quarkusio/quarkus · error · java.lang.IllegalArgumentException

Not a message bundle interface:

Error message

Not a message bundle interface: 

What it means

MessageBundles.get() resolves a CDI bean implementing the given message bundle interface at runtime. Before lookup it validates the argument is an interface; passing a class throws IllegalArgumentException('Not a message bundle interface: ...').

Source

Thrown at extensions/qute/runtime/src/main/java/io/quarkus/qute/i18n/MessageBundles.java:41

import io.quarkus.qute.TemplateInstance;
import io.quarkus.qute.Variant;
import io.quarkus.qute.runtime.MessageBundleRecorder.BundleContext;

public final class MessageBundles {

    public static final String ATTRIBUTE_LOCALE = TemplateInstance.LOCALE;
    public static final String DEFAULT_LOCALE = "<<default>>";

    private MessageBundles() {
    }

    public static <T> T get(Class<T> bundleInterface) {
        return get(bundleInterface, null);
    }

    public static <T> T get(Class<T> bundleInterface, Localized localized) {
        if (!bundleInterface.isInterface()) {
            throw new IllegalArgumentException("Not a message bundle interface: " + bundleInterface.getName());
        }
        if (!bundleInterface.isAnnotationPresent(MessageBundle.class)
                && !bundleInterface.isAnnotationPresent(Localized.class)) {
            throw new IllegalArgumentException(
                    "Message bundle interface must be annotated either with @MessageBundle or with @Localized: "
                            + bundleInterface.getName());
        }
        ArcContainer container = Arc.requireContainer();
        InstanceHandle<T> handle = localized != null ? container.instance(bundleInterface, localized)
                : container.instance(bundleInterface);
        if (handle.isAvailable()) {
            return handle.get();
        }
        throw new IllegalStateException(Qute.fmt(
                "Unable to obtain a message bundle for interface [{ifacename}]{#if loc} and locale [{loc.value}]{/if}")
                .data("ifacename", bundleInterface.getName())
                .data("loc", localized)
                .render());

View on GitHub (pinned to e1c734241f)

Solutions

1. Pass only the message bundle interface (annotated with @MessageBundle or @Localized)
2. If the type became a class, restore it as an interface to keep bundle support
3. Check imports — make sure you reference the interface, not a similarly named impl class

Example fix

// before
MyMessages m = MessageBundles.get(MyMessagesImpl.class);
// after
MyMessages m = MessageBundles.get(MyMessages.class);

if (!bundleInterface.isInterface()) {
    throw new IllegalArgumentException(bundleInterface + " is not an interface");
}

static <T> boolean isBundleCandidate(Class<T> c) {
    return c.isInterface() && (c.isAnnotationPresent(MessageBundle.class) || c.isAnnotationPresent(Localized.class));
}

try {
    MyMessages m = MessageBundles.get(MyMessages.class);
} catch (IllegalArgumentException e) {
    if (e.getMessage().startsWith("Not a message bundle interface")) {
        throw new IllegalStateException("Pass the bundle interface, not a class", e);
    }
    throw e;
}

When it happens

Trigger: Calling MessageBundles.get(SomeClass.class) or MessageBundles.get(iface, locale) where the Class argument is a concrete class, enum, or record rather than an interface.

Common situations: Autocompleting to a wrong class type; confusing MessageBundles.get with a generic service locator API; refactoring an interface into an abstract class while call sites remain.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Message bundle interface must be annotated either with @Mess
• Unable to obtain a message bundle for interface [{ifacename}
• Bean not found for localized interface [{e.value}] and local
• Multiple beans found for localized interface [{e.value}] and
• Locale of [%s] conflicts with the locale [%s] of the default

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/14535973f0f616f5. Report an issue: GitHub.