protected function importMapFromFromJsonFile($file)
    {
        // get content from file
        $content = $this->validate(
            $this->readFile($file)
        );

        if (false === $content) {
            throw new Doozr_Di_Exception(
                sprintf('Error while importing dependencies: "%s".', json_last_error_msg())
            );
        }

        if (false === isset($content['map'][0])) {
            throw new Doozr_Di_Exception(
                sprintf('Require key "%s" not found!', 'map')
            );
        }

        return $content['map'][0];
    }