laravel5.5源码笔记（三、门面类facade）

上次说了provider，那么这次来说说facade

首先是启动的源头，从laravel的kernel类中的$bootstrappers 数组，我们可以看到它的一些系统引导方法，其中的RegisterFacades便是用来注册facade门面类的了。

    protected $bootstrappers = [
        IlluminateFoundationBootstrapLoadEnvironmentVariables::class,
        IlluminateFoundationBootstrapLoadConfiguration::class,
        IlluminateFoundationBootstrapHandleExceptions::class,
        IlluminateFoundationBootstrapRegisterFacades::class,
        IlluminateFoundationBootstrapRegisterProviders::class,
        IlluminateFoundationBootstrapBootProviders::class,
    ];

 同样是有一个register类，通过这个类进行别名等注册操作

namespace IlluminateFoundationBootstrap;

use IlluminateFoundationAliasLoader;
use IlluminateSupportFacadesFacade;
use IlluminateFoundationPackageManifest;
use IlluminateContractsFoundationApplication;

class RegisterFacades
{
    /**
     * Bootstrap the given application.
     *
     * @param  IlluminateContractsFoundationApplication  $app
     * @return void
     */
    public function bootstrap(Application $app)
    {
        //清除facade所有已绑定实例
        Facade::clearResolvedInstances();
        //将app存入对象
        Facade::setFacadeApplication($app);
        //将这些别名数组通过构造函数存入对象中
        AliasLoader::getInstance(array_merge(
            //通过IlluminateConfigRepository获取config/app.php中的aliases数组
            $app->make('config')->get('app.aliases', []),
            //还记得最开始的博文中提到的那个包清单吗，这里也从中获取了它的aliases
            $app->make(PackageManifest::class)->aliases()
        //通过spl_autoload_register函数注册另一种自动加载函数
        ))->register();
    }
}

    public static function getInstance(array $aliases = [])
    {
        //注册时的实例是空的，会通过构造方法把刚刚传入的别名数组存入对象
        if (is_null(static::$instance)) {
            return static::$instance = new static($aliases);
        }

        $aliases = array_merge(static::$instance->getAliases(), $aliases);

        static::$instance->setAliases($aliases);

        return static::$instance;
    }

    private function __construct($aliases)
    {
        $this->aliases = $aliases;
    }

    public function register()
    {
        if (! $this->registered) {
            $this->prependToLoaderStack();

            $this->registered = true;
        }
    }

    /**
     * Prepend the load method to the auto-loader stack.
     *
     * @return void
     */
    protected function prependToLoaderStack()
    {
        //最后通过自动加载函数将本对象中的load方法放入自动加载队列的前端，在我们通过类名调用方法时，会触发自动加载函数队列，会优先触发这个函数，查找到对应文件的路径然后加载相应文件
        spl_autoload_register([$this, 'load'], true, true);
    }

    public function load($alias)
    {
        //若传入的命名空间不为当前facade数组内才会通过这个方法加载
        if (static::$facadeNamespace && strpos($alias, static::$facadeNamespace) === 0) {
            $this->loadFacade($alias);

            return true;
        }
        //否则直接返回其别名
        if (isset($this->aliases[$alias])) {
            return class_alias($this->aliases[$alias], $alias);
        }
    }

    /**
     * Load a real-time facade for the given alias.
     *
     * @param  string  $alias
     * @return void
     */
    protected function loadFacade($alias)
    {
        require $this->ensureFacadeExists($alias);
    }

    /**
     * Ensure that the given alias has an existing real-time facade class.
     *
     * @param  string  $alias
     * @return string
     */
    protected function ensureFacadeExists($alias)
    {
        //从缓存中返回路径
        if (file_exists($path = storage_path('framework/cache/facade-'.sha1($alias).'.php'))) {
            return $path;
        }
        
        file_put_contents($path, $this->formatFacadeStub(
            $alias, file_get_contents(__DIR__.'/stubs/facade.stub')
        ));

        return $path;
    }

 由于laravel中composer的执行过程过于繁琐，这里就不做深究了。原理是一样的，通过别名找到命名空间的类名，再由composer的类名与文件路径映射关系，自动加载函数找到相应文件加载进来。

