When the Symfony Framework (or anything using the :class:`Symfony\\Component\\HttpKernel\\HttpKernel`) handles a request, a few core events are dispatched so that you can add listeners throughout the process. These are called the "kernel events". For a larger explanation, see :doc:`/components/http_kernel/introduction`.
Each event dispatched by the kernel is a subclass of :class:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent`. This means that each event has access to the following information:
- :method:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent::getRequestType`
- Returns the type of the request (
HttpKernelInterface::MASTER_REQUESTorHttpKernelInterface::SUB_REQUEST). - :method:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent::getKernel`
- Returns the Kernel handling the request.
- :method:`Symfony\\Component\\HttpKernel\\Event\\KernelEvent::getRequest`
- Returns the current
Requestbeing handled.
Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\GetResponseEvent`
This event is dispatched very early in Symfony, before the controller is determined.
.. seealso::
Read more on the :ref:`kernel.request event <component-http-kernel-kernel-request>`.
These are the built-in Symfony listeners registered to this event:
Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\FilterControllerEvent`
This event can be an entry point used to modify the controller that should be executed:
use Symfony\Component\HttpKernel\Event\FilterControllerEvent;
public function onKernelController(FilterControllerEvent $event)
{
$controller = $event->getController();
// ...
// the controller can be changed to any PHP callable
$event->setController($controller);
}
.. seealso::
Read more on the :ref:`kernel.controller event <component-http-kernel-kernel-controller>`.
This is the built-in Symfony listener related to this event:
| Listener Class Name | Priority |
|---|---|
| :class:`Symfony\\Bundle\\FrameworkBundle\\DataCollector\\RequestDataCollector` | 0 |
Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\GetResponseForControllerResultEvent`
This event is not used by the FrameworkBundle, but it can be used to implement
a view sub-system. This event is called only if the Controller does not
return a Response object. The purpose of the event is to allow some
other return value to be converted into a Response.
The value returned by the Controller is accessible via the getControllerResult
method:
use Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent;
use Symfony\Component\HttpFoundation\Response;
public function onKernelView(GetResponseForControllerResultEvent $event)
{
$val = $event->getControllerResult();
$response = new Response();
// ... somehow customize the Response from the return value
$event->setResponse($response);
}
.. seealso::
Read more on the :ref:`kernel.view event <component-http-kernel-kernel-view>`.
Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\FilterResponseEvent`
The purpose of this event is to allow other systems to modify or replace
the Response object after its creation:
public function onKernelResponse(FilterResponseEvent $event)
{
$response = $event->getResponse();
// ... modify the response object
}
The FrameworkBundle registers several listeners:
- :class:`Symfony\\Component\\HttpKernel\\EventListener\\ProfilerListener`
- Collects data for the current request.
- :class:`Symfony\\Bundle\\WebProfilerBundle\\EventListener\\WebDebugToolbarListener`
- Injects the Web Debug Toolbar.
- :class:`Symfony\\Component\\HttpKernel\\EventListener\\ResponseListener`
- Fixes the Response
Content-Typebased on the request format. - :class:`Symfony\\Component\\HttpKernel\\EventListener\\EsiListener`
- Adds a
Surrogate-ControlHTTP header when the Response needs to be parsed for ESI tags.
.. seealso::
Read more on the :ref:`kernel.response event <component-http-kernel-kernel-response>`.
These are the built-in Symfony listeners registered to this event:
Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\PostResponseEvent`
The purpose of this event is to perform tasks after the response was already served to the client.
.. seealso::
Read more on the :ref:`kernel.terminate event <component-http-kernel-kernel-terminate>`.
This is the built-in Symfony listener related to this event:
| Listener Class Name | Priority |
|---|---|
| EmailSenderListener | 0 |
Event Class: :class:`Symfony\\Component\\HttpKernel\\Event\\GetResponseForExceptionEvent`
The TwigBundle registers an :class:`Symfony\\Component\\HttpKernel\\EventListener\\ExceptionListener`
that forwards the Request to a given controller defined by the
exception_listener.controller parameter.
A listener on this event can create and set a Response object, create
and set a new Exception object, or do nothing:
use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;
use Symfony\Component\HttpFoundation\Response;
public function onKernelException(GetResponseForExceptionEvent $event)
{
$exception = $event->getException();
$response = new Response();
// setup the Response object based on the caught exception
$event->setResponse($response);
// you can alternatively set a new Exception
// $exception = new \Exception('Some special exception');
// $event->setException($exception);
}
Note
As Symfony ensures that the Response status code is set to the most
appropriate one depending on the exception, setting the status on the
response won't work. If you want to overwrite the status code (which you
should not without a good reason), set the X-Status-Code header:
$response = new Response(
'Error',
404, // this status code will be ignored
array(
'X-Status-Code' => 200 // this status code will actually be sent to the client
)
);
.. seealso::
Read more on the :ref:`kernel.exception event <component-http-kernel-kernel-exception>`.
These are the built-in Symfony listeners registered to this event:
| Listener Class Name | Priority |
|---|---|
| :class:`Symfony\\Component\\HttpKernel\\EventListener\\ProfilerListener` | 0 |
| :class:`Symfony\\Component\\HttpKernel\\EventListener\\ExceptionListener` | -128 |