laravel里所谓的provider服务提供者，其实是对某一类功能进行整合，与做一些使用前的初始化引导工作。laravel里的服务提供者也分为，系统核心服务提供者、与一般系统服务提供者。例如上一篇博文里介绍的，最早在application中进行注册的event、log、routing这些就是系统的核心服务，laravel的初始化需要他们。那么现在就先来看一下provider的运行流程。

    protected function registerBaseServiceProviders()
    {
        $this->register(new EventServiceProvider($this));

        $this->register(new LogServiceProvider($this));

        $this->register(new RoutingServiceProvider($this));
    }

其他的serviceProvider则是指config/app.php中providers数组所配置的provider了，基本都是些laravel系统提供的工具型provider

    'providers' => [

        /*
         * Laravel Framework Service Providers...
         */
        Illuminate\Auth\AuthServiceProvider::class,
        Illuminate\Broadcasting\BroadcastServiceProvider::class,
        Illuminate\Bus\BusServiceProvider::class,
        Illuminate\Cache\CacheServiceProvider::class,
        Illuminate\Foundation\Providers\ConsoleSupportServiceProvider::class,
        Illuminate\Cookie\CookieServiceProvider::class,
        Illuminate\Database\DatabaseServiceProvider::class,
        Illuminate\Encryption\EncryptionServiceProvider::class,
        Illuminate\Filesystem\FilesystemServiceProvider::class,
        Illuminate\Foundation\Providers\FoundationServiceProvider::class,
        Illuminate\Hashing\HashServiceProvider::class,
        Illuminate\Mail\MailServiceProvider::class,
        Illuminate\Notifications\NotificationServiceProvider::class,
        Illuminate\Pagination\PaginationServiceProvider::class,
        Illuminate\Pipeline\PipelineServiceProvider::class,
        Illuminate\Queue\QueueServiceProvider::class,
        Illuminate\Redis\RedisServiceProvider::class,
        Illuminate\Auth\Passwords\PasswordResetServiceProvider::class,
        Illuminate\Session\SessionServiceProvider::class,
        Illuminate\Translation\TranslationServiceProvider::class,
        Illuminate\Validation\ValidationServiceProvider::class,
        Illuminate\View\ViewServiceProvider::class,
        //Maatwebsite\Excel\ExcelServiceProvider::class,  这个是我自己测试的时候加的

        /*
         * Package Service Providers...
         */

        /*
         * Application Service Providers...
         */
        App\Providers\AppServiceProvider::class,
        App\Providers\AuthServiceProvider::class,
        // App\Providers\BroadcastServiceProvider::class,
        App\Providers\EventServiceProvider::class,
        App\Providers\RouteServiceProvider::class,

    ],

那么这些配置中的provider会在什么时候加载呢？上一篇博文中介绍的当$kernel对象通过handle方法传入request时，会执行sendRequestThroughRouter方法，这个方法中的bootstrap方法会加载laravel系统初始化所需的对象并运行，其中RegisterProviders类便是用来注册刚刚config文件内所记录的provider的

    public function bootstrap()
    {
        if (! $this->app->hasBeenBootstrapped()) {
            $this->app->bootstrapWith($this->bootstrappers());
        }
    }

    protected $bootstrappers = [
        \Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::class,
        \Illuminate\Foundation\Bootstrap\LoadConfiguration::class,
        \Illuminate\Foundation\Bootstrap\HandleExceptions::class,
        //注册facade门面类
        \Illuminate\Foundation\Bootstrap\RegisterFacades::class,
        //注册provider
        \Illuminate\Foundation\Bootstrap\RegisterProviders::class,
        //引导provider执行其中boot方法内的代码
        \Illuminate\Foundation\Bootstrap\Boot