class FieldNormalizer

class FieldNormalizer extends ListNormalizer implements DenormalizerInterface {
    
    /**
     * {@inheritdoc}
     */
    public function denormalize($data, $class, $format = NULL, array $context = []) : mixed {
        if (!isset($context['target_instance'])) {
            throw new InvalidArgumentException('$context[\'target_instance\'] must be set to denormalize with the FieldNormalizer');
        }
        if ($context['target_instance']->getParent() == NULL) {
            throw new InvalidArgumentException('The field passed in via $context[\'target_instance\'] must have a parent set.');
        }
        
        /** @var \Drupal\Core\Field\FieldItemListInterface $items */
        $items = $context['target_instance'];
        $item_class = $items->getItemDefinition()
            ->getClass();
        if (!is_array($data)) {
            throw new UnexpectedValueException(sprintf('Field values for "%s" must use an array structure', $items->getName()));
        }
        foreach ($data as $item_data) {
            // Create a new item and pass it as the target for the unserialization of
            // $item_data. All items in field should have removed before this method
            // was called.
            // @see \Drupal\serialization\Normalizer\ContentEntityNormalizer::denormalize().
            $context['target_instance'] = $items->appendItem();
            $this->serializer
                ->denormalize($item_data, $item_class, $format, $context);
        }
        return $items;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getSupportedTypes(?string $format) : array {
        return [
            FieldItemListInterface::class => TRUE,
        ];
    }

}