中间件是什么?
每个中间件是一个定义了handle方法的类或是一个匿名函数，一般所有中间件放在同一个文件夹middleware中，方便管理
public function handle($request, Closure $next)
中间件有什么用

一: 路由前中间件(也叫全局中间件)

这些中间件，在根据请求找到匹配的路由之前就开始执行

1.配置

// 在 \App\Http\Kernel::$middleware中定义，是一个数组，如
$middleware = [\Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,\Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,\App\Http\Middleware\TrimStrings::class,\Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,\App\Http\Middleware\TrustProxies::class,
];// 在 \Zhiyi\Plus\Http\Kernel::$middleware的值为
$middleware = [\Zhiyi\Plus\Http\Middleware\CrossDomain::class,\Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,\Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,\Zhiyi\Plus\Http\Middleware\TrimStrings::class,\Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,\Zhiyi\Plus\Http\Middleware\TrustProxies::class,
];

2.执行顺序

是按上下执行，这里面的中间执行完后，再执行\Illuminate\Foundation\Http\Kernel::dispatchToRouter()

框架内置的中间件放在Illuminate\Foundation\Http\Middleware下面，一共有6个

二： 路由中间件

这些中间件是在路由匹配之后，与当前匹配路由及控制器有关

1: 在控制器中定义

在控制器的构造函数中定义

public function __construct(){$this->middleWare('auth');$this->middleWare('log',['only'=>['show','detail']]);
}

覆盖getMiddleware()方法

public function getMiddleware(){return ['auth','log',['middleware'=>'hello','options'=>['only'=>['index','show']]]];
}

2: 在路由中定义

在第二个参数中定义middleware

Route::get('/login',['uses'=>'LoginController@index','middleware'=>['abc','def']
])

直接给路由使用middleware()方法

Route::get('/login','')->middleware('中间件1'，'中间件2');//数组也行

在group中定义

Route::group(['middleware' => ['has-permission:access-dashboard']], function (Router $router) use ($adminRoute) {...
});

为什么全局中间件是一个完整的类名，而路由中间件是键名或群组名
键名或群组名其实是对应一个中间件类，它们的对应关系在Kernel中定义，如

kernel中 $routeMiddleware  对应 router中 middleware属性
kernel中 $middlewareGroups 对应 router中 middlewareGroups属性$routeMiddleware = [别名         => 有handle方法的类名或匿名函数'auth'       => \Illuminate\Auth\Middleware\Authenticate::class,'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,'bindings'   => \Illuminate\Routing\Middleware\SubstituteBindings::class,'can'        => \Illuminate\Auth\Middleware\Authorize::class,'guest'      => \Zhiyi\Plus\Http\Middleware\RedirectIfAuthenticated::class,'throttle'   => \Illuminate\Routing\Middleware\ThrottleRequests::class,'ability'    => \Zhiyi\Plus\Http\Middleware\UserAbility::class,'sensitive'  => \Zhiyi\Plus\Http\Middleware\DisposeSensitive::class,'operation'  => \Zhiyi\Plus\Http\Middleware\SensitiveOperation::class,'wang'       => function(){这是一个闭包}
];$middlewareGroups = ['web' => [\Zhiyi\Plus\Http\Middleware\EncryptCookies::class,\Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,\Illuminate\Session\Middleware\StartSession::class,// \Illuminate\Session\Middleware\AuthenticateSession::class,\Illuminate\View\Middleware\ShareErrorsFromSession::class,\Zhiyi\Plus\Http\Middleware\VerifyCsrfToken::class,\Illuminate\Routing\Middleware\SubstituteBindings::class,'api' //可以是另一组名,这样，如果指定的中间件中web，那么包括上面的和api组中合起来的所有中间件'wang' // 也可以是$routeMiddleware中的一个别名(键名)],'api' => ['throttle:120,1',// :前面是中间件名，:后面是参数'bindings',],'admin' => ['ability:admin: login,你没有权限访问后台。',],
];

路由中间件在进入管道之前，会转为以下一个由完整类名组成的一维数组

Array([0] => Illuminate\Routing\Middleware\ThrottleRequests:120,1[1] => Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse[2] => Illuminate\Session\Middleware\StartSession[3] => Illuminate\View\Middleware\ShareErrorsFromSession[4] => Zhiyi\Plus\Http\Middleware\VerifyCsrfToken[5] => Illuminate\Routing\Middleware\SubstituteBindings
)

中间件的格式

1. 别名
   $this->middleWare('auth');
2. 组名

$this->middleWare('api')

1. 闭包

$this->middleWare(function($request,$next){})

1. 完整类名 $this->middleWare(IlluminateRoutingMiddlewareThrottleRequests)

三: 使用场景

全局中间件

new Pipeline($this->app))->send($request) ->through($this->middleware) ->then($this->dispatchToRouter())

路由中间件

new Pipeline($this->container))->send($request)->through($middleware)->then(function ($request) use ($route) {                       return $this->prepareResponse($request, $route->run());}
);