WebFlux functional: How to detect an empty Flux and return 404?

Question

I\'m having the following simplified handler function (Spring WebFlux and the functional API using Kotlin). However, I need a hint how to detect an empty Flux and then use n

Answer 1

In addition to the solution of Brian, if you are not want to do an empty check of the list all the time, you could create a extension function:

fun  Flux.collectListOrEmpty(): Mono> = this.collectList().flatMap {
        val result = if (it.isEmpty()) {
            Mono.empty()
        } else {
            Mono.just(it)
        }
        result
    }

And call it like you do it for the Mono:

return customerFlux().collectListOrEmpty()
                     .switchIfEmpty(notFound().build())
                     .flatMap(c -> ok().body(BodyInserters.fromObject(c)))