Java 9 javax.money.MonetaryAmount（JSR 354）：无法将Pojo转换为XML，反之亦然

Question

I'm using Rest Api call to convert Pojo to XML.

Below is my code snippet:

TestAccount.java

  import javax.money.MonetaryAmount;

    public class TestAccount {


        private MonetaryAmount paymentAmount;

private String accountNumber;


    public String getAccountNumber() {
        return this.accountNumber;
    }


    public void setAccountNumber(String accountNumber) {
        this.accountNumber = accountNumber;
    }
        public MonetaryAmount getPaymentAmount() {
            return this.paymentAmount;
        }


        public void setPaymentAmount(MonetaryAmount paymentAmount) {
            this.paymentAmount = paymentAmount;
        }

        }

Controller.java

public class Controller extends BaseController {

    @RequestMapping(value = "/javaTest", method = RequestMethod.GET, produces = { "application/xml" })
    public TestAccount testMoneyPackage() {
        TestAccount obj = new TestAccount();
        obj.setAccountNumber("101423");
        obj.setPaymentAmount(MoneyUtilityCls.of(10.898));
        return obj;
    }
}

when running the url on browser

http://localhost:8080/api/javaTest

output:

<OverdueAccount>
<accountNumber>101423</accountNumber>
<paymentAmount>
<currency>
<context>
<providerName>java.util.Currency</providerName>
<empty>false</empty>
</context>
<defaultFractionDigits>2</defaultFractionDigits>
<currencyCode>USD</currencyCode>
<numericCode>840</numericCode>
</currency>
<number>10.9</number>*****loss of precision*******
<negative>false</negative>
<zero>false</zero>
<precision>3</precision>
<scale>1</scale>
<positiveOrZero>true</positiveOrZero>
<positive>true</positive>
<negativeOrZero>false</negativeOrZero>
<factory>
<defaultMonetaryContext>
<precision>0</precision>
<amountType>org.javamoney.moneta.RoundedMoney</amountType>
<fixedScale>false</fixedScale>
<maxScale>-1</maxScale>
<providerName/>
<empty>false</empty>
</defaultMonetaryContext>
<amountType>org.javamoney.moneta.RoundedMoney</amountType>
<maxNumber/>
<minNumber/>
<maximalMonetaryContext>
<precision>0</precision>
<amountType>org.javamoney.moneta.RoundedMoney</amountType>
<fixedScale>false</fixedScale>
<maxScale>-1</maxScale>
<providerName/>
<empty>false</empty>
</maximalMonetaryContext>
</factory>
<context>
<precision>0</precision>
<amountType>org.javamoney.moneta.RoundedMoney</amountType>
<fixedScale>false</fixedScale>
<maxScale>-1</maxScale>
<providerName/>
<empty>false</empty>
</context>
</paymentAmount>
</OverdueAccount>

As you can see When setting

od.setPaymentAmount(MoneyUtil.of(10.898));

I'm getting loss of precision in XML as

<number>10.9</number>

Also what are those extra XML tags?

This problem occurs only with MonetaryAmount field otherwise code is running properly. So, What is the Correct way to convert MonetaryAmount field to Pojo to XML and vice versa without losing precision.

Answer 1

Could you share the code of your MoneyUtil/MoneyUtilityCls class?

I am guessing the implementation of MonetaryAmount used is RoundedMoney with a default fraction digits of 1, which would lead to the described behaviour.

The solution in this case would be to make the Utility return another class(Money for example) or to change the number of fraction digits of the returned RoundedMoney object.

Answer 2

"Representing money as a double or float will probably look good at first as the software rounds off the tiny errors, but as you perform more additions, subtractions, multiplications and divisions on inexact numbers, you'll lose more and more precision as the errors add up. This makes floats and doubles inadequate for dealing with money, where perfect accuracy for multiples of base 10 powers is required."

Finally Java has a standard way to work with Currency And Money!

JSR 354: Money and Currency API

JSR 354 provides an API for representing, transporting, and performing comprehensive calculations with Money and Currency. You can download it from this link:

JSR 354: Money and Currency API Download

The specification consists of the following things:

1. An API for handling eg monetary amounts and currencies
2. APIs to support interchangeable implementations
3. Factories for creating instances of the implementation classes
4. Functionality for calculations, conversion and formatting of monetary amounts
5. Java API for working with Money and Currencies, which is planned to be included in Java 9.
6. All specification classes and interfaces are located in the javax.money.* package.

Sample Examples of JSR 354: Money and Currency API:

An example of creating a MonetaryAmount and printing it to the console looks like this::

MonetaryAmountFactory<?> amountFactory = Monetary.getDefaultAmountFactory();
MonetaryAmount monetaryAmount = amountFactory.setCurrency(Monetary.getCurrency("EUR")).setNumber(12345.67).create();
MonetaryAmountFormat format = MonetaryFormats.getAmountFormat(Locale.getDefault());
System.out.println(format.format(monetaryAmount));

When using the reference implementation API, the necessary code is much simpler:

MonetaryAmount monetaryAmount = Money.of(12345.67, "EUR");
MonetaryAmountFormat format = MonetaryFormats.getAmountFormat(Locale.getDefault());
System.out.println(format.format(monetaryAmount));

The API also supports calculations with MonetaryAmounts:

MonetaryAmount monetaryAmount = Money.of(12345.67, "EUR");
MonetaryAmount otherMonetaryAmount = monetaryAmount.divide(2).add(Money.of(5, "EUR"));

CurrencyUnit and MonetaryAmount

// getting CurrencyUnits by locale
CurrencyUnit yen = MonetaryCurrencies.getCurrency(Locale.JAPAN);
CurrencyUnit canadianDollar = MonetaryCurrencies.getCurrency(Locale.CANADA);

MonetaryAmount has various methods that allow accessing the assigned currency, the numeric amount, its precision and more:

MonetaryAmount monetaryAmount = Money.of(123.45, euro);
CurrencyUnit currency = monetaryAmount.getCurrency();
NumberValue numberValue = monetaryAmount.getNumber();

int intValue = numberValue.intValue(); // 123
double doubleValue = numberValue.doubleValue(); // 123.45
long fractionDenominator = numberValue.getAmountFractionDenominator(); // 100
long fractionNumerator = numberValue.getAmountFractionNumerator(); // 45
int precision = numberValue.getPrecision(); // 5

// NumberValue extends java.lang.Number. 
// So we assign numberValue to a variable of type Number
Number number = numberValue;

MonetaryAmounts can be rounded using a rounding operator:

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

When working with collections of MonetaryAmounts, some nice utility methods for filtering, sorting and grouping are available.

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"));

Custom MonetaryAmount operations

// 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

Resources:

Handling money and currencies in Java with JSR 354

Looking into the Java 9 Money and Currency API (JSR 354)

See Also: JSR 354 - Currency and Money