How do I submit requests to REST api in batches in SpringBoot?

Question

I have a list of bulk request objects like

List<BulkRequests> bulkRequest;

I want submit them one by one to an external REST API I have already built a FiegnClient for that. Is there any optimised way to submit them one by one (submit next one only when the last one succeeds or in reactive manner) ? The bulk request class is something like this.

class BulkRequest {
  String traceId;
  List<MyRequest> myRequests;
}

Answer 1

For that you should maybe follow a reactive approach for send bulk requests.

Considering that you feign client is already implemented or looks like this :

  @FeignClient(name = "external-api", url = "http://your-api-url.com")
public interface ExternalAPIFeignClient {
    @PostMapping("/endpoint")
    Mono<ResponseEntity<?>> sendRequest(@RequestBody MyRequest request);
}

Keys things to do ar the following.

• Configure my Bulk request service.

• Map all of my requests from the batch

• Use Flux or MonoFlux reactive approach to send them in bulk.

   @Service
   public class RequestService {
  
       private final ExternalAPIFeignClient externalAPIFeignClient;
  
       @Autowired
       public RequestService(ExternalAPIFeignClient externalAPIFeignClient) {
           this.externalAPIFeignClient = externalAPIFeignClient;
       }
  
       public Flux<ResponseEntity<?>> sendRequestsInBatch(List<MyRequest> bulkRequests) {
           return Flux.fromIterable(bulkRequests)
                   .flatMapSequential(request -> externalAPIFeignClient.sendRequest(request));
       }
   }
  

fromIterable creates a reactive stream and flatMapSequential makes sure sequences executed one after the other.

Your controller should look like this :

@RestController
@RequestMapping("/api")
public class RequestController {

    private final RequestService requestService;

    @Autowired
    public RequestController(RequestService requestService) {
        this.requestService = requestService;
    }

    @PostMapping("/bulk-requests")
    public Flux<ResponseEntity<?>> sendBulkRequests(@RequestBody List<MyRequest> bulkRequests) {
        return requestService.sendRequestsInBatch(bulkRequests);
    }
}

Please bear in mind that you might need also to deal with error handling and retry mechanism, by implementing error and retry events.