How can I validate an unbounded wildcards elements?

Question

I'm writing a code with spring-boot-starter-web:2.1.6.RELEASE which transitively depends on hibernate-validator:6.0.17.

And I got following error.

java.lang.IllegalArgumentException: HV000116:
    type is not a reference type: ? extends java.math.BigDecimal

from

default @NotNull BigDecimal divide(
        @Size(min = 2, max = 2) @NotNull
        List<@NotNull ? extends BigDecimal> positioned) {
    ...
}

Especially from <@NotNull ? extends BigDecimal>.

What did I do wrong?

Here comes the stacktraces

java.lang.IllegalArgumentException: HV000116: type is not a reference type: ? extends java.math.BigDecimal
    at org.hibernate.validator.internal.util.Contracts.assertTrue(Contracts.java:73)
    at org.hibernate.validator.internal.util.TypeHelper.getErasedReferenceType(TypeHelper.java:193)
    at org.hibernate.validator.internal.metadata.core.MetaConstraints.addValueExtractorDescriptorForWrappedValue(MetaConstraints.java:82)
    at org.hibernate.validator.internal.metadata.core.MetaConstraints.create(MetaConstraints.java:55)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.createTypeArgumentMetaConstraint(AnnotationMetaDataProvider.java:795)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.lambda$findTypeUseConstraints$2(AnnotationMetaDataProvider.java:783)
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
    at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1654)
    at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:658)
    at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:274)
    at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
    at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.findTypeUseConstraints(AnnotationMetaDataProvider.java:784)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.findTypeArgumentsConstraints(AnnotationMetaDataProvider.java:762)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.findTypeAnnotationConstraintsForExecutableParameter(AnnotationMetaDataProvider.java:716)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.getParameterMetaData(AnnotationMetaDataProvider.java:429)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.findExecutableMetaData(AnnotationMetaDataProvider.java:300)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.getMetaData(AnnotationMetaDataProvider.java:285)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.getMethodMetaData(AnnotationMetaDataProvider.java:272)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.retrieveBeanConfiguration(AnnotationMetaDataProvider.java:134)
    at org.hibernate.validator.internal.metadata.provider.AnnotationMetaDataProvider.getBeanConfiguration(AnnotationMetaDataProvider.java:124)
    at org.hibernate.validator.internal.metadata.BeanMetaDataManager.getBeanConfigurationForHierarchy(BeanMetaDataManager.java:232)
    at org.hibernate.validator.internal.metadata.BeanMetaDataManager.createBeanMetaData(BeanMetaDataManager.java:199)
    at org.hibernate.validator.internal.metadata.BeanMetaDataManager.getBeanMetaData(BeanMetaDataManager.java:166)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateParameters(ValidatorImpl.java:265)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateParameters(ValidatorImpl.java:233)
    at org.springframework.validation.beanvalidation.MethodValidationInterceptor.invoke(MethodValidationInterceptor.java:112)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)

Answer 1

Your usage is correct. It's probably an implementation bug I think.

Look at how hibernate resolve type reference TypeHelper#getErasedReferenceType:

public static Class<?> getErasedReferenceType(Type type) {
    Contracts.assertTrue( isReferenceType( type ), "type is not a reference type: %s", type );
    return (Class<?>) getErasedType( type );
}

isReferenceType does not check for wildcard type TypeHelper#isReferenceType:

private static boolean isReferenceType(Type type) {
    return type == null
            || type instanceof Class<?>
            || type instanceof ParameterizedType
            || type instanceof TypeVariable<?>
            || type instanceof GenericArrayType;
}

So the assert failed when hibernate try to validate the content of list (caused of <@NotNull ? extends BigDecimal>)

But somehow the TypeHelper#getErasedType supports for wild card type:

public static Type getErasedType(Type type) {
    ...
    if ( type instanceof WildcardType ) {
        Type[] upperBounds = ( (WildcardType) type ).getUpperBounds();

        return getErasedType( upperBounds[0] );
    }
    ...
}

I will try to open an issue about this.