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Localization (aka L10n) is all about getting the right text to the user, in the right language.

Localization support is well integrated into Tapestry. Tapestry allows you to easily separate the text you present to your users from the rest of your application ... pull it out of your Java code and even out of your component templates. You can then translate your messages into other languages and let Tapestry put everything together.

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The messages in the catalog are accessed by keys. Tapestry ignores the case of the keys when accessing messages in the catalog.

Properties File Charset

Tapestry uses the UTF-8 charset when reading the properties files in a message catalog. This means that you don't have to use the Java native2ascii tool. Make sure that your properties files don't contain byte order marks (BOM) as Java - and thus Tapestry - doesn't support BOM in properties files (see http://bugs.sun.com/view_bug.do?bug_id=4508058^{Image Removed}). Some editors write them out when saving a file in UTF-8, so watch out.

Component Message Catalog Inheritance

If a component class is a subclass of another component class, then it inherits that base class' message catalog. Its own message catalog extends and overrides the values inherited from the base class.

In this way, you could have a base component class that contained common messages, and extend or override those messages in subclasses (just as you would extend or override the methods of the base component class). This, of course, works for as many levels of inheritance as you care to support.

Application-wide Message Catalog

If the file WEB-INF/AppName.properties exists in the context, it will be used as an application-wide message catalog. The AppName is derived from the name of the filter inside the web.xml file; this is most often just "app", thus WEB-INF/app.properties. The search for the file is case sensitive. The properties files may be localized.

Individual pages and components can override the values defined in the message catalog.

Properties File Charset

Tapestry uses the UTF-8 character set (charset) when reading the properties files in a message catalog. This means that you don't have to use the Java native2ascii tool.

Localized Component Templates

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• Using the "message:" binding expression in a component template
• By injecting the component's Messages object
  In the first case, you may use the message: binding prefix with component parameters, or with template expansions:

<t:layout title="message:page-title">

  ${message:greeting}, ${user.name}!
  
  . . .
</t:layout>

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You would extend this with a set of properties files:

page-title=Your Account
greeting=Welcome back

Or, perhaps, a French version:

page-title=Votre Compte
greeting=Bienvenue en arriere

Programatically, you may inject your component message catalog into your class, as an instance of the Messages interface:

  @Inject
  private Messages messages;

You could then get() messages, or format() them:

  public String getCartSummary()     
  {
    if (items.isEmpty())
      return messages.get("no-items");
      
    return messages.format("item-summary", _items.size());
  }

The format() option works using a java.util.Formatter, with all the printf-style loveliness you've come to expect:

no-items=Your shopping cart is empty.     
item-summary=You have %d items in your cart.

As easy as conditionals are to use inside a Tapestry template, sometimes it's even easier to do it in Java code.

Missing Keys

Wiki MarkupIf you reference a key that is not in the message catalog, Tapestry does not throw an exception (because that would make initially developing an application very frustrating). When a key can not be located, a "placeholder" message is generated, such as "\[\[missing key: key-not-found\]\]".

Reloading

If you change a property file in a message catalog, you'll see the change immediately, just as with component classes and component templates (provided you're not running in production mode).

Asset Localization

When injecting assets, the injected asset will be localized as well. A search for the closest match for the active locale is made, and the final Asset will reflect that.

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@Inject 
private PersistentLocale persistentLocale;

void onActionFromLocaleToggle() {
    if ("en".equalsIgnoreCase(persistentLocale.get().getLanguage())) {
        persistentLocale.set(new Locale("de"));
    } else {
        persistentLocale.set(new Locale("en"));
    }
    return this;
}
public String getDisplayLanguage() {
    return persistentLocale.get().getDisplayLanguage();
}

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While your application can support any locale (and thus any language) that you want, Tapestry provides only a limited set of translations for its own built-in messages. As of Tapestry 5.3, the following locales have translations provided:

¹ as of Tapestry 5.3.8

 ² as of Tapestry 5.4

Providing translations for Tapestry built-in messages

Fortunately, Tapestry uses all the same mechanisms for its own locale support as it provides for your application. So, to support other locales, just translate the built-in message catalog (property) files yourself:

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<style type="text/css">table.sectionMacro { width: auto; }</style>

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