Dependency Injection

title: Dependency Injection in Spring description: Spring DI ke types aur examples

Object apni dependencies khud create nahi karta — Spring inject karta hai.

Types

1. Constructor Injection (Recommended)

java exampleWoHoTech

@Service
public class OrderService {
    private final UserRepository userRepo;
    private final ProductRepository productRepo;

    // @Autowired optional when single constructor
    public OrderService(UserRepository userRepo, ProductRepository productRepo) {
        this.userRepo = userRepo;
        this.productRepo = productRepo;
    }
}

2. Setter Injection

java exampleWoHoTech

@Service
public class EmailService {
    private MailSender mailSender;

    @Autowired
    public void setMailSender(MailSender mailSender) {
        this.mailSender = mailSender;
    }
}

3. Field Injection (Simple but not recommended for testing)

java exampleWoHoTech

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    @Autowired
    private PasswordEncoder passwordEncoder;
}

Annotations

Annotation	Use
`@Autowired`	Inject dependency
`@Component`	Generic bean
`@Service`	Service layer
`@Repository`	Data layer
`@Controller`	Web controller
`@Configuration`	Config class
`@Bean`	Method produces a bean

Qualifier — Multiple implementations

java exampleWoHoTech

interface PaymentGateway { void pay(double amount); }

@Component("stripe")
class StripeGateway implements PaymentGateway { ... }

@Component("paypal")
class PayPalGateway implements PaymentGateway { ... }

@Service
class CheckoutService {
    @Autowired
    @Qualifier("stripe")
    private PaymentGateway gateway;
}

title: Dependency Injection in Spring description: Spring DI ke types aur examples

Object apni dependencies khud create nahi karta — Spring inject karta hai.

Types

1. Constructor Injection (Recommended)

java exampleWoHoTech

@Service
public class OrderService {
    private final UserRepository userRepo;
    private final ProductRepository productRepo;

    // @Autowired optional when single constructor
    public OrderService(UserRepository userRepo, ProductRepository productRepo) {
        this.userRepo = userRepo;
        this.productRepo = productRepo;
    }
}

2. Setter Injection

java exampleWoHoTech

@Service
public class EmailService {
    private MailSender mailSender;

    @Autowired
    public void setMailSender(MailSender mailSender) {
        this.mailSender = mailSender;
    }
}

3. Field Injection (Simple but not recommended for testing)

java exampleWoHoTech

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    @Autowired
    private PasswordEncoder passwordEncoder;
}

Annotations

Annotation	Use
`@Autowired`	Inject dependency
`@Component`	Generic bean
`@Service`	Service layer
`@Repository`	Data layer
`@Controller`	Web controller
`@Configuration`	Config class
`@Bean`	Method produces a bean

Qualifier — Multiple implementations

java exampleWoHoTech

interface PaymentGateway { void pay(double amount); }

@Component("stripe")
class StripeGateway implements PaymentGateway { ... }

@Component("paypal")
class PayPalGateway implements PaymentGateway { ... }

@Service
class CheckoutService {
    @Autowired
    @Qualifier("stripe")
    private PaymentGateway gateway;
}

Dependency Injection

Types

1. Constructor Injection (Recommended)

2. Setter Injection

3. Field Injection (Simple but not recommended for testing)

Annotations

Qualifier — Multiple implementations

Continue learning this concept

Dependency Injection

Types

1. Constructor Injection (Recommended)

2. Setter Injection

3. Field Injection (Simple but not recommended for testing)

Annotations

Qualifier — Multiple implementations

Continue learning this concept