code: public static <I> JMFileSubscriber<I> buildJsonStringFileSubscriber(
              String filePath, Function<Object, String> toStringFunction) {
          return new JMFileSubscriber<>(filePath, toStringFunction);
      }
docs: Build json string file subscriber jm file subscriber.
  
  @param <I>              the type parameter
  @param filePath         the file path
  @param toStringFunction the to string function
  @return the jm file subscriber