protected $middlewareGroups = [
  //中间件web
  'web' => [
   \App\Http\Middleware\EncryptCookies::class,
   \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
   //看到这里了吗！StartSession！！！！要把路由放在这个中间件了才会启动Session！！
   \Illuminate\Session\Middleware\StartSession::class,
   \Illuminate\View\Middleware\ShareErrorsFromSession::class,
   \App\Http\Middleware\VerifyCsrfToken::class,
  ],
 
  'api' => [
   'throttle:60,1',
  ],
 ];

//两种路由中间件写法各人喜好！
Route::get('/', function () {
 //路由放在这里
})->middleware('web');
 
Route::group(['middleware' => ['web']], function () {
 //路由放在这里
});
//routes.php

class Middleware implements HttpKernelInterface
{
 ...
 public function handle(Request $request, $type = HttpKernelInterface::MASTER_REQUEST, $catch = true)
 {
  $this->checkRequestForArraySessions($request);
  if ($this->sessionConfigured()) {
   $session = $this->startSession($request); // 启动session
   $request->setSession($session);
  }
  $response = $this->app->handle($request, $type, $catch); // 调用controller的method
  if ($this->sessionConfigured()) {
   $this->closeSession($session);   //关闭session
   $this->addCookieToResponse($response, $session);
  }
  return $response;
 }
 ...
 
 protected function closeSession(SessionInterface $session)
 {
  $session->save(); // 保存session
  $this->collectGarbage($session);
 }
}