code: public static String toJSONString(Object o) {
      try {
        return objectMapper.writer().without(SerializationFeature.INDENT_OUTPUT).writeValueAsString(o);
      } catch (JsonProcessingException e) {
        throw new RuntimeException(e);
      }
    }
docs: A not-pretty printed JSON string. Returns a portable JSON string.
  
  @param o the object to serialize
  @return a string representation of the object.