Reducing a list of Mono<Boolean>

Question

I am working on a task which I have to reduce a list of Mono to a single Mono.

fun isValid(val: Int): Mono<Boolean> {
    return Mono.just(true)
}

fun checkValue(): Mono<Boolean> {
    val times = listOf(5, 10)
    
    return times.map{ 
        isValid(it)
    }.reduce()
}

Would someone able to help with finding a way to reduce a list of Mono's to a single Mono

Answer 1

Combine the Monos into a Flux. Then apply the reduce operator.

Given a list of Mono<Boolean>:

List<Mono<Boolean>> monos = listOf(
    Mono.just(true),
    Mono.just(false)
);

Combine them into a Flux:

Flux<Boolean> flux = Flux.merge(monos);

// or if you want sequential evaluation instead of concurrent...
// Flux<Boolean> flux = Flux.concat(monos);

Apply the reduce operator:

Mono<Boolean> reduced = flux.reduce((a, b) -> a && b);
// if you only need at least one value to be true, replace && with ||

And finally evaluate it:

Boolean evaluated = reduced.block();

All together, the whole thing looks like this:

Boolean evaluated = Flux.merge(monos)
    .reduce((a, b) -> a || b)
    .block();