What I want to show in this example is, how you could deal with a dynamic page title per view (or time or what ever) that will handle your browser Locale as well.
Quite often I can see code like this one you will find in solution 01. The solution in Version 01 is based on a Message-Holder that will load all Ressource-Bundles and it is the static entry point into the message key to message world.
The holder is responsible to load and hold the resource bundles.
public class Messages {
public static final String RESOURCE_BUNDLE_NAME = "vaadinapp";
private static final ResourceBundle RESOURCE_BUNDLE_DEFAULT = getBundle(RESOURCE_BUNDLE_NAME);
private static final ResourceBundle RESOURCE_BUNDLE_EN = getBundle(RESOURCE_BUNDLE_NAME , ENGLISH);
private static final ResourceBundle RESOURCE_BUNDLE_DE = getBundle(RESOURCE_BUNDLE_NAME , GERMAN);
private static final List<Locale> locales = List.of(ENGLISH ,
GERMAN);
public static String get(String key , Locale locale) {
Objects.requireNonNull(key);
return match(
matchCase(() -> success(RESOURCE_BUNDLE_DEFAULT)) ,
matchCase(() -> locale == null , () -> success(RESOURCE_BUNDLE_DEFAULT)) ,
matchCase(() -> ENGLISH.getLanguage().equals(locale.getLanguage()) ,
() -> success(RESOURCE_BUNDLE_EN)) ,
matchCase(() -> GERMAN.getLanguage().equals(locale.getLanguage()) ,
() -> success(RESOURCE_BUNDLE_DE))
)
.flatMap((CheckedFunction<ResourceBundle, String>) resourceBundle -> resourceBundle.getString(key))
.ifFailed(System.out::println)
.getOrElse(() -> "##" + key + "##-" + locale);
}
}So far so good. You can implement this in different ways. The only thing you should have in mind is, that your solution is able to handle more than one Thread at the same time. Even during the initialisation phase. Sometimes I see solutions with a critical init-phase. For example, that a public constructor will set a static attribute. If you want to build a Singleton, build a thread save version, please. Having in mind, that this will be used heavily, the call to get a translation should not be blocking.
In this solution the title is set inside a constructor of a view.
public class View001() {
UI current = UI.getCurrent();
Locale locale = current.getLocale();
current
.getPage()
.setTitle(Messages.get("global.app.name" , locale)
+ " | "
+ Messages.get("view001.title" , locale));
}Here are some points I would like to discuss. The first is based on the assumption that your application is not only based on one view. Are you sure you want to write this peace of code a few times? And how often your colleges in your team will forget this? The next is, that here is an implicit definition of a format for the page title. xx + " | " + yy
We have to extract the repeating part.. This could lead to version 02...
We are extracting the formatting part, first. For this a class with the name TitleFormatter is created. Inside you can define the way, how the page title will be formatted.
public class TitleFormatter {
public String format(String key, Locale locale){
return Messages.get("global.app.name" , locale)
+ " | "
+ Messages.get(key , locale);
}
}With this class, we have a central place for the definition, how the title should look like. The next step is, to remove the invocation method out of the constructor. Vaadin provides an interface called HasDynamicTitle. Implementing this, you can overwrite the method getPageTitle(). But again, you would implement this in every view...
@Route(View002.VIEW_002)
public class View002 extends Composite<Div> implements HasDynamicTitle {
public static final String VIEW_002 = "view002";
@Override
public String getPageTitle() {
UI current = UI.getCurrent();
Locale locale = current.getLocale();
return new TitleFormatter().format("view.title", locale);
}
}One solution could be based on inheritance, packing this stuff into a parent class. But how to get the actual key to resolve without implementing something in every child class?
Vaadin will give you one other way to define the page title. The other solution is based on an annotation called PageTitle
@PageTitle("My PapeTitle")
@Route(View002.VIEW_002)
public class View002 extends Composite<Div> {
public static final String VIEW_002 = "view002";
}The usage of this Annotation is XOR to the usage of the interface HasDynamicTitle. So, make sure that there is nothing in your inheritance.
