quarkusio/quarkus · error · IllegalStateException

Cannot instantiate JSON-B component:

Error message

Cannot instantiate JSON-B component: 

What it means

QuarkusJsonbComponentInstanceCreator resolves JSON-B components (Jsonb, JsonbBuilder, custom components) from CDI; fallbackCreate is a last resort that tries a no-arg constructor. When reflection-based instantiation fails (abstract class, missing no-arg constructor, throwing constructor, illegal access), it throws IllegalStateException 'Cannot instantiate JSON-B component: <class>'. This almost always means a custom JSON-B component was registered that Quarkus cannot construct.

Source

Thrown at extensions/jsonb/runtime/src/main/java/io/quarkus/jsonb/QuarkusJsonbComponentInstanceCreator.java:57

            ArcContainer container = Arc.container();
            if (container == null) { // this class can be used in unit tests where Arc obviously doesn't run
                return fallbackCreate(componentClass);
            }

            InstanceHandle<T> beanHandle = container.instance(componentClass);
            if (beanHandle.isAvailable()) {
                beanHandles.add(beanHandle);
                return beanHandle.get();
            }
            return fallbackCreate(componentClass);
        });
    }

    private <T> Object fallbackCreate(Class<T> componentClass) {
        try {
            return componentClass.getDeclaredConstructor().newInstance();
        } catch (InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException e) {
            throw new IllegalStateException("Cannot instantiate JSON-B component: " + componentClass, e);
        }
    }

}

View on GitHub (pinned to e1c734241f)

Solutions

1. Give the component class a public no-arg constructor and make it concrete (non-abstract)
2. Register the component instance via JsonbConfig.withSerializers/withAdapters using an explicit instance instead of relying on class-based registration
3. Make the component a CDI bean and configure it through Quarkus's JSON-B CDI integration instead of the fallback path
4. Check the cause chain for the exception thrown inside the component constructor

Example fix

// before
public class ZonedDateTimeSerializer implements JsonbSerializer<ZonedDateTime> {
    private final ZoneId zone; // no no-arg ctor
    ...
}
// after
public class ZonedDateTimeSerializer implements JsonbSerializer<ZonedDateTime> {
    public ZonedDateTimeSerializer() { this.zone = ZoneId.systemDefault(); }
    ...
}

static <T> boolean canInstantiate(Class<T> c) {
    try {
        c.getDeclaredConstructor().newInstance();
        return true;
    } catch (ReflectiveOperationException | RuntimeException e) {
        return false;
    }
}

static <T> boolean hasPublicNoArgCtor(Class<T> c) {
    try { return java.lang.reflect.Modifier.isPublic(c.getModifiers())
        && !java.lang.reflect.Modifier.isAbstract(c.getModifiers())
        && c.getDeclaredConstructor().getParameterCount() == 0; }
    catch (NoSuchMethodException e) { return false; }
}

try {
    // Quarkus JSON-B setup that triggers component creation
} catch (IllegalStateException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("Cannot instantiate JSON-B component:")) {
        log.errorf(e.getCause(), "Fix component %s: needs public no-arg ctor or explicit registration", e.getMessage());
    } else throw e;
}

When it happens

Trigger: Registering a custom JsonbConfig component, JsonbAdapter, JsonbSerializer/Deserializer, or instance creator class that has no public no-arg constructor, is abstract, or whose constructor throws; and the component was not available as a CDI bean so the fallback path was used.

Common situations: User adds a JSON-B serializer/adapter class with only constructor arguments and registers it globally; upgrading Quarkus/Yasson where the component resolution path changed; a component class throwing inside its constructor (e.g. reading a missing config).

Related errors

• Cache key generator instantiation failed
• Unable to instantiate the class:
• Couldn't extract all parameters information for constructor
• Multiple @Inject constructors on ${theClass}
• Failed to set dev services config

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/e295e83743f7ed0a. Report an issue: GitHub.