClass'), <span>true</span>, <span>$prepend</span><span>);
}</span>这里设置了 欲注册的自动装载函数 $this->loadClass()，关于 spl_autoload_register 和 spl_autoload_unregister 的更多信息随后会有专门的解释。现在打开loadClass()的定义
<span>public</span> <span>function</span> loadClass(<span>$class</span><span>)
{
</span><span>if</span> (<span>$file</span> = <span>$this</span>->findFile(<span>$class</span><span>)) {
includeFile(</span><span>$file</span><span>);
</span><span>return</span> <span>true</span><span>;
}
}</span>这里有个 findFile() 函数，如果相关类的声明所在文件的路径找到了，就包含并运行该文件，然后返回 true 。接着打开findFile()的定义
<span>public</span> <span>function</span> findFile(<span>$class</span><span>)
{
</span><span>//</span><span> work around for PHP 5.3.0 - 5.3.2 https://bugs.php.net/50731</span>
<span>if</span> ('\\' == <span>$class</span>[0<span>]) {
</span><span>$class</span> = <span>substr</span>(<span>$class</span>, 1<span>);
}
</span><span>//</span><span> class map lookup</span>
<span>if</span> (<span>isset</span>(<span>$this</span>->classMap[<span>$class</span><span>])) {
</span><span>return</span> <span>$this</span>->classMap[<span>$class</span><span>];
}
</span><span>$file</span> = <span>$this</span>->findFileWithExtension(<span>$class</span>, '.php'<span>);
</span><span>//</span><span> Search for Hack files if we are running on HHVM</span>
<span>if</span> (<span>$file</span> === <span>null</span> && <span>defined</span>('HHVM_VERSION'<span>)) {
</span><span>$file</span> = <span>$this</span>->findFileWithExtension(<span>$class</span>, '.hh'<span>);
}
</span><span>if</span> (<span>$file</span> === <span>null</span><span>) {
</span><span>//</span><span> Remember that this class does not exist.</span>
<span>return</span> <span>$this</span>->classMap[<span>$class</span>] = <span>false</span><span>;
}
</span><span>return</span> <span>$file</span><span>;
}</span>先是判断类名是否以'\'开始，如果是的话，清除开头的'\'
接着，检查当前类的名字是否在 类名与声明当前类的文件的路径的关系数组 中，如果存在，直接返回相关键值（类文件路径信息）
如果上一步没有返回路径信息，执行 findFileWithExtension($class, '.php') 继续查找类文件路径信息，findFileWithExtension的定义后面将会列出。
如果仍未找到类的文件路径信息，返回值为 null 且定义了 HHVM_VERSION 信息，则用“.hh”后缀继续查找类文件信息。
HHVM_VERSION 是 HHVM版本信息？ HHVM 是 Facebook 开发的高性能 PHP 虚拟机，宣称比官方的快9倍。
如果仍未找到，则返回 false 。Remember that this class does not exist.（这句注释很有喜感？哈哈）
代码清单 findFileWithExtension()
<span> 1</span> <span>private</span> <span>function</span> findFileWithExtension(<span>$class</span>, <span>$ext</span><span>)
</span><span> 2</span> <span>{
</span><span> 3</span> <span>//</span><span> PSR-4 lookup</span>
<span> 4</span> <span>$logicalPathPsr4</span> = <span>strtr</span>(<span>$class</span>, '\\', DIRECTORY_SEPARATOR) . <span>$ext</span><span>;
</span><span> 5</span>
<span> 6</span> <span>$first</span> = <span>$class</span>[0<span>];
</span><span> 7</span> <span>if</span> (<span>isset</span>(<span>$this</span>->prefixLengthsPsr4[<span>$first</span><span>])) {
</span><span> 8</span> <span>foreach</span> (<span>$this</span>->prefixLengthsPsr4[<span>$first</span>] <span>as</span> <span>$prefix</span> => <span>$length</span><span>) {
</span><span> 9</span> <span>if</span> (0 === <span>strpos</span>(<span>$class</span>, <span>$prefix</span><span>)) {
</span><span>10</span> <span>foreach</span> (<span>$this</span>->prefixDirsPsr4[<span>$prefix</span>] <span>as</span> <span>$dir</span><span>) {
</span><span>11</span> <span>if</span> (<span>file_exists</span>(<span>$file</span> = <span>$dir</span> . DIRECTORY_SEPARATOR . <span>substr</span>(<span>$logicalPathPsr4</span>, <span>$length</span><span>))) {
</span><span>12</span> <span>return</span> <span>$file</span><span>;