The challenge here is based on the fact, that the annotation ony consumes static Strings. I18N is not possible with this solution.
After playing around with this solutions, I developed a a solution that could handle
- message bundles
- is not inside inheritance
- is based on Annotations
- is easy to extend
- can change the language during runtime
Mostly it is a good approach to develop a solution for a developer from the perspective of a developer. Here it means, what should a developer see if he/she have to use your solution.
The developer will see this Annotation. Three things can be defined here.
- The message key that will be used to resolve the message based on the actual Locale
- A default value the will be used, if no corresponding resource key was found neither fallback language is provided
- Definition of the message formatter, default Formatter will only return the translated key.
@Retention(RetentionPolicy.RUNTIME)
public @interface I18NPageTitle {
String messageKey() default "";
String defaultValue() default "";
Class< ? extends TitleFormatter> formatter() default DefaultTitleFormatter.class;
}The default usage should look like the following one.
@Route(View003.VIEW_003)
@I18NPageTitle(messageKey = "view.title")
public class View003 extends Composite<Div> implements HasLogger {
public static final String VIEW_003 = "view003";
}Now we need a way to resolve the final message and the right point in time to set the title. Here we could use the following interfaces.
- VaadinServiceInitListener,
- UIInitListener,
- BeforeEnterListener
With this interfaces we are able to hook into the life cycle of a view. At this time slots we have all information's we need. The Annotation to get the message key and the locale of the current request.
The class that is implementing all these interfaces is called I18NPageTitleEngine
public class I18NPageTitleEngine
implements VaadinServiceInitListener,
UIInitListener, BeforeEnterListener, HasLogger {
public static final String ERROR_MSG_NO_LOCALE = "no locale provided and i18nProvider #getProvidedLocales()# list is empty !! ";
public static final String ERROR_MSG_NO_ANNOTATION = "no annotation found at class ";
@Override
public void beforeEnter(BeforeEnterEvent event) {
Class<?> navigationTarget = event.getNavigationTarget();
I18NPageTitle annotation = navigationTarget.getAnnotation(I18NPageTitle.class);
match(
matchCase(() -> success(annotation.messageKey())) ,
matchCase(() -> annotation == null ,
() -> failure(ERROR_MSG_NO_ANNOTATION + navigationTarget.getName())) ,
matchCase(() -> annotation.messageKey().isEmpty() ,
() -> success(annotation.defaultValue()))
)
.ifPresentOrElse(
msgKey -> {
final I18NProvider i18NProvider = VaadinService
.getCurrent()
.getInstantiator()
.getI18NProvider();
final Locale locale = event.getUI().getLocale();
final List<Locale> providedLocales = i18NProvider.getProvidedLocales();
match(
matchCase(() -> success(providedLocales.get(0))) ,
matchCase(() -> locale == null && providedLocales.isEmpty() ,
() -> failure(ERROR_MSG_NO_LOCALE + i18NProvider.getClass().getName())) ,
matchCase(() -> locale == null ,
() -> success(providedLocales.get(0))) ,
matchCase(() -> providedLocales.contains(locale) ,
() -> success(locale))
).ifPresentOrElse(
finalLocale -> ((CheckedFunction<Class<? extends TitleFormatter>, TitleFormatter>) f -> f.getDeclaredConstructor().newInstance())
.apply(annotation.formatter())
.ifPresentOrElse(
formatter -> formatter
.apply(i18NProvider , finalLocale , msgKey).
ifPresentOrElse(title -> UI.getCurrent()
.getPage()
.setTitle(title) ,
failed -> logger().info(failed)) ,
failed -> logger().info(failed)) ,
failed -> logger().info(failed));
}
, failed -> logger().info(failed));
}
@Override
public void uiInit(UIInitEvent event) {
final UI ui = event.getUI();
ui.addBeforeEnterListener(this);
//addListener(ui, PermissionsChangedEvent.class, e -> ui.getPage().reload());
}
@Override
public void serviceInit(ServiceInitEvent event) {
event
.getSource()
.addUIInitListener(this);
}
}The method with the name beforeEnter is the important part. Here you can see how the key is resolved. But there is one new thing... let´s have a look ot the following lines.
final I18NProvider i18NProvider = VaadinService
.getCurrent()
.getInstantiator()
.getI18NProvider();This few lines are introducing a new thing, that is available in Vaadin 10. The interface I18NProvider is used to implement a mechanism for the internationalization of Vaadin applications.
