Analysis of Laravel's Facade appearance system

This article mainly introduces the analysis of Laravel's Facade appearance system. It has certain reference value. Now I share it with you. Friends in need can refer to it.

Today we will learn about Laravel's core architecture. Another theme "Facade".

This article will start from the following aspects to comprehensively explain the operating principle ofFacadein Laravel. In order to facilitate the understanding of allFacadein the following translation, it is translated as "appearance":

• A brief introduction to the "appearance" design pattern;

• The loading principle of Laravel's "appearance";

• Basic use of Laravel "appearance".

What is the "Appearance" design pattern

Appearance pattern definition

Provides a unified entry for a set of interfaces in a subsystem. The facade pattern defines a high-level interface that makes this subsystem easier to use.

The appearance pattern is a very frequently used structural design pattern. It simplifies the interaction between the client and the subsystem by introducing a appearance role,
provides a complex subsystem call The unified entrance reduces the coupling between the subsystem and the client, and the client call is very convenient. - Design Pattern Java Edition

Coreis to introduce a link betweenclient (user)andsubsystem (interface or service)"Appearance" character.

Transform the direct coupling between users and subsystems into a unified interface provided by the "appearance" class for users to reduce the coupling between the client and the subsystem.

Structural diagram:

called services, contracts or what we usually call in Laravel). "Interface"), which is encapsulated into each "appearance" service in a static and callable way for us to use.

Appearance component configuration

The configuration data of all built-in appearance components is defined in the

file like other Laravel services. Let's take a look at the configuration data of thealiasesnode:

... 'aliases' => [ 'App' => Illuminate\Support\Facades\App::class, 'Artisan' => Illuminate\Support\Facades\Artisan::class, ... ], ...

. When an HTTP request is received, these "look and feel" components are loaded into the service during the request processing phase.Next, we will conduct an in-depth analysis of the loading process of the appearance service.

Load Appearance Service

The loading work of the "Appearance" service is defined in the

kernel\Illuminate\Foundation\Bootstrap \RegisterFacades::classLauncher completes.Boot Start Appearance Service

If you have read my other article on in-depth analysis of Laravel service provider implementation principles, you should not be too unfamiliar with the bootstrap program.

The bootstrap will complete the boot startup

after processing the HTTP request. So here we need to go deep into theRegisterFacadesclass to understand more detailed processing.

make('config')->get('app.aliases', []), $app->make(PackageManifest::class)->aliases() ))->register(); } }

component completion:

First, it will be loaded from the configuration file
• config/app.php

  Read all "appearance" service configurationaliases;

Then read the alias service from the manifest file
• $app->make(PackageManifest ::class)->aliases()

  ;

Combine the two configuration arrays and inject them into
• AliasLoader

  Completeregistration (register).

Register Appearance Service

Finally let’s take a look at how the

loader loads all “appearance” services into the system.

getAliases(), $aliases); static::$instance->setAliases($aliases); return static::$instance; } /** * Set the registered aliases. 设置需注册别名数据。 */ public function setAliases(array $aliases) { $this->aliases = $aliases; } /** * Register the loader on the auto-loader stack. 将加载器注册到自动加载中。 */ public function register() { if (! $this->registered) { $this->prependToLoaderStack(); $this->registered = true; } } /** * Prepend the load method to the auto-loader stack. 设置自动加载方法。 */ protected function prependToLoaderStack() { // 将 AliasLoader 的 load 方法作为 __autoload 的实现 spl_autoload_register([$this, 'load'], true, true); } /** * Load a class alias if it is registered.从注册过的服务中加载这个「外观」服务。 */ public function load($alias) { if (static::$facadeNamespace && strpos($alias, static::$facadeNamespace) === 0) { $this->loadFacade($alias); return true; } if (isset($this->aliases[$alias])) { return class_alias($this->aliases[$alias], $alias); } } }

Here is a knowledge point. Completing "Foreign Service Registration" inAliasLoader->register()involves the application of two PHP knowledge:

Usage of PHP built-in magic method
• __autoload

  ;

How to create aliases for classes in PHP.
➤ 1. Dynamic introduction of appearance service

We know that the

magic method is to try to load undefined classes, so that when When we use an unintroduced class, this class will be automatically introduced for us.

更优的解决方案是通过spl_autoload_register函数，将自定义的类加载程序作为__autoload的实现，以替代默认__autoload()模式函数或方法的行为。

所有prependToLoaderStack()方法：

/** * Prepend the load method to the auto-loader stack. 设置自动加载方法。 */ protected function prependToLoaderStack() { // 将 AliasLoader 的 load 方法作为 __autoload 的实现 spl_autoload_register([$this, 'load'], true, true); }

就是去完成这样的作用，将AliasLoader->load()方法作为自动加载程序的实现，在使用「外观」服务时动态引入这个类。

➤ 2. 支持外观服务别名

我们已经了解到当「外观」服务被使用时，由AliasLoader->load()去自动加载这个类。

与此同时，load 方法通过class_alias($original, $alias)函数完成别名注册。

这样，当我们使用App类时实际上就是在使用Illuminate\Support\Facades\App类。

很完美么，我们的「狗蛋」终于与「世界上最好的语言」画上了等号。你就是我，我就是你。

到这里其实已经完成了「外观」服务工作原理分析工作的70%。

探秘 Facade

最后我们将揭开Facade的神秘面纱，研究一下 Laravel 是如何实现 Facade 设计模式的。

我们拿IlluminateSupportFacadesApp外观服务开刀，去解开类似App::make()静态方法使用的奥秘。

深入FacadesApp：

$method(...$args); } }

/** *@link https://github.com/laravel/framework/blob/5.6/src/Illuminate/Container/Container.php */ class Container implements ArrayAccess, ContainerContract { /** * Get the value at a given offset. 获取一个偏移位置的值，实际上从容器中解析出服务。 */ public function offsetGet($key) { return $this->make($key); } }