CompletableFuture.allOf that doens't return Void(CompletableFuture.allOf不能返回Void的解决方法)

import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {

    static CompletableFuture<List<?>> allOf(CompletableFuture<?>... cfs) {
        return CompletableFuture.allOf(cfs)
                .thenApply(ignore -> Stream.of(cfs)
                        .map(cf -> cf.join())
                        .collect(Collectors.toList()));
    }

    public static void main(String[] args) {

        // we have 3 (or any number) of CompletableFutures
        CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {sleep(1); return "HELLO";});
        CompletableFuture<Integer> cf2 = CompletableFuture.supplyAsync(() -> {sleep(1); return 10;});
        CompletableFuture<Double> cf3 = CompletableFuture.supplyAsync(() -> {sleep(1); return 20d;});

        CompletableFuture<List<?>> allOf = allOf(cf1, cf2, cf3); //we call the method we just created above

        // we can get the -already there - result either using then
        // Get result using:
        allOf.thenAccept(l -> l.forEach(System.out::println));

        // or using CompletableFuture.join() (or CompletableFuture.get())
        // OR (non-typesafe)
        String s = (String) allOf.join().get(0);
        Integer i = (Integer) allOf.join().get(1);
        Double d = (Double) allOf.join().get(2);
        System.out.println(s + ", " + i + ", "+ d);

        sleep(2); // because default CompletableFuture Executor is a daemon-thread based executor
    }

    private static void sleep(int seconds) {
        try {
            TimeUnit.SECONDS.sleep(seconds);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

摘录地址:​​http://m-hewedy.blogspot.com/2017/02/completablefutureallof-that-doenst.html​​