quarkusio/quarkus · error · IllegalArgumentException

Unsupported annotation target kind

Error message

Unsupported annotation target kind 

What it means

The ConfigurationPropertiesProcessor scans the application index for Spring @ConfigurationProperties annotations. It handles targets on classes and methods (@Produces), but if the annotation appears on another target kind (field, parameter, etc.) the default branch throws IllegalArgumentException 'Unsupported annotation target kind <kind>'.

Source

Thrown at extensions/spring-boot-properties/deployment/src/main/java/io/quarkus/spring/boot/properties/deployment/ConfigurationPropertiesProcessor.java:73

            boolean ignoreMismatching = true;
            AnnotationValue ignoreUnknownFieldsValue = annotation.value("ignoreUnknownFields");
            if (ignoreUnknownFieldsValue != null) {
                ignoreMismatching = ignoreUnknownFieldsValue.asBoolean();
            }
            switch (annotation.target().kind()) {
                case CLASS:
                    metadata.add(
                            new ConfigurationPropertiesMetadataBuildItem(annotation.target().asClass(), getPrefix(annotation),
                                    namingStrategy, !ignoreMismatching));
                    break;
                case METHOD:
                    onMethodInstances.add(annotation.target().asMethod());
                    metadata.add(new ConfigurationPropertiesMetadataBuildItem(
                            index.getClassByName(annotation.target().asMethod().returnType().name()), getPrefix(annotation),
                            namingStrategy, !ignoreMismatching, ArcInstanceFactory.INSTANCE));
                    break;
                default:
                    throw new IllegalArgumentException(
                            "Unsupported annotation target kind " + annotation.target().kind().name());
            }
        }

        if (!onMethodInstances.isEmpty()) {
            // the idea here is to transform the producer to add a special qualifier that will then be
            // used by the generated code in order to obtain the instance of the class
            transformerProducer.produce(new AnnotationsTransformerBuildItem(new AnnotationsTransformer() {

                @Override
                public boolean appliesTo(AnnotationTarget.Kind kind) {
                    return kind == AnnotationTarget.Kind.METHOD;
                }

                @Override
                public void transform(TransformationContext transformationContext) {
                    Collection<AnnotationInstance> instances = transformationContext.getAnnotations();
                    boolean matches = false;

View on GitHub (pinned to e1c734241f)

Solutions

1. Move @ConfigurationProperties onto the class declaration (the supported style).
2. Alternatively place it on a @Produces producer method that returns the config class.
3. Remove the annotation from fields/parameters where it is invalid.

Example fix

// before
public class App {
    @ConfigurationProperties(prefix = "app")
    private AppProps props; // unsupported target
}

// after
@ConfigurationProperties(prefix = "app")
public class AppProps { ... }

// verify @ConfigurationProperties is only on classes or @Produces methods
class App {
  // INVALID: @ConfigurationProperties on a field
}

When it happens

Trigger: Placing @ConfigurationProperties on an annotation target Quarkus does not support — e.g. on a field or a constructor parameter — instead of on a class or on a @Produces method; raised in produceConfigPropertiesMetadata while iterating indexed annotation instances.

Common situations: Annotating a field because Spring also allows constructor binding there; IDE auto-import placing the annotation on the wrong element; copying code from a Spring Boot project where field placement worked.

Related errors

• Name cannot start with '/':${name}
• messageStarts cannot be empty
• 'target' can only be a class, a field or a method: <target>
• Unsupported target:
• Unsupported object of type ${object.getClass()}. Supported t

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/f23e7cbbf4f5a66d. Report an issue: GitHub.