quarkusio/quarkus · error · RuntimeException

Unknown parameter type

Error message

Unknown parameter type 

What it means

EndpointIndexer.toClassName encountered a Type.Kind it cannot translate to a Java class name when resolving a resource method parameter/return type. The switch's default branch throws RuntimeException('Unknown parameter type ' + indexType) for kinds not explicitly handled (e.g. parameterized types in unexpected positions, intersection types).

Source

Thrown at independent-projects/resteasy-reactive/common/processor/src/main/java/org/jboss/resteasy/reactive/common/processor/EndpointIndexer.java:1162

            case WILDCARD_TYPE:
                WildcardType wildcardType = indexType.asWildcardType();
                Type extendsBound = wildcardType.extendsBound();
                if (extendsBound.name().equals(OBJECT)) {
                    // this is a super bound type that we don't support
                    throw new RuntimeException("Cannot handle wildcard type " + indexType);
                }
                // this is an extend bound type, so we just user the bound
                return wildcardType.name().toString();
            case TYPE_VARIABLE:
                TypeVariable typeVariable = indexType.asTypeVariable();
                if (typeVariable.bounds().isEmpty()) {
                    return Object.class.getName();
                }

                return toClassName(resolveTypeVariable(typeVariable, currentClass, actualEndpointClass, indexView),
                        currentClass, actualEndpointClass, indexView);
            default:
                throw new RuntimeException("Unknown parameter type " + indexType);
        }
    }

    private static Type resolveTypeVariable(TypeVariable typeVariable, ClassInfo currentClass, ClassInfo actualEndpointClass,
            IndexView indexView) {
        if (typeVariable.bounds().isEmpty()) {
            return Type.create(DotName.createSimple(Object.class.getName()), Kind.CLASS);
        }
        int pos = -1;
        List<TypeVariable> typeVariables = currentClass.typeParameters();
        for (int i = 0; i < typeVariables.size(); ++i) {
            if (typeVariables.get(i).identifier().equals(typeVariable.identifier())) {
                pos = i;
                break;
            }
        }
        if (pos != -1) {
            Type resolved = resolveTypeParameters(pos, actualEndpointClass, currentClass, indexView);

View on GitHub (pinned to e1c734241f)

Solutions

1. Simplify the endpoint method signature to concrete, non-generic or simple-generic types
2. Move complex generic types out of the REST layer into internal service code
3. Check the Quarkus/RESTEasy Reactive version; upgrade, since type-kind support grows over time; file an issue with a reproducer if it persists

Example fix

// before
@POST
public void create(Map<String, Map<String, List<Set<?>>>> payload) { ... }
// after
@POST
public void create(MyDto payload) { ... }

// Keep endpoint signatures to supported kinds: Class, simple ParameterizedType, arrays
static void validateEndpoint(Method m) {
    java.util.ArrayDeque<java.lang.reflect.Type> q = new java.util.ArrayDeque<>();
    q.add(m.getGenericReturnType());
    for (java.lang.reflect.Type p : m.getGenericParameterTypes()) q.add(p);
    while (!q.isEmpty()) {
        java.lang.reflect.Type t = q.poll();
        if (t instanceof ParameterizedType pt) {
            for (java.lang.reflect.Type a : pt.getActualTypeArguments()) {
                if (!(a instanceof Class) && !(a instanceof ParameterizedType))
                    throw new IllegalStateException("Unsupported type in " + m + ": " + a);
                q.add(a);
            }
        }
    }
}

When it happens

Trigger: Deploying an endpoint whose method signature contains a Jandex Type kind the processor does not support — typically exotic generics, intersection bounds, or nested parameterized types in the endpoint declaration.

Common situations: Very complex generic declarations (nested generics of generics) in resource methods; generated or bytecode-enhanced types with unusual type structures; framework versions encountering a new type shape from newer Java features.

Related errors

• Cannot handle wildcard type
• Failed to find Collection supertype of ${field}
• Unsupported type: " + type
• Parameter: ${i} of the constructor of class '${resourceDotNa
• Unable to load handled exception type ${i.getProvidedType()}

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/1d992255515a4ab9. Report an issue: GitHub.