How can I get a hold of the argument of an asynchronous callback 'onResponse'?

Question

I'm implementing a GraphQL client in a Java application using Apollo's auto generation of queries, and so far I've been able to chain calls and I also get the data I want. The issue is that Apollo makes me implement the anonymous method ApolloCall.Callback<>() which overrides void onResponse(Response response) and void onFailure(), but I'm unable to find a way to get a hold of this Response object, which I want to collect and make sure I have.

This is a Spring Boot project on Java 11, I've tried to make use of CompletableFuture but with limited knowledge of it and how to use it for this particular problem I feel out of luck. I've also tried to implement the RxJava support that Apollo is supposed to have but I couldn't resolve dependency issues with that approach.

I'm pretty sure that futures will solve it but again I don't know how.

  public void getOwnerIdFromClient() {
    client
        .query(getOwnerDbIdQuery)
        .enqueue(
            new ApolloCall.Callback<>() {
              @Override
              public void onResponse(@Nonnull Response<Optional<GetOwnerDbIdQuery.Data>> response) {
                int ownerId =
                    response
                        .data()
                        .get()
                        .entities()
                        .get()
                        .edges()
                        .get()
                        .get(0)
                        .node()
                        .get()
                        .ownerDbId()
                        .get();

                System.out.println("OwnerId = " + ownerId);
              }

              @Override
              public void onFailure(@Nonnull ApolloException e) {
                logger.error("Could not retrieve response from GetOwnerDbIdQuery.", e);
              }
            });
  }

Since I wish to work with this int ownerId outside of the onResponse this isn't a sufficient solution. I'd actually like to make this call x amount of times, and create a list of all the id's I actually got, since this might return a null id as well, which means I need some way to wait for them all to finish.

Answer 1

You are right, this can be done using Futures:

• change return type to Future
• complete the future in onResponse

Approximately:

public Future<Integer> getOwnerIdFromClient(){
    Future<Integer> result=new CompletableFuture<Integer>();

    client
    .query(getOwnerDbIdQuery)
    .enqueue(
    new ApolloCall.Callback<>(){
        @Override
        public void onResponse(@Nonnull Response<Optional<GetOwnerDbIdQuery.Data>>response){
                // get owner Id
                System.out.println("OwnerId = "+ownerId);
                result.complete(ownerId)
                }

        @Override
        public void onFailure(@Nonnull ApolloException e){
                logger.error("Could not retrieve response from GetOwnerDbIdQuery.",e);result.completeExceptionally(e);


                }
        });

    return result;

}