Sample Normalizers (see http://thomas.jarrand.fr/blog/serialization/ )

CollectionNormalizer.php

<?php

namespace Acme\Serializer\Normalizer;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
use Symfony\Component\Serializer\Normalizer\SerializerAwareNormalizer;

/**
 * Collection Normalizer
 */
class CollectionNormalizer extends SerializerAwareNormalizer implements NormalizerInterface, DenormalizerInterface
{
    /**
     * {@inheritdoc}
     */
    public function supportsNormalization($data, $format = null)
    {
        return is_object($data) && $data instanceof Collection;
    }

    /**
     * {@inheritdoc}
     */
    public function supportsDenormalization($data, $type, $format = null)
    {
        return is_array($data) && in_array('\Doctrine\Common\Collections\Collection', class_implements($type));
    }

    /**
     * {@inheritdoc}
     */
    public function normalize($object, $format = null, array $context = array())
    {
        return $object->map(function ($item) use ($format, $context) {
            return $this->serializer->normalize($item, $format, $context);
        })->getValues();
    }

    /**
     * {@inheritdoc}
     */
    public function denormalize($data, $class, $format = null, array $context = array())
    {
        return new ArrayCollection(array_map(function ($item) use ($class, $format, $context) {
            return $this->deserialize($item, $class, $format, $context);
        }, $data));
    }
}

DateTimeNormalizer.php

<?php

namespace Acme\Serializer\Normalizer;

use DateTime;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;

/**
 * DateTime Normalizer
 */
class DateTimeNormalizer implements NormalizerInterface, DenormalizerInterface
{
    /**
     * Date format
     *
     * @var string
     */
    protected $dateFormat = 'Y-m-d';

    /**
     * {@inheritdoc}
     */
    public function supportsNormalization($data, $format = null)
    {
        return is_object($data) && $data instanceof DateTime;
    }

    /**
     * {@inheritdoc}
     */
    public function supportsDenormalization($data, $type, $format = null)
    {
        return $type === 'DateTime';
    }

    /**
     * {@inheritdoc}
     */
    public function normalize($object, $format = null, array $context = array())
    {
        return $object->format($this->dateFormat);
    }

    /**
     * {@inheritdoc}
     */
    public function denormalize($data, $class, $format = null, array $context = array())
    {
        return new DateTime($data);
    }
}

FormErrorNormalizer.php

<?php

namespace Acme\Serializer\Normalizer;

use Symfony\Component\Form\FormError;
use Symfony\Component\Form\FormErrorIterator;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
use Symfony\Component\Validator\ConstraintViolation;

/**
 * Form Error Normalizer
 */
class FormErrorNormalizer implements NormalizerInterface
{
    /**
     * {@inheritdoc}
     */
    public function supportsNormalization($data, $format = null)
    {
        return is_object($data) && ($data instanceof FormError || $data instanceof FormErrorIterator);
    }

    /**
     * {@inheritdoc}
     */
    public function normalize($object, $format = null, array $context = array())
    {
        if ($object instanceof FormErrorIterator) {
            $errors = [];

            foreach ($object as $key => $error) {
                $errors[] = $this->normalizeError($error);
            }

            return $errors;
        }

        return $this->normalizeError($object);
    }

    /**
     * Normalize error
     *
     * @param FormError $error
     *
     * @return array
     */
    private function normalizeError(FormError $error)
    {
        return [
            'message'    => $error->getMessage(),
            'parameters' => $error->getMessageParameters(),
            'plural'     => $error->getMessagePluralization(),
            'code'       => $error->getMessageTemplate(),
            'path'       => $this->getPath($error),
        ];
    }

    /**
     * Get path for the given error
     *
     * @param FormError $error
     *
     * @return string
     */
    private function getPath(FormError $error)
    {
        if ($error->getCause() instanceof ConstraintViolation) {
            return $error->getCause()->getPropertyPath();
        }

        return null;
    }
}