private function __getQueryString($queryAr = array(), $prefixIfNotEmpty = '')
{
$queryAr = array_filter($queryAr);
array_walk($queryAr, function (&$val, $key) {
$val = urlencode($key) . '=' . urlencode($val);
});
return $queryAr ? $prefixIfNotEmpty . join('&', $queryAr) : '';
}