service返回的默认格式

RESTServer::getResponseFormatter()在没有找到请求格式时,通过getResponseFormatContentTypeNegotiations()方法获取返回格式,没仔细看,貌似是services后台管理界面上面排序的倒序

    if (empty($response_format)) {
      $response_format = $this->getResponseFormatContentTypeNegotiations($mime_type, $canonical_path_not_parsed, $this->formatters);
    }