Performing Localization - The J2EE 1.4 Tutorial

Performing Localization

As mentioned in Using Localized Messages, data and messages in the Duke's Bookstore application have been localized for French, German, Spanish, and American English.

This section explains how to produce the localized messages as well as how to localize dynamic data and messages.

Using Localized Messages describes how page authors access localized data from the page using the loadBundle tag.

If you are not familiar with the basics of localizing web applications, see Chapter 22.

Creating a Resource Bundle

A ResourceBundle contains a set of localized messages. To learn how to create a ResourceBundle, see
http://java.sun.com/docs/books/tutorial/i18n/index.html 
After you create the ResourceBundle, put it in the same directory as your classes. Much of the data for the Duke's Bookstore application is stored in a ResourceBundle called BookstoreMessages, located in <INSTALL>/j2eetutorial14/examples/web/bookstore/src/messages/.

Localizing Dynamic Data

The Duke's Bookstore application has some data that is set dynamically in backing beans. Because of this, the beans must load the localized data themselves; the data can't be loaded from the page.

The message method in AbstractBean is a general-purpose method that looks up localized messages used in the backing beans:
protected void message(String clientId, String key) {
  // Look up the requested message text
  String text = null;
  try {
    ResourceBundle bundle =
      ResourceBundle.getBundle("messages.BookstoreMessages",
        context().getViewRoot().getLocale());
    text = bundle.getString(key);
  } catch (Exception e) {
    text = "???" + key + "???";
  }
  // Construct and add a FacesMessage containing it
  context().addMessage(clientId, new FacesMessage(text));
} 
This method gets the current locale from the UIViewRoot instance of the current request and loads the localized data for the messages using the getBundle method, passing in the path to the ResourceBundle and the current locale.

The other backing beans call this method by using the key to the message that they are trying to retrieve from the resource bundle. Here is a call to the message method from ShowCartBean:
message(null, "Quantities Updated"); 
Localizing Messages

The JavaServer Faces API provides two ways to create messages from a ResourceBundle:

You can register the ResourceBundle with the application configuration resource file and use a message factory pattern to examine the ResouceBundle and to generate localized FacesMessage instances, which represent single localized messages. The message factory pattern is required to access messages that are registered with the Application instance. Instead of writing your own message factory pattern, you can use the one included with the Duke's Bookstore application. It is called MessageFactory and is located in <INSTALL>/j2eetutorial14/examples/web/bookstore6/src/util/.

You can use the FacesMessage class to get the localized string directly from the ResourceBundle.

Registering Messages includes an example of registering a ResourceBundle in the application configuration resource file.

Creating a Message with a Message Factory

To use a message factory to create a message, follow these steps:

Register the ResourceBundle with the application. This is explained in Registering Messages.

Create a message factory implementation. You can simply copy the MessageFactory class included with the Duke's Bookstore application to your application.

Access a message from your application by calling the getMessage(FacesContext, String, Object) method of the MessageFactory class. The MessageFactory class uses the FacesContext to access the Application instance on which the messages are registered. The String argument is the key that corresponds to the message in the ResourceBundle. The Object instance typically contains the substitution parameters that are embedded in the message. For example, the custom validator described in Implementing the Validator Interface will substitute the format pattern for the {0} in this error message:

Input must match one of the following patterns {0}

Implementing the Validator Interface gives an example of accessing messages.

Using FacesMessage to Create a Message

Instead of registering messages in the application configuration resource file, you can access the ResourceBundle directly from the code. The validateEmail method from the Coffee Break example does this:
...
String message = "";
...
message = CoffeeBreakBean.loadErrorMessage(context,
  CoffeeBreakBean.CB_RESOURCE_BUNDLE_NAME, 
    "EMailError");
context.addMessage(toValidate.getClientId(context),
  new FacesMessage(message));
... 
These lines also call the loadErrorMessage to get the message from the ResourceBundle. Here is the loadErrorMessage method from CoffeeBreakBean:
public static String loadErrorMessage(FacesContext context, 
  String basename, String key) {
  if ( bundle == null ) { 
    try {
      bundle = ResourceBundle.getBundle(basename, 
        context.getViewRoot().getLocale());
    } catch (Exception e) {
      return null;
    }
  }
  return bundle.getString(key);
} 