What is laravel's service provider?

If you have used the Laravel framework, then it is impossible that you have not heard of service container and service provider. In fact, they are the core of the Lavavel framework and they perform the difficult task of starting services in Larvel applications.

In this article, we will introduce to youWhat is laravel’s service provider?

Before learning about service providers, let’s briefly introduce service containers. Service containers will be frequently used in service providers.

In short, the Laravel service container is a box used to store bound components, and it will also provide the required services for the application.

Laravel documentation describes it as follows:

Laravel 服务容器是用于管理类的依赖和执行依赖注入的工具 - Laravel 文档

In this way, when we need to inject a built-in component or service, we can use the type hint function in the constructor or method Inject, and then automatically resolve the required instances and their dependencies from the service container when used! Isn’t it cool? This feature frees us from manual management of components, thereby reducing system coupling.

Let us look at a simple example to deepen our understanding.

<?php
Class SomeClass
{
    public function __construct(FooBar $foobarObject)
    {
        // use $foobarObject object
    }
}

As you can see, SomeClass requires a FooBar instance. In other words it needs to depend on other components. Laravel's implementation of automatic injection requires finding and executing the injection of appropriate dependencies from the service container.

If you want to know how Laravel knows which component or service needs to be bound to the service container, the answer is through the service provider. Service providers complete the work of binding components to service containers. Within the service provider, this work is called service container binding, and the binding processing is completed by the service provider.

The service provider implements service binding, and the binding processing is completed by the register method.

At the same time, this will introduce a new question: How does Laravel know which service providers there are? It seems we haven’t discussed this yet, right? When I arrived, I saw that it was said before that Laravel would automatically find the service! Friend, you have too many questions: Laravel is just a framework, it's not a superhero, is it? Of course we need to explicitly tell the Laravel framework which service providers we have.

Let’s take a look at the config/app.php configuration file. You will find a list of service provider configurations that are loaded during Laravel application startup.

'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,
        /*
         * Package Service Providers...
         */
        Laravel\Tinker\TinkerServiceProvider::class,
        /*
         * Application Service Providers...
         */
        App\Providers\AppServiceProvider::class,
        App\Providers\AuthServiceProvider::class,
        // App\Providers\BroadcastServiceProvider::class,
        App\Providers\EventServiceProvider::class,
        App\Providers\RouteServiceProvider::class,
],

The above are the basic concepts about service containers.

What is a service provider

If the service container is a tool that provides binding and dependency injection, then the service provider is a tool that implements binding.

Let's first look at a content provider service to understand how it works. Open the vender/laravel/framework/src/Illuminate/Cache/CacheServiceProvider.php file.

public function register()
{
    $this->app->singleton('cache', function ($app) {
        return new CacheManager($app);
    });
    $this->app->singleton('cache.store', function ($app) {
        return $app['cache']->driver();
    });
    $this->app->singleton('memcached.connector', function () {
        return new MemcachedConnector;
    });
}

Here we need to focus on the register method, which is used to bind the service to the service container. As you can see, a total of three service binding processes are performed here: cache, cache.store and memcached.connector.

Then, when we need to use the cache service in Laravel, the service container will resolve the CacheManager instance and return it. In other words, we only provide a correspondence table that can be accessed from $this->app .

Binding services through service providers is the correct way to open Laravel service container binding services. At the same time, through the service provider's register method, it is also helpful to understand how the Laravel service container manages all services. We mentioned before that all services are registered in the service container by reading the service provider configuration list from the config/app.php configuration file.

The above is the introduction of the service provider.

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