TitleShoppingCart=Shopping Cart
TitleReceipt=Receipt
TitleBookCatalog=Book Catalog
TitleCashier=Cashier
TitleBookDescription=Book Description
Visitor=You are visitor number
What=What We\'re Reading
Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial |
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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
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 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 the
getLocale
method to retrieve the locale.
public class LocaleBean {
...
private FacesContext ctx = FacesContext.getCurrentInstance();
private Locale locale = ctx.getViewRoot().getLocale();;
...
}
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.
For more information on using this element, see Registering Application 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:inputText>
...
<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 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, and
message
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.
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