Flux into Mono List Object - project reactor

Question

I'm using project reactor and I've the next issue:

I've one method that return Mono<CustomerResponse> that contains a CustomerDto list, each client has attributes, one of theirs attributes is a payment list. But this payment list is null.

I've another method that receive client id and returns a Flux payment Flux<PaymentDto> for that client.

This are the model

public class CustomerResponse {
    private List<CustomerDto> customers;
}

public class CustomerDto {
    private int id;
    private String fullname;
    private String documentNumber;
    private List<PaymentDto> payments;
}

These are the interfaces

public interface CustomerService {
    public Mono<CustomerResponse> customerSearch(CustomerRequest request);
}
public interface PaymentService {
    public Flux<PaymentDto> getPayments(int clientId);
}

This is my method

public Mono<CustomerResponse> getCustomer(CustomerRequest request) {
    return customerService.customerSearch(request).map(resp -> resp.getCustomers())
            .flatMap(customerList -> {
                List<CustomerDto> newCustomerList = customerList.parallelStream().map(customer -> {
                    Flux<PaymentDto> paymentFlux = 
                            paymentService.getPayments(customer.getId());
                    
                    // Here: java.lang.IllegalStateException: block()/blockFirst()/blockLast()
                    customer.setPayments(paymentFlux.collectList().block());
                    return customer;
                }).collect(Collectors.toList());
                
                return Mono.just(new CustomerResponse(newCustomerList));
            });
}

I've the next exception:

java.lang.IllegalStateException: block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-4
    at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:83) ~[reactor-core-3.3.6.RELEASE.jar:3.3.6.RELEASE]
    Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:

I would like to know if there is a non-blocking or optimal way to do it

It seems like the payment call must be blocking since the customer depends on the payment list. Did you try running this without using parallelStream()? That may be giving you issues. Perhaps there's a way you can restructure the code. You could get the customer and then in some service class make the call to get the payments and set them there. — Steven Diamante, Jul 22 '20 at 03:05

score 0 · Answer 1 · answered Jul 22 '20 at 12:42

You can refactor your code like this to avoid blocking call:

  public Mono<CustomerResponse> getCustomer(CustomerRequest request) {
    Flux<CustomerDto> customerDtoFluxEnriched = customerService.customerSearch(request)
        .map(CustomerResponse::getCustomers).flatMapMany(Flux::fromIterable).flatMap(customerDto -> {
          Flux<PaymentDto> paymentFlux = paymentService.getPayments(customerDto.getId());
          Mono<List<PaymentDto>> paymentListMono = paymentFlux.collectList();
          return paymentListMono.map(paymentList -> {
            customerDto.setPayments(paymentList);
            return customerDto;
          });
        });
    return customerDtoFluxEnriched.collectList().map(customerList -> {
      CustomerResponse customerResponse = new CustomerResponse();
      customerResponse.setCustomers(customerList);
      return customerResponse;
    });
  }

Flux into Mono List Object - project reactor

1 Answers1