上次说了provider，那么这次来说说facade

首先是启动的源头，从laravel的kernel类中的$bootstrappers 数组，我们可以看到它的一些系统引导方法，其中的RegisterFacades便是用来注册facade门面类的了。

protected $bootstrappers = [        \Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::class,        \Illuminate\Foundation\Bootstrap\LoadConfiguration::class,        \Illuminate\Foundation\Bootstrap\HandleExceptions::class,        \Illuminate\Foundation\Bootstrap\RegisterFacades::class,        \Illuminate\Foundation\Bootstrap\RegisterProviders::class,        \Illuminate\Foundation\Bootstrap\BootProviders::class,    ];

 

 同样是有一个register类，通过这个类进行别名等注册操作

namespace Illuminate\Foundation\Bootstrap;use Illuminate\Foundation\AliasLoader;use Illuminate\Support\Facades\Facade;use Illuminate\Foundation\PackageManifest;use Illuminate\Contracts\Foundation\Application;class RegisterFacades{    /**     * Bootstrap the given application.     *     * @param  \Illuminate\Contracts\Foundation\Application  $app     * @return void     */    public function bootstrap(Application $app)    {        //清除facade所有已绑定实例        Facade::clearResolvedInstances();        //将app存入对象        Facade::setFacadeApplication($app);        //将这些别名数组通过构造函数存入对象中        AliasLoader::getInstance(array_merge(            //通过Illuminate\Config\Repository获取config/app.php中的aliases数组            $app->make('config')->get('app.aliases', []),            //还记得最开始的博文中提到的那个包清单吗，这里也从中获取了它的aliases            $app->make(PackageManifest::class)->aliases()        //通过spl_autoload_register函数注册另一种自动加载函数        ))->register();    }}

public static function getInstance(array $aliases = [])    {        //注册时的实例是空的，会通过构造方法把刚刚传入的别名数组存入对象        if (is_null(static::$instance)) {            return static::$instance = new static($aliases);        }        $aliases = array_merge(static::$instance->getAliases(), $aliases);        static::$instance->setAliases($aliases);        return static::$instance;    }    private function __construct($aliases)    {        $this->aliases = $aliases;    }

public function register()    {        if (! $this->registered) {            $this->prependToLoaderStack();            $this->registered = true;        }    }    /**     * Prepend the load method to the auto-loader stack.     *     * @return void     */    protected function prependToLoaderStack()    {        //最后通过自动加载函数将本对象中的load方法放入自动加载队列的前端，在我们通过类名调用方法时，会触发自动加载函数队列，会优先触发这个函数，查找到对应文件的路径然后加载相应文件        spl_autoload_register([$this, 'load'], true, true);    }

public function load($alias)    {        //若传入的命名空间不为当前facade数组内才会通过这个方法加载        if (static::$facadeNamespace && strpos($alias, static::$facadeNamespace) === 0) {            $this->loadFacade($alias);            return true;        }        //否则直接返回其别名        if (isset($this->aliases[$alias])) {            return class_alias($this->aliases[$alias], $alias);        }    }    /**     * Load a real-time facade for the given alias.     *     * @param  string  $alias     * @return void     */    protected function loadFacade($alias)    {        require $this->ensureFacadeExists($alias);    }    /**     * Ensure that the given alias has an existing real-time facade class.     *     * @param  string  $alias     * @return string     */    protected function ensureFacadeExists($alias)    {        //从缓存中返回路径        if (file_exists($path = storage_path('framework/cache/facade-'.sha1($alias).'.php'))) {            return $path;        }                file_put_contents($path, $this->formatFacadeStub(            $alias, file_get_contents(__DIR__.'/stubs/facade.stub')        ));        return $path;    }

 由于laravel中composer的执行过程过于繁琐，这里就不做深究了。原理是一样的，通过别名找到命名空间的类名，再由composer的类名与文件路径映射关系，自动加载函数找到相应文件加载进来。

 

那么我们来自定义一个门面类试一下

1、新建一个facade类，这里返回的test是上一篇博客中定义的对象

namespace App\Facades;use Illuminate\Support\Facades\Facade;class Test extends Facade{    protected static function getFacadeAccessor()    {        return 'App\Contracts\Test';    }}

2、将它添加到config/app.php的aliases别名数组中

'aliases' => [        'App' => Illuminate\Support\Facades\App::class,        'Artisan' => Illuminate\Support\Facades\Artisan::class,        'Auth' => Illuminate\Support\Facades\Auth::class,        'Blade' => Illuminate\Support\Facades\Blade::class,        'Broadcast' => Illuminate\Support\Facades\Broadcast::class,        'Bus' => Illuminate\Support\Facades\Bus::class,        'Cache' => Illuminate\Support\Facades\Cache::class,        'Config' => Illuminate\Support\Facades\Config::class,        'Cookie' => Illuminate\Support\Facades\Cookie::class,        'Crypt' => Illuminate\Support\Facades\Crypt::class,        'DB' => Illuminate\Support\Facades\DB::class,        'Eloquent' => Illuminate\Database\Eloquent\Model::class,        'Event' => Illuminate\Support\Facades\Event::class,        'File' => Illuminate\Support\Facades\File::class,        'Gate' => Illuminate\Support\Facades\Gate::class,        'Hash' => Illuminate\Support\Facades\Hash::class,        'Lang' => Illuminate\Support\Facades\Lang::class,        'Log' => Illuminate\Support\Facades\Log::class,        'Mail' => Illuminate\Support\Facades\Mail::class,        'Notification' => Illuminate\Support\Facades\Notification::class,        'Password' => Illuminate\Support\Facades\Password::class,        'Queue' => Illuminate\Support\Facades\Queue::class,        'Redirect' => Illuminate\Support\Facades\Redirect::class,        'Redis' => Illuminate\Support\Facades\Redis::class,        'Request' => Illuminate\Support\Facades\Request::class,        'Response' => Illuminate\Support\Facades\Response::class,        'Route' => Illuminate\Support\Facades\Route::class,        'Schema' => Illuminate\Support\Facades\Schema::class,        'Session' => Illuminate\Support\Facades\Session::class,        'Storage' => Illuminate\Support\Facades\Storage::class,        'URL' => Illuminate\Support\Facades\URL::class,        'Validator' => Illuminate\Support\Facades\Validator::class,        'View' => Illuminate\Support\Facades\View::class,        //刚刚新建的facades        'Test' => \App\Facades\Test::class,    ],

3、在路由文件中调用它

Route::any('/index', function (){    Test::doing();});

我们会发现，即使我们没有通过app对象进行make也没有任何命名空间的引入，它就这样被调用了。

如果是在类中调用，那么就要麻烦一些了，需要ues这个别名，注意这一点

namespace App\Http\Controllers;use Illuminate\Http\Request;//use App\Contracts\Test;//注意这里只引入了别名，由于命名空间冲突，所以我注释了其他部分use Test;class IndexController extends Controller{//    public function __construct(Test $test)//    {//        $this->test = $test;//    }    public function index(Test $test)    {        Test::doing();//        app()->make('App\Contracts\Test')->doing();//        echo '
';////        //只有通过构造方法进行自动加载依赖的方式才能触发契约的when绑定//        $this->test->doing();////        echo '
';//        //因为laravel中的上下文绑定只能具体到类，所以这里的$test实例依然为普通绑定//        $test->doing();    }}

 通过这个demo的实践，facade还是比较简单的。