symfony2 and throwing exception error

Try:

use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

and

throw new NotFoundHttpException("Page not found");

I think you got it a bit backwards :-)

If its in a controller, you can do it this way :

throw $this->createNotFoundException('Unable to find entity.');

In the controller, you can simply do:

public function someAction(){    // ...    // Tested, and the user does not have permissions    throw $this->createAccessDeniedException("You don't have access to this page!");    // or tested and didn't found the product    throw $this->createNotFoundException('The product does not exist');    // ...}

In this situation, there'se no need to include the use Symfony\Component\HttpKernel\Exception\HttpNotFoundException; at the top. The reason for that is that you're not using the class directly, like using the constructor.

Outside the controller, you must indicate where the class can be found, and throw an exception as you would normally do. Like this:

use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;// ...// Something is missingthrow new HttpNotFoundException('The product does not exist');

or

use Symfony\Component\Security\Core\Exception\AccessDeniedException;// ...// Permissions were deniedthrow new AccessDeniedException("You don't have access to this page!");