How to return null if the Mono is empty

Question

I am calling an external service to get externalId, in case of that service doesn't work, all what i need is just populate the value with null

return externalClient.getExternalId() //returns Mono<String> or Mono.empty()
                    .map(id -> {
                        //in case of empty stream, i need call entity.setExternalId(null);
                        entity.setExternalId(id);
                        return entity;
                    });

you could check the streams length with stream().count(). Which terminal operation do you use on the stream? — kosta.dani, Oct 06 '21 at 09:31
Its been awhile, but I thought there was an "empty" Mono, failing that you have two options as I see it, return an `Optional` to indicate your method could return a value or not, or if its an error condition use `Error` i.e `Mono.error` — Gavin, Oct 06 '21 at 09:34

João Dias · Accepted Answer · 2021-10-06T11:05:38.507

1

Try the following:

return externalClient.getExternalId()
                     .map(id -> {
                        entity.setExternalId(id);
                        return entity;
                     })
                     .switchIfEmpty(() -> {
                        entity.setExternalId(null);
                        return Mono.just(entity);
                     });

edited Oct 06 '21 at 11:05

answered Oct 06 '21 at 09:59

João Dias

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the second solution will throw an exception at java.base/java.util.Objects.requireNonNull(Objects.java:246) – Melad Basilius Oct 06 '21 at 11:03
Thanks! The suggestion was removed (I don't use plain webflux for some time now). – João Dias Oct 06 '21 at 11:06

How to return null if the Mono is empty

1 Answers1