如何在symfony2中将对象转换为JSON

composer require jms/serializer-bundle

public function registerBundles()
{
    $bundles = array(
        // ...
        new JMS\SerializerBundle\JMSSerializerBundle(),
    );
    // ...
}

namespace AppBundle\Entity;

class User
{
    private $id;
    private $name;
    private $email;

    // Getter and setter methods
    // ...
}

public function someAction()
{
    // ...
    $user = new User();
    $user->setId(1);
    $user->setName('John Doe');
    $user->setEmail('john.doe@example.com');

    $serializer = $this->get('serializer');
    $json = $serializer->serialize($user, 'json');
    // ...
}