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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;
    }
}

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 {
}