📝 Legacy Todo App – Spring Boot 2 + Hibernate + SQLite

This is a deliberately outdated Todo application built with legacy Java and Spring technologies. It serves as a sandbox for testing automated code migration and refactoring using GenAI tools (e.g., LLM-based assistants).

---

✅ Technologies Used

• Java 11
• Spring Boot 2.1.0.RELEASE
• Spring Web MVC
• Spring Data JPA (CrudRepository)
• Hibernate ORM 5.3.7.Final
• SQLite (JDBC 3.28.0)
• JUnit 5, Spring Boot Test

---

1. Requirements

• Java 11 or newer
• Maven 3.6+

2. Build and Run

mvn clean install
mvn spring-boot:run

3. Available endpoints

Method	Endpoint	Description
GET	/todos	Fetch all todo items
POST	/todos	Create a new todo item

Example for adding a todo

{
  "title": "Migrate to Spring Boot 3",
  "completed": false
}

4. Project Structure

src/
├── main/
│   ├── java/com/example/todo/
│   │   ├── controller/
│   │   │   └── HelloController.java         # basic ping endpoint
│   │   ├── entity/
│   │   │   └── TodoItem.java                # todo entity with ID, title, completed
│   │   ├── repository/
│   │   │   └── TodoRepository.java          # extends CrudRepository
│   │   └── service/
│   │       └── TodoService.java             # simple service class
│   └── resources/
│       └── application.properties           # DB config for SQLite
└── test/
    └── java/com/example/todo/
        └── TodoTests.java                   # integration test for repository

5. Known issues and migration challenges

This project includes deliberate technical debt and legacy practices, useful for training AI or developers to detect and modernize codebases:

• No use of DTOs (entity is exposed directly)
• Business logic partially in controller
• Field injection using @Autowired (discouraged)
• No @Valid or request validation
• No error handling (e.g. @ControllerAdvice)
• SQLite used as production-like database (rare and unsupported officially in Spring Boot)
• Hibernate uses a non-official dialect for SQLite compatibility
• Minimal use of interfaces or abstraction
• No pagination or filtering
• Single-layer repository design (CrudRepository only)
• These issues are great examples for:
• Migrating to Spring Boot 3.x + Jakarta
• Replacing Hibernate with Spring Data JPA improvements
• Introducing layered architecture
• Applying validation, exception handling, DTO mapping, logging, pagination, etc.

6. Tests

mvn test

7. Purpose of the project

This project is intentionally legacy and minimal. It is meant for:

• ✅ Testing automated migration tools (e.g., GenAI/LLM-based refactoring)
• 🔍 Practicing code smell detection and refactoring
• 🛠️ Demonstrating modernization pipelines
• 📚 Teaching how to go from legacy monolith to a clean, modular Spring Boot 3 app

You are encouraged to:

• Add validation
• Introduce DTOs and mapping
• Upgrade to Spring Boot 3 and Java 17+
• Replace deprecated APIs
• Add exception handling, OpenAPI docs, and more