code: private XmlReaders readResp(final String xml) {
          XmlReaders readers = XmlReaders.create(xml, wepay.respEncode);
          String returnCode = readers.getNodeStr(WepayField.RETURN_CODE);
          if (WepayField.SUCCESS.equals(returnCode)){
              String resultCode = readers.getNodeStr(WepayField.RESULT_CODE);
              if (WepayField.SUCCESS.equals(resultCode)){
                  return readers;
              }
              throw new WepayException(
                      readers.getNodeStr(WepayField.ERR_CODE),
                      readers.getNodeStr(WepayField.ERR_CODE_DES));
          }
          throw new WepayException(
                  readers.getNodeStr(WepayField.RETURN_CODE),
                  readers.getNodeStr(WepayField.RETURN_MSG));
      }
docs: 读取微信xml响应
  @param xml xml字符串
  @return 若成功，返回对应Reader，反之抛WepayException