Using Localized Data

JavaServer Faces applications make use of three different kinds of data that can be localized:

• Static text, such as labels, alternative text, and tool tips

• Error messages, such as those displayed when validation of user input data fails

• Dynamic data, which is data that must be set dynamically by server-side objects, such as by backing beans

This section discusses how to access the first two kinds of data from the page. Performing Localization (page 402) explains how to produce localized error messages as well as how to localize dynamic data. If you are not familiar with the basics of localizing web applications, see Chapter 14.

All data in the Duke's Bookstore application have been localized for Spanish, French, German, and American English. The image map on the first page allows you to select your preferred locale. See Chapter 12 for information on how the image map custom component was created.

All the localized data is stored in resource bundles, which are represented as either ResourceBundle classes or text files, usually with the extension .properties. For more information about resource bundles, see

http://java.sun.com/docs/books/tutorial/i18n/index.html

After the application developer has produced a resource bundle, the application architect puts it in the same directory as the application classes. The static text data for the Duke's Bookstore application is stored in a ResourceBundle class called BookstoreMessages. The error messages are stored in another resource bundle called ApplicationMessages. After the resource bundles have been created and before their data can be accessed, they must be made available to the application, as explained in the following section.

Loading a Resource Bundle

To reference error messages or static data from the page, you first need to make available the resource bundle containing the data.

To make available resource bundles that contain static data, you need to do one of two things:

• Register the resource bundle with the application in the configuration file using the resource-bundle element, as explained in Registering Custom Localized Static Text (page 471).
  
  
• Load the resource bundle into the current view using the loadBundle tag.
  
  

Here is an example loadBundle tag from bookstore.jsp:

   <f:loadBundle var="bundle"      basename="messages.BookstoreMessages" />

The basename attribute value specifies the fully-qualified class name of the ResourceBundle class, which in this case is located in the messages package of the bookstore application.

The var attribute is an alias to the ResourceBundle class. This alias can be used by other tags in the page in order to access the localized messages.

In the case of resource bundles that contain error messages, you need to register the resource bundle with the application in the configuration file using the message-bundle element, as explained in Registering Custom Error Messages (page 470). One exception is if you are referencing the error messages from the input component attributes described in Referencing Error Messages (page 358). In that case, you load the resource bundles containing these messages in the same way you load resource bundles containing static text.

Referencing Localized Static Data

To reference static localized data from a resource bundle, you use a value expression from an attribute of the component tag that will display the localized data. You can reference the message from any component tag attribute that is enabled to accept value expressions.

The value expression has the notation var.message, in which var matches the var attribute of the loadBundle tag or the var element in 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 bookstore.jsp:

   <h:outputText value="#{bundle.Talk}"/>

Notice that bundle matches the var attribute from the loadBundle tag and that Talk matches the key in the ResourceBundle.

Another example is the graphicImage tag from chooselocale.jsp:

   <h:graphicImage  url="/template/world.jpg"      alt="#{bundle.ChooseLocale}"      usemap="#worldMap" />

The alt attribute is enabled to accept value expressions. In this case, the alt attribute refers to localized text that will be included in the alternative text of the image rendered by this tag.

See Creating Custom Component Classes (page 437) and Enabling Component Properties to Accept Expressions (page 443) for information on how to enable value binding on your custom component's attributes.

Referencing Error Messages

A JavaServer Faces page uses the message or messages tags to access error messages, as explained in Displaying Error Messages with the message and messages Tags (page 354).

The error messages that these tags access include:

• The standard error messages that accompany the standard converters and validators that ship with the API. See section 2.5.4 of the JavaServer Faces specification, version 1.2, for a complete list of standard error messages.

• Custom error messages contained in resource bundles registered with the application by the application architect using the message-bundle element in the configuration file.

• Custom error messages hardcoded in custom converter and validator classes.

When a converter or validator is registered on an input component, the appropriate error message is automatically queued on the component.

A page author can override the error messages queued on a component by using the following attributes of the component's tag:

• converterMessage: References the error message to display when the data on the enclosing component can not be converted by the converter registered on this component.

• requiredMessage: References the error message to display when no value has been entered into the enclosing component.

• validatorMessage: References the error message to display when the data on the enclosing component cannot be validated by the validator registered on this component.

All three attributes are enabled to take literal values and value expressions. If an attribute uses a value expression, this expression references the error message in a resource bundle. This resource bundle must be made available to the application in one of the following ways:

• By the page author using the loadBundle tag

• By the application architect using the resource-bundle element in the configuration file.

Conversely, the message-bundle element must be used to make available to the application those resource bundles containing custom error messages that are queued on the component as a result of a custom converter or validator being registered on the component.

The bookcashier.jsp page includes an example of the requiredMessage attribute using a value expression to reference an error message:

   <h:inputText  size="19"      required="true"      requiredMessage="#{customMessages.ReqMessage}" >      ...    </h:inputText>    <h:message style  for="ccno"/>

The value expression that requiredMessage is using in this example references the error message with the ReqMessage key in the resource bundle, customMessages.

This message replaces the corresponding message queued on the component and will display wherever the message or messages tag is placed on the page.

See Registering Custom Error Messages (page 470) and Registering Custom Localized Static Text (page 471) for information on how to use the message-bundle and resource-bundle element to register resource bundles that contain error messages.