Internationalization Tags

Chapter 23 covers how to design Web applications so that they conform to the language and formatting conventions of client locales. This section describes tags that support the internationalization of JSP pages.

JSTL defines tags for: setting the locale for a page, creating locale-sensitive messages, and formatting and parsing data elements such as numbers, currencies, dates, and times in a locale-sensitive or customized manner. Table 17-6 lists the tags.

Table 17-6 Internationalization Tags
Area	Function	Tags	Prefix
I18n	Setting Locale	`setLocale` `requestEncoding`	`fmt`
	Messaging	`bundle` `message` `param` `setBundle`
	Number and Date Formatting	`formatNumber` `formatDate` `parseDate` `parseNumber` `setTimeZone` `timeZone`

JSTL i18n tags use a localization context to localize their data. A localization context contains a locale and a resource bundle instance. To specify the localization context, you define the context parameter javax.servlet.jsp.jstl.fmt.localizationContext, whose value can be a javax.servlet.jsp.jstl.fmt.LocalizationContext or a String. A String context parameter is interpreted as the name of a resource bundle basename. For the Duke's Bookstore application, the context parameter is the String messages.BookstoreMessages, which is set with deploytool in the Context tab of the WAR inspector. This setting can be overridden in a JSP page by using the JSTL fmt:setBundle tag. When a request is received, JSTL automatically sets the locale based on the value retrieved from the request header and chooses the correct resource bundle using the basename specified in the context parameter.

Setting the Locale

The setLocale tag is used to override the client-specified locale for a page. The requestEncoding tag is used to set the request's character encoding, in order to be able to correctly decode request parameter values whose encoding is different from ISO-8859-1.

Messaging Tags

By default, browser-sensing capabilities for locales are enabled. This means that the client determines (via its browser settings) which locale to use, and allows page authors to cater to the language preferences of their clients.

bundle Tag

To define a resource bundle for a Web application you specify the context parameter javax.servlet.jsp.jstl.fmt.localizationContext in the Web application deployment descriptor.

message Tag

The message tag is used to output localized strings. The following tag from bookcatalog.jsp

is used to output a string inviting customers to choose a book from the catalog.

The param subtag provides a single argument (for parametric replacement) to the compound message or pattern in its parent message tag. One param tag must be specified for each variable in the compound message or pattern. Parametric replacement takes place in the order of the param tags.

Formatting Tags

JSTL provides a set of tags for parsing and formatting locale-sensitive numbers and dates.

The formatNumber tag is used to output localized numbers. The following tag from bookshowcart.jsp

is used to display a localized price for a book. Note that since the price is maintained in the database in dollars, the localization is somewhat simplistic, because the formatNumber tag is unaware of exchange rates. The tag formats currencies but does not convert them.

Analogous tags for formatting dates (formatDate), and parsing numbers and dates (parseNumber, parseDate) are also available. The timeZone tag establishes the time zone (specified via the value attribute) to be used by any nested formatDate tags.

In bookreceipt.jsp, a "pretend" ship date is created and then formatted with the formatDate tag:

<jsp:useBean id="now" class="java.util.Date" />
<jsp:setProperty name="now" property="time" 
  value="${now.time + 432000000}" />
<fmt:message key="ShipDate"/> 
<fmt:formatDate value="${now}" type="date"
  dateStyle="full"/>.