Migrate from Java 8 / Spring Boot 2.0.2 to Java 21 / Spring Boot 3.3.5

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Summary

Migrates the project from Java 8 + Spring Boot 2.0.2.RELEASE to Java 21 + Spring Boot 3.3.5, updating all build tooling and fixing breaking changes.

Changes

pom.xml

• Spring Boot parent version: 2.0.2.RELEASE → 3.3.5
• Java version: 1.8 → 21
• Removed spring-boot-properties-migrator dependency (only needed for 1.x→2.x migration)
• Fixed packaging: pom → jar (was preventing Maven from compiling sources)

build.gradle

• Spring Boot Gradle plugin: 2.0.2.RELEASE → 3.3.5
• sourceCompatibility / targetCompatibility: 1.8 → 21
• compile → implementation, testCompile → testImplementation
• baseName / version → archiveBaseName / archiveVersion
• Added missing spring-boot-starter-jdbc and h2 dependencies (to match pom.xml)

src/main/java/hello/Application.java

• Fixed H2 SQL syntax: DROP TABLE customers IF EXISTS → DROP TABLE IF EXISTS customers (H2 2.x requires standard SQL)
• Fixed deprecated JdbcTemplate.query(): swapped new Object[]{"Josh"} to varargs overload (RowMapper before args)
• Removed defunct gturnquist-quoters.cfapps.io REST calls (service is offline, caused ResourceAccessException crash on startup in Spring Boot 3.x)

.mvn/wrapper/maven-wrapper.properties

• Maven: 3.3.9 → 3.9.9

gradle/wrapper/gradle-wrapper.properties

• Gradle: 4.6 → 8.10.2

Files intentionally unchanged

All model/controller/service/declaration files use Java 8 features (streams, lambdas, java.time, NIO, functional interfaces) that are fully forward-compatible with Java 21.

Review & Testing Checklist for Human

• Verify the Maven build compiles and packages: ./mvnw clean package
• Verify the Gradle build compiles: ./gradlew clean build
• Run ./gradlew bootRun and test endpoints at localhost:8080 (GET /, GET /topic, GET /datetime)

Notes

• JDK 21 must be installed to build/run
• Three pre-existing build issues were fixed: Maven <packaging>pom</packaging> prevented compilation, build.gradle was missing JDBC/H2 dependencies, and defunct REST calls crashed the app on startup
• All endpoints tested and working: GET / returns greeting JSON, GET /topic returns topic list, GET /datetime returns datetime info, GET /topic/sort returns sorted topics

Link to Devin session: https://app.devin.ai/sessions/1a864a864ae94267a807f2c2b35cc84d
Requested by: @clivingston-cognition

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End-to-End Test Results

All 4 tests passed. App runs on JDK 21 + Spring Boot 3.3.5, H2 operations work, all REST endpoints respond correctly.

Test 1: App startup with H2 + JDBC operations (proves migration fixes)

Assertion	Result
Startup log shows Java 21.0.10	PASSED
Startup log shows Spring Boot :: (v3.3.5)	PASSED
Tomcat started on port 8080	PASSED
Creating tables logged (CommandLineRunner entered)	PASSED
Inserting customer record for Josh Bloch + Josh Long (H2 SQL fix works)	PASSED
Customer{id=3, firstName='Josh', lastName='Bloch'} returned (JdbcTemplate varargs fix works)	PASSED
No JdbcSQLSyntaxErrorException or IllegalArgumentException	PASSED

Key log excerpt:

hello.Application : Creating tables
hello.Application : Inserting customer record for Josh Bloch
hello.Application : Inserting customer record for Josh Long
hello.Application : Querying for customer records where first_name = 'Josh':
hello.Application : Customer{id=3, firstName='Josh', lastName='Bloch'}
hello.Application : Customer{id=4, firstName='Josh', lastName='Long'}

Test 2: REST endpoints (Spring Boot 3.x runtime)

Endpoint	Expected	Actual	Result
GET /	JSON with "Hello, World!"	{"id":1,"content":"Hello, World!"}	PASSED
GET /topic	JSON array with topics	3 topics with id, subjectName, subjectDescription	PASSED
GET /datetime	String with datetime	Greetings from Spring Boot! ...2026-04-28T04:23:55...	PASSED
GET /topic/sort	Sorted JSON array	Sorted by id: java < javascript < spring	PASSED

Test 3 & 4: Build systems

Build	Command	Result
Gradle 8.10.2	./gradlew clean build	BUILD SUCCESSFUL in 2s
Maven 3.9.9	./mvnw clean package	BUILD SUCCESS, produced gs-spring-boot-0.1.0.jar

Devin session