code: public static String toXml(final Map<String, String> params) {
          XmlWriters writers = XmlWriters.create();
          for (Map.Entry<String, String> param : params.entrySet()){
              if (!Strings.isNullOrEmpty(param.getValue())){
                  writers.element(param.getKey(), param.getValue());
              }
          }
          return writers.build();
      }
docs: Map转换为XML
  @param params Map参数
  @return XML字符串