🛠 Kotlin Migration Project

Overview

This project is focused on migrating an existing Java-based server to Kotlin. The goal is to leverage Kotlin’s concise syntax, enhanced null-safety, and improved maintainability, while enhancing object-oriented design and overall code quality.

Purpose

• Modernization: Improve code readability, reduce boilerplate, and adopt modern language features.
• Refactoring: Redesign the system with better object-oriented principles during migration.
• Performance Improvement: Review the legacy code and optimize performance where possible.
• Stability and Reliability: Strengthen testing coverage to ensure system reliability.
• Maintainability and Scalability: Make the system easier to maintain and extend in the future.

Scope

• Migrate all server-side Java classes to Kotlin.
• Refactor to enhance object-oriented design during migration.
• Review the existing code for potential performance improvements and optimize where needed.
• Increase test coverage across unit, integration, and system tests.
• Maintain or improve compatibility with existing functionalities.

Migration Principles

• Behavior Preservation: System behavior must remain correct after migration.
• Object-Oriented Refactoring: Improve the domain model and responsibilities of classes.
• Kotlin Best Practices: Use Kotlin idioms safely and appropriately.
• Incremental Migration: Migrate module-by-module with validation after each phase.
• Testing First: Strengthen tests before, during, and after migration to detect regressions.

Stack

• Language: Kotlin 1.9.25 (JVM Target 21)
• Framework: Spring Boot 3.4.4
• Database: PostgreSQL, MySQL
• Build Tool: Gradle
• ORM: Hibernate ORM 6.6.11.Final
• API Documentation: SpringDoc OpenAPI
• Query Building: QueryDSL 5.0.0
• Security: Spring Security, JWT (io.jsonwebtoken)
• Resilience: Resilience4j
• Reactive Support: Spring WebFlux
• Batch Processing: Spring Batch
• Cloud Integration: Firebase Admin SDK

Notes

• This project focuses on both language migration and architecture improvement.
• We are not simply translating code — we are rethinking and improving design decisions.
• Priority is given to system stability and long-term codebase maintainability.