Right using of mapping in WebFlux

Question

public Mono<EmailDto> getEmail() {
Mono<EmailService> emailService = ReactiveSecurityContextHolder.getContext()
                    .map(securityContext -> (Principal) securityContext.getAuthentication().getPrincipal())
                    .map(principal -> emailServiceSelector.selectSuitable(principal.getInfo()));

return emailService.map(service -> service.findInfoByEmail(dto.getManagerEmail())) }

But I have a problem with this method, because emailService.map(service -> service.findInfoByEmail(dto.getManagerEmail())) returns Mono<Mono<EmailDto>>. Implementation of findInfoByEmail(String email) is

public Mono<EmailDto> findInfoByEmail(String email) {
        return webClient.get()
                .uri(emailServiceProperties.getUrl(), email)
                .retrieve()
                .bodyToMono(EmailDto.class);
}

My method returns Mono<EmailDto>, not Mono<Mono<EmailDto>>. So, my question is: How to tranform Mono<Mono<EmailDto>> to Mono<EmailDto>? Or mb I am totally wrong and method should return Mono<Mono<EmailDto>>? Looking forward to any help.

If you have a `Mono` and another `Mono` you need to pass control to then use `Mono::flatMap`. — K.Nicholas, Jul 21 '20 at 04:54
@AbhinabaChakraborty yes, ty very much. It's exactly what I couldn't understand. — Vladimir Safonov, Jul 22 '20 at 07:45

score 0 · Accepted Answer · answered Jul 20 '20 at 16:54

There is a difference between a flatmap and map. flatMap should be used for non-blocking operations, or in short anything which returns back Mono,Flux. map should be used when you want to do the transformation of an object /data in fixed time. The operations which are done synchronously.

Your findInfoByEmail is making an async call.

Thus you should use:

return emailService.flatMap(service -> service.findInfoByEmail(dto.getManagerEmail())) }

This is from the official doc

score 0 · Answer 2 · answered Dec 16 '20 at 07:59

You are doing everything right but you need to use flatMap() in place of map(). map is used to transform the particular object into other where as flatMap() is used to transform all 1 to N objects into Mono in you case. So you can use below snippet:-

return emailService.flatMap(service -> service.findInfoByEmail(dto.getManagerEmail())) }

Right using of mapping in WebFlux

2 Answers2