You can automatically encode into Json, your complex entity with:
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Normalizer\GetSetMethodNormalizer;
use Symfony\Component\Serializer\Encoder\JsonEncoder;
$serializer = new Serializer(array(new GetSetMethodNormalizer()), array('json' => new
JsonEncoder()));
$json = $serializer->serialize($entity, 'json');