HttpExceptionSubscriberBase::onException

public HttpExceptionSubscriberBase::onException(GetResponseForExceptionEvent $event)

public function onException(GetResponseForExceptionEvent $event) {
  $exception = $event->getException();

  // Make the exception available for example when rendering a block.
  $request = $event->getRequest();
  $request->attributes->set('exception', $exception);

  $handled_formats = $this->getHandledFormats();

  $format = $request->query->get(MainContentViewSubscriber::WRAPPER_FORMAT, $request->getRequestFormat());

  if ($exception instanceof HttpExceptionInterface && (empty($handled_formats) || in_array($format, $handled_formats))) {
    $method = 'on' . $exception->getStatusCode();
    // We want to allow the method to be called and still not set a response
    // if it has additional filtering logic to determine when it will apply.
    // It is therefore the method's responsibility to set the response on the
    // event if appropriate.
    if (method_exists($this, $method)) {
      $this->$method($event);
    }
  }
}