Upgrade Java version to 21 on iteration 2

[hu-jin-aws]

Java Version Upgrade Project - Executive Report 📊

Executive Summary 🎯

Successfully completed a comprehensive Java version upgrade project, transforming a legacy Java 8 Spring Boot application to Java 21 with Spring Boot 3.0.13. The automated upgrade process using OpenRewrite tools achieved a 47-minute time savings estimate, followed by manual refinement to eliminate all deprecation warnings and ensure full Java 21 compatibility. The application now runs cleanly with zero compilation errors, all tests passing, and modern API usage throughout the codebase.

Application Changes 🔄

• Java Runtime: Upgraded from Java 8 to Java 21 (13 major version jump)
• Spring Boot Framework: Migrated from 2.x to 3.0.13 with Jakarta EE namespace migration
• Testing Framework: Modernized from JUnit 4 to JUnit 5 with updated annotations
• Mockito Library: Upgraded from 1.x to 4.11.0 with modern API patterns
• Maven Compiler: Updated to 3.14.0 with Java 21 release configuration
• Dependency Management: Resolved duplicate JSON library conflicts
• Security APIs: Migrated from deprecated javax.security.cert to java.security.cert
• Date/Time APIs: Replaced deprecated Date constructors with java.time APIs

Tools Used 🛠️

• Java SDK: Amazon Corretto 21.0.7 (LTS version)
• OpenRewrite: Version 6.13.0 for automated code transformations

• com.amazonaws.java.migrate.UpgradeToJava21 recipe
• com.amazonaws.java.spring.boot3.UpgradeSpringBoot_3_0 recipe
  • Amazon Q CLI: Claude-4-Sonnet model for intelligent code analysis and manual fixes
  • Maven: 3.9.10 for build automation and dependency management
  • Build Tools: Maven Compiler Plugin 3.14.0 with Java 21 release target

Code Changes 📝

Automated Transformations (OpenRewrite)

• pom.xml: Java version property updated to 21, Spring Boot parent to 3.0.13
• Security.java: Base64 encoding migration from sun.misc to java.util.Base64
• Math.java: BigDecimal rounding constants to enums, primitive wrapper constructors to valueOf
• Test Classes: JUnit 4 to 5 migration, Mockito API modernization
• Jakarta Migration: javax.validation to jakarta.validation namespace changes

Manual Refinements (Amazon Q)

• Security.java: Replaced deprecated javax.security.cert with java.security.cert.CertificateFactory
• Encoder.java: Modernized Date(1999,0,1) to LocalDate.of(1999,1,1) with ZoneId conversion
• MockTest.java: Added @SuppressWarnings("unchecked") for Mockito generic type safety
• pom.xml: Excluded duplicate android-json dependency to resolve JSONObject conflicts

Time Savings Estimate ⏱️

• OpenRewrite Automation: 47 minutes saved (20m Java upgrade + 27m Spring Boot upgrade)
• Manual Code Review: Estimated 2-3 hours for comprehensive deprecated API analysis
• Testing & Validation: Estimated 1-2 hours for thorough compatibility testing
• Total Project Effort: ~4-5 hours vs estimated 8-10 hours manual approach
• Efficiency Gain: ~50-60% time reduction through intelligent automation

Next Steps 🚀

Immediate Validation

• ✅ Build Verification: Clean compilation with zero warnings achieved
• ✅ Test Suite: All 7 unit tests passing successfully
• ✅ JAR Packaging: Executable artifact (28.8MB) generated successfully
• 🔄 Integration Testing: Deploy to staging environment for end-to-end validation
• 🔄 Performance Testing: Benchmark Java 21 performance improvements

Recommended Improvements

• Dependency Updates: Consider upgrading AWS SDK from 2.14.27 to latest version
• Security Enhancements: Implement modern certificate validation patterns
• Observability: Add Micrometer metrics for Java 21 performance monitoring
• Documentation: Update deployment guides for Java 21 runtime requirements
• CI/CD Pipeline: Update build environments to Java 21 compatible versions

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Report generated on 2025-07-10 | Project completed with zero critical issues