Load texts from your own source

Add your own string resource loader when texts do not come from properties files next to your classes: translations kept in a database so that editors can change them, an existing Java ResourceBundle shared with other applications, or a translation service. Wicket asks its loaders in turn until one returns a text; see Where Wicket looks for texts for the default chain.

Write a loader

Implement IStringResourceLoader. It has two methods: one that gets the component asking for the text, and one that gets only a class. Return null when you have no text for the key, so that the next loader gets its turn. Do not throw an exception for a missing key.

DatabaseStringResourceLoader.java

public class DatabaseStringResourceLoader implements IStringResourceLoader {

    private final TranslationRepository translations;

    public DatabaseStringResourceLoader(TranslationRepository translations) {
        this.translations = translations;
    }

    @Override
    public String loadStringResource(Class<?> clazz, String key, Locale locale,
            String style, String variation) {
        return translations.find(key, locale).orElse(null);
    }

    @Override
    public String loadStringResource(Component component, String key, Locale locale,
            String style, String variation) {
        return loadStringResource(component != null ? component.getClass() : null,
            key, locale, style, variation);
    }
}

TranslationRepository stands for your own data access. Wicket passes the locale as it is, for example de_CH. Falling back from de_CH to de and then to a default text is up to the repository.

The locale, style and variation are already resolved from the component; use the arguments, not the component, to read them.

Register the loader

Add the loader to the list in the resource settings, in the init() method of your application. The position decides its priority:

@Override
protected void init() {
    super.init();
    List<IStringResourceLoader> loaders = getResourceSettings().getStringResourceLoaders();

    // database texts override the properties files
    loaders.add(0, new DatabaseStringResourceLoader(translationRepository));

    // or: properties files first, database as a fallback
    // loaders.add(new DatabaseStringResourceLoader(translationRepository));
}

The list is modifiable, so you can also remove a default loader, or clear it and build your own chain.

Make changed texts visible

The Localizer caches every lookup by key, component path, locale, style and variation, including lookups that found nothing. When a text in your source changes, clear the cache:

Localizer.get().clearCache();

Localizer#setEnableCache(false) turns the cache off, which helps while you edit texts during development and costs a lookup in every loader on every request.

Reuse an existing Java ResourceBundle

BundleStringResourceLoader reads texts from a standard ResourceBundle by its base name, with Java’s own lookup by locale:

getResourceSettings().getStringResourceLoaders()
    .add(new BundleStringResourceLoader("com.example.i18n.Messages"));

It ignores style, variation and the component.

Refer to other keys from a text

NestedStringResourceLoader wraps a list of loaders and replaces references to other keys inside a text. You choose the syntax with a regular expression whose first group is the key:

List<IStringResourceLoader> loaders = getResourceSettings().getStringResourceLoaders();
NestedStringResourceLoader nested = new NestedStringResourceLoader(loaders,
    Pattern.compile("#\\(([^ ]*?)\\)"));
loaders.clear();
loaders.add(nested);

app.name=Acme Shop
welcome=Welcome to #(app.name)!

When a referenced key is not found, the whole text is not found.

Rename the package bundle files

Package bundles are called wicket-package.properties. To use another name, replace the PackageStringResourceLoader in the list with one that has another file name:

PackageStringResourceLoader packageLoader = new PackageStringResourceLoader();
packageLoader.setFilename("messages");
List<IStringResourceLoader> loaders = getResourceSettings().getStringResourceLoaders();
loaders.replaceAll(loader -> loader instanceof PackageStringResourceLoader ? packageLoader : loader);