@Autowired

@Autowired — Dependency Injection

@Service
public class OrderService {

    private final OrderRepository repository;
    private final PaymentService paymentService;

    // Constructor injection (recommended)
    @Autowired
    public OrderService(OrderRepository repository, PaymentService paymentService) {
        this.repository = repository;
        this.paymentService = paymentService;
    }
}

Injection Types

// 1. Constructor injection (RECOMMENDED)
@Autowired
public OrderService(OrderRepository repo) {
    this.repo = repo;
}

// 2. Setter injection (optional dependencies)
@Autowired
public void setCache(Cache cache) {
    this.cache = cache;
}

// 3. Field injection (AVOID)
@Autowired
private OrderRepository repo;

Why Constructor Injection Is Preferred

Aspect	Constructor	Field
Immutability	Yes (final)	No
Testing	Easy to mock	Hard to test
Null safety	Fails fast at startup	NPE at runtime
Dependencies	Explicit	Hidden

@Autowired in Spring Boot

When a class has only one constructor, @Autowired is optional:

@Service
public class OrderService {
    private final OrderRepository repo;

    // @Autowired is optional here
    public OrderService(OrderRepository repo) {
        this.repo = repo;
    }
}

Configuration

• Use properties over YAML for simple configs
• Externalize configuration
• Use profiles for environments
• Validate on startup

Bean Management

• Prefer constructor injection
• Use appropriate scope
• Implement lazy initialization
• Clean up resources

Security

• Use Spring Security
• Implement CSRF protection
• Use method-level security
• Log security events

Key Points

• Understanding @Autowired Annotation is essential for production systems
• Always consider scalability and maintainability
• Test thoroughly before deploying to production
• Monitor performance and set up alerting

Common Patterns

1. Validation: Always validate input at the boundary
2. Error Handling: Use structured error responses
3. Logging: Log key events for debugging
4. Testing: Unit, integration, and load tests
5. Documentation: Keep docs updated with code changes