Building your own Framework with the MicroKernelTrait
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Building your own Framework with the MicroKernelTrait
The default Kernel
class included in Symfony applications uses a
MicroKernelTrait to configure
the bundles, the routes and the service container in the same class.
This micro-kernel approach is so flexible that let you control your application structure and features quite easily.
A Single-File Symfony Application
Start with a completely empty directory and install these Symfony components via Composer:
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$ composer require symfony/config symfony/http-kernel \
symfony/http-foundation symfony/routing \
symfony/dependency-injection symfony/framework-bundle
Next, create an index.php
file that defines the kernel class and executes it:
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use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Component\Config\Loader\LoaderInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;
use Symfony\Component\Routing\RouteCollectionBuilder;
require __DIR__.'/vendor/autoload.php';
class Kernel extends BaseKernel
{
use MicroKernelTrait;
public function registerBundles()
{
return array(
new Symfony\Bundle\FrameworkBundle\FrameworkBundle()
);
}
protected function configureContainer(ContainerBuilder $c, LoaderInterface $loader)
{
// PHP equivalent of config/packages/framework.yaml
$c->loadFromExtension('framework', array(
'secret' => 'S0ME_SECRET'
));
}
protected function configureRoutes(RouteCollectionBuilder $routes)
{
// kernel is a service that points to this class
// optional 3rd argument is the route name
$routes->add('/random/{limit}', 'kernel:randomNumber');
}
public function randomNumber($limit)
{
return new JsonResponse(array(
'number' => rand(0, $limit)
));
}
}
$kernel = new Kernel('dev', true);
$request = Request::createFromGlobals();
$response = $kernel->handle($request);
$response->send();
$kernel->terminate($request, $response);
That's it! To test it, you can start the built-in web server:
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$ php -S localhost:8000
Then see the JSON response in your browser:
The Methods of a "Micro" Kernel
When you use the MicroKernelTrait
, your kernel needs to have exactly three methods
that define your bundles, your services and your routes:
- registerBundles()
-
This is the same
registerBundles()
that you see in a normal kernel. - configureContainer(ContainerBuilder $c, LoaderInterface $loader)
-
This method builds and configures the container. In practice, you will use
loadFromExtension
to configure different bundles (this is the equivalent of what you see in a normalconfig/packages/*
file). You can also register services directly in PHP or load external configuration files (shown below). - configureRoutes(RouteCollectionBuilder $routes)
-
Your job in this method is to add routes to the application. The
RouteCollectionBuilder
has methods that make adding routes in PHP more fun. You can also load external routing files (shown below).
Advanced Example: Twig, Annotations and the Web Debug Toolbar
The purpose of the MicroKernelTrait
is not to have a single-file application.
Instead, its goal to give you the power to choose your bundles and structure.
First, you'll probably want to put your PHP classes in an src/
directory. Configure
your composer.json
file to load from there:
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{
"require": {
"...": "..."
},
"autoload": {
"psr-4": {
"App\\": "src/"
}
}
}
Now, suppose you want to use Twig and load routes via annotations. Instead of
putting everything in index.php
, create a new src/Kernel.php
to
hold the kernel. Now it looks like this:
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// src/Kernel.php
namespace App;
use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Component\Config\Loader\LoaderInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;
use Symfony\Component\Routing\RouteCollectionBuilder;
use Doctrine\Common\Annotations\AnnotationRegistry;
$loader = require __DIR__.'/../vendor/autoload.php';
// auto-load annotations
AnnotationRegistry::registerLoader(array($loader, 'loadClass'));
class Kernel extends BaseKernel
{
use MicroKernelTrait;
public function registerBundles()
{
$bundles = array(
new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
new Symfony\Bundle\TwigBundle\TwigBundle(),
);
if ($this->getEnvironment() == 'dev') {
$bundles[] = new Symfony\Bundle\WebProfilerBundle\WebProfilerBundle();
}
return $bundles;
}
protected function configureContainer(ContainerBuilder $c, LoaderInterface $loader)
{
$loader->load(__DIR__.'/config/framework.yaml');
// configure WebProfilerBundle only if the bundle is enabled
if (isset($this->bundles['WebProfilerBundle'])) {
$c->loadFromExtension('web_profiler', array(
'toolbar' => true,
'intercept_redirects' => false,
));
}
}
protected function configureRoutes(RouteCollectionBuilder $routes)
{
// import the WebProfilerRoutes, only if the bundle is enabled
if (isset($this->bundles['WebProfilerBundle'])) {
$routes->import('@WebProfilerBundle/Resources/config/routing/wdt.xml', '/_wdt');
$routes->import('@WebProfilerBundle/Resources/config/routing/profiler.xml', '/_profiler');
}
// load the annotation routes
$routes->import(__DIR__.'/../src/Controller/', '/', 'annotation');
}
// optional, to use the standard Symfony cache directory
public function getCacheDir()
{
return __DIR__.'/../var/cache/'.$this->getEnvironment();
}
// optional, to use the standard Symfony logs directory
public function getLogDir()
{
return __DIR__.'/../var/log';
}
}
Unlike the previous kernel, this loads an external config/framework.yaml
file,
because the configuration started to get bigger:
- YAML
- XML
- PHP
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# config/framework.yaml
framework:
secret: S0ME_SECRET
templating:
engines: ['twig']
profiler: { only_exceptions: false }
This also loads annotation routes from an src/Controller/
directory, which
has one file in it:
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// src/Controller/MicroController.php
namespace App\Controller;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\Routing\Annotation\Route;
class MicroController extends Controller
{
/**
* @Route("/random/{limit}")
*/
public function randomNumber($limit)
{
$number = rand(0, $limit);
return $this->render('micro/random.html.twig', array(
'number' => $number
));
}
}
Template files should live in the Resources/views/
directory of whatever directory
your kernel lives in. Since Kernel
lives in src/
, this template lives
at src/Resources/views/micro/random.html.twig
:
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<!-- src/Resources/views/micro/random.html.twig -->
<!DOCTYPE html>
<html>
<head>
<title>Random action</title>
</head>
<body>
<p>{{ number }}</p>
</body>
</html>
Finally, you need a front controller to boot and run the application. Create a
public/index.php
:
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// public/index.php
use Symfony\Component\HttpFoundation\Request;
require __DIR__.'/../src/Kernel.php';
$kernel = new Kernel('dev', true);
$request = Request::createFromGlobals();
$response = $kernel->handle($request);
$response->send();
$kernel->terminate($request, $response);
That's it! This /random/10
URL will work, Twig will render, and you'll even
get the web debug toolbar to show up at the bottom. The final structure looks like
this:
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your-project/
├─ config/
│ └─ framework.yaml
├─ public/
| └─ index.php
├─ src/
| ├─ Kernel.php
| ├─ Controller
| | └─ MicroController.php
│ └─ Resources
| └─ views
| └─ micro
| └─ random.html.twig
├─ var/
| ├─ cache/
│ └─ log/
├─ vendor/
│ └─ ...
├─ composer.json
└─ composer.lock
As before you can use PHP built-in server:
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cd public/
$ php -S localhost:8000
Then see webpage in browser: