Set locale from langauge stored in cookie before loading pages

Flow
1

When a user select a language in my app, the language is stored in a cookie, to remember the language the next session.

But where/when is it appropriate to read the cookie and set the language when starting a new session - such that is set before any page is loaded (e.g. login page, about page, etc)?

2

The simplest would be to read the cookie in the BeforeEnterObserver.beforeEnter in every view.

You can create a base class that implements that code for your views.

Then you don’t have to care if it’s already set or not.

3

In my example app I do it in afterNavigation of the login view.

The same app provides you example how to persist the selected language to cookie as well using request handler.

4

I’m usually doing this, if you’re using Spring Boot:

@Component
public class ApplicationFormBaseUIInitializer implements VaadinServiceInitListener {

    @Override
    public void serviceInit(ServiceInitEvent event) {
        event.addIndexHtmlRequestListener(indexHtmlResponse -> {
            String lang = readCookie(indexHtmlResponse.getVaadinRequest().getCookies(), "locale").orElse("de-DE");
            Locale locale = Locale.forLanguageTag(lang);
            indexHtmlResponse.getDocument().getElementsByTag("html")
                    .attr("lang", locale.getLanguage());

            VaadinSession.getCurrent().setLocale(locale);
        });
    }

    public Optional<String> readCookie(Cookie[] cookies, String key) {
        if (cookies == null) {
            return Optional.empty();
        }
        return Arrays.stream(cookies)
                .filter(c -> key.equals(c.getName()))
                .map(Cookie::getValue)
                .findFirst();
    }
}

It will be set the correct html tag from the cookie and set the locale of the Vaadin session. (see the open ticket here: Lang attribute on the html tag is not in sync with the UI locale · Issue #18585 · vaadin/flow · GitHub )

5

I do indeed. This looks pretty neat. I’ll try it out