I have a validator method that returns a Mono<Boolean>.
The validation is happening as expected and returns bad request exception in case of invalid id1 or id2.

public static Mono<Boolean> validate(String id1, String id2) {
   //some condition to check id1 & id2.
   // either return Mono.just(false)/mono.just(true)
   // or return Mono.error(new BadRequestException("")); 
}

However, the control is going to the next line instead of returning from the execution.
Here is the method where the validator method is referred:

public Flux<FacilitiesResponse> validateAndGetFacilityResponse(String id1, String id2) {
    validate(id1,id2);
    return facilityService.getFacilityResponse(id1,id2);  
 }

The validator method returns Mono<Boolean>, but the method returns Flux<FacilitiesResponse>. How to re-write this whole method in reactive way such that it returns Flux< FacilitiesResponse> ?

I tried something like below:

return validate(id1,id2)
       .filter(valid -> valid)
       .map(valid -> facilityService.getFacilityResponse(id1,id2)) 

but it gives me Mono<Flux< FacilitiesResponse>> instead.

Unfortunately, I cannot change the return type of facilityService.getFacilityResponse(id1,id2).

>Solution :

In your first example nothing happens with validate(id1,id2); because no one subscribes to it. You should build your reactive chain from the start to the end.

To return Flux after the successful validation you should use flatMapMany()

return validate(id1,id2)
        .filter(valid -> valid)
        .flatMapMany(__ -> facilityService.getFacilityResponse(id1,id2));

From flatMapMany() docs:

 * Transform the item emitted by this {@link Mono} into a Publisher, then forward  * its emissions into the returned {@link Flux}.