</span><span>13</span> <span> }
</span><span>14</span> <span> }
</span><span>15</span> <span> }
</span><span>16</span> <span> }
</span><span>17</span> <span> }
</span><span>18</span>
<span>19</span> <span>//</span><span> PSR-4 fallback dirs</span>
<span>20</span> <span>foreach</span> (<span>$this</span>->fallbackDirsPsr4 <span>as</span> <span>$dir</span><span>) {
</span><span>21</span> <span>if</span> (<span>file_exists</span>(<span>$file</span> = <span>$dir</span> . DIRECTORY_SEPARATOR . <span>$logicalPathPsr4</span><span>)) {
</span><span>22</span> <span>return</span> <span>$file</span><span>;
</span><span>23</span> <span> }
</span><span>24</span> <span> }
</span><span>25</span>
<span>26</span> <span>//</span><span> PSR-0 lookup</span>
<span>27</span> <span>if</span> (<span>false</span> !== <span>$pos</span> = <span>strrpos</span>(<span>$class</span>, '\\'<span>)) {
</span><span>28</span> <span>//</span><span> namespaced class name</span>
<span>29</span> <span>$logicalPathPsr0</span> = <span>substr</span>(<span>$logicalPathPsr4</span>, 0, <span>$pos</span> + 1<span>)
</span><span>30</span> . <span>strtr</span>(<span>substr</span>(<span>$logicalPathPsr4</span>, <span>$pos</span> + 1), '_',<span> DIRECTORY_SEPARATOR);
</span><span>31</span> } <span>else</span><span> {
</span><span>32</span> <span>//</span><span> PEAR-like class name</span>
<span>33</span> <span>$logicalPathPsr0</span> = <span>strtr</span>(<span>$class</span>, '_', DIRECTORY_SEPARATOR) . <span>$ext</span><span>;
</span><span>34</span> <span> }
</span><span>35</span>
<span>36</span> <span>if</span> (<span>isset</span>(<span>$this</span>->prefixesPsr0[<span>$first</span><span>])) {
</span><span>37</span> <span>foreach</span> (<span>$this</span>->prefixesPsr0[<span>$first</span>] <span>as</span> <span>$prefix</span> => <span>$dirs</span><span>) {
</span><span>38</span> <span>if</span> (0 === <span>strpos</span>(<span>$class</span>, <span>$prefix</span><span>)) {
</span><span>39</span> <span>foreach</span> (<span>$dirs</span> <span>as</span> <span>$dir</span><span>) {
</span><span>40</span> <span>if</span> (<span>file_exists</span>(<span>$file</span> = <span>$dir</span> . DIRECTORY_SEPARATOR . <span>$logicalPathPsr0</span><span>)) {
</span><span>41</span> <span>return</span> <span>$file</span><span>;
</span><span>42</span> <span> }
</span><span>43</span> <span> }
</span><span>44</span> <span> }
</span><span>45</span> <span> }
</span><span>46</span> <span> }
</span><span>47</span>
<span>48</span> <span>//</span><span> PSR-0 fallback dirs</span>
<span>49</span> <span>foreach</span> (<span>$this</span>->fallbackDirsPsr0 <span>as</span> <span>$dir</span><span>) {
</span><span>50</span> <span>if</span> (<span>file_exists</span>(<span>$file</span> = <span>$dir</span> . DIRECTORY_SEPARATOR . <span>$logicalPathPsr0</span><span>)) {
</span><span>51</span> <span>return</span> <span>$file</span><span>;
</span><span>52</span> <span> }
</span><span>53</span> <span> }
</span><span>54</span>
<span>55</span> <span>//</span><span> PSR-0 include paths.</span>
<span>56</span> <span>if</span> (<span>$this</span>->useIncludePath && <span>$file</span> = stream_resolve_include_path(<span>$logicalPathPsr0</span><span>)) {
</span><span>57</span> <span>return</span> <span>$file</span><span>;
</span><span>58</span> <span> }
</span><span>59</span> }该函数唯一的目的就是根据刚才通过$loader->set($namespace, $path)和$loader->setPsr4($namespace, $path)方法设置的信息找出类文件的路径信息。
接下来，我们回到代码清单laravel/vendor/composer/autoload_real.php ，为精简篇幅，这里只贴出片段（续上节的 $loader->register(true)）。
