update deprecated org.springframework.lang.Nullable for Spring Boot 4

[raichuchuchu]

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Summary by cubic

Switches Spring generators to use org.jspecify.annotations.Nullable when targeting Spring Boot 4, replacing deprecated org.springframework.lang.Nullable. Also fixes CppHttplibServer test package names and refreshes Java client samples.

• New Features

  • SpringCodegen: Nullable now resolves to org.jspecify.annotations.Nullable when useSpringBoot4 is enabled; otherwise it remains org.springframework.lang.Nullable.

• Bug Fixes

  • Fixed incorrect package declarations in cpphttplibserver tests.
  • Regenerated restclient-enum-in-multipart Java client samples to match current generator output.

^{Written for commit 68fc0c9. Summary will update on new commits.}

[jpfinne]

@raichuchuchu there is already #23256 to generate jspecify nullable annotations. Can you review it?

[raichuchuchu]

Hello,

After submitting this draft, I happened to be reviewing #23256. I fully agree with the transition to org.jspecify.annotations.Nullable via useJspecify to replace the deprecated org.springframework.lang.Nullable.

That said, I’ve noticed some edge cases with the JSpecify annotations, so I am also considering whether jakarta.annotation.Nullable might be a viable alternative. I plan to wait until #23256 is merged before further updating my draft. In the meantime, I’d like to take some time to test the changes from #23256 within a real Spring Boot 4 project.

[jpfinne]

@raichuchuchu if you want to use jakarta nullable, just configure it. For example in the maven plugin

<importMappings>
   <importMapping>Nullable=org.jakarta.annotations.Nullable</importMapping>
</importMappings>

So no need for an extra config. Maybe better documentation is enough