ReflectionException Class UserController does not exist Laravel5.4

Everytime i hit the Submit Button i got this problem ReflectionException Class UserController does not exist

 <?php
 namespace app\Http\Controllers;
  use App\User;
  use Illuminate\Http\Request;




   class UserController extends Controller {

   public function postSignUp(Request $request)
        {
       $email = $request['email'];
        $first_name = $request['first_name'];
        $password = bcrypt($request['password']);
        $user = new User();
         $user->email =$email;
         $user->first_name=$first_name;
          $user->password = $password;
           $user->save();

            return redirect()->back();

                   }

               public function postSignIn(Request $request)
                   {

                       }
                       }

My route file:

<?php

namespace App\Providers;

use Illuminate\Support\Facades\Route;
use Illuminate\Foundation\Support\Providers\RouteServiceProvider as ServiceProvider;


class RouteServiceProvider extends ServiceProvider
{
    /**
     * This namespace is applied to your controller routes.
     *
     * In addition, it is set as the URL generator's root namespace.
     *
     * @var string
     */
    protected $namespace = 'App\Http\Controllers';

    /**
     * Define your route model bindings, pattern filters, etc.
     *
     * @return void
     */
    public function boot()
    {
        //

        parent::boot();
    }

    /**
     * Define the routes for the application.
     *
     * @return void
     */
    public function map()
    {
        $this->mapApiRoutes();

        $this->mapWebRoutes();

        //
    }

    /**
     * Define the "web" routes for the application.
     *
     * These routes all receive session state, CSRF protection, etc.
     *
     * @return void
     */
    protected function mapWebRoutes()
    {
       Route::middleware('web')
             ->namespace($this->namespace)
             ->group(base_path('routes/web.php'));


        Route::post('/signup',[
            'uses'=>'UserController@postSignUp',
            'as'=>'signup'
        ]);



    }

    /**
     * Define the "api" routes for the application.
     *
     * These routes are typically stateless.
     *
     * @return void
     */
    protected function mapApiRoutes()
    {
        Route::prefix('api')
             ->middleware('api')
             ->namespace($this->namespace)
             ->group(base_path('routes/api.php'));
    }
}

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