Providing Localized Messages and Labels (original) (raw)

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:setLocaletag.

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 thegetLocale 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>
        javaeetutorial.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(
            "javaeetutorial.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="javaeetutorial.dukesbookstore.web.messages.Messages"
    var="bundle"/>

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

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 amessage tag that displays the error message queued on the userNoinput 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"/>

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 JavaServer 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, andmessage 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.