MonetaryAmount的使用
可以在MonetaryAmount上进行算术运算:
MonetaryAmount twelveEuro = fiveEuro.add(sevenEuro); // "EUR 12"
MonetaryAmount twoEuro = sevenEuro.subtract(fiveEuro); // "EUR 2"
MonetaryAmount sevenPointFiveEuro = fiveEuro.multiply(1.5); // "EUR 7.5"
// MonetaryAmount can have a negative NumberValue
MonetaryAmount minusTwoEuro = fiveEuro.subtract(sevenEuro); // "EUR -2"
// some useful utility methods
boolean greaterThan = sevenEuro.isGreaterThan(fiveEuro); // true
boolean positive = sevenEuro.isPositive(); // true
boolean zero = sevenEuro.isZero(); // false
// Note that MonetaryAmounts need to have the same CurrencyUnit to do mathematical operations
// this fails with: javax.money.MonetaryException: Currency mismatch: EUR/USD
fiveEuro.add(tenUsDollar);
舍入操作是金额换算里面非常重要的一部分。MonetaryAmount可以使用舍入操作符来进行四舍五入:
CurrencyUnit usd = MonetaryCurrencies.getCurrency("USD");
MonetaryAmount dollars = Money.of(12.34567, usd);
MonetaryOperator roundingOperator = MonetaryRoundings.getRounding(usd);
MonetaryAmount roundedDollars = dollars.with(roundingOperator); // USD 12.35
这里12.3456美金就会按当前货币默认的舍入规则来进行换算。
在操作MonetaryAmount集合时,有许多实用的工具方法可以用来进行过滤,排序以及分组。这些方法还可以与Java 8的流API一起配套使用。
看一下下面这个集合:
List<MonetaryAmount> amounts = new ArrayList<>();
amounts.add(Money.of(2, "EUR"));
amounts.add(Money.of(42, "USD"));
amounts.add(Money.of(7, "USD"));
amounts.add(Money.of(13.37, "JPY"));
amounts.add(Money.of(18, "USD"));
我们可以根据CurrencyUnit来进行金额过滤:
CurrencyUnit yen = MonetaryCurrencies.getCurrency("JPY");
CurrencyUnit dollar = MonetaryCurrencies.getCurrency("USD");
// 根据货币过滤,只返回美金
// result is [USD 18, USD 7, USD 42]
List<MonetaryAmount> onlyDollar = amounts.stream()
.filter(MonetaryFunctions.isCurrency(dollar))
.collect(Collectors.toList());
// 根据货币过滤,只返回美金和日元
// [USD 18, USD 7, JPY 13.37, USD 42]
List<MonetaryAmount> onlyDollarAndYen = amounts.stream()
.filter(MonetaryFunctions.isCurrency(dollar, yen))
.collect(Collectors.toList());
我们还可以过滤出大于或小于某个阈值的金额:
MonetaryAmount tenDollar = Money.of(10, dollar);
// [USD 42, USD 18]
List<MonetaryAmount> greaterThanTenDollar = amounts.stream()
.filter(MonetaryFunctions.isCurrency(dollar))
.filter(MonetaryFunctions.isGreaterThan(tenDollar))
.collect(Collectors.toList());
排序也是类似的:
// Sorting dollar values by number value
// [USD 7, USD 18, USD 42]
List<MonetaryAmount> sortedByAmount = onlyDollar.stream()
.sorted(MonetaryFunctions.sortNumber())
.collect(Collectors.toList());
// Sorting by CurrencyUnit
// [EUR 2, JPY 13.37, USD 42, USD 7, USD 18]
List<MonetaryAmount> sortedByCurrencyUnit = amounts.stream()
.sorted(MonetaryFunctions.sortCurrencyUnit())
.collect(Collectors.toList());
还有分组操作:
// 按货币单位进行分组
// {USD=[USD 42, USD 7, USD 18], EUR=[EUR 2], JPY=[JPY 13.37]}
Map<CurrencyUnit, List<MonetaryAmount>> groupedByCurrency = amounts.stream()
.collect(MonetaryFunctions.groupByCurrencyUnit());
// 分组并进行汇总
Map<CurrencyUnit, MonetarySummaryStatistics> summary = amounts.stream()
.collect(MonetaryFunctions.groupBySummarizingMonetary()).get();
// get summary for CurrencyUnit USD
MonetarySummaryStatistics dollarSummary = summary.get(dollar);
MonetaryAmount average = dollarSummary.getAverage(); // "USD 22.333333333333333333.."
MonetaryAmount min = dollarSummary.getMin(); // "USD 7"
MonetaryAmount max = dollarSummary.getMax(); // "USD 42"
MonetaryAmount sum = dollarSummary.getSum(); // "USD 67"
long count = dollarSummary.getCount(); // 3
MonetaryFunctions还提供了归约函数,可以用来获取最大值,最小值,以及求和:
List<MonetaryAmount> amounts = new ArrayList<>();
amounts.add(Money.of(10, "EUR"));
amounts.add(Money.of(7.5, "EUR"));
amounts.add(Money.of(12, "EUR"));
Optional<MonetaryAmount> max = amounts.stream().reduce(MonetaryFunctions.max()); // "EUR 7.5"
Optional<MonetaryAmount> min = amounts.stream().reduce(MonetaryFunctions.min()); // "EUR 12"
Optional<MonetaryAmount> sum = amounts.stream().reduce(MonetaryFunctions.sum()); // "EUR 29.5"
自定义的MonetaryAmount操作
MonetaryAmount还提供了一个非常友好的扩展点叫作MonetaryOperator。MonetaryOperator是一个函数式接口,它接收一个MonetaryAmount入参并返回一个新的MonetaryAmount对象。
// A monetary operator that returns 10% of the input MonetaryAmount
// Implemented using Java 8 Lambdas
MonetaryOperator tenPercentOperator = (MonetaryAmount amount) -> {
BigDecimal baseAmount = amount.getNumber().numberValue(BigDecimal.class);
BigDecimal tenPercent = baseAmount.multiply(new BigDecimal("0.1"));
return Money.of(tenPercent, amount.getCurrency());
};
MonetaryAmount dollars = Money.of(12.34567, "USD");
// apply tenPercentOperator to MonetaryAmount
MonetaryAmount tenPercentDollars = dollars.with(tenPercentOperator); // USD 1.234567
标准的API特性都是通过MonetaryOperator的接口来实现的。比方说,前面看到的舍入操作就是以MonetaryOperator接口的形式来提供的。
汇率
货币兑换率可以通过ExchangeRateProvider来获取。JavaMoney自带了多个不同的ExchangeRateProvider的实现。其中最重要的两个是ECBCurrentRateProvider与 IMFRateProvider。
ECBCurrentRateProvider查询的是欧洲中央银行(European Central Bank,ECB)的数据而IMFRateProvider查询的是国际货币基金组织(International Monetary Fund,IMF)的汇率。
// get the default ExchangeRateProvider (CompoundRateProvider)
ExchangeRateProvider exchangeRateProvider = MonetaryConversions.getExchangeRateProvider();
// get the names of the default provider chain
// [IDENT, ECB, IMF, ECB-HIST]
List<String> defaultProviderChain = MonetaryConversions.getDefaultProviderChain();
// get a specific ExchangeRateProvider (here ECB)
ExchangeRateProvider ecbExchangeRateProvider = MonetaryConversions.getExchangeRateProvider("ECB");