JavaServer Pages, 3rd Edition

Formatting Numbers and Dates

Let’s look at how a locale can be used. One thing we who live on this planet have a hard time agreeing on is how to write dates and numbers. The order of the month, the day, and the year; if the numeric value or the name should be used for the month; what character to use to separate the fractional part of a number; all of these details differ between countries, even between countries that speak the same language. And even though these details may seem picky, using an unfamiliar format can cause a great deal of confusion. For instance, if you ask for something to be done by 5/2, an American thinks you mean May 2 while a Swede believes that it’s due by February 5.

Java provides two classes to deal with formatting of numbers and dates for a specific locale, appropriately named java.text.NumberFormat and java.text.DateFormat, respectively.

The JSTL <fmt:formatNumber> action, used in Chapter 10 to format the price information for items in a shopping cart, is based on the NumberFormat class. By default, the NumberFormat class formats numbers based on the locale of the underlying operating system. If used on a server configured to use a U.S. English locale, it formats them according to American customs; on a server configured with an Italian locale, it formats them according to Italian customs, and so forth. But you can also explicitly specify a locale, to format numbers according to the rules for other locales than the one used by the operating system. You ...