Laravel 5：在Http / Controllers中找不到控制器，尽管它在那里

I get this error when accessing the route calling a method from LoginController:

 ReflectionException
Class App\Http\Controllers\LoginController does not exist

The problem is that the file "LoginController.php" IS there in the directory "App\Http\Controllers" but laravel refuses to see it. I'm stumped!

My controller file:

use Illuminate\Http\Request;
use DB;
use Session;
use App\Http\Controllers\Controller;
namespace App\Http\Controllers;

class LoginController extends Controller
{
    public function loginAuthentication(Request $request) {
      // method code here
    }
}

My routes file:

<?php
    Route::get('/', function() {
            session('userLevelKey', '1');
            return view('layout');
    });

    Route::post('/', 'LoginController@loginAuthentication');
    // some more routes

edit 1: added namepace to controller file.

change your controller file to

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use DB;
use Session;
use App\Http\Controllers\Controller;

class LoginController extends Controller
{
    public function loginAuthentication(Request $request) {
      // method code here
    }
}