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Internationalization Tags

In Internationalizing and Localizing Web Applications we discussed the how to adapt Web applications 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
Formatting and parsing data elements such as numbers, currencies, dates, and times in a locale-sensitive or customized manner

Table 6-6 Internationalization Tags 

Area	Function	Tags
I18n	Setting Locale	setLocale requestEncoding
	Messaging	bundle message   param setBundle
	Number and Date Formatting	formatNumber formatDate parseDate parseNumber setTimeZone timeZone

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

You use the bundle tag to specify a resource bundle for a page.

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. Here is the declaration from the Duke's Bookstore descriptor:

<context-param>
  <param-name>
    javax.servlet.jsp.jstl.fmt.localizationContext
  </param-name>
  <param-value>messages.BookstoreMessages</param-value>
</context-param>   

message Tag

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

<h3><fmt:message key="Choose"/></h3> 

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 showcart.jsp

<fmt:formatNumber value="${book.price}" type="currency"/> 

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 receipt.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.getTime() + 432000000 %>" />
<fmt:message key="ShipDate"/> 
<fmt:formatDate value="${now}" type="date"
  dateStyle="full"/>. 

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