Upgrade Java version to 21 on iteration 6

[van-vothanh]

Java 21 Upgrade Project - Executive Report

🎯 Executive Summary

Successfully completed automated Java 8 to Java 21 upgrade for Spring Boot application using OpenRewrite and Amazon Kiro CLI. The project achieved full compatibility with Java 21 and Spring Boot 3.0.13 while maintaining all existing functionality. Build process now executes without compilation errors and all tests pass successfully.

📋 Application Changes

• Java Version: ⬆️ Upgraded from Java 8 to Java 21
• Spring Boot: ⬆️ Upgraded from legacy version to 3.0.13
• Testing Framework: 🔄 Migrated from JUnit 4 to JUnit 5
• Gradle Wrapper: 🔧 Updated from 1.11 to 8.5 for Java 21 compatibility
• Build Configuration: ✅ Updated source/target compatibility settings

🛠️ Tools Used

• Java SDK: ☕ OpenJDK 21 runtime environment
• OpenRewrite: 🤖 Automated code transformation engine

• Java migration recipes (Java 8→11→17→21)
• Spring Boot upgrade recipes (2.x→3.0)
• JUnit 4 to 5 migration recipes
  • Amazon Kiro CLI: 🚀 AI-powered development assistant (v1.22.0)
• Claude Sonnet 4 model for intelligent code analysis
• Automated build error resolution
• Real-time compilation feedback

💻 Code Changes

• build.gradle:

• ⚙️ Java compatibility updated to VERSION_21
• 📦 Spring Boot plugin upgraded to 3.0.13
• 🧪 JUnit 5 platform configuration added
  • GreeterTest.java:
• 🔄 JUnit 4 annotations replaced with JUnit 5 equivalents
• ✅ Assert statements updated to JUnit 5 Assertions class
  • gradle-wrapper.properties:
• 🔧 Distribution URL updated to Gradle 8.5

⏱️ Time Savings Estimate

• OpenRewrite Automation: 15 minutes saved (Java + Spring Boot upgrades)
• Manual Migration Avoided: 2-3 hours of dependency research and compatibility testing
• Build Error Resolution: 30 minutes saved through AI-assisted troubleshooting
• Total Estimated Savings: 3+ hours of development time

🚀 Next Steps

• Validation Steps:

• ✅ Run full test suite in CI/CD pipeline
• 🔍 Performance testing with Java 21 runtime
• 📊 Memory usage analysis and optimization
  • Improvement Recommendations:
• 🆕 Leverage Java 21 features (pattern matching, virtual threads)
• 🔒 Update security configurations for Spring Boot 3.0
• 📈 Consider migrating to Spring Boot 3.2+ for latest features
• 🧹 Review and remove deprecated code patterns