一旦用户（浏览器）发送了一个HTTP请求，我们的apache或者Nginx一般都转到index.PHP，因此，之后的一系列步骤都是从index.PHP开始的，我们先来看一看这个文件代码。
<?PHP
require __DIR__.'/../bootstrap/autoload.PHP';
$app = require_once __DIR__.'/../bootstrap/app.PHP';
/*
|--------------------------------------------------------------------------
| Run The Application
|--------------------------------------------------------------------------
|
| Once we have the application,we can handle the incoming request
| through the kernel,and send the associated response back to
| the client's browser allowing them to enjoy the creative
| and wonderful application we have prepared for them.
|
*/
$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);
$response = $kernel->handle(
$request = Illuminate\Http\Request::capture()
);
$response->send();
$kernel->terminate($request,$response);
这里在注释里谈了kernel的作用，kernel处理来访的请求，并且发送相应返回给用户浏览器。
这里又涉及到了一个app对象，所以附上app对象的源码，这份源码是\bootstrap\app.PHP
1 <?PHP 2 /* 3 |-------------------------------------------------------------------------- 4 | Create The Application 5 |-------------------------------------------------------------------------- 6 | 7 | The first thing we will do is create a new Laravel application instance 8 | which serves as the "glue" for all the components of Laravel,and is 9 | the IoC container for the system binding all of the varIoUs parts. 10 | 11 */ 12 $app = new Illuminate\Foundation\Application( 13 realpath(__DIR__.'/../') 14 ); 15 /* 16 |-------------------------------------------------------------------------- 17 | Bind Important Interfaces 18 |-------------------------------------------------------------------------- 19 | 20 | Next,we need to bind some important interfaces into the container so 21 | we will be able to resolve them when needed. The kernels serve the 22 | incoming requests to this application from both the web and CLI. 23 | 24 */ 25 $app->singleton( 26 Illuminate\Contracts\Http\Kernel::class,27 App\Http\Kernel::class 28 ); 29 $app->singleton( 30 Illuminate\Contracts\Console\Kernel::class,31 App\Console\Kernel::class 32 ); 33 $app->singleton( 34 Illuminate\Contracts\Debug\ExceptionHandler::class,35 App\Exceptions\Handler::class 36 ); 37 /* 38 |-------------------------------------------------------------------------- 39 | Return The Application 40 |-------------------------------------------------------------------------- 41 | 42 | This script returns the application instance. The instance is given to 43 | the calling script so we can separate the building of the instances 44 | from the actual running of the application and sending responses. 45 | 46 */ 47 return $app;
请看app变量是Illuminate\Foundation\Application类的对象，所以调用了这个类的构造函数，具体做了什么事，我们看源码。
1 public function __construct($basePath = null) 2 { 3 if ($basePath) { 4 $this->setBasePath($basePath); 5 } 6 $this->registerBaseBindings(); 7 $this->registerBaseServiceProviders(); 8 $this->registerCoreContainerAliases(); 9 }
构造器做了3件事，前两件事很好理解，创建Container，注册了ServiceProvider，看代码
1 /** 2 * Register the basic bindings into the container. 3 * 4 * @return void 5 */ 6 protected function registerBaseBindings() 7 { 8 static::setInstance($this); 9 $this->instance('app',$this); 10 $this->instance(Container::class,$this); 11 } 12 /** 13 * Register all of the base service providers. 14 * 15 * @return void 16 */ 17 protected function registerBaseServiceProviders() 18 { 19 $this->register(new EventServiceProvider($this)); 20 $this->register(new LogServiceProvider($this)); 21 $this->register(new RoutingServiceProvider($this)); 22 }
最后一件事，是做了个很大的数组，定义了大量的别名，侧面体现程序员是聪明的懒人。
1 /** 2 * Register the core class aliases in the container. 3 * 4 * @return void 5 */ 6 public function registerCoreContainerAliases() 7 { 8 $aliases = [ 9 'app' => [\Illuminate\Foundation\Application::class,\Illuminate\Contracts\Container\Container::class,\Illuminate\Contracts\Foundation\Application::class],10 'auth' => [\Illuminate\Auth\AuthManager::class,\Illuminate\Contracts\Auth\Factory::class],11 'auth.driver' => [\Illuminate\Contracts\Auth\Guard::class],12 'blade.compiler' => [\Illuminate\View\Compilers\BladeCompiler::class],13 'cache' => [\Illuminate\Cache\CacheManager::class,\Illuminate\Contracts\Cache\Factory::class],14 'cache.store' => [\Illuminate\Cache\Repository::class,\Illuminate\Contracts\Cache\Repository::class],15 'config' => [\Illuminate\Config\Repository::class,\Illuminate\Contracts\Config\Repository::class],16 'cookie' => [\Illuminate\Cookie\CookieJar::class,\Illuminate\Contracts\Cookie\Factory::class,\Illuminate\Contracts\Cookie\QueueingFactory::class],17 'encrypter' => [\Illuminate\Encryption\Encrypter::class,\Illuminate\Contracts\Encryption\Encrypter::class],18 'db' => [\Illuminate\Database\DatabaseManager::class],19 'db.connection' => [\Illuminate\Database\Connection::class,\Illuminate\Database\ConnectionInterface::class],20 'events' => [\Illuminate\Events\Dispatcher::class,\Illuminate\Contracts\Events\Dispatcher::class],21 'files' => [\Illuminate\Filesystem\Filesystem::class],22 'filesystem' => [\Illuminate\Filesystem\FilesystemManager::class,\Illuminate\Contracts\Filesystem\Factory::class],23 