Java 8 - 如何使用 CompletableFuture 跟踪异步并行流中调用的异常数

Question

Sorry for the confusing title, what I am trying to is track the number of times a method that is executed asynchronously has thrown an exception, while also retrieving the results that executed successfully into a class variable. I think my implementation is quite off though, would a List of CompletableFutures be more appropriate here than a CompletableFuture of a List?

public class testClass {

    private List<Integer> resultNumbers;

    public void testMethod() {

        int exceptions = 0;
        try {
            methodWithFuture();
        catch (InterruptedException | ExecutionException e) {
            exceptions++;
        }
        System.out.println("Number of times the addNumber method threw an exception=" + exceptions);
    }

    public void methodWithFuture() throws InterruptedException, ExecutionException {

        List<Integer> numbersList = Arrays.asList(new Integer[] { 1, 2, 3 })
        CompletableFuture<List<Integer>> futuresList = CompletableFuture.supplyAsync(() -> 
            numbersList.parallelStream().map(number -> addNumber(number))).collect(Collectors.toList()),
            new ForkJoinPool(3));

        resultNumbers.addAll(futuresList.get());
    }
}

Answer 1

So looking at your code you will only ever get at most 1 exception. A better CompletableFuture call for each call to addNumber. Then check whether it is exceptional.

public void testMethod(){

    int exceptions = 0;

    List<Integer> numbersList = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13);
    List<CompletableFuture<Integer>> cfList = new ArrayList<>();

    for(int number : numbersList){
        CompletableFuture<Integer> cf = methodWithFuture(number);
        cfList.add(cf);
    }

    CompletableFuture<Void> allOfCF = CompletableFuture.allOf(cfList.toArray(new CompletableFuture[0]));       
    try {allOf.get();} catch (InterruptedException | ExecutionException ignored) {}

    int sum = 0;
    for(CompletableFuture<Integer> cf : cfList){
        if(cf.isCompletedExceptionally()){
            exceptions ++;
        } else {
            sum += cf.get();
        }
    }

    System.out.println("Number of times the addNumber method threw an exception=" + exceptions);
    System.out.println("SUM " + sum);
}


public CompletableFuture<Integer> methodWithFuture(int number) {
    return CompletableFuture.supplyAsync(() -> addNumber(number));
}

Here I have submitted each call to addNumber asynchronously and waited to join them all after they are completed by using allOf