Doctrine 2 orm：schema-tool无法创建模式

I'm learning Doctrine 2 with the Doctrine 2 ORM tutorial on Marco Pivetta's website.

Now I'm staying on the sheet 33 "Generating the schema" and trying to execute the code $ php doctrine-cli.php orm:schema-tool:create. But instead of the expected success message, I'm getting the complete content of my entity class file:

namespace Entity;

use Doctrine\ORM\Mapping as ORM;

/** 
 * @ORM\Entity
 */
class Greeting
{
    /**
      * @ORM\Id()
      * @ORM\Column(type="integer")
      * @ORM\GeneratedValue(strategy="AUTO")
      * @var int
      */
    private $id;

    /**
     * @ORM\Column(type="string", length=255)
     * @var string
     */
    private $content;

    public function __construct($content) {
        $this->setContent($content);
    }

    /**
     * @return int
     */
    public function getId() {
        return $this->id;
    }

    /**
     * @return string
     */
    public function getContent() {
        return $this->content;
    }

    /**
     * @param string $content
     */
    public function setContent($content) {
        $this->content = (string) $content;
    }

}

And following message under it:

No Metadata Classes to process.

What can be the cause of this problem? How to fix it?