Laravel 契约和门面简单解读（Cache）

最近笔者正在理解Larvael服务容器、服务提供者、门面、契约的关系。
今天主要是记录自己借Laravel自带的Cache模块进行一个讲解。

代码和流程

首先我们打开config\app.php中providers下有一个服务提供者Illuminate\Cache\CacheServiceProvider::class
我们看看他的服务提供者是怎么写的：

public function register()
    {
        $this->app->singleton('cache', function ($app) {
            return new CacheManager($app);
        });

        $this->app->singleton('cache.store', function ($app) {
            return $app['cache']->driver();
        });

        $this->app->singleton('cache.psr6', function ($app) {
            return new Psr16Adapter($app['cache.store']);
        });

        $this->app->singleton('memcached.connector', function () {
            return new MemcachedConnector;
        });
    }

我们主要看cache这个门面，它所单例绑定的是CacheManager，我们继续深入

<?php

namespace Illuminate\Cache;

use Aws\DynamoDb\DynamoDbClient;
use Closure;
use Illuminate\Contracts\Cache\Factory as FactoryContract;
use Illuminate\Contracts\Cache\Store;
use Illuminate\Contracts\Events\Dispatcher as DispatcherContract;
use Illuminate\Support\Arr;
use InvalidArgumentException;

/**
 * @mixin \Illuminate\Contracts\Cache\Repository
 */
class CacheManager implements FactoryContract
{
    /**
     * The application instance.
     *
     * @var \Illuminate\Contracts\Foundation\Application
     */
    protected $app;

    /**
     * The array of resolved cache stores.
     *
     * @var array
     */
    protected $stores = [];

    /**
     * The registered custom driver creators.
     *
     * @var array
     */
    protected $customCreators = [];

    /**
     * Create a new Cache manager instance.
     *
     * @param  \Illuminate\Contracts\Foundation\Application  $app
     * @return void
     */
    public function __construct($app)
    {
        $this->app = $app;
    }

    /**
     * Get a cache store instance by name, wrapped in a repository.
     *
     * @param  string|null  $name
     * @return \Illuminate\Contracts\Cache\Repository
     */
    public function store($name = null)
    {
        $name = $name ?: $this->getDefaultDriver();

        return $this->stores[$name] = $this->get($name);
    }

    /**
     * Get a cache driver instance.
     *
     * @param  string|null  $driver
     * @return \Illuminate\Contracts\Cache\Repository
     */
    public function driver($driver = null)
    {
        return $this->store($driver);
    }

    /**
     * Attempt to get the store from the local cache.
     *
     * @param  string  $name
     * @return \Illuminate\Contracts\Cache\Repository
     */
    protected function get($name)
    {
        return $this->stores[$name] ?? $this->resolve($name);
    }

    /**
     * Resolve the given store.
     *
     * @param  string  $name
     * @return \Illuminate\Contracts\Cache\Repository
     *
     * @throws \InvalidArgumentException
     */
    protected function resolve($name)
    {
        $config = $this->getConfig($name);

        if (is_null($config)) {
            throw new InvalidArgumentException("Cache store [{$name}] is not defined.");
        }

        if (isset($this->customCreators[$config['driver']])) {
            return $this->callCustomCreator($config);
        } else {
            $driverMethod = 'create'.ucfirst($config['driver']).'Driver';

            if (method_exists($this, $driverMethod)) {
                return $this->{$driverMethod}($config);
            } else {
                throw new InvalidArgumentException("Driver [{$config['driver']}] is not supported.");
            }
        }
    }

    /**
     * Call a custom driver creator.
     *
     * @param  array  $config
     * @return mixed
     */
    protected function callCustomCreator(array $config)
    {
        return $this->customCreators[$config['driver']]($this->app, $config);
    }

    ......

    /**
     * Create an instance of the file cache driver.
     *
     * @param  array  $config
     * @return \Illuminate\Cache\Repository
     */
    protected function createFileDriver(array $config)
    {
        return $this->repository(new FileStore($this->app['files'], $config['path']));
    }

    /**
     * Create a new cache repository with the given implementation.
     *
     * @param  \Illuminate\Contracts\Cache\Store  $store
     * @return \Illuminate\Cache\Repository
     */
    public function repository(Store $store)
    {
        return tap(new Repository($store), function ($repository) {
            $this->setEventDispatcher($repository);
        });
    }

    /**
     * Set the event dispatcher on the given repository instance.
     *
     * @param  \Illuminate\Cache\Repository  $repository
     * @return void
     */
    protected function setEventDispatcher(Repository $repository)
    {
        if (! $this->app->bound(DispatcherContract::class)) {
            return;
        }

        $repository->setEventDispatcher(
            $this->app[DispatcherContract::class]
        );
    }

    ......

    /**
     * Get the cache connection configuration.
     *
     * @param  string  $name
     * @return array
     */
    protected function getConfig($name)
    {
        return $this->app['config']["cache.stores.{$name}"];
    }

    ......

    /**
     * Dynamically call the default driver instance.
     *
     * @param  string  $method
     * @param  array  $parameters
     * @return mixed
     */
    public function __call($method, $parameters)
    {
        return $this->store()->$method(...$parameters);
    }
}

我们以Laravel默认的File存储讲起：

1. 当我们的控制器中使用Cache::get(),框架查找门面Illuminate\Support\Facades\Cache,返回一个叫cache的服务提供商
2. 框架查找叫cache的服务提供商，实例化CacheManager()
3. 实例化CacheManager调用get方法,发现没有关于get的静态函数，于是触发了__call魔术方法

4. __call调用函数store

   • store判断是否需要携带参数
   • get方法判断是否需要从配置中读取，并进行FileStore的实例化，如果不需要直接返回store[]中的实例化过的FileStore::class
5. FileStore实现了契约Contracts\Cahce\Store

6. createXXXDriver中发现返回的是Cache\Repository，并发现使用了控制反转，注入了不同的Store

   总结

   这样的设计控制器不需要去管理实现的是哪一种Cache，是file、redis还是memcached，同时Cache\Repository也规定了必须注入满足契约的实现类，规范整体设计和方法，上层无感知切换。