浅析laravel路由执行原理

目前很多文章已经对Laravel的执行原理做了详细介绍，这里只是为了个人做一下简单记录

首先看入口 index.php

<?php

/**
 * Laravel - A PHP Framework For Web Artisans
 *
 * @package  Laravel
 * @author   Taylor Otwell <taylor@laravel.com>
 */

define('LARAVEL_START', microtime(true));

/*
|--------------------------------------------------------------------------
| Register The Auto Loader
|--------------------------------------------------------------------------
|
| Composer provides a convenient, automatically generated class loader for
| our application. We just need to utilize it! We'll simply require it
| into the script here so that we don't have to worry about manual
| loading any of our classes later on. It feels great to relax.
|
*/

require __DIR__ . '/../vendor/autoload.php';

/*
|--------------------------------------------------------------------------
| Turn On The Lights
|--------------------------------------------------------------------------
|
| We need to illuminate PHP development, so let us turn on the lights.
| This bootstraps the framework and gets it ready for use, then it
| will load up this application so that we can run it and send
| the responses back to the browser and delight our users.
|
*/

$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);

关键的执行函数就是 handle方法 ，但是前面的几个预处理函数，包括了整合框架的大知识点。

进入

require_once __DIR__.'/../bootstrap/app.php';

发现 $app初始化了Application对象

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

紧接着有一个关键操作 singleton

$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
);

这里的单例，将抽象类绑定给了实体类

包括后面 index.php 里面马上在make方法中用到的

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

$response = $kernel->handle(
    $request = Illuminate\Http\Request::capture()
);

因此$kernel 得到的是 App\Http\Kernel::class 的实例对象。

继续看后面

$kernel执行handle

App\Http\Kernel::class 继承了 

Illuminate\Foundation\Http\Kernel

因此执行的是

public function handle($request)
    {
        try {
            $request->enableHttpMethodParameterOverride();

            $response = $this->sendRequestThroughRouter($request);
        } catch (Exception $e) {
            $this->reportException($e);

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

            $response = $this->renderException($request, $e);
        }

        $this->app['events']->dispatch(
            new Events\RequestHandled($request, $response)
        );

        return $response;
    }

我们关键留意 

sendRequestThroughRouter 方法

protected function sendRequestThroughRouter($request)
    {
        $this->app->instance('request', $request);

        Facade::clearResolvedInstance('request');

        $this->bootstrap();

        return (new Pipeline($this->app))
                    ->send($request)
                    ->through($this->app->shouldSkipMiddleware() ? [] : $this->middleware)
                    ->then($this->dispatchToRouter());
    }

这里的首先将 $request 注册到公共容器中

through 方法会将原本定义在 App\Http\Kernel::class 里面的 中间件

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,
    //\App\Http\Middleware\Api\V1\Statistics\Common\CommonStatisticsMiddleware::class
];

成员变量注入到管道中,

->through($this->app->shouldSkipMiddleware() ? [] : $this->middleware)

通过array_reduce 方法会依次将中间件中handle方法执行

最后执行 $this->dispatchToRouter()；

可能有些朋友不解了

public function then(Closure $destination)
    {
        $pipeline = array_reduce(
            array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
        );

        return $pipeline($this->passable);
    }

按照array_reduce方法不是将 

$this->prepareDestination($destination)

首先执行吗，这个也的确没毛病，关键是这个prepareDestination 只是作为一个预加载的作用，执行后返回的是一个后调函数，回调函数里面才是我们前面提到的$this->dispatchToRouter() , 因此它会被注入到管道的最底部，将倒序之后的中间件执行注入之后，最后得到的就是 首个中间件的 

Closure 闭包方法。

public function then(Closure $destination)
    {
        $pipeline = array_reduce(
            array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
        );

        return $pipeline($this->passable);
    }

最后一步，将这个闭包执行，就可以依次执行中间件的验证，和dispatchToRouter方法了