How to access, modify and append the final element in Multi<String>?

[Aravinda93]

Within my application I am dynamically creating and returning the customers in JSON format. I would like to differentiate each customer so I am adding a comma after the creation of each customer but I do not wish to add the comma separation to last element so I would like to remove it.

Hence, I need to access last element and make the modification but I am running into some problem when doing the same. I tried to do this but unable to concatenate the same. I am unable to get the last customer without comma. Following is the code I have:

  public static Multi <String> generate(final Input input) {
      final ObjectMapper objectMapper = new ObjectMapper();

      try {
          final Multi < String > generatedCustomer = Multi.createFrom().publisher(CustomerGenerator.createModels(input)).onItem().transform(
              event - > {
                  try {
                      return objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(event) + ",";
                  } catch (JsonProcessingException e) {
                      e.printStackTrace();
                  }
                  return null;
              });

          final Multi < String > lastCustomer = generatedEvents.select().last().onItem().transform(i - > i.substring(0, i.length() - 1));

          return Multi.createBy().concatenating().streams(generatedCustomer, lastCustomer);

      } catch (Exception e) {
          throw new CustomerException("Exception occurred during the generation of Customer : " + e);
      }
  }

How to achieve this?