Null Handling of HTTP Interface

[m-titov]

https://docs.spring.io/spring-framework/docs/6.0.0/reference/html/integration.html#rest-http-interface

I would like to have the default behavior (even without using of @NonNullApi or with @NonNullApi if that is impossible ) for parameters and return values is, respectively, neither to accept nor to produce null values and use @Nullable on a parameter or return value that can be null.

[sdeleuze]

I think we should try to be consistent with null-handling in Spring MVC/WebFlux controllers.

For method parameters, that means HTTP interfaces should (if that's not already the case) leverage MethodParameter#isOptional which checks whether this method parameter is annotated with any variant of a Nullable in order to conceptually infer the value of the required annotation attribute of annotations like @RequestPart, @RequestParam, @RequestBody, etc.

For return values, I am not sure Spring MVC/WebFlux controllers are doing some special null-safety handling, so not sure something should be done in HTTP Interfaces.

@m-titov Would interpreting @Nullable on method parameters as required = false annotation attribute fit your need? Could you confirm it is currently not the case and provide a reproducer?

[m-titov]

Hi @sdeleuze ,

@m-titov Would interpreting @nullable on method parameters as required = false annotation attribute fit your need? Could you confirm it is currently not the case and provide a reproducer?

Yes, it seems Ok to me.
But I would also like to be able to have (or at least to make) return values not null by default globally and to annotate with @Nullable those of them which are actually cound be null.

[sdeleuze]

For this kind of need, you can maybe try to use bean validation.

Can you please provide a repro to ensure we need to do something for @Nullable handling on parameters?

[m-titov]

For this kind of need, you can maybe try to use bean validation.

Well..
Then it would be inconsistent with spring data https://docs.spring.io/spring-data/data-jpa/reference/repositories/null-handling.html#repositories.nullability.annotations:~:text=%40Nullable%3A%20Used%20on%20a%20parameter%20or%20return%20value%20that%20can%20be%20null. where if we annotate the corresponding package with @NonNullApi, then only the method which returns value annotated with @Nullable can return null; otherwise, it throws an exception for null return value out of the box

[sdeleuze]

Good point about Spring Data, more consistency would be welcomed between Spring Framework and Spring Data (but that has a wider scope than this issue).

@mp911de Could you please point me to the Spring Data code that performs null handling? I am especially interested in understanding how you manage package-level annotations, and if you support only Spring Framework null-safety annotations or if you implemented generic JSR 305 support.

[mp911de]

The entry point to method invocation validation is at https://github.com/spring-projects/spring-data-commons/blob/main/src/main/java/org/springframework/data/repository/core/support/MethodInvocationValidator.java We support Spring‘s annotations, JSR 305 (as add-on if on the class path) and Kotlin nullability metadata via Kotlin reflection. It would make sense to move our code into Framework at some point.