Laravel生命周期与原理

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

 <?php
 /*
 |--------------------------------------------------------------------------
 | Create The Application
 |--------------------------------------------------------------------------
 |
 | The first thing we will do is create a new Laravel application instance
 | which serves as the "glue" for all the components of Laravel, and is
 | the IoC container for the system binding all of the various parts.
 |
 */
 $app = new Illuminate\Foundation\Application(
   realpath(__DIR__.'/../')
 );
 /*
 |--------------------------------------------------------------------------
 | Bind Important Interfaces
 |--------------------------------------------------------------------------
 |
 | Next, we need to bind some important interfaces into the container so
 | we will be able to resolve them when needed. The kernels serve the
 | incoming requests to this application from both the web and CLI.
 |
 */
 $app->singleton(
   Illuminate\Contracts\Http\Kernel::class,
   App\Http\Kernel::class
 );
 $app->singleton(
   Illuminate\Contracts\Console\Kernel::class,
   App\Console\Kernel::class
 );
 $app->singleton(
   Illuminate\Contracts\Debug\ExceptionHandler::class,
   App\Exceptions\Handler::class
 );
 /*
 |--------------------------------------------------------------------------
 | Return The Application
 |--------------------------------------------------------------------------
 |
 | This script returns the application instance. The instance is given to
 | the calling script so we can separate the building of the instances
 | from the actual running of the application and sending responses.
 |
 */
 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。

 public function __construct($basePath = null)
 {
   if ($basePath) {
     $this->setBasePath($basePath);
   }
   $this->registerBaseBindings();
   $this->registerBaseServiceProviders();
   $this->registerCoreContainerAliases();
 }

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

 /**
  * Register the basic bindings into the container.
  *
  * @return void
  */
 protected function registerBaseBindings()
 {
   static::setInstance($this);
   $this->instance('app', $this);
   $this->instance(Container::class, $this);
 }
 /**
  * Register all of the base service providers.
  *
  * @return void
  */
 protected function registerBaseServiceProviders()
 {
   $this->register(new EventServiceProvider($this));
   $this->register(new LogServiceProvider($this));
   $this->register(new RoutingServiceProvider($this));
 }

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。

 /**
  * Register the core class aliases in the container.
  *
  * @return void
  */
 public function registerCoreContainerAliases()
 {
   $aliases = [
     'app'         => [\Illuminate\Foundation\Application::class, \Illuminate\Contracts\Container\Container::class, \Illuminate\Contracts\Foundation\Application::class],
     'auth'         => [\Illuminate\Auth\AuthManager::class, \Illuminate\Contracts\Auth\Factory::class],
     'auth.driver'     => [\Illuminate\Contracts\Auth\Guard::class],
     'blade.compiler'    => [\Illuminate\View\Compilers\BladeCompiler::class],
     'cache'        => [\Illuminate\Cache\CacheManager::class, \Illuminate\Contracts\Cache\Factory::class],
     'cache.store'     => [\Illuminate\Cache\Repository::class, \Illuminate\Contracts\Cache\Repository::class],
     'config'        => [\Illuminate\Config\Repository::class, \Illuminate\Contracts\Config\Repository::class],
     'cookie'        => [\Illuminate\Cookie\CookieJar::class, \Illuminate\Contracts\Cookie\Factory::class, \Illuminate\Contracts\Cookie\QueueingFactory::class],
     'encrypter'      => [\Illuminate\Encryption\Encrypter::class, \Illuminate\Contracts\Encryption\Encrypter::class],
     'db'          => [\Illuminate\Database\DatabaseManager::class],
     'db.connection'    => [\Illuminate\Database\Connection::class, \Illuminate\Database\ConnectionInterface::class],
     'events'        => [\Illuminate\Events\Dispatcher::class, \Illuminate\Contracts\Events\Dispatcher::class],
     'files'        => [\Illuminate\Filesystem\Filesystem::class],
     'filesystem'      => [\Illuminate\Filesystem\FilesystemManager::class, \Illuminate\Contracts\Filesystem\Factory::class],
     'filesystem.disk'   => [\Illuminate\Contracts\Filesystem\Filesystem::class],
     'filesystem.cloud'   => [\Illuminate\Contracts\Filesystem\Cloud::class],
     'hash'         => [\Illuminate\Contracts\Hashing\Hasher::class],
     'translator'      => [\Illuminate\Translation\Translator::class, \Illuminate\Contracts\Translation\Translator::class],
     'log'         => [\Illuminate\Log\Writer::class, \Illuminate\Contracts\Logging\Log::class, \Psr\Log\LoggerInterface::class],
     'mailer'        => [\Illuminate\Mail\Mailer::class, \Illuminate\Contracts\Mail\Mailer::class, \Illuminate\Contracts\Mail\MailQueue::class],
     'auth.password'    => [\Illuminate\Auth\Passwords\PasswordBrokerManager::class, \Illuminate\Contracts\Auth\PasswordBrokerFactory::class],
     'auth.password.broker' => [\Illuminate\Auth\Passwords\PasswordBroker::class, \Illuminate\Contracts\Auth\PasswordBroker::class],
     'queue'        => [\Illuminate\Queue\QueueManager::class, \Illuminate\Contracts\Queue\Factory::class, \Illuminate\Contracts\Queue\Monitor::class],
     'queue.connection'   => [\Illuminate\Contracts\Queue\Queue::class],
     'queue.failer'     => [\Illuminate\Queue\Failed\FailedJobProviderInterface::class],
     'redirect'       => [\Illuminate\Routing\Redirector::class],
     'redis'        => [\Illuminate\Redis\RedisManager::class, \Illuminate\Contracts\Redis\Factory::class],
     'request'       => [\Illuminate\Http\Request::class, \Symfony\Component\HttpFoundation\Request::class],
     'router'        => [\Illuminate\Routing\Router::class, \Illuminate\Contracts\Routing\Registrar::class, \Illuminate\Contracts\Routing\BindingRegistrar::class],
     'session'       => [\Illuminate\Session\SessionManager::class],
     'session.store'    => [\Illuminate\Session\Store::class, \Illuminate\Contracts\Session\Session::class],
     'url'         => [\Illuminate\Routing\UrlGenerator::class, \Illuminate\Contracts\Routing\UrlGenerator::class],
     'validator'      => [\Illuminate\Validation\Factory::class, \Illuminate\Contracts\Validation\Factory::class],
     'view'         => [\Illuminate\View\Factory::class, \Illuminate\Contracts\View\Factory::class],
   ];
   foreach ($aliases as $key => $aliases) {
     foreach ($aliases as $alias) {
       $this->alias($key, $alias);
     }
   }
 }

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

 /**
  * 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。

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。

 /**
 * Call the terminate method on any terminable middleware.
 *
 * @param \Illuminate\Http\Request $request
 * @param \Illuminate\Http\Response $response
 * @return void
 */
 public function terminate($request, $response)
 {
     $this->terminateMiddleware($request, $response);
     $this->app->terminate();
 }

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

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