00 - Types of Layered Architectures

Layered Architecture

Client
   │
   ▼
Controller
   │
   ▼
Service
   │
   ▼
Repository
   │
   ▼
Database

Responsibilities

• Controller → Receives HTTP requests and returns HTTP responses.
• Service → Contains the application’s business logic.
• Repository → Handles communication with the database.
• Entity → Represents a database table (JPA).
• DTO (Data Transfer Object) → Object used for API requests and responses.
• Config → Spring configuration classes.
• Utility → Reusable helper functions.

Feature-based Architecture (Package by Feature)

user/
 ├── UserController
 ├── UserService
 ├── UserRepository
 ├── UserDTO
 └── User

product/
 ├── ProductController
 ├── ProductService
 ├── ProductRepository
 ├── ProductDTO
 └── Product

Each feature contains all the classes related to a specific business capability.

Hexagonal Architecture (Ports & Adapters)

Commonly used in large enterprise applications, fintechs, and banks.

Controller
      │
      ▼
Application Service
      │
      ▼
Domain
      ▲
      │
Repository Interface
      ▲
      │
JPA Repository

The domain layer does not depend on Spring, HTTP, or the database.

Advantages

• Easy to test
• Loosely coupled
• Easy to replace the database
• Easy to replace REST with Kafka, GraphQL, or gRPC

Clean Architecture

An evolution of Hexagonal Architecture.

Controller
      │
      ▼
Use Cases
      │
      ▼
Domain
      │
      ▼
Infrastructure