Java Return Future that gets executed first with a specific condition, or process both

Question

I have two APIs that return two different Results classes. We combine these two results to get a finalClass.

Basically, if these Apis are run at the Same time ,

1. if it receives Class A first with a certain result (G,H), it doesn't matter what class B is (we will not wait for serviceAPI B), just return Final class from table below.

2. If Class A does not have a certain result, we have to wait for combine both results (A & B) to get Final class.

I'm trying to use these stackoverflow articles, to process this. I prefer not to mark them with an interface marker class (these are legacy objects), however open to it as second option.

Return the future that gets executed first with a specific condition on the response

In java, how do I process CompletableFutures and get the first desireable result that completes?

public class A {
   public String resultA;
}

public class B {
   public int resultB;
}

public class Final {
   public String resultFinal;
}

CompletableFuture<A> futureA = CompletableFuture.supplyAsync(() -> serviceA.getAPI());
CompletableFuture<B> futureB = CompletableFuture.supplyAsync(() -> serviceB.getAPI());

CompletableFuture.allOf(futureA,futureB).join(); 

open to making both classes a marker interface

public class A implements MarkerResponse  {
public class B implements MarkerResponse  {

public interface MarkerResponse  {}

Marker interface

Currently using Spring Boot with Java 8. Context: the real service dual apis can be variable 1-5 min, so trying to do performance improvement if possible.

Answer 1

Since you need the result of A in either case, to determine whether you need the result of B, you can simply chain the decision as a dependent operation on A:

CompletableFuture<Final> result = futureA.thenCompose(a ->
    a.resultA.equals("G") || a.resultA.equals("H")?
        CompletableFuture.completedFuture(new Final("success")):
    futureB.thenApply(b -> new Final(b.resultB == 1? "fail": "error")));

Note that when success is likely and the benefit of running A and B in parallel rather low, you may even decide to commence B only when necessary:

CompletableFuture<Final> result = futureA.thenCompose(a ->
    a.resultA.equals("G") || a.resultA.equals("H")?
        CompletableFuture.completedFuture(new Final("success")):
        CompletableFuture.supplyAsync(
            () -> new Final(serviceB.getAPI().resultB == 1? "fail": "error")));