quarkusio/quarkus · error · UnsupportedOperationException

AnnotationTransformation is not an AnnotationsTransformer: <

Error message

AnnotationTransformation is not an AnnotationsTransformer: <transformer>

What it means

AnnotationsTransformerBuildItem wraps either a legacy AnnotationsTransformer or the newer AnnotationTransformation API. This deprecated accessor throws UnsupportedOperationException when the wrapped object is an AnnotationTransformation (lambda-style) rather than an instance of the old AnnotationsTransformer interface, because it cannot be downcast.

Source

Thrown at extensions/arc/deployment/src/main/java/io/quarkus/arc/deployment/AnnotationsTransformerBuildItem.java:45

     */
    @Deprecated(forRemoval = true)
    public AnnotationsTransformerBuildItem(AnnotationsTransformer transformer) {
        this.transformer = transformer;
    }

    public AnnotationsTransformerBuildItem(AnnotationTransformation transformation) {
        this.transformer = transformation;
    }

    /**
     * @deprecated use {@link #getAnnotationTransformation()}
     */
    @Deprecated(forRemoval = true)
    public AnnotationsTransformer getAnnotationsTransformer() {
        if (transformer instanceof AnnotationsTransformer) {
            return (AnnotationsTransformer) transformer;
        }
        throw new UnsupportedOperationException("AnnotationTransformation is not an AnnotationsTransformer: " + transformer);
    }

    public AnnotationTransformation getAnnotationTransformation() {
        return transformer;
    }

}

View on GitHub (pinned to e1c734241f)

Solutions

1. Use getAnnotationTransformation() instead of the deprecated getAnnotationsTransformer()
2. If you need an AnnotationsTransformer, construct the build item with an AnnotationsTransformer instance (transformation(combine(AnnotationsTransformer)) style)
3. Check `transformer instanceof AnnotationsTransformer` before calling the getter

Example fix

// before
AnnotationsTransformer t = item.getAnnotationsTransformer();
// after
AnnotationTransformation t = item.getAnnotationTransformation();

if (item.getAnnotationTransformation() instanceof AnnotationsTransformer at) { /* legacy path */ }

boolean isLegacyTransformer(AnnotationsTransformerBuildItem item) {
    return item.getAnnotationTransformation() instanceof AnnotationsTransformer;
}

When it happens

Trigger: Calling getAnnotationsTransformer() on a build item constructed with an AnnotationTransformation (e.g. via AnnotationsTransformerBuildItem.builder()...transformation(...)), i.e. anything not created with an AnnotationsTransformer instance.

Common situations: Old code or third-party extensions migrated to the new AnnotationTransformation API still consuming the item through the deprecated getter; build steps written before the API split being paired with transformers written after it.

Related errors

• Invalid configuration value set for 'quarkus.arc.remove-unus
• Different default scopes defined for additional bean class:
• Unexpected value: <arcConfig.optimizeContexts()>
• A matching predicate must be set!
• 'target' can only be a class, a field or a method: <target>

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/70f97278f99340f6. Report an issue: GitHub.