Seam FrameworkCommunity Documentation
Seam makes it easy to build internationalized applications. First, let's walk through all the stages needed to internationalize and localize your app. Then we'll take a look at the components Seam bundles.
A JEE application consists of many components and all of them must be configured properly for your application to be localized.
Note that all i18n features in Seam work only in JSF context.
Starting at the bottom, the first step is to ensure that your database server and client is using the correct character encoding for your locale. Normally you'll want to use UTF-8. How to do this is outside the scope of this tutorial.
To ensure that the application server receives the request
parameters in the correct encoding from client requests you have to
configure the tomcat connector. If you use JBoss AS, add the system
properties
org.apache.catalina.connector.URI_ENCODING and
org.apache.catalina.connector.USE_BODY_ENCODING_FOR_QUERY_STRING
to the server configuration. For JBoss AS 7.1.1 change
${JBOSS_HOME}/standalone/configuration/standalone.xml
:
<system-properties>
<property name="org.apache.catalina.connector.URI_ENCODING" value="UTF-8"/>
<property name="org.apache.catalina.connector.USE_BODY_ENCODING_FOR_QUERY_STRING" value="true"/>
</system-properties>
You'll also need localized strings for all the messages in your application (for example field labels on your views). First you need to ensure that your resource bundle is encoded using the desired character encoding. By default ASCII is used. Although ASCII is enough for many languages, it doesn't provide characters for all languages.
Resource bundles must be created in ASCII, or use Unicode escape codes to represent Unicode characters. Since you don't compile a property file to byte code, there is no way to tell the JVM which character set to use. So you must use either ASCII characters or escape characters not in the ASCII character set. You can represent a Unicode character in any Java file using \uXXXX, where XXXX is the hexadecimal representation of the character.
You can write your translation of labels (
Section 17.3, “Labels”) to your messages resource bundle in the
native encoding and then convert the content of the file into the
escaped format through the tool native2ascii
provided in the JDK. This tool will convert a file written in your
native encoding to one that represents non-ASCII characters as
Unicode escape sequences.
Usage of this tool is described here for Java 5 or here for Java 6. For example, to convert a file from UTF-8:
$ native2ascii -encoding UTF-8 messages_cs.properties > messages_cs_escaped.properties
We need to make sure that the view displays your localized data and messages using the correct character set and also any data submitted uses the correct encoding.
To set the display character encoding, you need to use the
<f:view locale="cs_CZ"/>
tag
(here we tell JSF to use the Czech locale). You may want to change
the encoding of the xml document itself if you want to embed
localized strings in the xml. To do this alter the encoding
attribute in xml declaration <?xml
version="1.0" encoding="UTF-8"?>
as
required.
Also JSF/Facelets should submit any requests using the
specified character encoding, but to make sure any requests that
don't specify an encoding you can force the request encoding
using a servlet filter. Configure this in
components.xml
:
<web:character-encoding-filter encoding="UTF-8"
override-client="true"
url-pattern="*.seam" />
Each user login session has an associated instance of
java.util.Locale
(available to the application as a
component named locale
). Under normal
circumstances, you won't need to do any special configuration to
set the locale. Seam just delegates to JSF to determine the active
locale:
If there is a locale associated with the HTTP request (the
browser locale), and that locale is in the list of supported
locales from faces-config.xml
, use that locale
for the rest of the session.
Otherwise, if a default locale was specified in the
faces-config.xml
, use that locale for the rest of the
session.
Otherwise, use the default locale of the server.
It is possible to set the locale manually
via the Seam configuration properties
org.jboss.seam.international.localeSelector.language
,
org.jboss.seam.international.localeSelector.country
and
org.jboss.seam.international.localeSelector.variant
, but we
can't think of any good reason to ever do this.
It is, however, useful to allow the user to set the locale manually via the application user interface. Seam provides built-in functionality for overriding the locale determined by the algorithm above. All you have to do is add the following fragment to a form in your JSP or Facelets page:
<h:selectOneMenu value="#{localeSelector.language}">
<f:selectItem itemLabel="English" itemValue="en"/>
<f:selectItem itemLabel="Deutsch" itemValue="de"/>
<f:selectItem itemLabel="Francais" itemValue="fr"/>
</h:selectOneMenu>
<h:commandButton action="#{localeSelector.select}"
value="#{messages['ChangeLanguage']}"/>
Or, if you want a list of all supported locales from
faces-config.xml
, just use:
<h:selectOneMenu value="#{localeSelector.localeString}">
<f:selectItems value="#{localeSelector.supportedLocales}"/>
</h:selectOneMenu>
<h:commandButton action="#{localeSelector.select}"
value="#{messages['ChangeLanguage']}"/>
When the user selects an item from the drop-down, then clicks the command button, the Seam and JSF locales will be overridden for the rest of the session.
The brings us to the question of where the supported locales
are defined. Typically, you provide a list of locales for which you
have matching resource bundles in the
<locale-config>
element of the JSF configuration file
(/META-INF/faces-config.xml). However, you have learned to appreciate
that Seam's component configuration mechanism is more powerful
than what is provided in Java EE. For that reason, you can configure
the supported locales, and the default locale of the server, using
the built-in component named
org.jboss.seam.international.localeConfig
. To use it, you
first declare an XML namespace for Seam's international package
in the Seam component descriptor. You then define the default locale
and supported locales as follows:
<international:locale-config default-locale="fr_CA" supported-locales="en fr_CA fr_FR"/>
Naturally, if you pronounce that you support a locale, you better provide a resource bundle to match it! Up next, you'll learn how to define the language-specific labels.
