quarkusio/quarkus · error · IllegalArgumentException

Raw MultivaluedMap parameter types are not supported. Offend

Error message

Raw MultivaluedMap parameter types are not supported. Offending method is: {jandexMethod}

What it means

Same build-time check as the raw Map case, but specifically for `jakarta.ws.rs.core.MultivaluedMap`. The client processor must know the key/value types to generate code that populates headers or form params, and a raw MultivaluedMap provides no type information. Deployment aborts with this IllegalArgumentException.

Source

Thrown at extensions/resteasy-reactive/rest-client-jaxrs/deployment/src/main/java/io/quarkus/jaxrs/client/reactive/deployment/JaxrsClientReactiveProcessor.java:3405

        }

        isParamNull.trueBranch().assign(result, webTarget);

        return result;
    }

    private Map.Entry<Type, Type> resolveMapTypes(Type type, MethodInfo jandexMethod) {
        if (type.name().equals(ResteasyReactiveDotNames.MAP)) {
            if (type.kind() != PARAMETERIZED_TYPE) {
                throw new IllegalArgumentException(
                        "Raw Map parameter types are not supported. Offending method is: " + jandexMethod);
            }
            var parameterizedType = type.asParameterizedType();
            var arguments = parameterizedType.arguments();
            return new AbstractMap.SimpleEntry<>(arguments.get(0), arguments.get(1));
        } else if (type.name().equals(ResteasyReactiveDotNames.MULTI_VALUED_MAP)) {
            if (type.kind() != PARAMETERIZED_TYPE) {
                throw new IllegalArgumentException(
                        "Raw MultivaluedMap parameter types are not supported. Offending method is: " + jandexMethod);
            }
            var parameterizedType = type.asParameterizedType();
            var arguments = parameterizedType.arguments();
            return new AbstractMap.SimpleEntry<>(arguments.get(0), ParameterizedType.create(ResteasyReactiveDotNames.LIST,
                    new Type[] { arguments.get(1) }, null));
        }
        // TODO: we could support this if necessary by looking up the resolved types via JandexUtil.resolveTypeParameters
        throw new IllegalArgumentException("Unsupported Map type '" + type.name() + "'. Offending method is: " + jandexMethod);
    }

    private BranchResult iteratorHasNext(BytecodeCreator creator, ResultHandle iterator) {
        return creator.ifTrue(
                creator.invokeInterfaceMethod(ofMethod(Iterator.class, "hasNext", boolean.class), iterator));
    }

    private void addWebTargetParamToWebTarget(BytecodeCreator creator, ResultHandle paramName,
            ResultHandle webTarget,

View on GitHub (pinned to e1c734241f)

Solutions

Declare `MultivaluedMap<String, String>` with explicit type arguments (the processor wraps the value type in List automatically)
If you need multiple values per key as a plain body, use `Map<String, List<String>>` instead
For arbitrary JSON bodies use `Map<String, Object>` or `String` with a custom serializer

Example fix

// before
@POST void submit(MultivaluedMap form);
// after
@POST void submit(MultivaluedMap<String, String> form);

Defensive patterns

Strategy: validation

Validate before calling

if (param instanceof MultivaluedMap mv) { if (mv.getClass().getGenericSuperclass() instanceof ParameterizedType) { /* ok */ } else throw new IllegalArgumentException("MultivaluedMap must be parameterized"); }

Type guard

static boolean isParameterizedMultivaluedMap(java.lang.reflect.Type t) { return t instanceof ParameterizedType pt && MultivaluedMap.class.isAssignableFrom((Class<?>) pt.getRawType()); }

Prevention

Prefer MultivaluedMap<String,String> for form/headers
Run build with -Xlint:rawtypes
Add code review checklist item for REST client interface generics

When it happens

Trigger: A REST client interface method with a raw `MultivaluedMap` parameter (e.g. `@FormParam` body `MultivaluedMap form`), processed at build time by JaxrsClientReactiveProcessor.

Common situations: Copying resource method signatures from tutorials that omit generics; refactoring `Map` to `MultivaluedMap` without adding type arguments; legacy JAX-RS code using raw types.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/2c899242d85a764c. Report an issue: GitHub.