The interface is simple and with only two methods to implement.
public interface I18NProvider extends Serializable {
List<Locale> getProvidedLocales();
String getTranslation(String key, Locale locale, Object... params);
}The first one should give back the list of Locales that could be handled from this implementation. The second method is used to translate the message key itself. In this method the handling of a default translation or better the switch into a default language should be handled. Missing keys can be handled differently. Some developers are throwing an exception, but I prefer to return the key itself, together with the locale from the original request. This information is mostly better to use as a stacktrace.
The solution that is bundled with this demo is able to handle the Locales EN ad DE, fallback will be the locale EN. The implementation is not dealing with reloads of message bundles during runtime or other features that are needed for professional environments.
public class VaadinI18NProvider implements I18NProvider, HasLogger {
public VaadinI18NProvider() {
logger().info("VaadinI18NProvider was found..");
}
public static final String RESOURCE_BUNDLE_NAME = "vaadinapp";
private static final ResourceBundle RESOURCE_BUNDLE_EN = getBundle(RESOURCE_BUNDLE_NAME , ENGLISH);
private static final ResourceBundle RESOURCE_BUNDLE_DE = getBundle(RESOURCE_BUNDLE_NAME , GERMAN);
@Override
public List<Locale> getProvidedLocales() {
logger().info("VaadinI18NProvider getProvidedLocales..");
return List.of(ENGLISH ,
GERMAN);
}
@Override
public String getTranslation(String key , Locale locale , Object... params) {
// logger().info("VaadinI18NProvider getTranslation.. key : " + key + " - " + locale);
return match(
matchCase(() -> success(RESOURCE_BUNDLE_EN)) ,
matchCase(() -> GERMAN.equals(locale) , () -> success(RESOURCE_BUNDLE_DE)) ,
matchCase(() -> ENGLISH.equals(locale) , () -> success(RESOURCE_BUNDLE_EN))
)
.map(resourceBundle -> {
if (! resourceBundle.containsKey(key))
logger().info("missing ressource key (i18n) " + key);
return (resourceBundle.containsKey(key)) ? resourceBundle.getString(key) : key;
})
.getOrElse(() -> key + " - " + locale);
}
}The Interface I18NProvider is implemented for example by the abstract class Component. Having this in mind, we are now using the same mechanism for the page title as well as inside a Component.
The last thing you should not forget is the activation of the I18NProvider implementation itself. There are several ways you can use, I am using a simple approach inside the main method that will start my app itself.
setProperty("vaadin.i18n.provider", VaadinI18NProvider.class.getName());
public class BasicTestUIRunner {
private BasicTestUIRunner() {
}
public static void main(String[] args) {
setProperty("vaadin.i18n.provider", VaadinI18NProvider.class.getName());
new Meecrowave(new Meecrowave.Builder() {
{
// randomHttpPort();
setHttpPort(8080);
setTomcatScanning(true);
setTomcatAutoSetup(false);
setHttp2(true);
}
})
.bake()
.await();
}
}The Vaadin documentation will give you more detailed information´s about this.
Last step for today, is the activation of our I18NPageTitleEngine This is done inside the file with the name com.vaadin.flow.server.VaadinServiceInitListener you have to create inside the folder META-INF/services The only line we have to add is the full qualified name of our class.
org.rapidpm.vaadin.v10.tb.demo.views.v03.i18n.I18NPageTitleEngine
If you have questions or something to discuss.. ping me via email mailto::sven.ruppert@gmail.com or via Twitter : https://twitter.com/SvenRuppert