Laravel 生命周期解析 · 一只贱熊猫的博客

0x00 前言

闲来无事看看 Laravel 源码，初步了解一下其生命周期方便理解和使用它。

0x01 从入口文件开始

因为 Laravel 是单一入口的框架，所以我们第一步从 public/index.php 这个文件读起。

以下代码均基于 Laravel 5.7，原注释被本人替换。

<?php
// 定义常量，记录框架开始运行的时间
define('LARAVEL_START', microtime(true));

// 引入 composer 的 autoload.php
require __DIR__.'/../vendor/autoload.php';

// 引入 bootstrap/app.php 获得 Application 的实例
$app = require_once __DIR__.'/../bootstrap/app.php';

// 获得 app 容器中 Illuminate\Contracts\Http\Kernel 接口绑定的类的实例
$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);

// 通过 kernel 处理请求并返回响应
$response = $kernel->handle(
    // 获取请求
    $request = Illuminate\Http\Request::capture()
);

// 发送响应
$response->send();

// 调用 terminate 类型的中间件
$kernel->terminate($request, $response);

上面的代码简明清晰的表达了 Laravel 的处理流程，但是我们还是想要了解其中细节，比如 $app、$kernel到底是什么？$kernel->handle 发生了什么？所以我们接着看吧！

0x02 Application 实例，从 bootstrap/app.php 开始

上面的 index.php 代码里通过 require 引入了 bootstrap/app.php 文件获得了 Application 实例，下面我们看看这个文件内容。

<?php

// 实例化 Application 类
$app = new Illuminate\Foundation\Application(
    $_ENV['APP_BASE_PATH'] ?? dirname(__DIR__)
);

// 容器通过単例的方式
// 绑定 Illuminate\Contracts\Http\Kernel 接口
// 给 App\Http\Kernel 类
$app->singleton(
    Illuminate\Contracts\Http\Kernel::class,
    App\Http\Kernel::class
);

// 容器通过単例的方式
// 绑定 Illuminate\Contracts\Console\Kernel 接口
// 给 App\Console\Kernel::class 类
$app->singleton(
    Illuminate\Contracts\Console\Kernel::class,
    App\Console\Kernel::class
);

// 容器通过単例的方式
// 绑定 Illuminate\Contracts\Debug\ExceptionHandler 接口
// 给 App\Exceptions\Handler 类
$app->singleton(
    Illuminate\Contracts\Debug\ExceptionHandler::class,
    App\Exceptions\Handler::class
);

// 返回 app
return $app;

如果你熟悉容器这个概念那么阅读上面的代码应该是没有障碍的，因为 Application 类继承了 Container，所以 $app 也是一个容器而已，然后 $app->singleton(...) 只是绑定了一些接口对应的类。因为将 Illuminate\Contracts\Http\Kerne 接口绑定到了 App\Http\Kernel，所以在 index.php 的这行代码：

1	$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);

$kernel 就是 App\Http\Kernel 的实例。

现在我们看看 Illuminate\Foundation\Application 是什么，由于该类有 1000 多行所以代码就只贴声明和构造函数了喔～

use Illuminate\Container\Container;
use Illuminate\Contracts\Foundation\Application as ApplicationContract;
use Symfony\Component\HttpKernel\HttpKernelInterface;

class Application extends Container implements ApplicationContract, HttpKernelInterface
{
    public function __construct($basePath = null)
    {
        // 设置根路径
        if ($basePath) {
            $this->setBasePath($basePath);
        }
        // 注册基本绑定 app、Container::class、PackageManifest::class
        $this->registerBaseBindings();
        // 注册基本服务提供者 EventServiceProvider、LogServiceProvider、RoutingServiceProvider
        $this->registerBaseServiceProviders();
        // 注册类别名
        $this->registerCoreContainerAliases();
    }
    // ... 其它代码省略
}

首先看声明 Application 继承了 Container 类，说明它也是一个容器。然后它还实现了 ApplicationContract 这个自定义的接口和 HttpKernelInterface 这个 Symfony 提供的接口。而在构造函数中它向自己这个容器注册了一些基本的绑定（binding）、服务提供者（service provider）和别名（alias）。

