Worker Thread ClassLoader cannot load property files on Java 21

[MichaelPluessErni]

Description of the bug

With the upgrade from Java 17 to Java 21 we stumbled upon a bug when retrieving translations in worker threads.
We need this because we call slower services asynchronously and update the UI after receiving the responses.

Specifically, when calling getTranslation on the worker thread, the TranslationService is not able to locate/load the property file with the translations, thus returning the key of the property instead of the translated text.

Important to note: This does not occur when running the application in DEV mode! It only occurs in Production mode.

We use Vaadin 24.4.22 together with Spring Boot 3.3.8. (Error also occurs with Vaadin 24.6.4)

Expected behavior

It should be possible to call getTranslation asynchronously. (like it is possible for Java 17)

Minimal reproducible example

Template to reproduce:

// inside component code, in UI thread
Component holder = this;
CompletableFuture
    .supplyAsync(() -> {
        // expensive operation
        return "1234";
    })
    .thenAccept(orderNumber -> {
        // in worker thread
        Optional<UI> ui = holder.getUI();
        if (ui.isPresent()) {
            ui.get().access(() -> {
                // this will return "order.number.title" instead of translated text
                holder.add(new Span(getTranslation("order.number.title", orderNumber)));
            });
        }
    });

Versions

• Vaadin / Flow version: 24.4.22 / 24.6.4
• Java version: 21
• Spring Boot: 3.3.8
• OS version:
• Browser version (if applicable):
• Application Server (if applicable): Spring Boot: 3.3.8
• IDE (if applicable):

[MichaelPluessErni]

We ended up using this work-around in the worker thread, to still be able to build UI asynchronously:

Thread.currentThread().setContextClassLoader(component.getClass().getClassLoader());

[mcollovati]

I cannot reproduce using the provided code with Vaadin 24.4.22,Spring Boot: 3.3.8 and Java 21.0.6 (Temurin) and running the application for the production JAR. The translations are correctly loaded and show on the page.

Can you provide an example project that reproduces the issue?

[mcollovati]

BTW, 24.4 is EOL. I suggest upgrading to the latest supported version.

[mcollovati]

Works for me also with Vaadin 24.6.4 and Spring Boot 3.4.1

[mshabarov]

@MichaelPluessErni what JVM implementation/supplier do you use?

Could you also elaborate more what is the TranslationService that you refer to, is it something that Vaadin provides? I could find TranslationService in Vaadin Control Center, but not sure if it's the one you mentioned.

[MichaelPluessErni]

@mcollovati @mshabarov Thank you both for taking a look at this issue.

We use Java 21.0.5 Temurin.

For getTranslation we use the default implementation of ch.coop.vaadin.i18n.TranslationService (which itself uses org.springframework.context.MessageSource).

I cannot say whether I'll be able to create a full example project to demonstrate the bug. But if I succeed, I'll be sure to post it here.

[mshabarov]

ch.coop.vaadin.i18n.TranslationService is not a part of Vaadin framework.

Vaadin ships DefaultI18nProvider for Spring which uses ResourceBundle.
You have probably hit by a similar issue as in #18977.

Do you mind to try using Vaadin default implementation for i18n, see https://vaadin.com/docs/latest/flow/advanced/i18n-localization ?

[MichaelPluessErni]

The DefaultI18NProvider is not an option for our project, because we consume translations not only from our module, but also from a parent module.
Specifically, the issue lies with ResourceBundle, because it cannot load from different classpaths. Thus we have to use ReloadableResourceBundleMessageSource in our implementation of I18NProvider.