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javakotlinreactor

Create Mono Array Object with keeping original ordering

I need to implement function that returns Mono< Array< ProcessedObject>>. As argument it takes list of objects and process them with function that returns Mono< ProcessedObject>. Function needs to keep original order, meaning first element on returned list must be created from first element from argument list. So far i have following solution but it doesn't keep required order. Is it even possible with Flux?

       private fun createItems(objects: List<Someobjects>): Mono<Array<ProcessedObject>> {
         return Flux.fromIterable(objects)
           .flatMap {
             processObject(it)
           }.collectList().map { it.toTypedArray() }
}

Edit: to clarify a little processObject returns Mono< ProcessedObject>

Solution

  • You can try with concatMap instead of flatMap.

    Here is a link for the Docu https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Flux.html#concatMap-java.util.function.Function-

    private fun createItems(objects: List<Someobjects>): Mono<Array<ProcessedObject> {
         return Flux.fromIterable(objects)
           .concatMap {
             processObject(it)
           }.collectList().map { it.toTypedArray() }
}

    The difference between flatMap and concatMap is that the later preserves the original order.