Layered Architecture

Spring Boot Layered Architecture (N-Tier)

This N-Tier architecture provides a clean separation that makes Spring Boot applications easier to develop, test, and maintain.

1. Presentation Layer

Explanation:

• Controllers: Handle HTTP requests, map URLs to methods, and manage API endpoints
• DTOs (Data Transfer Objects): Separate objects for request/response to decouple API from domain models
• Exception Handlers: Centralize exception handling and transform exceptions to proper HTTP responses
• Validation: Validate incoming requests using annotations like @Valid
• Responsibilities: Receive requests, validate input, invoke business logic, and return appropriate HTTP responses

2. Business/Service Layer

Explanation:

• Service Interfaces: Define contracts for business operations
• Service Implementations: Contain the actual business logic and rules
• Business Logic: Core application functionality, workflows, and rules
• Transaction Management: Handle ACID properties using @Transactional
• Domain Models: Represent business entities and concepts
• Responsibilities: Implement business rules, coordinate transactions, and orchestrate data flow

3. Persistence Layer

Explanation:

• Repository Interfaces: Define data access contracts
• Repository Implementations: Concrete data access implementations (often provided by Spring Data)
• Entity Classes: JPA entities that map to database tables
• DAO Pattern: Data Access Objects for custom database operations
• ORM Mapping: Object-Relational Mapping configuration
• Query Builders: Programmatic query construction
• Responsibilities: Handle all database operations, SQL generation, and object-relational mapping

4. Complete N-Tier Architecture

flowchart TD
    External[External Client] --> PresentationLayer
    
    subgraph PresentationLayer [Presentation Layer]
        Controller[Controllers]
        DTO[DTOs]
        ExceptionHandler[Exception Handlers]
        Validation[Validation]
    end
    
    PresentationLayer --> BusinessLayer
    
    subgraph BusinessLayer [Business Layer]
        ServiceInterface[Service Interfaces]
        ServiceImpl[Service Implementations]
        BusinessLogic[Business Logic]
        TransactionMgmt[Transaction Management]
    end
    
    BusinessLayer --> PersistenceLayer
    
    subgraph PersistenceLayer [Persistence Layer]
        Repository[Repositories]
        Entity[Entities]
        DAO[DAOs]
        ORM[ORM Mapping]
    end
    
    PersistenceLayer --> Database[(Database)]
    
    style PresentationLayer fill:#e1f5fe,stroke:#01579b,stroke-width:2px
    style BusinessLayer fill:#f1f8e9,stroke:#33691e,stroke-width:2px
    style PersistenceLayer fill:#ffecb3,stroke:#ff6f00,stroke-width:2px
    style Database fill:#e8f5e9,stroke:#2e7d32,stroke-width:2px
    style External fill:#f3e5f5,stroke:#4a148c,stroke-width:2px

Complete Architecture Flow:

1. Request Flow: External Client → Presentation Layer → Business Layer → Persistence Layer → Database
2. Response Flow: Database → Persistence Layer → Business Layer → Presentation Layer → External Client
3. Dependency Direction: Higher layers depend on lower layers, but not vice versa

Key Benefits of This Architecture:

1. Separation of Concerns: Each layer has a distinct responsibility
2. Testability: Layers can be tested independently using mocks
3. Maintainability: Changes in one layer don’t necessarily affect others
4. Scalability: Components can be scaled independently
5. Flexibility: Implementation details can change without affecting other layers