🔧 Spring Boot Task 2 – Building a RESTful API with Layers and Exception Handling

I built a full REST API using the Layered Architecture pattern (Controller → Service → Repository), simulated a database with HashMap, handled exceptions, and added Swagger UI for documentation and testing.

🎯 Objective

• Create a backend-only Spring Boot application (no frontend this time)
• Structure the project using clean architectural layers
• Use stereotypes: @Controller, @RestController, @Service, @Repository, @Component
• Simulate data persistence using a HashMap (later replaced with a real DB)
• Handle HTTP requests: GET, POST, PUT, DELETE
• Add proper exception handling
• Visualize and test API with Swagger UI
• Later connect to a real H2 in-memory database

⚙️ Project Setup

• Created using: IntelliJ’s built-in Spring Initializr
• Dependencies:
  • Spring Web
  • Spring Boot DevTools
  • H2 Database (for future use)
  • Spring Data JPA
  • Lombok
  • OpenAPI (Swagger)

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✅ What I Did

1. Built a Complete REST API

   • Created endpoints to create, read, update, delete, and list products.
   • Used path variables (@PathVariable) and request bodies (@RequestBody).

2. Implemented Clean Separation of Concerns

   • Created a ProductService for logic.
   • Used a ProductMapper to convert between entities and DTOs.

3. Simulated a Database

   • Used a HashMap<Long, Product> to store data before integrating H2.

4. Handled Exceptions Properly

   • Created ProductNotFoundException and global handler with @ControllerAdvice.
   • Returned clean error responses instead of 500s.

5. Documented and Tested with Swagger

   • Added springdoc-openapi-ui to pom.xml.
   • Accessed interactive UI at /swagger-ui/index.html.

6. Connected to a Real Database

   • Switched to H2 in-memory DB with JPA and annotations like @Entity, @Id.

7. Added PUT and DELETE functionality

   • Enabled full CRUD operations using HTTP methods
   • Tested with Postman, Swagger, and browser

🧠 What I Learned

• How to build a real REST API using Spring Boot
• Why layering (controller/service/repo) matters for maintainability
• The power of annotations like @RestController, @Service, @Component
• How to use Optional, orElseThrow(), and Supplier for clean null handling
• How to handle exceptions with @ControllerAdvice and return user-friendly messages
• Swagger UI integration for API testing and docs
• Transitioning from in-memory mocks to actual databases (H2)

📬 API Endpoints

Method	Endpoint	Description
GET	/api/v1/products/{id}	Get product by ID
GET	/api/v1/products	Get all products
POST	/api/v1/products	Create a new product
PUT	/api/v1/products/{id}	Update an existing product
DELETE	/api/v1/products/{id}	Delete a product by ID

🖼️ Screenshots

Author: Winifred Imade Ogbeiwi
School: Vistula University
Track: Computer Engineering