laravel5.5源码笔记（三、门面类facade）

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 '<br>';
//
//        //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
//        $this->test->doing();
//
//        echo '<br>';
//        //因为laravel中的上下文绑定只能具体到类，所以这里的$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。