public function validate()
    {
        if (!empty($this->required)) {
            $invalid = array_diff($this->required, array_keys($this->request->args()));
            if (!empty($invalid)) {
                foreach ($invalid as $argKey) {
                    $this->request->addResult("{$argKey} required for this request.");
                }
                throw new ActionException($this, "Required arguments " . implode(', ', $invalid) . " not specified.");
            }
        }
    }