java - 将循环转换为 lambda 并抛出异常

Question

我如何在 java8 中使用 lambda 表达式编写以下代码。我是 Java 8 的新手。

for (GlobalPricingRequest globalPricingRequest : globalPricingRequests) {
    BigDecimal feePerTrans = globalPricingRequest.getFeePerTransact();
    if (feePerTrans != null && feePerTrans.intValue() < 0) {
        throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");
    }
    List<EventTypePricingMapping> eventTypePricingMappings = globalPricingRequest.getEventTypePricingList();
    for (EventTypePricingMapping eventTypePricingMapping : eventTypePricingMappings) {
        BigDecimal feePerRevenue = eventTypePricingMapping.getFeePerRevenue();
        if (feePerRevenue != null && feePerRevenue.intValue() < 0) {
            throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");
        }
        if (eventTypePricingMapping.getFeePerRevenue().intValue() < 0) {
            throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");
        }
    }
}

我已经按照建议尝试了以下代码。我们是否可以在此代码中改进其他任何东西，以便更多地使用 lambda 来编写它。

globalPricingRequests.forEach((globalPricingRequest) -> {
    if (checkIfValueLessThanZero(globalPricingRequest.getFeePerTransact())) {
        throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");
    }
    List<EventTypePricingMapping> eventTypePricingMappings = globalPricingRequest.getEventTypePricingList();
    eventTypePricingMappings.forEach((eventTypePricingMapping) -> {
        if (checkIfValueLessThanZero(eventTypePricingMapping.getFeePerRevenue())) {
            throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");
        }
        if (checkIfValueLessThanZero(eventTypePricingMapping.getFeePerReg())) {
            throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");
        }
    });
});


private boolean checkIfValueLessThanZero(Object object) {
    if (object instanceof BigDecimal) {
       if (object != null && ((BigDecimal) object).intValue() < 0) {
           return true;
       }
    }
    return false;
}

Answer 1

问题

您的问题不在于 lambda，而在于代码组织。你有一个数据，即 List<GlobalPricingRequest>和一组验证规则。您需要做的就是将这些验证规则应用于给定数据。

这种方法使您可以灵活地轻松添加或删除验证规则。并分别测试或检查每条规则。

解决方案

最佳解决方案是将每个验证拆分为单独的类。

首先，为验证规则创建管理器和接口(interface):

public final class GlobalPricingRequestValidationManager {

    private final List<ValidationRule> validationRules =
            Arrays.asList(
                new TransactionFeeEqualOrGreaterThanZeroValidationRule(),
                new RevenueFeeEqualOrGreaterThanZeroValidationRule());

    public void validate(List<GlobalPricingRequest> globalPricingRequests) {
        validationRules.forEach(validationRule -> validationRule.validate(globalPricingRequests));
    }

    public interface ValidationRule {

        void validate(List<GlobalPricingRequest> globalPricingRequests);
    }

}

其次，在单独的类中实现每个验证规则(已添加到管理器):

public final class TransactionFeeEqualOrGreaterThanZeroValidationRule implements GlobalPricingRequestValidationManager.ValidationRule {

    @Override
    public void validate(List<GlobalPricingRequest> globalPricingRequests) {
        if (globalPricingRequests.stream()
                                 .map(GlobalPricingRequest::getFeePerTransact)
                                 .filter(Objects::nonNull)
                                 .anyMatch(val -> val.signum() == -1)))
            throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");
    }
}

public final class RevenueFeeEqualOrGreaterThanZeroValidationRule implements GlobalPricingRequestValidationManager.ValidationRule {

    @Override
    public void validate(List<GlobalPricingRequest> globalPricingRequests) {
        if (globalPricingRequests.stream()
                                 .map(GlobalPricingRequest::getEventTypePricingList)
                                 .flatMap(List::stream)
                                 .map(EventTypePricingMapping::getFeePerRevenue)
                                 .filter(Objects::nonNull)
                                 .anyMatch(val -> val.signum() == -1)))
            throw ExceptionHelper.badRequest("Fee Per Transaction can't be less than zero");

    }
}

---

客户端代码:

GlobalPricingRequestValidationManager validationManager = new GlobalPricingRequestValidationManager();
List<GlobalPricingRequest> globalPricingRequests = Collections.emptyList();
validationManager.validate(globalPricingRequests);