如何实现具有可完成未来的具有 Mono/Flux 的 Reactive Framework 中存在的.switchIfEmpty() 类型的方法？

Question

Mono<String> getData1(){
  return someApiClient.getData();
}

Mono<String> getData2(){
  return someCacheClient.getData();
}

Mono<Object> callingMethod(){
  return getData2().switchIfEmpty(getData1());
}

How do I convert the "callingMethod" if my implementation is like this

CompletableFuture<String> getData1(){
  return someApiClient.getData().toFuture();
}

CompletableFuture<String> getData2(){
  return someCacheClient.getData().toFuture();
}

CompletableFuture<String> callingMethod(){
  // How to do it here? I am not getting any way. 
  // I need to achieve similar functionality like .switchIfEmpty here
}

I tried to search different articles online but did not find any. Please help me out here.

Answer 1

Unlike Reactor types, CompletableFuture is able to handle null values, so you can use that to represent empty state and do action based on that:

CompletableFuture<String> callingMethod(){
    return getData2()
        .thenCompose(cached -> cached == null 
            ? getData1() 
            : CompletableFuture.completedFuture(cached));
}