Spring WebFlux WebClient: delay execution

Question

When I define and call a client method like this:

webClient.get()
            .uri(endpoint)
            .headers(this::configureHttpHeaders)
            .retrieve()
            .bodyToMono(String.class)

the retrieve method gets executed even if I do nothing with the returned Mono.

I would have expected that it only gets called when someone (a subscriber ?) actually want to get data from the Mono.

Why does it get called immediately? How can I change this behaviour?

For more context: in my case I only want it to be executed when CacheFlux onCacheMissResume gets triggered:

    Flux<T> defaulValue= client.getStringMono()
            .flatMapIterable(mapper::readObjects);

    CacheFlux.<String, T>lookup(key -> readFluxFromCache(cacheName, key), cacheKey)
                .onCacheMissResume(defaulValue)
                .andWriteWith((key, valueSignal) -> writeFluxToCache(cacheName, key, valueSignal))

Answer 1

I think it has to do with what is called hot and cold publishers.

You can read more about them here projectreactor.io/docs/core/release/reference/#reactor.hotCold To transform a hot publisher to a cold publisher you can use the defer function.