那么我们来自定义一个门面类试一下

1、新建一个facade类，这里返回的test是上一篇博客中定义的对象

namespace AppFacades;

use IlluminateSupportFacadesFacade;

class Test extends Facade
{
    protected static function getFacadeAccessor()
    {
        return 'AppContractsTest';
    }
}

2、将它添加到config/app.php的aliases别名数组中

'aliases' => [

        'App' => IlluminateSupportFacadesApp::class,
        'Artisan' => IlluminateSupportFacadesArtisan::class,
        'Auth' => IlluminateSupportFacadesAuth::class,
        'Blade' => IlluminateSupportFacadesBlade::class,
        'Broadcast' => IlluminateSupportFacadesBroadcast::class,
        'Bus' => IlluminateSupportFacadesBus::class,
        'Cache' => IlluminateSupportFacadesCache::class,
        'Config' => IlluminateSupportFacadesConfig::class,
        'Cookie' => IlluminateSupportFacadesCookie::class,
        'Crypt' => IlluminateSupportFacadesCrypt::class,
        'DB' => IlluminateSupportFacadesDB::class,
        'Eloquent' => IlluminateDatabaseEloquentModel::class,
        'Event' => IlluminateSupportFacadesEvent::class,
        'File' => IlluminateSupportFacadesFile::class,
        'Gate' => IlluminateSupportFacadesGate::class,
        'Hash' => IlluminateSupportFacadesHash::class,
        'Lang' => IlluminateSupportFacadesLang::class,
        'Log' => IlluminateSupportFacadesLog::class,
        'Mail' => IlluminateSupportFacadesMail::class,
        'Notification' => IlluminateSupportFacadesNotification::class,
        'Password' => IlluminateSupportFacadesPassword::class,
        'Queue' => IlluminateSupportFacadesQueue::class,
        'Redirect' => IlluminateSupportFacadesRedirect::class,
        'Redis' => IlluminateSupportFacadesRedis::class,
        'Request' => IlluminateSupportFacadesRequest::class,
        'Response' => IlluminateSupportFacadesResponse::class,
        'Route' => IlluminateSupportFacadesRoute::class,
        'Schema' => IlluminateSupportFacadesSchema::class,
        'Session' => IlluminateSupportFacadesSession::class,
        'Storage' => IlluminateSupportFacadesStorage::class,
        'URL' => IlluminateSupportFacadesURL::class,
        'Validator' => IlluminateSupportFacadesValidator::class,
        'View' => IlluminateSupportFacadesView::class,
        //刚刚新建的facades
        'Test' => AppFacadesTest::class,
    ],

3、在路由文件中调用它

Route::any('/index', function (){
    Test::doing();
});

我们会发现，即使我们没有通过app对象进行make也没有任何命名空间的引入，它就这样被调用了。

如果是在类中调用，那么就要麻烦一些了，需要ues这个别名，注意这一点

namespace AppHttpControllers;

use IlluminateHttpRequest;
//use AppContractsTest;
//注意这里只引入了别名，由于命名空间冲突，所以我注释了其他部分
use Test;

class IndexController extends Controller
{
//    public function __construct(Test $test)
//    {
//        $this->test = $test;
//    }

    public function index(Test $test)
    {
        Test::doing();
//        app()->make('AppContractsTest')->doing();
//        echo '<br>';
//
//        //只有通过构造方法进行自动加载依赖的方式才能触发契约的when绑定
//        $this->test->doing();
//
//        echo '<br>';
//        //因为laravel中的上下文绑定只能具体到类，所以这里的$test实例依然为普通绑定
//        $test->doing();

    }
}

 通过这个demo的实践，facade还是比较简单的。