文档:Facades - Laravel - The PHP Framework For Web Artisans
Facades 为应用程序的服务容器中可用的类提供“静态”接口。
也就是Facade为容器中注册的对象提供静态代理
Illuminate\Foundation\Bootstrap\RegisterFacades是初始引导器之一,作用就是初始化Facade
public function bootstrap(Application $app)
{
Facade::clearResolvedInstances();
Facade::setFacadeApplication($app);
AliasLoader::getInstance(array_merge(
$app->make('config')->get('app.aliases', []),
$app->make(PackageManifest::class)->aliases()
))->register();
}