Upgrade to Spring Boot 4.0.1 with springdoc-openapi 3.0.1

[teetangh]

Summary

• Upgrades Spring Boot from 3.5.7 to 4.0.1
• Upgrades springdoc-openapi from 2.8.14 to 3.0.1
• Fixes all breaking changes from Spring Boot 4 migration

Changes

• build.gradle: Updated Spring Boot to 4.0.1 and springdoc-openapi to 3.0.1, added test dependencies
• Application.java: Removed SecurityAutoConfiguration exclusion (class moved in Spring Boot 4)
• RestResponsePage.java / RestResponseSlice.java: Fixed Jackson 3 compatibility (replaced JsonNode with Object)
• Test files: Updated TestRestTemplate import to new package and added @AutoConfigureTestRestTemplate
• application.properties / README.md: Updated version references to Spring Boot 4.0+

Test plan

• All 18 integration tests pass locally with Java 17
• CI passes with Java 17 and Java 21

Related PRs

This PR supersedes:

• Bump org.springframework.boot from 3.5.7 to 4.0.1 #70 (Spring Boot 3.5.7 → 4.0.1)
• Bump org.springdoc:springdoc-openapi-starter-webmvc-ui from 2.8.14 to 3.0.1 #71 (springdoc-openapi 2.8.14 → 3.0.1)

[gemini-code-assist]

Summary of Changes

Hello @teetangh, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request primarily focuses on a significant upgrade of the application's core frameworks, moving from Spring Boot 3.5.7 to 4.0.1 and updating springdoc-openapi to version 3.0.1. This modernization effort involves resolving various breaking changes, updating build configurations, and ensuring continued functionality and test coverage with the new versions. The goal is to leverage the latest features and maintain compatibility with the evolving Spring ecosystem.

Highlights

• Spring Boot Upgrade: The project has been upgraded from Spring Boot 3.5.7 to 4.0.1, incorporating the latest features and improvements from the new major version.
• springdoc-openapi Update: The springdoc-openapi library has been updated from version 2.8.14 to 3.0.1, aligning with the new Spring Boot version and enabling API documentation by default.
• Breaking Change Resolution: All identified breaking changes resulting from the Spring Boot 4 migration have been addressed, ensuring application compatibility and smooth operation.
• Test Infrastructure Modernization: Test dependencies and configurations have been updated, including the TestRestTemplate import and the addition of @AutoConfigureTestRestTemplate for improved testing practices.
• Jackson Compatibility Fixes: RestResponsePage and RestResponseSlice models were updated to use Object instead of JsonNode to maintain compatibility with Jackson 3, which is a dependency of Spring Boot 4.

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[gemini-code-assist]

Code Review

This pull request upgrades Spring Boot to 4.0.1 and springdoc-openapi to 3.0.1, including necessary code changes to address breaking changes. The dependency updates, configuration changes, and test adjustments seem correct for the migration. However, I found a potential issue in the updated deserialization logic for RestResponseSlice that could lead to incorrect pagination behavior on the client-side. My review includes a specific suggestion to fix this.