quarkusio/quarkus · error · DefinitionException

Producer method must not have an @Observes parameter (altern

Error message

Producer method must not have an @Observes parameter (alternatively, observer method must not be annotated @Produces): 

What it means

ArC throws this DefinitionException when a producer method declares a parameter annotated @Observes, or an observer method is annotated @Produces. Observer parameters are exclusive to observer methods; producer methods only accept plain injection parameters. forBean's METHOD branch validates producer parameters against OBSERVES.

Source

Thrown at independent-projects/arc/processor/src/main/java/io/quarkus/arc/processor/Injection.java:287

                }
            }
            validateInjections(injections, beanType);
            return injections;
        } else if (Kind.METHOD.equals(beanTarget.kind())) {
            MethodInfo producerMethod = beanTarget.asMethod();

            if (beanDeployment.hasAnnotation(producerMethod, DotNames.INJECT)) {
                throw new DefinitionException("Producer method must not be annotated @Inject "
                        + "(alternatively, initializer method must not be annotated @Produces): "
                        + producerMethod);
            }
            if (Annotations.hasParameterAnnotation(beanDeployment, producerMethod, DotNames.DISPOSES)) {
                throw new DefinitionException("Producer method must not have a @Disposes parameter "
                        + "(alternatively, disposer method must not be annotated @Produces): "
                        + producerMethod);
            }
            if (Annotations.hasParameterAnnotation(beanDeployment, producerMethod, DotNames.OBSERVES)) {
                throw new DefinitionException("Producer method must not have an @Observes parameter "
                        + "(alternatively, observer method must not be annotated @Produces): "
                        + producerMethod);
            }
            if (Annotations.hasParameterAnnotation(beanDeployment, producerMethod, DotNames.OBSERVES_ASYNC)) {
                throw new DefinitionException("Producer method must not have an @ObservesAsync parameter "
                        + "(alternatively, async observer method must not be annotated @Produces): "
                        + producerMethod);
            }

            if (producerMethod.parameterTypes().isEmpty()) {
                return Collections.emptyList();
            }
            // All parameters are injection points
            List<Injection> injections = Collections.singletonList(new Injection(producerMethod,
                    InjectionPointInfo.fromMethod(producerMethod, declaringBean.getImplClazz(), beanDeployment, transformer)));
            validateInjections(injections, beanType);
            return injections;
        }

View on GitHub (pinned to e1c734241f)

Solutions

1. Remove @Observes from the producer method parameter
2. Add a dedicated observer method in the bean if event handling is needed
3. Pass any required dependencies as plain producer parameters (injection points)
4. Rebuild; failure occurs during Quarkus augmentation

Example fix

// before
@Produces
State state(@Observes RefreshEvent e) { return compute(); }

// after
@Produces
State state() { return compute(); }

void onRefresh(@Observes RefreshEvent e) { refresh(); }

void checkProducer(Method m) {
    if (!m.isAnnotationPresent(jakarta.enterprise.inject.Produces.class)) return;
    for (var p : m.getParameters()) {
        if (p.isAnnotationPresent(jakarta.enterprise.event.Observes.class)) {
            throw new IllegalStateException("@Observes on producer param: " + m);
        }
    }
}

When it happens

Trigger: Declaring @Produces Foo produce(@Observes MyEvent e); caught by Annotations.hasParameterAnnotation(producerMethod, DotNames.OBSERVES) in forBean.

Common situations: Combining event-driven production with the producer API; copy-paste from an observer method; attempting lazy/event-based bean creation which CDI does not support via @Observes on producers.

Related errors

• Bean constructor must not have an @Observes parameter:
• Initializer method must not have an @Observes parameter (alt
• Producer method must not be annotated @Inject (alternatively
• Producer method must not have a @Disposes parameter (alterna
• Bean constructor must not have a @Disposes parameter:

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/988636aedf3ec78e. Report an issue: GitHub.