0x04 App\Http\Kernel 是如何 handle 请求的？

上面我们知道 $kernel 其实就是 App\Http\Kernel 的实例，下面我们来看看这个类，打开 app/Http/Kernel.php 代码如下：

<?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 = [
        \App\Http\Middleware\CheckForMaintenanceMode::class,
        \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,
        \App\Http\Middleware\TrimStrings::class,
        \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,
        \App\Http\Middleware\TrustProxies::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\Session\Middleware\AuthenticateSession::class,
            \Illuminate\View\Middleware\ShareErrorsFromSession::class,
            \App\Http\Middleware\VerifyCsrfToken::class,
            \Illuminate\Routing\Middleware\SubstituteBindings::class,
        ],

        'api' => [
            'throttle:60,1',
            'bindings',
        ],
    ];

    /**
     * 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,
        'bindings' => \Illuminate\Routing\Middleware\SubstituteBindings::class,
        'cache.headers' => \Illuminate\Http\Middleware\SetCacheHeaders::class,
        'can' => \Illuminate\Auth\Middleware\Authorize::class,
        'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
        'signed' => \Illuminate\Routing\Middleware\ValidateSignature::class,
        'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
        'verified' => \Illuminate\Auth\Middleware\EnsureEmailIsVerified::class,
    ];

    /**
     * The priority-sorted list of middleware.
     *
     * This forces non-global middleware to always be in the given order.
     *
     * @var array
     */
    protected $middlewarePriority = [
        \Illuminate\Session\Middleware\StartSession::class,
        \Illuminate\View\Middleware\ShareErrorsFromSession::class,
        \App\Http\Middleware\Authenticate::class,
        \Illuminate\Session\Middleware\AuthenticateSession::class,
        \Illuminate\Routing\Middleware\SubstituteBindings::class,
        \Illuminate\Auth\Middleware\Authorize::class,
    ];
}

看完如上代码发现其实真正的重点在父类 Illuminate\Foundation\Http\Kernel，因为 App\Http\Kernel 类只是覆盖了父类的中间件相关的属性而已。那我们来看看 Illuminate\Foundation\Http\Kernel 类：

class Kernel implements KernelContract
{
     /**
     * Create a new HTTP kernel instance.
     *
     * @param  \Illuminate\Contracts\Foundation\Application  $app
     * @param  \Illuminate\Routing\Router  $router
     * @return void
     */
    public function __construct(Application $app, Router $router)
    {
        $this->app = $app;
        $this->router = $router;
        // 下面的代码都只是将 kernel 的中间件添加到 $router 而已
        $router->middlewarePriority = $this->middlewarePriority;

        foreach ($this->middlewareGroups as $key => $middleware) {
            $router->middlewareGroup($key, $middleware);
        }

        foreach ($this->routeMiddleware as $key => $middleware) {
            $router->aliasMiddleware($key, $middleware);
        }
    }
    
     /**
     * Handle an incoming HTTP request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Illuminate\Http\Response
     */
    public function handle($request)
    {
        try {
            // [不重要]开启请求重载，就是将 _method 参数值覆盖原始请求的方法
            $request->enableHttpMethodParameterOverride();
            // 发送请求给路由
            $response = $this->sendRequestThroughRouter($request);
        } catch (Exception $e) { // 捕获异常
            $this->reportException($e);

            $response = $this->renderException($request, $e);
        } catch (Throwable $e) { // 捕获错误
            $this->reportException($e = new FatalThrowableError($e));

            $response = $this->renderException($request, $e);
        }
        // 触发请求被处理事件
        $this->app['events']->dispatch(
            new Events\RequestHandled($request, $response)
        );
        // 返回响应
        return $response;
    }
     /**
     * Send the given request through the middleware / router.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Illuminate\Http\Response
     */
    protected function sendRequestThroughRouter($request)
    {
        // 容器绑定 request 实例
        $this->app->instance('request', $request);
        // 清除旧的 request 实例
        Facade::clearResolvedInstance('request');
        // 执行引导程序
        $this->bootstrap();
        // 通过 Pipeline 将所有中间件打包后执行，返回响应
        return (new Pipeline($this->app))
                    ->send($request)
                    ->through($this->app->shouldSkipMiddleware() ? [] : $this->middleware)
                    ->then($this->dispatchToRouter());
    }
    // ... 省略其它代码
}