Use Symfony2 Validator Annotations outside of Core - symfony

Question

How do you configure Symfony2 Validator to use annotations outside of Core?
In core you would do the following:
$container->loadFromExtension('framework', array(
'validation' => array(
'enable_annotations' => true,
),
));
Taken from: http://symfony.com/doc/2.0/book/validation.html#configuration
For now to make validation work the rules are set within the method loadValidatorMetadata(ClassMetadata $metadata), it works but I prefer annotations.
Example Entity with validation annotations and alternative php method to set validation rules:
<?php
namespace Foo\BarBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Mapping\ClassMetadata;
use Symfony\Component\Validator\Constraints as Assert;
/**
* #ORM\Entity(repositoryClass="Foo\BarBundle\Entity\Repository\FooRepository")
* #ORM\Table(name="foo")
*/
class Foo {
/**
* #ORM\Column(type="integer", name="bar")
* #Assert\Type(
* type="integer",
* message="The value {{ value }} is not a valid {{ type }}."
* )
*/
protected $bar;
public static function loadValidatorMetadata(ClassMetadata $metadata)
{
$metadata->addPropertyConstraint('bar', new Assert\Type(array(
'type' => 'integer',
'message' => 'The value {{ value }} is not a valid {{ type }}.',
)));
}
}
Update 1
The issue now seems to be that the annotations are not being autoloaded correctly.
I load the annotations in to the namespace with:
\Doctrine\Common\Annotations\AnnotationRegistry
::registerAutoloadNamespace("Symfony\Component\Validator\Constraints\\", __DIR__.'/vendor/symfony/validator');
Then when it tries to autoload the annotations it looks for /vendor/symfony/validator/Symfony/Component/Validator/Constraints/Length.php which does not exist. The file is actually located at /vendor/symfony/validator/Constraints/Length.php
I could create a registerLoader() but would rather fix the code. When using Validator within Symfony2 Core that file location would be correct.
How do I make it autoload correctly or get composer to install Symfony2 components to the same location as core?

Answer 1

You need to register the Autoloader with AnnotationRegistry, so where ever you require vendor/autoload, for example bootstrap.php add the registerLoader().
//Composer libraries
$loader = require_once 'vendor/autoload.php';
\Doctrine\Common\Annotations\AnnotationRegistry::registerLoader([$loader, 'loadClass']);
Turns out the solution is quite straight forward.

Answer 2

The accepted answer provides a solution without giving any explaination regarding the failure.
The reason is simple. The default annotation loader which is provided by the Doctrine\Common\Annotations\AnnotationRegistry only handle PSR-0 namespaces, while the Symfony\Component\Validator\Constraints is a PSR-4 namespace. Thus, the loader fail to load the class. Registering the composer auloader with the AnnotationRegistry::registerLoader method solves the problem because that autoloader handle the PSR-4 namespaces.
You can refer to this question to get more detaits about PSR-0 and PSR-4 differences: What is the difference between PSR-0 and PSR-4?