终止或中断java 8流循环

terminate or break java 8 stream loop

提问by vach

I have a java 8 stream loop with the following content:

我有一个包含以下内容的 java 8 流循环：

    void matchSellOrder(Market market, Order sellOrder) {
        System.out.println("selling " + market.pair() + " : " + sellOrder);

        market.buyOrders()
                .stream()
                .filter(buyOrder -> buyOrder.price >= sellOrder.price)
                .sorted(BY_ASCENDING_PRICE)
                .forEach((buyOrder) -> {
                    double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
                    double price = buyOrder.price;

                    buyOrder.quantity -= tradeVolume;
                    sellOrder.quantity -= tradeVolume;

                    Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
                    CommonUtil.convertToJSON(trade);

                    if (sellOrder.quantity == 0) {
                        System.out.println("order fulfilled");
                        // break loop there
                    }
                });
    }

How can I break out of loop when some condition is met? Whats the right way to close stream anyway?

满足某些条件时如何跳出循环？无论如何，关闭流的正确方法是什么？

UPDATE

更新

I was misusing streams tecnique assuming that it is a loop, it is not designed for that. Here's the code I've ended up using answer provided below:

我误用了流技术，假设它是一个循环，它不是为此而设计的。这是我最终使用下面提供的答案的代码：

        List<Order> applicableSortedBuyOrders = market.buyOrders()
                .stream()
                .filter(buyOrder -> buyOrder.price >= sellOrder.price)
                .sorted(BY_ASCENDING_PRICE)
                .collect(toList());

        for(Order buyOrder : applicableSortedBuyOrders){
            double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
            double price = buyOrder.price;

            buyOrder.quantity -= tradeVolume;
            sellOrder.quantity -= tradeVolume;

            Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
            CommonUtil.printAsJSON(trade);

            if (sellOrder.quantity == 0) {
                System.out.println("order fulfilled");
                break;
            }
        }

采纳答案by fabian

Stream.forEachis not a loop and it's not designed for being terminated using something like break. If the stream is a parallel stream the lambda body could be executed on different threads at the same time (not easy to break that and it could easyly produce incorrect results).

Stream.forEach不是循环，也不是为了使用类似的东西终止而设计的break。如果流是并行流，则 lambda 主体可以同时在不同线程上执行（不容易破坏它，并且很容易产生不正确的结果）。

Better use a iterator with a while loop:

最好使用带有 while 循环的迭代器：

Iterator<BuyOrderType> iter = market.buyOrders() // replace BuyOrderType with correct type here
            .stream()
            .filter(buyOrder -> buyOrder.price >= sellOrder.price)
            .sorted(BY_ASCENDING_PRICE).iterator();
while (iter.hasNext()) {
    BuyOrderType buyOrder = iter.next()  // replace BuyOrderType with correct type here
    double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
    double price = buyOrder.price;

    buyOrder.quantity -= tradeVolume;
    sellOrder.quantity -= tradeVolume;

    Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
    CommonUtil.convertToJSON(trade);

    if (sellOrder.quantity == 0) {
        System.out.println("order fulfilled");
        break;
    }
}

回答by Tiago Henrique Engel

Well, there is no method to do this in the stream api, (as far as i know).

好吧，在流 api 中没有方法可以做到这一点（据我所知）。

But if you really need it, you can use an Exception.

但是如果你真的需要它，你可以使用异常。

EDIT:For the people giving -1 to this answer I'm not advertising this as an approach one should follow, it's just an option for the cases where you need it, and it does answer the question.

编辑：对于给这个答案给出 -1 的人，我不是在宣传这是一种应该遵循的方法，它只是您需要它的情况下的一种选择，它确实回答了这个问题。

public class BreakException extends RuntimeException {...}

try {
    market.buyOrders()
            .stream()
            .filter(buyOrder -> buyOrder.price >= sellOrder.price)
            .sorted(BY_ASCENDING_PRICE)
            .forEach((buyOrder) -> {
                double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
                double price = buyOrder.price;

                buyOrder.quantity -= tradeVolume;
                sellOrder.quantity -= tradeVolume;

                Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
                CommonUtil.convertToJSON(trade);

                if (sellOrder.quantity == 0) {
                    System.out.println("order fulfilled");
                    throw new BreakException()
                }
            });
} catch (BreakException e) {
    //Stoped
}