Encode doctrine entities to json symfony 2

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');