feat: Migrate from Java 17 to Java 21 LTS with Spring Boot 3.3.13

[devin-ai-integration]

Summary

Migrates the BankApp from Java 17 to Java 21 LTS (latest long-term support release) and upgrades all related dependencies to their latest compatible versions.

Changes

Component	Before	After
Java	17	21 (LTS)
Spring Boot	3.3.3	3.3.13 (latest 3.3.x patch)
maven-compiler-plugin	3.8.0 (source/target 1.8)	3.15.0 (source/target 21)
MySQL Connector	mysql:mysql-connector-java:8.0.33	com.mysql:mysql-connector-j:8.0.33 (updated artifact name)
Hibernate Dialect	MySQL8Dialect (deprecated)	MySQLDialect
Dockerfile build stage	maven:3.8.3-openjdk-17	maven:3.9-eclipse-temurin-21-alpine
Dockerfile runtime stage	openjdk:17-alpine	eclipse-temurin:21-jre-alpine

Why these versions

• Java 21 is the current long-term support release with virtual threads, pattern matching, record patterns, and sequenced collections.
• Spring Boot 3.3.13 is the latest patch of the 3.3.x line, providing security fixes while minimizing breaking changes.
• Eclipse Temurin replaces the deprecated openjdk Docker images with actively maintained, production-ready builds.
• The old mysql:mysql-connector-java artifact was renamed to com.mysql:mysql-connector-j — version pinned at 8.0.33 to match the original.
• The maven-compiler-plugin source/target was inconsistently set to 1.8 despite the project declaring Java 17 — now correctly aligned to 21.

Review & Testing Checklist for Human

• Verify the application starts successfully with docker-compose up (rebuild the image with docker build -t bankapp:java21 .)
• Confirm login, registration, deposit, withdrawal, and transfer flows work end-to-end against a MySQL instance
• Validate Kubernetes deployment manifests are compatible (no Java-version-specific changes needed)
• Review Snyk check failures — they may require org-level Snyk policy adjustments

Notes

• The Maven build compiles and packages successfully with Java 21 (mvn clean install -DskipTests passes).
• No Java source code changes were required — the codebase is fully compatible with Java 21.
• Snyk security/license checks are failing — I do not have access to the cognition-default Snyk org to diagnose the specific issue. This may require an org admin to review the Snyk policy or approve the dependency changes.

Link to Devin session: https://app.devin.ai/sessions/56a7d4ebfcb54417b6c23a74a72c0694
Requested by: @joao-cognition

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Devin Review

Status	Commit
⚪ Not started	—

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[devin-ai-integration]

End-to-End Test Results — Java 17 → 21 Migration

Tested locally with Maven (mvn spring-boot:run) + MySQL 8.0 Docker container. All 7 tests passed.

Escalations

• Snyk CI failing — both security/snyk and license/snyk checks fail on any dependency change. This appears to be an org-level Snyk policy issue, not specific to this PR's code. Needs org admin review.

Results

#	Test	Result
1	Java 21 runtime verification (startup logs show Java 21.0.10)	Passed
2	Docker image build with Eclipse Temurin 21 base images	Passed
3	Register new user account	Passed
4	Login → Dashboard shows correct username and $0 balance	Passed
5	Deposit $500 → Balance updates to $500	Passed
6	Withdraw $100 → Balance updates to $400	Passed
7	Transaction history shows Deposit + Withdrawal entries	Passed

Shell test evidence

Java 21 runtime confirmed from startup logs:

Starting BankappApplication using Java 21.0.10 with PID 47349

Docker image also runs Java 21:

Starting BankappApplication v0.0.1-SNAPSHOT using Java 21.0.10 with PID 1

Stack versions: Spring Boot 3.3.13, Hibernate ORM 6.5.3.Final, Apache Tomcat 10.1.42

Browser test screenshots

Dashboard after login — "Welcome, testuser", Balance: $0.00

After $500 deposit — Balance: $500.00

After $100 withdrawal — Balance: $400.00

Transaction history — Deposit $500 + Withdrawal $100

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Devin session