Migrate from Java 11 to Java 17

[devin-ai-integration]

Migrate from Java 11 to Java 17

Summary

This PR migrates the Spring Boot RealWorld example application from Java 11 to Java 17 (LTS). The changes include:

• Build configuration: Updated sourceCompatibility and targetCompatibility to Java 17 in build.gradle
• CI/CD pipeline: Updated GitHub Actions workflow to use JDK 17 and upgraded actions/cache from v2 to v4 (v2 was deprecated)
• Tooling: Upgraded Spotless plugin from 6.2.1 to 6.13.0 for Java 17 compatibility (older version's Google Java Format doesn't work with Java 17's module system)
• Documentation: Updated README.md to reflect Java 17 requirement
• Code formatting: Applied updated Google Java Format rules (one test file reformatted)

All 68 unit tests pass locally and in CI with Java 17. Spring Boot 2.6.3 officially supports Java 17, and all dependencies (MyBatis 2.2.2, Netflix DGS 4.9.21, JJWT 0.11.2, SQLite JDBC 3.36.0.3) are compatible.

Review & Testing Checklist for Human

• Test the application end-to-end with Java 17 - CI only runs unit tests; verify the app works correctly in a real Java 17 environment (e.g., ./gradlew bootRun and test API endpoints)
• Verify deployment environments have Java 17 available - Check staging/production environments and update if needed to prevent deployment failures
• Review any Java 11-specific workarounds or configurations - Check if there are any production configs, JVM flags, or code workarounds that were Java 11-specific and might need updating

Recommended Test Plan

1. Run the application locally with Java 17: ./gradlew bootRun
2. Test the REST API endpoints: curl http://localhost:8080/tags
3. Test the GraphQL endpoint at http://localhost:8080/graphql
4. Run full test suite: ./gradlew clean test
5. Verify formatting still works: ./gradlew spotlessCheck

Notes

• No javax.* to jakarta.* migration required (only needed for Spring Boot 3.x)
• Java 17 has stricter module system enforcement and different default GC settings than Java 11, which could surface subtle behavioral differences in production
• The Spotless plugin upgrade was necessary because the old version's Google Java Format cannot access Java compiler internals in Java 17

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Link to Devin run: https://app.devin.ai/sessions/3e26d95ce8bf4a73bb0fef06ecae3889
Requested by: Ibs (@ibrahim-sowunmi)

[devin-ai-integration]

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