如何避免方法中的 if 语句获取可选参数

Question

当我们有带有可选参数的服务方法时，如何避免 if 语句？下面是例子。目前只有 3 个参数是可选的，我必须有很多 if 语句。是否存在解决此问题的设计模式？

public List<Order> getForHotelOrders(Long hotelId, Optional<LocalDate> fromDate, Optional<LocalDate> toDate, Optional<List<String>> paymentTypes) {
    List<Order> orders;
    if (fromDate.isPresent() && toDate.isPresent()) {
        if (paymentTypes.isPresent()) {
            orders = orderRepository.getForHotel(hotelId, fromDate.get(), toDate.get(), paymentTypes.get());
        } else {
            orders = orderRepository.getForHotel(hotelId, fromDate.get(), toDate.get(), Arrays.asList("CASH", "CARD"));
        }
    } else {
        if (paymentTypes.isPresent()) {
            orders = orderRepository.getForHotel(hotelId, paymentTypes.get());
        } else {
            orders = orderRepository.getForHotel(hotelId, Arrays.asList("CASH", "CARD"));
        }

    }
    return orders;
}

Answer 1

我会用orElse

static final List<String> CASH_CARD = Arrays.asList("CASH", "CARD");

public List<Order> getForHotelOrders(Long hotelId, 
                                     Optional<LocalDate> fromDate, 
                                     Optional<LocalDate> toDate, 
                                     Optional<List<String>> paymentTypes) {
    List<String> paymentTypes2 = paymentTypes.orElse(CASH_CARD);
    return fromDate.isPresent() && toDate.isPresent() 
       ? orderRepository.getForHotel(hotelId, fromDate.get(), toDate.get(), paymentTypes2)
       : orderRepository.getForHotel(hotelId, paymentTypes);
}

或

public List<Order> getForHotelOrders(long hotelId, 
                                     Optional<LocalDate> fromDate, 
                                     Optional<LocalDate> toDate, 
                                     Optional<List<String>> paymentTypes) {
    return orderRepository.getForHotel(hotelId, 
                                       fromDate.orElse(LocalDate.MIN),
                                       toDate.orElse(LocalDate.MAX),
                                       paymentTypes.orElse(CASH_CARD));
}

顺便说一句：如果您要避免使用 null 值，我会将 hotelId 设置为 long 或 OptionalLong。具有可为空的 Long 似乎不一致。

Answer 2

可以使用 orElse（默认），克服多个 if else...

public List<Order> getForHotelOrders(Long hotelId, Optional<LocalDate> fromDate, Optional<LocalDate> toDate, Optional<List<String>> paymentTypes) {
    List<Order> orders;
    LocalDate defaultDate = LocalDate.now();
    orders = orderRepository.getForHotel(hotelId, fromDate.orElse(defaultDate), toDate.orElse(defaultDate), paymentTypes.orElse(Arrays.asList("CASH", "CARD")));
    return orders;
}

如何避免方法中的 if 语句获取可选参数

How to avoid if statements in method which gets Optional arguments

java

spring-data-jpa

spring-restcontroller