Dependant webclient calls - Spring Reactive

Question

I am trying to do two API calls, the second API call is dependent on the first API response. The following piece of code gives response for first weblient call.Here I am not getting the response from second API call. On log I could see that the request for the second webclient call is not even started with onSubscribe(). Can you please tell me what mistake am I doing.

@Autowired
Issue issue;

List issueList = new ArrayList<>();

public Mono<Response> getResponse(Request request) {
   return webClient.post()
     .uri("myURI")
     .body(Mono.just(request),Request.class)
     .retrieve()
     .bodyToMono(Response.class)
     .flatMap(resp->{
           resp.getIssues().stream()
              .forEach(issueTemp -> {
                 issue = issueTemp;
                 webClient.get()
                    .uri("mySecondURI" + issueTemp.getId())
                    .retrieve()
                    .bodyToMono(Issue.class)
                     .flatMap(issueTemp2-> {
                        issue.setSummary(issueTemp2.getSummary());
                        return Mono.just(issue);
                     }).log();
           issueList.add(issue);
        });

        Response responseFinal = new Response();
        responseFinal.setIssues(issueList);
        return Mono.just(responseFinal);
    }).log();
}

UPDATE 2:

I have changed my code to Functions and used Flux instead of stream iterations.What I am facing now is , all the iterations are get filtered out in doSecondCall method. Please refer my comment in doSecondCall method. Due to which the second call is not triggered. If i dont apply the filter, there are requests triggered like "issue/null" which also causes my service to go down.

 public Mono<Response> getResponse(Request request) {
   return webClient.post()
     .uri("myURI")
     .body(Mono.just(request),Request.class)
     .retrieve()
     .bodyToMono(Response.class)
     .flatMap(r->
         doSecondCall(r).flatMap(issueList->{
             r.setIssues(issueList);
             return Mono.just(r);
           })
     );
}

public Mono<Issue> doSecondCall(Response r) {
          return Flux.fromIterable(r.getIssues())
                      .filter(rf->rf.getId()!=null) //everything gets filtered out
                      .flatMap(issue->getSummary(issue.getId()))
                      .collectList();
  }


public Mono<Issue> getSummary(Response r) {
          return webClient.get()
                       .uri("issue/"+id)
                       .retrieve()
                       .bodyToMono(Issue.class).log();

   }

[ How does Reactive programming using WebFlux handles dependent external api calls ] @Thomas- Also ,Just found this thread. He basically says unless you block the first call, there is no way to declare the second one. Is that the case?

Answer 1

Why you are not triggering the second calls is because you are breaking the chain as i have mentioned in this answer (with examples).

Stop breaking the chain

// here...
.forEach(issueTemp -> {
    issue = issueTemp; // and this is just silly? why?
    webClient.get() // Here you are calling the webClient but ignoring the return value, so you are breaking the chain.
        .uri("mySecondURI" + issueTemp.getId())
        .retrieve()
        .bodyToMono(Issue.class)
        .flatMap(issueTemp2-> {
            issue.setSummary(issueTemp2.getSummary());
            return Mono.just(issue); // Return here but you are ignoring this return value
        }).log();
    issueList.add(issue);
});

You should use more functions to divide up your code. Make it a habit by writing a function and always start with the return statement. You code is very hard to read.

I think you should instead use a FLux instead of iterating a stream.

// something like the following i'm writing by free hand without IDE
// i have no idea what your logic looks like but you should get the point.
Flux.fromIterable(response.getIssues())
   .flatMap(issue -> {
       return getIssue(issue.getId())
           .flatMap(response -> {
               return issue.setSummary(reponse.getSummary());
           });
   }).collectList();