Join the result of several microservice in a Mono - spring-webflux

Question

I try to develop a api with spring-cloud-gateway but it's not easy for me
My "microservice A" return an Mono. This Object contains a List of id "Object B"
My "microservice B" return an Flux
In my api-gateway, how can i aggregate in a Mono the result of the microservices ?
#Service
public class ServiceAClient {
private final WebClient webClient;
public ServiceAClient(WebClient.Builder builder) {
this.webClient = builder.baseUrl("lb://microservice-A/A/").build();
}
public Mono<ObjectA> getObjectA(String id){
return webClient
.get()
.uri("{id}" , id)
.retrieve()
.bodyToMono(ObjectA.class)
.onErrorResume(ex->Mono.empty());
}
}
#Service
public class ServiceBClient {
private final WebClient webClient;
public ServiceAClient(WebClient.Builder builder) {
this.webClient = builder.baseUrl("lb://microservice-B/B/").build();
}
public Flux<ObjectB> getListObjectB(List<Long> ids){
return webClient
.get()
.uri("{ids}" , ids)
.retrieve()
.bodyToFlux(ObjectB.class);
}
}
#Data
public class ObjectA {
private UUID id;
private String name;
private String description;
private Date start;
private Date end;
private List<Long> listIdObjectB;
}
#Data
public class ObjectB {
private Long id;
private String name;
private String localisation;
}
#Data
public class MyDto {
private UUID id;
private String name;
private String description;
private Date start;
private Date end;
private List<ObjectB> listObjectB;
}
#Service
#AllArgsConstructor
public class CombinedService {
private final ServiceAClient serviceAClient;
private final ServiceBClient serviceBClient;
public Mono<MyDto> getDetails(String id){
// return MyDto who join a Mono Service A an Flux service B
}
}
The desired result
{
"id": "2355e7eb-edf7-428c-b51b-ac06c146ed3c",
"name": "toto",
"description": "lorem ipsum",
"debut": 01/06/2022,
"fin": 10/06/2022,
"ListObjectB": [
{
"id": 1,
"name": "foo",
"localisation": "here"
},
{
"id": 2,
"name": "bar",
"localisation": "here"
}
]
}
Thank you in advance for your help

Answer 1

You can take it as a start point to understand a possible solution.
I highly recommend you to read about reactive streams(https://www.reactive-streams.org/) and spring-webflux(https://docs.spring.io/spring-framework/docs/current/reference/html/web-reactive.html).
Your CombinedService should looks like:
#Service
#AllArgsConstructor
public class CombinedService {
private final ServiceAClient serviceAClient;
private final ServiceBClient serviceBClient;
public Mono<MyDto> getDetails(String id) {
return serviceAClient.getObjectA(id)
.map(objectA -> {
final Flux<ObjectB> fluxB = serviceBClient.getListObjectB(objectA.getListIdObjectB());
final List<ObjectB> listObjectB = fluxB.toStream().collect(Collectors.toList());
final MyDto myDto = new MyDto();
myDto.setName(objectA.getDescription());
myDto.setDescription(objectA.getDescription());
myDto.setListObjectB(listObjectB);
//More setters, etc
return myDto;
});
}
}