Q:

How to include a custom php file?

I have added a new directory and a new file into src/AppBundle. So the path is: src/AppBundle/Helper/Helper.php
The path of my controller is as usual src/AppBundle/Controller/MyController.php.
I would now like to include the file Helper.php to my Controller. How can I do this?

A:

One possibility,  assuming your AppBundle/Controller/MyController in Symfony 2.8 it looks something like this:
namespace AppBundle\Controller\MyController

use Symfony\Bundle\FrameworkBundle\Controller\Controller;

class MyController extends Controller
{
...
}

and your Helper class includes public function getSomeHelp()
you can then define a service in services.yml:
services
    app.helper:
        class: 'AppBundle\Helper\Helper'

and in your MyController:
public function someFunctionAction() {
    ...
    $helper = $this->get('app.helper');
    $something = $helper->getSomeHelp();

