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Internationalization Tag Library

Chapter 15, Internationalizing and Localizing Web Applications covers how to design web applications so that they conform to thelanguage and formatting conventions of client locales. This section describes tags that supportthe 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 timesin a locale-sensitive or customized manner.Table 7-6 lists the tags.

Table 7-6 Internationalization Tags

Area	Function	Tags	Prefix
I18N	Setting Locale	setLocalerequestEncoding	`fmt`
	Messaging	bundlemessage paramsetBundle
	Number andDate Formatting	formatNumberformatDateparseDateparseNumbersetTimeZonetimeZone

JSTL I18N tags use a localization context to localize their data. Alocalization contextcontains a locale and a resource bundle instance. To specify the localization context atdeployment time, you define the context parameterjavax.servlet.jsp.jstl.fmt.localizationContext, whose value can beajavax.servlet.jsp.jstl.fmt.LocalizationContext or aString. AString context parameter is interpreted as aresource bundle base name. For the Duke’s Bookstore application, the context parameter istheStringmessages.BookstoreMessages. When a request is received, JSTL automatically sets the localebased on the value retrieved from the request header and chooses the correctresource bundle using the base name specified in the context parameter.

Setting the Locale

ThesetLocale tag is used to override the client-specified locale for a page.TherequestEncoding tag is used to set the request’s character encoding, in orderto be able to correctly decode request parameter values whose encoding is differentfromISO-8859-1.

Messaging Tags

By default, the capability to sense the browser locale setting is enabled inJSTL. This means that the client determines (through its browser setting) which localeto use, and allows page authors to cater to the language preferences oftheir clients.

The`setBundle` and`bundle` Tags

You can set the resource bundle at runtime with the JSTLfmt:setBundle andfmt:bundle tags.fmt:setBundle is used to set the localization context in a variableor configuration variable for a specified scope.fmt:bundle is used to set theresource bundle for a given tag body.

The`message` Tag

Themessage tag is used to output localized strings. The following tagfromtut-install/javaeetutorial5/examples/web/bookstore4/web/books/bookcatalog.jsp is used to output a string inviting customers to choosea book from the catalog.

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

Theparam subtag provides a single argument (for parametric replacement) to the compoundmessage or pattern in its parentmessage tag. Oneparam tag must be specifiedfor each variable in the compound message or pattern. Parametric replacement takes placein the order of theparam tags.

Formatting Tags

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

TheformatNumber tag is used to output localized numbers. The following tag fromtut-install/javaeetutorial5/examples/web/bookstore4/web/books/bookshowcart.jsp is used to display a localized price for a book.

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

Note that because the price is maintained in the database in dollars, thelocalization is somewhat simplistic, because theformatNumber tag is unaware of exchange rates.The tag formats currencies but does not convert them.

Analogous tags for formatting dates (formatDate) and for parsing numbers and dates (parseNumber,parseDate) arealso available. ThetimeZone tag establishes the time zone (specified with thevalueattribute) to be used by any nestedformatDate tags.

Intut-install/javaeetutorial5/examples/web/bookstore4/web/books/bookreceipt.jsp, a “pretend” ship date is created and then formatted with theformatDate tag:

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