WARNING: You are browsing the documentation for Symfony 3.0 which is not maintained anymore. Consider upgrading your projects to Symfony 5.0.

The Separation of Concerns

3.0 version

Maintained

3.4 4.3 4.4 5.0 current 5.1 master

Unmaintained

2.3 2.7 2.8 3.1 3.2 3.3 4.0 4.1 4.2

The Separation of Concerns¶

One down-side of our framework right now is that we need to copy and paste the code in front.php each time we create a new website. 40 lines of code is not that much, but it would be nice if we could wrap this code into a proper class. It would bring us better reusability and easier testing to name just a few benefits.

If you have a closer look at the code, front.php has one input, the Request and one output, the Response. Our framework class will follow this simple principle: the logic is about creating the Response associated with a Request.

Let's create our very own namespace for our framework: Simplex. Move the request handling logic into its own Simplex\\Framework class:

// example.com/src/Simplex/Framework.php
namespace Simplex;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Matcher\UrlMatcher;
use Symfony\Component\Routing\Exception\ResourceNotFoundException;
use Symfony\Component\HttpKernel\Controller\ControllerResolver;

class Framework
{
    protected $matcher;
    protected $resolver;

    public function __construct(UrlMatcher $matcher, ControllerResolver $resolver)
    {
        $this->matcher = $matcher;
        $this->resolver = $resolver;
    }

    public function handle(Request $request)
    {
        $this->matcher->getContext()->fromRequest($request);

        try {
            $request->attributes->add($this->matcher->match($request->getPathInfo()));

            $controller = $this->resolver->getController($request);
            $arguments = $this->resolver->getArguments($request, $controller);

            return call_user_func_array($controller, $arguments);
        } catch (ResourceNotFoundException $e) {
            return new Response('Not Found', 404);
        } catch (\Exception $e) {
            return new Response('An error occurred', 500);
        }
    }
}

And update example.com/web/front.php accordingly:

// example.com/web/front.php

// ...
$request = Request::createFromGlobals();
$routes = include __DIR__.'/../src/app.php';

$context = new Routing\RequestContext();
$matcher = new Routing\Matcher\UrlMatcher($routes, $context);
$resolver = new HttpKernel\Controller\ControllerResolver();

$framework = new Simplex\Framework($matcher, $resolver);
$response = $framework->handle($request);

$response->send();

To wrap up the refactoring, let's move everything but routes definition from example.com/src/app.php into yet another namespace: Calendar.

For the classes defined under the Simplex and Calendar namespaces to be autoloaded, update the composer.json file:

{
    "...": "...",
    "autoload": {
        "psr-4": { "": "src/" }
    }
}

Note

For the Composer autoloader to be updated, run composer dump-autoload.

Move the controller to Calendar\Controller\LeapYearController:

// example.com/src/Calendar/Controller/LeapYearController.php
namespace Calendar\Controller;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Calendar\Model\LeapYear;

class LeapYearController
{
    public function indexAction(Request $request, $year)
    {
        $leapyear = new LeapYear();
        if ($leapyear->isLeapYear($year)) {
            return new Response('Yep, this is a leap year!');
        }

        return new Response('Nope, this is not a leap year.');
    }
}

And move the is_leap_year() function to its own class too:

// example.com/src/Calendar/Model/LeapYear.php
namespace Calendar\Model;

class LeapYear
{
    public function isLeapYear($year = null)
    {
        if (null === $year) {
            $year = date('Y');
        }

        return 0 == $year % 400 || (0 == $year % 4 && 0 != $year % 100);
    }
}

Don't forget to update the example.com/src/app.php file accordingly:

$routes->add('leap_year', new Routing\Route('/is_leap_year/{year}', array(
    'year' => null,
    '_controller' => 'Calendar\\Controller\\LeapYearController::indexAction',
)));

To sum up, here is the new file layout:

example.com
├── composer.json
├── composer.lock
├── src
│   ├── app.php
│   └── Simplex
│       └── Framework.php
│   └── Calendar
│       └── Controller
│       │   └── LeapYearController.php
│       └── Model
│           └── LeapYear.php
├── vendor
│   └── autoload.php
└── web
    └── front.php

That's it! Our application has now four different layers and each of them has a well defined goal:

web/front.php: The front controller; the only exposed PHP code that makes the interface with the client (it gets the Request and sends the Response) and provides the boiler-plate code to initialize the framework and our application;
src/Simplex: The reusable framework code that abstracts the handling of incoming Requests (by the way, it makes your controllers/templates easily testable -- more about that later on);
src/Calendar: Our application specific code (the controllers and the model);
src/app.php: The application configuration/framework customization.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.