Thursday June 28, 2007

Currency enhancements in JDK7

In the JDK, applications can use java.util.Currency class to deal with currencies. They can query what currency is used in a given country, or what localized symbol is used for that currency in a particular locale. To provide applications with those currency information, the JDK contains the currency data that is based on the ISO 4217 standard. From time to time, due to a variety of reasons, the ISO 4217 data are often updated by the maintenance agency. Keeping up with these updates in the JDK is critical for applications that deal with currencies, such as a banking application. Otherwise, those applications would result in a wrong financial transaction (cf. see my old entry regarding the Turkish pastry story here)

Now, one of the issues in the current JDK's currency support is that the currency data is embedded in "lib/rt.jar" as a class file. So every time the ISO 4217 maintenance agency releases a currency update, such as Slovenia switching to Euro currency, the rt.jar file needs to be updated. This makes it impossible for customers to replace just the currency data portion when needed, without upgrading the whole JDK. This issue is analogous to the TimeZone data being separated from the JDK class files, and they can be upgraded separately.

The purpose of this blog entry is to announce that this will no longer be an issue in the JDK7, as I have just checked-in the necessary changes for this issue (woohoo!), which will soon be public in the OpenJDK build. In the new structure, the currency data is separately placed in "<JAVA_HOME>/lib" directory as a binary file "currency.data", which can be replaced not in sync with the JDK update release schedule. One added feature to this is that you could even provide your own properties file to override the contents in the currency data file. If you create a properties file as "<JAVA_HOME>/lib/currency.properties", which contains "key=value" pairs where the "key" is a ISO 3166 country code, and the "value" consists of three-letter currency code, three-digit numeric code, and the minor unit (separeted by a comma), it would override the currency data for that country designated by the "key". For example if it has "JP=JPZ,999,2", this would override the Japanese currency data.

Also, along with this Currency enhancement, I added a couple of new APIs. First one is to acquire all the available currencies in the JDK as follows:

public static Set<Currency> getAvailableCurrencies()

Next one is to return a numeric ISO 4217 code for a Currency instance:

public int getNumericCode()

The last one is to return the display name for a Currency instance. Instead of getSymbol() returning "$" for the US Dollar ("USD"), this API returns "US Dollar" in the "US" locale.

public String getDisplayName()
public String getDisplayName(Locale displayLocale)

The initial release of this API contains localized currency names for 10 locales, i.e., English, French, German, Italian, Japanese, Korean, Simplified Chinese, Spanish, Swedish, and Traditional Chinese.

I also added an SPI in java.util.spi.CurrencyNameProvider for the languages other than the above, so that one could provide localized display names in any language:

public getDisplayName(String currencyCode,
                      Locale displayLocale)

These are the changes that I have checked in, and I hope this is useful for developers. I would have liked to provide a working demo, but it's not possible to do it with a yet released build :-)