Locale Sessions in Symfony

LocaleListener.php

<?php

class LocaleListener implements EventSubscriberInterface
{
    private $defaultLocale;

    public function __construct($defaultLocale = User::DEFAULT_LOCALE)
    {
        $this->defaultLocale = $defaultLocale;
    }

    public function onKernelRequest(GetResponseEvent $event)
    {
        $request = $event->getRequest();

        if (!$request->hasPreviousSession()) {
            return;
        }

        if (false === $request->getSession()->isStarted()) {
            $request->getSession()->start();
        }

        // try to see if the locale has been set as a _locale routing parameter
        if ($locale = $request->attributes->get('_locale')) {
            $request->getSession()->set('_locale', $locale);
        } else {
            // if no explicit locale has been set on this request, use one from the session
            $request->setLocale($request->getSession()->get('_locale', $this->defaultLocale));
        }
    }

    /**
     * Returns an array of event names this subscriber wants to listen to.
     *
     * The array keys are event names and the value can be:
     *
     *  * The method name to call (priority defaults to 0)
     *  * An array composed of the method name to call and the priority
     *  * An array of arrays composed of the method names to call and respective
     *    priorities, or 0 if unset
     *
     * For instance:
     *
     *  * array('eventName' => 'methodName')
     *  * array('eventName' => array('methodName', $priority))
     *  * array('eventName' => array(array('methodName1', $priority), array('methodName2'))
     *
     * @return array The event names to listen to
     *
     * @api
     */
    public static function getSubscribedEvents()
    {
        return array(
            // must be registered before the default Locale listener
            KernelEvents::REQUEST => array(
                array(
                    'onKernelRequest',
                    17,
                ),
            ),
        );
    }
}

services.yml

services:
    User.localeListener:
        class: User\UserBundle\EventListener\LocaleListener
        arguments: ["%kernel.default_locale%"]
        tags:
            - { name: kernel.event_subscriber }