/** * Register an existing instance as shared in the container. * * @param string $abstract * @param mixed $instance * @return void */ public function instance($abstract, $instance) { $this->removeAbstractAlias($abstract); unset($this->aliases[$abstract]); // We'll check to determine if this type has been bound before, and if it has // we will fire the rebound callbacks registered with the container and it // can be updated with consuming classes that have gotten resolved here. $this->instances[$abstract] = $instance; if ($this->bound($abstract)) { $this->rebound($abstract); } }
Application是Container的子类，所以$app不仅是Application类的对象，还是Container的对象，所以，新出现的singleton函数我们就可以到Container类的源代码文件里查。bind函数和singleton的区别见这篇博文。
singleton这个函数，前一个参数是实际类名，后一个参数是类的“别名”。
$app对象声明了3个单例模型对象，分别是HttpKernel，ConsoleKernel，ExceptionHandler。请注意，这里并没有创建对象，只是声明，也只是起了一个“别名”。
大家有没有发现，index.php中也有一个$kernel变量，但是只保存了make出来的HttpKernel变量，因此本文不再讨论，ConsoleKernel，ExceptionHandler。。。
继续在文件夹下找到App\Http\Kernel.php，既然我们把实际的HttpKernel做的事情都写在这个php文件里，就从这份代码里看看究竟做了哪些事？
<?php namespace App\Http; use Illuminate\Foundation\Http\Kernel as HttpKernel; class Kernel extends HttpKernel { /** * The application's global HTTP middleware stack. * * These middleware are run during every request to your application. * * @var array */ protected $middleware = [ \Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class, //\App\Http\Middleware\MyMiddleware::class, ]; /** * The application's route middleware groups. * * @var array */ protected $middlewareGroups = [ 'web' => [ \App\Http\Middleware\EncryptCookies::class, \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class, \Illuminate\Session\Middleware\StartSession::class, \Illuminate\View\Middleware\ShareErrorsFromSession::class, \App\Http\Middleware\VerifyCsrfToken::class, ], 'api' => [ 'throttle:60,1', ], ]; /** * The application's route middleware. * * These middleware may be assigned to groups or used individually. * * @var array */ protected $routeMiddleware = [ 'auth' => \App\Http\Middleware\Authenticate::class, 'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class, 'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class, 'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class, 'mymiddleware'=>\App\Http\Middleware\MyMiddleware::class, ]; }
一目了然，HttpKernel里定义了中间件数组。
该做的做完了，就开始了请求到响应的过程，见index.php
$response = $kernel->handle( $request = Illuminate\Http\Request::capture() ); $response->send();
最后在中止，释放所有资源。