CODEWITHSUNDEEP
javaspring-webfluxproject-reactor
Gabriel Magalhães
Gabriel Magalhães

Reputation: 100

Retrieving data from context and use it on doOnNext() from Spring Webflux

I have a correlation ID stored in context (by using contextWrite) and I'd like to recover and use it in the doOnNext(), in which I implement some logging from previous data transformations.

Here's an example of what I achieved till now:

Mono.just("message")
   ...
   .doOnNext(it -> Mono.deferContextual(ctx -> Mono.just(ctx)
      .doOnNext(c -> log.info("correlation-id: "+ c.get(CORRELATION_ID)))))
   .subscribe();

Is this the only way to achieve what I want? It seems a little odd to me somehow. I'm still learning and I've been reading the context section from the Reactor doc, but I couldn't find anything that approximates what I'm trying to achieve.

UPDATE 1

I managed to achieve something like that (and didn't have to Mono.just() 2x):

Mono.deferContextual(ctx ->
   Mono.just("message")
      ...
      .doOnNext(it -> log.info("correlation-id: " + ctx.get(CORRELATION_ID)))
);

Still don't know if that is a best practice, but looks way better than the previous one

UPDATE 2

Reading and digging a little deeper into the code and documentation, I discovered that Mono.deferContextual() returns a Mono (my mistake for not noticing that before).As a result, for the first scenario, flatMap() should be used instead of doOnNext(). To simulate the doOnNext() function, I'll have to refactor a little more to return the same received object on flatMap().

UPDATE 3

I think that I got to the final code with transformDeferredContextual(). According to the reactor documentation:

to access the context from the middle of an operator chain, use transformDeferredContextual(BiFunction)

Applying to my scenario:

Mono.just("message")
   ...
   .transformDeferredContextual((originalMono, context) -> {
         log.info("correlation-id: " + context.get(CORRELATION_ID)))
         
         return originalMono;
   })
   .subscribe();
);

It seems a bit odd, but till now, this seems like the best approach.

Upvotes: 1

Views: 4129

Answers (1)

lkatiforis
lkatiforis

Reputation: 6255

Something similar but prettier than your final approach:

Mono.just("message")
   ...
    .transformDeferredContextual((originalMono, context) -> originalMono.doOnNext(e -> {
           log.info("correlation-id: " + context.get(CORRELATION_ID));
   }))

Upvotes: 3

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