在命名空间下使用AnnotationReader

I have a class under namespace framework\ext\Library and use Doctrine\Common\Annotations\AnnotationReader, however when I try to create an instance of AnnotationReader, it throws a class not found exception.

namespace framework\ext\Library;

use Doctrine\Common\Annotations\AnnotationReader;
class CommonFunction {
  public function getAnno(){
    ...
    $annotationReader = new AnnotationReader();
    ...
  }
}

the error throws

Fatal error: Class 'Doctrine\Common\Annotations\AnnotationReader' not found

I have try to remove the namespace of my CommonFunction it works fine. How to fix it?