JSF supports internationalization of user interface labels and
descriptive text via the use of <f:loadBundle
/>
. You can use this approach in Seam applications.
Alternatively, you can take advantage of the Seam
messages
component to display templated labels with
embedded EL expressions.
Seam provides a java.util.ResourceBundle
(available to the application as a
org.jboss.seam.core.resourceBundle
). You'll need to
make your internationalized labels available via this special
resource bundle. By default, the resource bundle used by Seam is
named messages
and so you'll need to define
your labels in files named messages.properties
,
messages_en.properties
,
messages_en_AU.properties
, etc. These files usually belong
in the WEB-INF/classes
directory.
So, in messages_en.properties
:
Hello=Hello
And in messages_en_AU.properties
:
Hello=G'day
You can select a different name for the resource bundle by
setting the Seam configuration property named
org.jboss.seam.core.resourceLoader.bundleNames
. You can
even specify a list of resource bundle names to be searched (depth
first) for messages.
<core:resource-loader>
<core:bundle-names>
<value>mycompany_messages</value>
<value>standard_messages</value>
</core:bundle-names>
</core:resource-loader>
If you want to define a message just for a particular page,
you can specify it in a resource bundle with the same name as the
JSF view id, with the leading /
and trailing file
extension removed. So we could put our message in
welcome/hello_en.properties
if we only needed to display
the message on /welcome/hello.jsp
.
You can even specify an explicit bundle name in
pages.xml
:
<page view-id="/welcome/hello.jsp" bundle="HelloMessages"/>
Then we could use messages defined in
HelloMessages.properties
on
/welcome/hello.jsp
.
If you define your labels using the Seam resource bundle,
you'll be able to use them without having to type
<f:loadBundle ... />
on every page. Instead, you can
simply type:
<h:outputText value="#{messages['Hello']}"/>
or:
<h:outputText value="#{messages.Hello}"/>
Even better, the messages themselves may contain EL expressions:
Hello=Hello, #{user.firstName} #{user.lastName}
Hello=G'day, #{user.firstName}
You can even use the messages in your code:
@In private Map<String, String> messages;
@In("#{messages['Hello']}") private String helloMessage;
The facesMessages
component is a
super-convenient way to display success or failure messages to the
user. The functionality we just described also works for faces
messages:
@Name("hello")
@Stateless
public class HelloBean implements Hello {
@In FacesMessages facesMessages;
public String sayIt() {
facesMessages.addFromResourceBundle("Hello");
}
}
This will display Hello, Gavin King
or
G'day, Gavin
, depending upon the user's
locale.
There is also a session-scoped instance of
java.util.Timezone
, named
org.jboss.seam.international.timezone
, and a Seam component
for changing the timezone named
org.jboss.seam.international.timezoneSelector
. By default,
the timezone is the default timezone of the server. Unfortunately,
the JSF specification says that all dates and times should be assumed
to be UTC, and displayed as UTC, unless a timezone is explicitly
specified using <f:convertDateTime>
. This is
an extremely inconvenient default behavior.
You can use application parameter to set up different default time
zone for JSF 2 in
web.xml
.
<context-param>
<param-name>javax.faces.DATETIMECONVERTER_DEFAULT_TIMEZONE_IS_SYSTEM_TIMEZONE</param-name>
<param-value>true</param-value>
</context-param>
Seam overrides this behavior, and defaults all dates and times to the Seam timezone.
Seam also provides a default date converter to convert a string value to a date. This saves you from having to specify a converter on input fields that are simply capturing a date. The pattern is selected according the the user's locale and the time zone is selected as described above.
Seam applications are also very easily skinnable. The theme API is very similar to the localization API, but of course these two concerns are orthogonal, and some applications support both localization and themes.
First, configure the set of supported themes:
<theme:theme-selector cookie-enabled="true">
<theme:available-themes>
<value>default</value>
<value>accessible</value>
<value>printable</value>
</theme:available-themes>
</theme:theme-selector>
Note that the first theme listed is the default theme.
Themes are defined in a properties file with the same name as
the theme. For example, the default
theme is
defined as a set of entries in default.properties
.
For example, default.properties
might
define:
css ../screen.css template /template.xhtml
Usually the entries in a theme resource bundle will be paths to CSS styles or images and names of facelets templates (unlike localization resource bundles which are usually text).
Now we can use these entries in our JSP or facelets pages. For example, to theme the stylesheet in a facelets page:
<link href="#{theme.css}" rel="stylesheet" type="text/css" />
Or, when the page definition resides in a subdirectory:
<link href="#{facesContext.externalContext.requestContextPath}#{theme.css}"
rel="stylesheet" type="text/css" />
Most powerfully, facelets lets us theme the template used by a
<ui:composition>
:
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
template="#{theme.template}">
Just like the locale selector, there is a built-in theme selector to allow the user to freely switch themes:
<h:selectOneMenu value="#{themeSelector.theme}">
<f:selectItems value="#{themeSelector.themes}"/>
</h:selectOneMenu>
<h:commandButton action="#{themeSelector.select}" value="Select Theme"/>
The locale selector, theme selector and timezone selector all
support persistence of locale and theme preference to a cookie.
Simply set the cookie-enabled
property in
components.xml
:
<theme:theme-selector cookie-enabled="true">
<theme:available-themes>
<value>default</value>
<value>accessible</value>
<value>printable</value>
</theme:available-themes>
</theme:theme-selector>
<international:locale-selector cookie-enabled="true"/>