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 Tutoring application follows the second approach. Here are a few lines from the default resource bundle messages.properties:

nav.main=Main page
nav.status=View status
nav.current_session=View current tutoring session
nav.park=View students at the park
nav.admin=Administration

admin.nav.main=Administration main page
admin.nav.create_student=Create new student
admin.nav.edit_student=Edit student
admin.nav.create_guardian=Create new guardian
admin.nav.edit_guardian=Edit guardian
admin.nav.create_address=Create new address
admin.nav.edit_address=Edit address
admin.nav.activate_student=Activate student

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 other supported locales. This element in Duke’s Tutoring registers English as the default locale and indicates that German, Spanish, Portuguese, and Chinese are supported locales.

<locale-config>
    <default-locale>en</default-locale>
    <supported-locale>de</supported-locale>
    <supported-locale>es</supported-locale>
    <supported-locale>pt</supported-locale>
    <supported-locale>zh</supported-locale>
</locale-config>

The Status Manager in the Duke’s Tutoring application uses the getLocale method to retrieve the locale and a toString method to return a localized translation of a student’s status based on the locale.

public class StatusManager {
    
    private FacesContext ctx = FacesContext.getCurrentInstance();
    private Locale locale;

    /** Creates a new instance of StatusManager */
    public StatusManager() {
        locale = ctx.getViewRoot().getLocale();
    }
    
    public String getLocalizedStatus(StatusType status) {
        return status.toString(locale);
    }

}

Setting the Resource Bundle

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

<resource-bundle>
    <base-name>dukestutoring.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 to return a text string appropriate for the selected locale:

public String toString(Locale locale) {
    ResourceBundle res = ResourceBundle.getBundle(
            "dukestutoring.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="dukestutoring.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.

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: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 JavaServer Faces tag attribute.

The value expression that references a message has the same notation whether you loaded the resource bundle with the f: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 f: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 editAddress.xhtml in Duke’s Tutoring:

<h:outputLabel for="country" value="#{bundle['address.country']}:" />

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