'filesystem.disk' => [\Illuminate\Contracts\Filesystem\Filesystem::class],24 'filesystem.cloud' => [\Illuminate\Contracts\Filesystem\Cloud::class],25 'hash' => [\Illuminate\Contracts\Hashing\Hasher::class],26 'translator' => [\Illuminate\Translation\Translator::class,\Illuminate\Contracts\Translation\Translator::class],27 'log' => [\Illuminate\Log\Writer::class,\Illuminate\Contracts\Logging\Log::class,\Psr\Log\LoggerInterface::class],28 'mailer' => [\Illuminate\Mail\Mailer::class,\Illuminate\Contracts\Mail\Mailer::class,\Illuminate\Contracts\Mail\MailQueue::class],29 'auth.password' => [\Illuminate\Auth\Passwords\PasswordBrokerManager::class,\Illuminate\Contracts\Auth\PasswordBrokerFactory::class],30 'auth.password.broker' => [\Illuminate\Auth\Passwords\PasswordBroker::class,\Illuminate\Contracts\Auth\PasswordBroker::class],31 'queue' => [\Illuminate\Queue\QueueManager::class,\Illuminate\Contracts\Queue\Factory::class,\Illuminate\Contracts\Queue\Monitor::class],32 'queue.connection' => [\Illuminate\Contracts\Queue\Queue::class],33 'queue.failer' => [\Illuminate\Queue\Failed\FailedJobProviderInterface::class],34 'redirect' => [\Illuminate\Routing\Redirector::class],35 'redis' => [\Illuminate\Redis\RedisManager::class,\Illuminate\Contracts\Redis\Factory::class],36 'request' => [\Illuminate\Http\Request::class,\Symfony\Component\HttpFoundation\Request::class],37 'router' => [\Illuminate\Routing\Router::class,\Illuminate\Contracts\Routing\Registrar::class,\Illuminate\Contracts\Routing\BindingRegistrar::class],38 'session' => [\Illuminate\Session\SessionManager::class],39 'session.store' => [\Illuminate\Session\Store::class,\Illuminate\Contracts\Session\Session::class],40 'url' => [\Illuminate\Routing\UrlGenerator::class,\Illuminate\Contracts\Routing\UrlGenerator::class],41 'validator' => [\Illuminate\Validation\Factory::class,\Illuminate\Contracts\Validation\Factory::class],42 'view' => [\Illuminate\View\Factory::class,\Illuminate\Contracts\View\Factory::class],43 ]; 44 foreach ($aliases as $key => $aliases) { 45 foreach ($aliases as $alias) { 46 $this->alias($key,$alias); 47 } 48 } 49 }
这里出现了一个instance函数，其实这并不是Application类的函数，而是Application类的父类Container类的函数
1 /** 2 * Register an existing instance as shared in the container. 3 * 4 * @param string $abstract 5 * @param mixed $instance 6 * @return void 7 */ 8 public function instance($abstract,$instance) 9 { 10 $this->removeAbstractAlias($abstract); 11 unset($this->aliases[$abstract]); 12 // We'll check to determine if this type has been bound before,and if it has 13 // we will fire the rebound callbacks registered with the container and it 14 // can be updated with consuming classes that have gotten resolved here. 15 $this->instances[$abstract] = $instance; 16 if ($this->bound($abstract)) { 17 $this->rebound($abstract); 18 } 19 }
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。
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？
1 <?PHP 2 namespace App\Http; 3 use Illuminate\Foundation\Http\Kernel as HttpKernel; 4 class Kernel extends HttpKernel 5 { 6 /** 7 * The application's global HTTP middleware stack. 8 * 9 * These middleware are run during every request to your application. 10 * 11 * @var array 12 */ 13 protected $middleware = [ 14 \Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,15 //\App\Http\Middleware\MyMiddleware::class, 16 ]; 17 /** 18 * The application's route middleware groups. 19 * 20 * @var array 21 */ 22 protected $middlewareGroups = [ 23 'web' => [ 24 \App\Http\Middleware\EncryptCookies::class,25 \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,26 \Illuminate\Session\Middleware\StartSession::class,27 \Illuminate\View\Middleware\ShareErrorsFromSession::class,28 \App\Http\Middleware\VerifyCsrfToken::class,29 ],30 'api' => [ 31 'throttle:60,1',32 ],33 ]; 34 /** 35 * The application's route middleware. 36 * 37 * These middleware may be assigned to groups or used individually. 38 * 39 * @var array 40 */ 41 protected $routeMiddleware = [ 42 'auth' => \App\Http\Middleware\Authenticate::class,43 'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,44 'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,45 'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,46 'mymiddleware'=>\App\Http\Middleware\MyMiddleware::class,47 ]; 48 }
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
1 $response = $kernel->handle( 2 $request = Illuminate\Http\Request::capture() 3 ); 4 $response->send();
最后在中止，释放所有资源。
1 /** 2 * Call the terminate method on any terminable middleware. 3 * 4 * @param \Illuminate\Http\Request $request 5 * @param \Illuminate\Http\Response $response 6 * @return void 7 */ 8 public function terminate($request,$response) 9 { 10 $this->terminateMiddleware($request,$response); 11 $this->app->terminate(); 12 }
总结一下，简单归纳整个过程就是：
1.index.PHP加载\bootstrap\app.PHP，在Application类的构造函数中创建Container，注册了ServiceProvider，定义了别名数组，然后用app变量保存构造函数构造出来的对象。
2.使用app这个对象，创建1个单例模式的对象HttpKernel，在创建HttpKernel时调用了构造函数，完成了中间件的声明。
3.以上这些工作都是在请求来访之前完成的，接下来开始等待请求，然后就是：接受到请求-->处理请求-->发送响应-->中止app变量
