`BeanUtils.getPropertyDescriptors(…)` for Kotlin class with Java superclass does not include properties from its superclass

[cmdjulian]

After updating to Spring Boot 3.2, my Kotlin app does not start anymore with an exception of Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property 'queryLookupStrategyKey' of bean class [com.example.demo.JpaRepositoryFactoryBeanImpl]: Bean property 'queryLookupStrategyKey' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?.

After debugging for some time I found out that in 3.2 there seems to be some new property introspection for kotlin classes and their properties are active. The problem seems to be, that the setters from the super class, in that case JpaRepositoryFactoryBean are not recognized as they are not Kotlin properties.

I can work around that by including the following code:

private var queryLookupStrategyKey: Key
    get() = throw UnsupportedOperationException()
    @JvmName("setQueryLookupStrategyKeyKt") set(value) {
        super.setQueryLookupStrategyKey(value)
    }
private var lazyInit: Boolean
    get() = throw UnsupportedOperationException()
    @JvmName("setLazyInitKt") set(value) {
        super.setLazyInit(value)
    }
private var namedQueries: NamedQueries
    get() = throw UnsupportedOperationException()
    @JvmName("namedQueriesKt") set(value) {
        super.setNamedQueries(value)
    }
private var repositoryFragments: RepositoryFragments
    get() = throw UnsupportedOperationException()
    @JvmName("setRepositoryFragmentsKt") set(value) {
        super.setRepositoryFragments(value)
    }
private var transactionManager: String
    get() = throw UnsupportedOperationException()
    @JvmName("setTransactionManagerKt") set(value) {
        super.setTransactionManager(value)
    }
private var entityManager: EntityManager
    get() = throw UnsupportedOperationException()
    @JvmName("setEntityManagerKt") set(value) {
        super.setEntityManager(value)
    }
private var escapeCharacter: Char
    get() = throw UnsupportedOperationException()
    @JvmName("setEscapeCharacterKt") set(value) {
        super.setEscapeCharacter(value)
    }
private var mappingContext: MappingContext<*, *>
    get() = throw UnsupportedOperationException()
    @JvmName("setMappingContextKt") set(value) {
        super.setMappingContext(value)
    }
private var enableDefaultTransactions: Boolean
    get() = throw UnsupportedOperationException()
    @JvmName("setEnableDefaultTransactionsKt") set(value) {
        super.setEnableDefaultTransactions(value)
    }

Another workaround is writing that class in java, but this defeats the purpose of using Kotlin in the first place.

Attached is a minimal reproducible example: kotlin-jpa-bug.zip

[mp911de]

Did you notice that the JVM name is setQueryLookupStrategyKeyKt and not setQueryLookupStrategyKey?

Your class needs to adhere to Java beans standards by having getters and setters that adhere to that naming scheme.

[cmdjulian]

Yes, that is on purpose. Otherwise I get an accidental override error from the kotlin side of things. The problem here is, that my kotlin class inherits from a java class and the detector does not recognize the setter as its not a Kotlin property, as it isn't. When looking at the demo project I provided in the previous post, it makes more sense. The demo project is without any methods to showcase the error. It just inherits from the Spring provided JpaRepositoryFactoryBean class. In 3.1.5 this worked without any problems.
The logic seems not right here, as it affecting all kotlin class which do inherit from a java class

[mp911de]

In 3.2 we introduced KotlinBeanInfoFactory that uses Kotlin's reflection API to detect KProperty for Kotlin classes. It's likely that this updated scheme now reflects back into other beans as well.

[cmdjulian]

Yes, thats probably the reason why when defining the properties myself it is able to infer them. Kotlin is normally able to infer such properties from java as well, when they conform to the java bean standard. In the case of JpaRepositoryFactoryBean just a setter is present, no getter. I think thats the reason why Kotlin reflect is not able to detect it as a valid property.

I guess this will happen more often for all kind of kotlin class which do extend java classes / interfaces.

[mp911de]

Like you said, properties from a non-Kotlin superclass aren't taken into account by Kotlin reflection. We can add these ourselves by walking the type hierarchy and resolving properties from the superclass using the regular BeanInfo mechanism.

This adds back any inherited properties.