<span>$loader</span>->register(<span>true</span><span>);
</span><span>$includeFiles</span> = <span>require</span> __DIR__ . '/autoload_files.php'<span>;
</span><span>foreach</span> (<span>$includeFiles</span> <span>as</span> <span>$file</span><span>) {
composerRequire9b2a1b1cf01c9a870ab98748dc5f1256(</span><span>$file</span><span>);
}
</span><span>return</span> <span>$loader</span><span>;
}
}
</span><span>function</span> composerRequire9b2a1b1cf01c9a870ab98748dc5f1256(<span>$file</span><span>)
{
</span><span>require</span> <span>$file</span><span>;
}</span>在经历了一番长途跋涉后，终于从 laravel/vendor/composer/ClassLoader.php 中出来了。继 $loader->register(true) 之后，又引入了laravel/vendor/composer/autoload_files.php,相比之下，这个文件要简单得多，只是个数组，列出了几个文件路径。
<span>//</span><span> autoload_files.php @generated by Composer</span>
<span>$vendorDir</span> = <span>dirname</span>(<span>dirname</span>(<span>__FILE__</span><span>));
</span><span>$baseDir</span> = <span>dirname</span>(<span>$vendorDir</span><span>);
</span><span>return</span> <span>array</span><span>(
</span><span>$vendorDir</span> . '/ircmaxell/password-compat/lib/password.php',
<span>$vendorDir</span> . '/swiftmailer/swiftmailer/lib/swift_required.php',
<span>$vendorDir</span> . '/phpseclib/phpseclib/phpseclib/Crypt/Random.php',
<span>$vendorDir</span> . '/laravel/framework/src/Illuminate/Support/helpers.php',<span>
);</span>接着就是用 composerRequire9b2a1b1cf01c9a870ab98748dc5f1256() 函数 包含并运行 这几个文件。这四个文件的具体信息，随后会专门写博文来认识。
最后 ， 返回 ClassLoader 类的实例 $loader 。
现在在回到 代码清单 laravel/bootstrap/autoload.php 的第7行
<span>1</span> <span>define</span>('LARAVEL_START', <span>microtime</span>(<span>true</span><span>));
</span><span>2</span> <span>require</span> __DIR__.'/../vendor/autoload.php'<span>;
</span><span>3</span> <span>if</span> (<span>file_exists</span>(<span>$compiled</span> = __DIR__.'/compiled.php'<span>))
</span><span>4</span> <span>{
</span><span>5</span> <span>require</span> <span>$compiled</span><span>;
</span><span>6</span> <span>}
</span><span>7</span> Patchwork\Utf8\Bootup::initMbstring();注意这里第7行，之所以可以直接像 Patchwork\Utf8\Bootup::initMbstring() 这么使用而不需要手动required Bootup类文件，是因为 前面在ClassLoader中的register() 函数用 spl_autoload_register() 对Bootup类进行了注册。下面说一下 spl_autoload_register 。
spl_autoload_register
要使用 spl_autoload_register ，请保证你的PHP版本(PHP 5 >= 5.1.2)。
www.php.net 对 spl_autoload_register 的解释如下：注册__autoload()函数，将函数注册到SPL __autoload函数栈中。如果该栈中的函数尚未激活，则激活它们。刚接触 PHP 的同学肯定觉得这个解释云里雾里的，看完依然不知道什么意思。要想理解这句话，首先要弄明白 __autoload() 是个什么东西。
__autoload()
__autoload 的作用是尝试加载未定义的类，可以通过定义这个函数来启用类的自动加载。下面举个例子：
<span>function</span> __autoload(<span>$class</span><span>)
{
</span><span>echo</span> '尝试加载的类的名字是：'.<span>$class</span><span>;
}
</span><span>$say</span>= @ <span>new</span> say();上例会输出："尝试加载的类的名字是 say "。由于最后一行引用了尚未定义的类 box ，所以 __autoload 函数将被执行。
再看下面这段
class say { public function __construct() { echo 'say 类存在，并说出了hello，所以 __autoload 函数不会执行。'; } } <span>function</span> __autoload(<span>$class</span><span>) { </span><span>echo</span> '尝试加载的类的名字是：'.<span>$class</span><span>; } </span><span>$say</span>= @ <span>new</span> say();
这将会输出 : say 类存在，并说出了hello,所以 __autoload 函数不会执行。
理解完 __autoload 就好办了，再看上面：“将函数注册到SPL __autoload函数栈中”，意思是我们可以自定义 尝试加载未定义的类时 使用的函数。现在返回代码片段
spl_autoload_register(<span>array</span>(<span>$this</span>, 'loadClass'), <span>true</span>, <span>$prepend</span>);
这下是不是很明白了，当实例化一个类的时候，如果这个类没有定义，就执行 ClassLoader 类中的 loadClass 函数。loadClass 的定义前面我们说过了，就是找到声明相关类的文件，然后包含并运行该文件，随后加载相关类。至此，composer的自动加载机制学习完毕。
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