Internationalizing and Localizing Web Applications

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The process of preparing an application to support more than one language and data format is called internationalization. Localization is the process of adapting an internationalized application to support a specific region or locale. Examples of locale-dependent information include messages and user interface labels, character sets and encoding, and date and currency formats. Although all client user interfaces should be internationalized and localized, it is particularly important for web applications because of the global nature of the web.

Java Platform Localization Classes

In the Java platform, java.util.Locale (https://docs.oracle.com/javase/8/docs/api/java/util/Locale.html) represents a specific geographical, political, or cultural region. The string representation of a locale consists of the international standard two-character abbreviation for language and country and an optional variant, all separated by underscore (_) characters. Examples of locale strings include fr (French), de_CH (Swiss German), and en_US_POSIX (English on a POSIX-compliant platform).

Locale-sensitive data is stored in a java.util.ResourceBundle (https://docs.oracle.com/javase/8/docs/api/java/util/ResourceBundle.html). A resource bundle contains key-value pairs, where the keys uniquely identify a locale-specific object in the bundle. A resource bundle can be backed by a text file (properties resource bundle) or a class (list resource bundle) containing the pairs. You construct a resource bundle instance by appending a locale string representation to a base name.

The Duke’s Bookstore application (see Duke’s Bookstore Case Study Example) contains resource bundles with the base name messages.properties for the locales de (German), es (Spanish), and fr (French). The default locale, en (English), which is specified in the faces-config.xml file, uses the resource bundle with the base name, messages.properties.

For more details on internationalization and localization in the Java platform, see https://docs.oracle.com/javase/tutorial/i18n/index.html.

Providing Localized Messages and Labels

Messages and labels should be tailored according to the conventions of a user’s language and region. There are two approaches to providing localized messages and labels in a web application.

Provide a version of the web page in each of the target locales and have a controller servlet dispatch the request to the appropriate page depending on the requested locale. This approach is useful if large amounts of data on a page or an entire web application need to be internationalized.
Isolate any locale-sensitive data on a page into resource bundles, and access the data so that the corresponding translated message is fetched automatically and inserted into the page. Thus, instead of creating strings directly in your code, you create a resource bundle that contains translations and read the translations from that bundle using the corresponding key.

The Duke’s Bookstore application follows the second approach. Here are a few lines from the default resource bundle messages.properties:

TitleShoppingCart=Shopping Cart
TitleReceipt=Receipt
TitleBookCatalog=Book Catalog
TitleCashier=Cashier
TitleBookDescription=Book Description
Visitor=You are visitor number
What=What We\'re Reading

Establishing the Locale

To get the correct strings for a given user, a web application either retrieves the locale (set by a browser language preference) from the request using the getLocale method, or allows the user to explicitly select the locale.

A component can explicitly set the locale by using the fmt:setLocale tag.

The locale-config element in the configuration file registers the default locale and also registers other supported locales. This element in Duke’s Bookstore registers English as the default locale and indicates that German, French, and Spanish are supported locales.

<locale-config>
    <default-locale>en</default-locale>
    <supported-locale>es</supported-locale>
    <supported-locale>de</supported-locale>
    <supported-locale>fr</supported-locale>
</locale-config>

The LocaleBean in the Duke’s Bookstore application uses the getLocale method to retrieve the locale.

public class LocaleBean {

    ...
    private FacesContext ctx = FacesContext.getCurrentInstance();
    private Locale locale = ctx.getViewRoot().getLocale();;

    ...
}

Setting the Resource Bundle

The resource bundle is set with the resource-bundle element in the configuration file. The setting for Duke’s Bookstore looks like this:

<resource-bundle>
    <base-name>
        ee.jakarta.tutorial.dukesbookstore.web.messages.Messages
    </base-name>
    <var>bundle</var>
</resource-bundle>

After the locale is set, the controller of a web application could retrieve the resource bundle for that locale and save it as a session attribute (see Associating Objects with a Session) for use by other components or simply be used to return a text string appropriate for the selected locale:

public String toString(Locale locale) {
    ResourceBundle res =
        ResourceBundle.getBundle(
            "ee.jakarta.tutorial.dukesbookstore.web.messages.Messages", locale);
    return res.getString(name() + ".string");
}

Alternatively, an application could use the f:loadBundle tag to set the resource bundle. This tag loads the correct resource bundle according to the locale stored in FacesContext.

<f:loadBundle basename="ee.jakarta.tutorial.dukesbookstore.web.messages.Messages"
    var="bundle"/>

Resource bundles containing messages that are explicitly referenced from a Jakarta Faces tag attribute using a value expression must be registered using the resource-bundle element of the configuration file.

