Upgrade Java from 17 to 21

[devin-ai-integration]

Upgrade Java from 17 to 21

Summary

Upgrades the Spring Boot banking application from Java 17 to Java 21 across all configuration files and infrastructure components. This includes updates to Maven configuration, Docker images, and documentation to ensure consistency throughout the deployment pipeline.

Changes made:

• pom.xml: Updated Java version property from 17 to 21 and Maven compiler plugin source/target from 1.8 to 21
• Dockerfile: Updated both builder stage (maven:3.8.3-openjdk-17 → maven:3.8.3-openjdk-21) and runtime stage (openjdk:17-alpine → openjdk:21-alpine)
• README.md: Updated Jenkins installation documentation to use openjdk-21-jre instead of openjdk-17-jre

Spring Boot 3.3.3 already supports Java 21, so no framework version changes were required.

Review & Testing Checklist for Human

🟡 Medium Risk - 4 critical items to verify:

• Build and test application locally - Run mvn clean install and mvn spring-boot:run to verify compilation and startup with Java 21
• Docker build verification - Build the Docker image end-to-end: docker build -t bankapp-java21-test . and test container startup
• CI/CD pipeline compatibility - Run the full Jenkins pipeline including SonarQube analysis, Trivy scanning, and OWASP dependency checks to ensure all tools work with Java 21
• End-to-end application testing - Deploy to a test environment and verify core banking functionality (user registration, login, transactions) works correctly

Notes

• All Java 21 Docker base images should be verified to exist and be stable
• Pay special attention to the mysql-connector-java 8.0.33 dependency - may need updating for optimal Java 21 compatibility
• Consider running performance tests to identify any Java 21-specific performance characteristics

Link to Devin run: https://app.devin.ai/sessions/595db5c7fd5f4c3bb9342ee7c20c6d54
Requested by: Jia Wu (jia.wu@cognition.ai)

[devin-ai-integration]

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