Spring Webflux and @Cacheable - proper way of caching result of Mono / Flux type

I have used Oleh Dokuka's hacky solution worked great but there is a catch. You must use a greater Duration in Flux cache than your Cachable caches timetolive value. If you dont use a duration for Flux cache it wont invalidate it (Flux documentation says "Turn this Flux into a hot source and cache last emitted signals for further Subscriber."). So making Flux cache 2 minutes and timetolive 30 seconds can be valid configuration. If ehcahce timeout occurs first, than a new Flux cache reference is generated and it will be used.

Hack way

For now, there is no fluent integration of @Cacheable with Reactor 3. However, you may bypass that thing by adding .cache() operator to returned Mono

@Repository
interface TaskRepository : ReactiveMongoRepository<Task, String>

@Service
class TaskService(val taskRepository: TaskRepository) {

    @Cacheable("tasks")
    fun get(id: String): Mono<Task> = taskRepository.findById(id).cache()
}

That hack cache and share returned from taskRepository data. In turn, spring cacheable will cache a reference of returned Mono and then, will return that reference. In other words, it is a cache of mono which holds the cache :).

Reactor Addons Way

There is an addition to Reactor 3 which allows fluent integration with modern in-memory caches like caffeine, jcache, etc. Using that technique you will be capable to cache your data easily:

@Repository
interface TaskRepository : ReactiveMongoRepository<Task, String>

@Service
class TaskService(val taskRepository: TaskRepository) {

    @Autowire
    CacheManager manager;


    fun get(id: String): Mono<Task> = CacheMono.lookup(reader(), id)
                                               .onCacheMissResume(() -> taskRepository.findById(id))
                                               .andWriteWith(writer());

    fun reader(): CacheMono.MonoCacheReader<String, Task> = key -> Mono.<Signal<Task>>justOrEmpty((Signal) manager.getCache("tasks").get(key).get())
    fun writer(): CacheMono.MonoCacheWriter<String, Task> = (key, value) -> Mono.fromRunnable(() -> manager.getCache("tasks").put(key, value));
} 

Note: Reactor addons caching own abstraction which is Signal<T>, so, do not worry about that and following that convention