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Custom I18N Provider

Implementing a custom I18NProvider for advanced localization needs.

The built-in DefaultI18NProvider loads translations from property files in src/main/resources/vaadin-i18n/. If you need more control — loading translations from a database, using a different file structure, or applying custom fallback logic — implement the I18NProvider interface.

Implementing I18NProvider

The following example enables Finnish and English, with Finnish as the default. Translation files use the translate prefix (e.g., translate.properties, translate_fi_FI.properties, translate_en_GB.properties) and are loaded from the classpath (e.g., src/main/resources/):

Source code
Java
public class TranslationProvider implements I18NProvider {

    public static final String BUNDLE_PREFIX = "translate";

    public final Locale LOCALE_FI = new Locale("fi", "FI");
    public final Locale LOCALE_EN = new Locale("en", "GB");

    private List<Locale> locales = Collections
            .unmodifiableList(Arrays.asList(LOCALE_FI, LOCALE_EN));

    @Override
    public List<Locale> getProvidedLocales() {
        return locales;
    }

    @Override
    public String getTranslation(String key, Locale locale, Object... params) {
        if (key == null) {
            LoggerFactory.getLogger(TranslationProvider.class.getName())
                    .warn("Got lang request for key with null value!");
            return "";
        }

        final ResourceBundle bundle = ResourceBundle.getBundle(BUNDLE_PREFIX, locale);

        String value;
        try {
            value = bundle.getString(key);
        } catch (final MissingResourceException e) {
            LoggerFactory.getLogger(TranslationProvider.class.getName())
                    .warn("Missing resource", e);
            return "!" + locale.getLanguage() + ": " + key;
        }
        if (params.length > 0) {
            value = MessageFormat.format(value, params);
        }
        return value;
    }
}

In development mode, React views also need the getAllTranslations() method, which the example above doesn’t implement. See Custom I18N Providers in Localization in React Views.

Configuring the Provider

For Spring Boot projects, annotate your provider with @Component and it’s automatically detected — no further configuration needed:

Source code
Java
@Component
public class TranslationProvider implements I18NProvider {
    // ...
}

CDI-based projects can use a similar approach with CDI beans.

For other setups, set the i18n.provider property to the fully qualified class name of your provider, either as a system property:

Source code
terminal
mvn jetty:run -Dvaadin.i18n.provider=com.vaadin.example.ui.TranslationProvider

Or via the @WebServlet annotation:

Source code
Java
@WebServlet(urlPatterns = "/*", name = "slot", asyncSupported = true, loadOnStartup = 1,
   initParams = { @WebInitParam(name = "i18n.provider", value = "com.vaadin.example.ui.TranslationProvider") })
public class ApplicationServlet extends VaadinServlet {
}

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