The fix for this appears to be marking the controller method as `open fun` instead of fun. As it is ...

# spring

[geepawhill]

The fix for this appears to be marking the controller method as open fun instead of fun. As it is a leaf class, I don't understand why this would be so. Any ideas?

[Dariusz Kuc]

I believe you need to make the functions open for Spring to be able to create proxies to them (similarly to classes as well)

OR you could apply https://kotlinlang.org/docs/all-open-plugin.html#spring-support and remove the unnecessary open modifiers

[geepawhill]

Thank you! That was a heavy debugging situation with a friend. We found our fix, and you've explained it.

[nfrankel]

it seems as if you ported the code from java to kotlin
i’d suggest to create the project with https://start.spring.io/
and then port the code?

[geepawhill]

Thanks. Not my project, but I'll pass it on.

[Mike Vitale]

I’m the friend and owner of the aforementioned project. Thank you for the help in fixing the issue and understanding where I was going wrong.

[Mike Vitale]

The part I still don’t understand is now around “something something Kotlin and Spring, therefore Spring needs to subclass my controller classes and override its functions in order to perform validation”

[Mike Vitale]

Further, I wonder if there’s some way, somehow, to provide better error messages, or something (don’t really know what), when there’s validation in the class, but it’s not being applied.

[Dariusz Kuc]

afaik spring will run those validations through some aspect (or aspect like logic) which requires a proxy -> if your class is final or your method is final spring cannot create a proxy so it won't run the validation

[Dariusz Kuc]

thats why it needs the explicit open modifier (which is default in Java)

[Mike Vitale]

So does Spring do the same thing in Java (create an aspect/proxy/something), and the difference is the default behavior of classes being open/closed?

[Dariusz Kuc]

yep

[Mike Vitale]

Hmmm, ok.

[Mike Vitale]

So is there any ability to provide better messages to point people to a solution?

[Dariusz Kuc]

*thats why there is also an allopen compiler plugin that automatically marks springs beans as open to make the kotlin experience better and not require explicit open

[Dariusz Kuc]

i'd imagine the final/open part should be defined somewhere on the spring docs but hard to say

[Dariusz Kuc]

if you don't mark spring beans open then I guess it fail at startup, similarly it will fail if you don't open up the functions creating beans

[Dariusz Kuc]

in your case it was a valid bean but since method wasn't open it could not be proxied so it worked as if validation was not there

[Mike Vitale]

Correct

[Dariusz Kuc]

unsure if those misconfigurations could be detected -> guess probably? I'd recommend to open up an issue against Spring