在Vert.x中顺序减少Future

Question

在我的项目中，我使用Java中Vert.x的Future实现。到目前为止一切都很顺利。然而，目前我有问题执行一个动作的对象列表顺序。问题在于reduce方法在Java中分别“reduce”和“sombining”结果。这将导致所有操作同时启动。实现顺序执行是可能的，可以在easy方法中看到这一点。

private Future<Void> action(String object) {
    System.out.println("started " + object);
    Future<Void> f = Future.future();
    vertx.setTimer(1000, res -> {
        System.out.println("doing " + object);
        f.complete();
    });
    return f;
}

private void easy() {
    action("one")
        .compose(ignore -> action("two"))
        .compose(ignore -> action("three"))
        .setHandler(ignore -> System.out.println("completed"));
}

private void list() {
    List<String> l = new ArrayList<>();
    l.add("one");
    l.add("two");
    l.add("three");

    Future<Void> f = Future.future();
    l.stream().reduce(f,
        (f1, s) -> action(s),
        (f1, f2) -> f2.compose(ignore -> f1)
    ).setHandler(res -> {
        System.out.println("completed");
    });
}

执行Easy时的输出：

started one
doing one
started two
doing two
started three
doing three
completed

started one
started two
started three
doing one
doing two
doing three
completed

function action(object) {
  return new Promise((resolve, reject) => {
    console.log("started " + object)
    window.setTimeout(() => {
      console.log("doing " + object);
      resolve()
    }, 1000);
  });
}

function easy() {
  action("one")
    .then(() => action("two"))
    .then(() => action("three"))
    .then(() => console.log("completed"));
}

function list() {
  l = ["one", "two", "three"]
  l.reduce((p, s) => p.then(() => action(s)), Promise.resolve())
    .then(() => console.log("completed"));
}

// easy()
list()

easy和list的输出与Java代码的easy方法相同。我正在寻找的是一种修复Java中reduce方法的方法，或者一种实现相同结果的替代方法。

Answer 1

好啦。我在这里找到了一个foldLeft方法的实现，现在顺序执行工作正常...

private void list() {
    List<String> l = new ArrayList<>();
    l.add("one");
    l.add("two");
    l.add("three");

    Future<Void> f = Future.succeededFuture();

    foldLeft(l.iterator(), f,
        (f1, s) -> f1.compose(ignore -> action(s)))
        .setHandler(res -> {
            System.out.println("completed");
        });
}

private static <A, B> B foldLeft(Iterator<A> iterator, B identity, BiFunction<B, A, B> bf) {
    B result = identity;
    while(iterator.hasNext()) {
        A next = iterator.next();
        result = bf.apply(result, next);
    }
    return result;
}