I'm creating a REST-client with a `@Cacheable` method. Since `@Cacheable` is broken for suspend func...

# spring

[Emil Kantis]

I'm creating a REST-client with a @Cacheable method. Since @Cacheable is broken for suspend functions, I tried to do this with reactor-types for the specific method instead. Looks something like this:

@Cacheable("my-cache")
fun fetchThing(key: String): Mono<Thing> = 
  webClient.get("/thing/{key}", key)
    .retrieve()
    .bodyToMono()

Now, in the code where I use this. I want to bridge back into awesome realm of suspend (😉), so I do: restClient.fetchThing(key).awaitSingle() . However, it seems that invoking awaitSingle() twice on a Mono created this way will actually cause the webrequest to fire again, instead of lazily returning the already existing result in the Mono.. Does anyone know the proper way to get back to suspend functions after creating a Mono like this? Should I map the mono to a lazy mono of first result or something?

[nfrankel]

do you need annotations?

[Emil Kantis]

Hmm, not really, tbh prefer not to.. I just need to cache 🙂

[nfrankel]

then you can inject the cache
cf. https://github.com/hazelcast-demos/imperative-to-reactive/blob/kotlin/src/main/java/org/hazelcast/cache/CachingService.kt#L14-L22

[Emil Kantis]

Thanks, I'll give that a shot 🙂

[nfrankel]

hope it helps

[Emil Kantis]

It did. Integration test succeeds now.

suspend fun fetchThing(key: String): Thing =
        thingCache.get(key, Thing::class.java) ?: webClient.get()
            .uri("/thing/{key}", key)
            .retrieve()
            .awaitBody<Thing>().also {
                offeringCache.put(key, it)
            }

I guess this will put prometheus metrics that @Cacheable normally generates out of play however.. 😕

[nfrankel]

not sure...
@Cacheable just hides the magic
but metrics depend on the underlying cache
what are you using?

[Emil Kantis]

Using Caffeine, and the Cache and CacheManager are both registered in Spring context, so maybe it'll work then 🤔

[nfrankel]

yes, it has nothing to do with annotation
the annotation will just make the method a proxy
and spring will check the cache before calling the real method under the cover

[Emil Kantis]

True. And it's working.. 🙂

# HELP cache_gets_total the number of times cache lookup methods have returned an uncached (newly loaded) value, or null
# TYPE cache_gets_total counter
cache_gets_total{cache="things",cacheManager="cacheManager",name="things",result="hit",} 8.0
cache_gets_total{cache="things",cacheManager="cacheManager",name="things",result="miss",} 1.0

[Emil Kantis]

Thanks a lot Nicolas 🙇🙂

[nfrankel]

you’re welcome!