问没有应用Symfony 4 DateTimeNormalizer服务

EN

datetime_normalizer:
    class: App\Normalizer\DateTimeNormalizer
    public: true
    tags: [serializer.normalizer]

<?php
namespace App\Normalizer;

use Symfony\Component\Serializer\Normalizer\NormalizerInterface;

/**
 * Class DateTimeNormalizer
 */
class DateTimeNormalizer implements NormalizerInterface
{
    /**
     * {@inheritdoc}
     */
    public function normalize($object, $format = null, array $context = array())
    {
        return $object->format(\DateTime::ISO8601);
    }
    /**
     * {@inheritdoc}
     */
    public function supportsNormalization($data, $format = null)
    {
        return $data instanceof \DateTime;
    }
}

 $classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));

 $normalizer = new ObjectNormalizer($classMetadataFactory);

 $serializer = new Serializer([$normalizer]);

 $user = $serializer->normalize($token->getUser());

"datetime":{"timezone":{"name":"UTC","transitions":[{"ts":-9223372036854775808,"time":"-292277022657-01-27T08:29:52+0000","offset":0,"isdst":false,"abbr":"UTC"}],"location":{"country_code":"??","latitude":0,"longitude":0,"comments":""}},"offset":0,"timestamp":1527033600}