About the Tutorial

src/Controller/AppController.php
. The file contains the following code. 
namespace App\Controller; 
use Cake\Controller\Controller; 
use Cake\Event\Event; 
class AppController extends Controller 
{ 
public function initialize() 
{ 
parent::initialize(); 
$this->loadComponent('RequestHandler'); 
$this->loadComponent('Flash'); 
} 
public function beforeRender(Event $event) 
{ 
if (!array_key_exists('_serialize', $this->viewVars) && 
in_array($this->response->type(), ['application/json', application/xml'])
) { 
$this->set('_serialize', true); 
} 
} 
} 
9.
 
CakePHP — Controllers 

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CakePHP 
21 
AppController
can be used to load components that will be used in every controller of 
your application. The attributes and methods created in AppController will be available in 
all controllers that extend it. The 
initialize()
method will be invoked at the end of 
controller’s constructor to load components.