java - 使用java 8转换为map(拆分spring并制作key，对象的其他值作为value)

Question

我的Order类如下:

class Order {
    String orderId;
    String executionId;

    Order(String orderId, String executionId) {
        this.orderId = orderId;
        this.executionId = executionId;
    }

    public String getOrderId() {
        return orderId;
    }

    public void setOrderId(String orderId) {
        this.orderId = orderId;
    }

    public String getExecutionId() {
        return executionId;
    }

    public void setExecutionId(String executionId) { 
        this.executionId = executionId; 
    }
}

List<Order> orders =
                Arrays.asList( new Order("2", "23,21,25"),
                        new Order("4", "22,24"),
                        new Order("6", "27"),
                        new Order("2", "28,30"),
                        new Order("4", "29"),
                        new Order("5", "26"));

我需要根据以下结构输出一个map对象来获取与执行相关的订单

Map<String, String> = {"23","2"},{"21","2"},{"25","2"},{"22","4"},{"24","4"},{"27","6"},{"28","2"},{"30","2"},{"29","4"},{"26","5"};

逗号分隔的值应被视为映射键，对象的其他值应被视为值。

Answer 1

我会选择像下面这样的东西 -

    Map<String, String> flatMap = new HashMap<>();

    orders.forEach(order -> {
        String k = order.orderId;
        String values = order.executionId;

        for (String v : values.split(",")) {
            flatMap.put(v, k);
        }

    });

不是单行的方法，但我更喜欢可读性。

这是不太受欢迎的方法 -

Map<String, String> flatMap = orders.stream()
        .map(order -> Arrays.stream(order.executionId.split(","))
                .collect(Collectors.toMap(Function.identity(), x -> order.orderId)))
        .flatMap(map -> map.entrySet().stream())
        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));