Spring Annotations Decoded: When to Use @Component, @Controller, @Service & @Repository

Write Clean, Layered Code with Intent—Not Just Functionality

Struggling to choose between @Component, @Service, @Repository, and @Controller in Spring? You’re not alone. While they all register beans with the Spring container, each carries semantic meaning that enhances readability, tool support, and maintainability.

Let’s unpack these stereotype annotations with real-life examples and best practices.

🔹 1. @Component – The General Bean

🧠 What It Does:

• Declares the class as a Spring-managed bean.
• Acts as the base for all stereotype annotations.

✅ When to Use:

• For utility classes, validators, or any class that doesn’t belong strictly to a web, service, or DAO layer.

📦 Example:

@Component
public class EmailValidator {
    public boolean isValid(String email) {
        return email.contains("@");
    }
}

⚠️ Watch Out:

Overusing @Component everywhere hides the class’s intent and reduces clarity in layered architectures.

🔹 2. @Controller – Web Layer Specialist

🧠 What It Does:

• Specialized form of @Component for handling HTTP requests in MVC apps.
• Supports annotations like @GetMapping, @PostMapping, etc.

✅ When to Use:

• In web applications or REST APIs to map HTTP requests to Java methods.

📦 Example:

@Controller
public class ProductController {
    @GetMapping("/products")
    public String listProducts(Model model) {
        model.addAttribute("products", productService.getAll());
        return "product-list";
    }
}

💡 Pro Tip:

Use @RestController instead of @Controller + @ResponseBody when building REST APIs.

🔹 3. @Service – The Business Logic Boss

🧠 What It Does:

• Marks the class as a service layer component.
• Indicates it’s suitable for transaction boundaries and complex business rules.

✅ When to Use:

• For business logic, orchestrating calls to multiple DAOs, validations, or any non-web core logic.

📦 Example:

@Service
public class OrderService {
    @Autowired
    private OrderRepository orderRepo;

    public Order placeOrder(Order order) {
        // Apply business logic
        return orderRepo.save(order);
    }
}

🌟 Bonus:

Spring can apply AOP (e.g., transactions, logging) more effectively with @Service.

🔹 4. @Repository – Data Access Hero

🧠 What It Does:

• Specialized @Component for the persistence layer.
• Enables automatic translation of SQLException into DataAccessException.

✅ When to Use:

• For DAOs, JPA repositories, or classes that directly access a database.

📦 Example:

@Repository
public interface CustomerRepository extends JpaRepository<Customer, Long> {
    Customer findByEmail(String email);
}

🔍 Why It Matters:

Exception translation provides a consistent error-handling model across different data stores.

📊 Quick Comparison Table

⚠️ Common Mistakes to Avoid

❌ 1. Using @Component for Everything

• Makes your code harder to understand and refactor.

❌ 2. Skipping @Repository in DAO Classes

• You lose exception translation that Spring provides automatically.

❌ 3. Mixing Annotations Across Layers

• A @Service on a DAO or a @Repository on a controller? That’s a red flag for maintainers.

🤔 FAQ: What If I Use the Wrong One?

Q: Will it break my app?
A: Probably not immediately. But you’ll lose out on layer-specific features like exception translation or AOP hooks.

Q: Can I create custom annotations?
A: Absolutely. Just meta-annotate with @Component:

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Component
public @interface ScheduledTask {}

✅ Best Practices for Clean, Decoupled Code

• Use Specific Stereotypes: Let the class name and annotation reveal its role.
• Keep Layering Clean: @Controller → @Service → @Repository (not the other way around).
• Inject Dependencies Wisely: Use @Autowired, constructor injection, or Spring Boot’s auto-wiring magic.

Tags: Spring annotations, @Component, @Service, @Controller, @Repository, Java backend, Spring Boot, dependency injection, clean architecture

💬 Join the Discussion

Which annotation tripped you up the most? Ever created your own stereotype?
Drop your experience or interview question below 👇

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