join CompletableFuture vs synchronous method

Question

Having:

String getData(String key){
    // Slow operation
}

CompletableFuture<String> getDataAsync(String key){
    return CompletableFuture.supplyAsync(() -> getData(key));
}

What is the difference between the following?

a)

keyStream.map(key -> getData(key));

b)

keyStream.map(key -> getDataAsync(key).join());

Is there any advantage to use async in this case?

Answer 1

IF the stream in both approach a and b are sequentially. there is no different between them, and you should avoiding use it. because you just run the getData in the ForkJoinPool.commonPool() & join the the map method until getData was completed.

IF the stream in both approach a and b are parallelism. there is no different between them too, and you also should avoiding use it. because a parallel stream is already using the ForkJoinPool.commonPool() for its operations.

Answer 2

在您的示例中，此处的用法异步不会对您造成任何影响，因为您正在用此调用join，因此join阻止了呼叫，并且Async将不再是ASync