Modernize Spring Boot project: Java 8 → 21, Spring Boot 2.x → 3.4.5

[devin-ai-integration]

Summary

Full modernization of the Spring Boot demo project from Java 8 / Spring Boot 2.0.2 to Java 21 / Spring Boot 3.4.5, along with code quality improvements and new test coverage.

Version upgrades: Java 8→21, Spring Boot 2.0.2→3.4.5, Gradle 4.6→8.12, Maven 3.3.9→3.9.9. Both pom.xml and build.gradle updated consistently. build.gradle rewritten to modern plugin DSL.

Dead code removal: Removed broken gturnquist-quoters.cfapps.io REST calls (service is offline) and associated RestTemplate bean/imports from Application.java. Removed bean inspection loop from main().

Code quality:

• All controllers: @Autowired field injection → constructor injection; @RequestMapping → specific @GetMapping/@PostMapping/etc.
• TopicService: unsafe Optional.get() → orElseThrow() with descriptive message
• TopicService/TimeClient: System.out.println/System.err.println → SLF4J logger
• CustomPredicate: added @FunctionalInterface
• Greeting and Customer: converted to Java records
• Fixed H2 SQL syntax: DROP TABLE customers IF EXISTS → DROP TABLE IF EXISTS customers

New files: GlobalExceptionHandler (@ControllerAdvice), application.properties in src/main/resources/, three JUnit 5 test files (19 tests total).

Cleanup: Deleted .idea/, .iml, .gitignore.txt; fixed .gitignore; moved temp.txt to src/main/resources/.

Review & Testing Checklist for Human

• Verify Greeting record serialization: The class was converted to a Java record. Records expose id() not getId(), but Spring Boot 3.x Jackson should serialize them identically. Confirm GET / still returns {"id": ..., "content": ...} (not differently-named fields) by actually running the app.
• Quote.java and Value.java are now dead code: The REST calls that used them were removed, but the model files themselves were left in the codebase. Decide if these should be deleted.
• readFileWithStreamFunction uses a fragile relative path (Paths.get("src/main/resources/temp.txt")): This works when the working directory is the project root, but will break if the app is run from a packaged JAR. Consider loading via classpath resource instead.
• Run ./mvnw spring-boot:run and manually test endpoints: GET /, GET /topic, GET /datetime. The tests are unit/slice tests only — there is no @SpringBootTest integration test verifying the full context loads with H2.

Notes

• The @WebMvcTest controller tests require a @MockitoBean JdbcTemplate because Application (the @SpringBootApplication class) has JdbcTemplate as a constructor dependency. This is functional but unusual — a cleaner pattern would be to extract the CommandLineRunner logic into a separate @Component.
• packaging in pom.xml changed from pom to jar — this was necessary for the Spring Boot Maven plugin to produce a runnable JAR.

Link to Devin session: https://app.devin.ai/sessions/c47e2bfdd24f46e3bb7a955a0d906f66
Requested by: @bnob-git

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[devin-ai-integration]

End-to-End Test Results

Ran the app locally with ./mvnw spring-boot:run on Java 21 and tested all key endpoints in the browser.

Endpoint Tests (7/7 passed)

• App startup: PASSED — Started cleanly in 1.6s, no exceptions. H2 tables created, customers inserted and queried successfully.
• GET / (Greeting record serialization): PASSED — Returns {"id":1,"content":"Hello, World!"}. Java record fields serialize correctly.
• GET /?name=Devin (query param): PASSED — Returns {"id":2,"content":"Hello, Devin!"}. Counter increments, param works.
• GET /topic (topic list): PASSED — Returns JSON array with 3 topics (spring, java, javascript).
• GET /topic/java (single topic): PASSED — Returns {"id":"java","subjectName":"Core Java","subjectDescription":"Java Description"}.
• GET /topic/nonexistent (404 handling): PASSED — HTTP 404 with body "Topic not found with id: nonexistent". GlobalExceptionHandler works correctly.
• GET /datetime (HelloController): PASSED — Shows greeting, current datetime, tomorrow, previous month, leap year, timezone info.

Screenshots

GET / — Greeting record JSON serialization

GET /?name=Devin

GET /topic — Topic list

GET /topic/java — Single topic lookup

GET /topic/nonexistent — 404 error handling

GET /datetime

Devin session