Mono returning empty list - spring-boot

Question

I am trying to call getProductContract() but it returns an empty list. I think that's because the Mono is not being executed.
Can someone pls help me on how to execute the calls so that I get the populated resultList back?
Sample code
//Controller.java:
service.getProductContract()
// Service.java
public Mono<List<ProductContract>> getProductContract() {
Set<String> productIdList = new HashSet<>();
productIdList.add("p123");
productIdList.add("p456");
List<ProductContract> resultList = new ArrayList<>();
productIdList.forEach(productId -> prodRepository.getProductDetails(productId)
.flatMap(productDetail -> prodRepository.getProductContracts(productDetail.getProductContractId()))
.mapNotNull(contracts -> resultList.add(contracts.stream().findFirst().isPresent()? contracts.stream().findFirst().get():null))
.subscribeOn(Schedulers.boundedElastic())
);
log.info("size {}",String.valueOf(resultList.size())); //-> Size is ZERO
return Mono.just(resultList);
}
// Repository.java
public Mono<List<ProductContract>> getProductContracts (String contractId){...} // can return multiple contacts for 1 id
public Mono<String> getProductDetails(String productId){...}

Answer 1

This productIdList....flapMap... block is executed asynchronously, when printing the size in the log.info, it was zero indicates the execution is not completed.
A better way to assemble all resources in your case is like this.
return Flux.fromIterable(productIdList)
.flatMap(productId -> prodRepository.getProductDetails(productId))
.flatMap(p-> ....getContacts)
.map(....build a contact dto instance...)
If you want to return a Mono<List<ContactDto>>, just call Flux.collectList.