Flatten Java Futures

Just use the method thenCompose instead of thenApply:

CompletableFuture<Boolean> result = doA().thenCompose(b -> b
    ? CompletableFuture.completedFuture(Boolean.TRUE) : doB());

If the creation of the nested future is beyond your control, you can flatten it like this:

static <T> CompletableFuture<T> flatten(
  CompletableFuture<CompletableFuture<T>> nestedFuture) {
    return nestedFuture.thenCompose(Function.identity());
}