For more information on using this element, see Registering Application Messages.

Retrieving Localized Messages

A web component written in the Java programming language retrieves the resource bundle from the session:

ResourceBundle messages = (ResourceBundle)session.getAttribute("messages");

Then it looks up the string associated with the key person.lastName as follows:

messages.getString("person.lastName");

You can only use a message or messages tag to display messages that are queued onto a component as a result of a converter or validator being registered on the component. The following example shows a message tag that displays the error message queued on the userNo input component if the validator registered on the component fails to validate the value the user enters into the component.

<h:inputText id="userNo" value="#{UserNumberBean.userNumber}">
    <f:validateLongRange minimum="0" maximum="10" />
</h:inputText>
...
<h:message style="color: red; text-decoration: overline"
           id="errors1" for="userNo"/>

For more information on using the message or messages tags, see Displaying Error Messages with the h:message and h:messages Tags.

Messages that are not queued on a component and are therefore not loaded automatically are referenced using a value expression. You can reference a localized message from almost any Jakarta Faces tag attribute.

The value expression that references a message has the same notation whether you loaded the resource bundle with the loadBundle tag or registered it with the resource-bundle element in the configuration file.

The value expression notation is var.message, in which var matches the var attribute of the loadBundle tag or the var element defined in the resource-bundle element of the configuration file, and message matches the key of the message contained in the resource bundle, referred to by the var attribute.

Here is an example from bookcashier.xhtml in Duke’s Bookstore:

<h:outputLabel for="name" value="#{bundle.Name}" />

Notice that bundle matches the var element from the configuration file and that Name matches the key in the resource bundle.

Date and Number Formatting

Java programs use the DateFormat.getDateInstance(int, locale) method to parse and format dates in a locale-sensitive manner. Java programs use the NumberFormat.getXXXInstance(locale) method, where XXX can be Currency, Number, or Percent, to parse and format numerical values in a locale-sensitive manner.

An application can use date/time and number converters to format dates and numbers in a locale-sensitive manner. For example, a shipping date could be converted as follows:

<h:outputText value="#{cashier.shipDate}">
    <f:convertDateTime dateStyle="full"/>
</h:outputText>

For information on Jakarta Faces converters, see Using the Standard Converters.

Character Sets and Encodings

The following sections describe character sets and character encodings.

Character Sets

A character set is a set of textual and graphic symbols, each of which is mapped to a set of nonnegative integers.

The first character set used in computing was US-ASCII. It is limited in that it can represent only American English. US-ASCII contains uppercase and lowercase Latin alphabets, numerals, punctuation, a set of control codes, and a few miscellaneous symbols.

Unicode defines a standardized, universal character set that can be extended to accommodate additions. When the Java program source file encoding doesn’t support Unicode, you can represent Unicode characters as escape sequences by using the notation \uXXXX, where XXXX is the character’s 16-bit representation in hexadecimal. For example, the Spanish version of a message file could use Unicode for non-ASCII characters, as follows:

admin.nav.main=P\u00e1gina principal de administraci\u00f3n

Character Encoding

A character encoding maps a character set to units of a specific width and defines byte serialization and ordering rules. Many character sets have more than one encoding. For example, Java programs can represent Japanese character sets using the EUC-JP or Shift-JIS encodings, among others. Each encoding has rules for representing and serializing a character set.

The ISO 8859 series defines 13 character encodings that can represent texts in dozens of languages. Each ISO 8859 character encoding can have up to 256 characters. ISO-8859-1 (Latin-1) comprises the ASCII character set, characters with diacritics (accents, diaereses, cedillas, circumflexes, and so on), and additional symbols.

UTF-8 (Unicode Transformation Format, 8-bit form) is a variable-width character encoding that encodes 16-bit Unicode characters as one to four bytes. A byte in UTF-8 is equivalent to 7-bit ASCII if its high-order bit is zero; otherwise, the character comprises a variable number of bytes.

UTF-8 is compatible with the majority of existing web content and provides access to the Unicode character set. Current versions of browsers and email clients support UTF-8. In addition, many web standards specify UTF-8 as their character encoding. For example, UTF-8 is one of the two required encodings for XML documents (the other is UTF-16).

Web components usually use PrintWriter to produce responses; PrintWriter automatically encodes using ISO-8859-1. Servlets can also output binary data using OutputStream classes, which perform no encoding. An application that uses a character set that cannot use the default encoding must explicitly set a different encoding.