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

Use Flux.hasElements() : Mono function:

return customerFlux.hasElements()
                   .flatMap {
                     if (it) ok().body(customerFlux)
                     else noContent().build()
                   }