@Component, @Service, @Repository, @Controller in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a Spring component class.

Spring Boot

@[1]
public class MyComponent {
}

Drag options to blanks, or click blank then click option'

AController

BService

CRepository

DComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Service or @Repository when the class is a general component.

Forgetting the @Component annotation causes Spring not to detect the class.

The @Component annotation marks a class as a Spring component for dependency injection.

2fill in blank

medium

Complete the code to declare a service class in Spring Boot.

Spring Boot

@[1]
public class UserService {
}

Drag options to blanks, or click blank then click option'

AController

BService

CRepository

DComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @Service for service classes.

Confusing @Service with @Repository or @Controller.

The @Service annotation marks a class as a service layer component, typically holding business logic.

3fill in blank

hard

Fix the error in the annotation to mark a data access class.

Spring Boot

@[1]
public class UserRepository {
}

Drag options to blanks, or click blank then click option'

AComponent

BService

CRepository

DController

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Service or @Component instead of @Repository for data access classes.

Not annotating the repository class causes Spring not to manage it.

The @Repository annotation marks a class as a data access component, handling database operations.

4fill in blank

hard

Complete the code to declare a Spring MVC controller class with a request mapping.

Spring Boot

@[1]
@RequestMapping("/users")
public class UserController {
    @GetMapping
    public String listUsers() {
        return "userList";
    }
}

Drag options to blanks, or click blank then click option'

AController

BService

CComponent

DRepository

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component or @Service instead of @Controller for web controllers.

Forgetting @Controller causes Spring MVC not to detect the controller.

The @Controller annotation marks a class as a Spring MVC controller to handle web requests.

5fill in blank

hard

Fill all three blanks to complete a Spring Boot REST controller with service injection.

Spring Boot

@[1]
public class ProductController {

    private final ProductService productService;

    public ProductController([2] productService) {
        this.productService = productService;
    }

    @GetMapping("/products")
    public List<Product> getAllProducts() {
        return productService.[3]();
    }
}

Drag options to blanks, or click blank then click option'

ARestController

BProductService

CgetProducts

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Controller instead of @RestController for REST APIs.

Passing the wrong type in constructor parameter.

Calling a non-existent method on the service.

@RestController marks the class as a REST controller.
The constructor parameter must be the service type ProductService.
The method called on the service to get products is getProducts().

Practice

1. Which annotation is the most general one used to mark a Spring bean in a Spring Boot application?

easy

A. @Service

B. @Component

C. @Repository

D. @Controller

Solution

1. Step 1: Understand the purpose of each annotation

   @Component is the base annotation for any Spring-managed bean. @Service, @Repository, and @Controller are specialized stereotypes built on top of @Component.

2. Step 2: Identify the most general annotation

   Since @Component is the general-purpose annotation for any Spring bean, it is the correct answer.

3. Final Answer:

   @Component -> Option B

4. Quick Check:

   General Spring bean marker = @Component [OK]

Hint: General bean annotation is @Component, others are special cases [OK]

Common Mistakes:

• Confusing @Service as the general bean annotation
• Thinking @Repository is for all beans
• Assuming @Controller is the general annotation

2. Which annotation should you use to mark a class that handles HTTP requests in a Spring Boot application?

easy

A. @Repository

B. @Service

C. @Controller

D. @Component

Solution

1. Step 1: Recall the role of each annotation

   @Controller is specifically designed for classes that handle web requests and return views or data.

2. Step 2: Match the annotation to the web controller role

   Since the question asks about handling HTTP requests, @Controller is the correct annotation.

3. Final Answer:

   @Controller -> Option C

4. Quick Check:

   Web request handler = @Controller [OK]

Hint: Web controllers use @Controller annotation [OK]

Common Mistakes:

• Using @Service for web controllers
• Confusing @Repository with @Controller
• Using @Component instead of @Controller for HTTP handling

3. Consider the following Spring Boot class:

@Service
public class UserService {
    public String getUser() {
        return "Alice";
    }
}

What is the role of this class in the application?

medium

A. Contains business logic related to users

B. Accesses the database to retrieve user data

C. General Spring bean without specific role

D. Handles HTTP requests and responses

Solution

1. Step 1: Identify the annotation and its meaning

   The class is annotated with @Service, which is used for business logic components in Spring.

2. Step 2: Understand the method and class purpose

   The method getUser() returns a user name, indicating business logic rather than database access or HTTP handling.

3. Final Answer:

   Contains business logic related to users -> Option A

4. Quick Check:

   @Service = business logic class [OK]

Hint: @Service means business logic, not web or data access [OK]

Common Mistakes:

• Thinking @Service accesses the database directly
• Confusing @Service with @Controller
• Assuming @Service is a generic bean without role

4. What is wrong with this Spring Boot repository class?

@Repository
public class UserRepository {
    public void saveUser(String user) {
        // save logic
    }
}

Options: A) Class should be an interface extending JpaRepository B) Missing @Service annotation C) @Repository cannot be used on classes D) Method saveUser must return a value

medium

A. Class should be an interface extending JpaRepository

B. Missing @Service annotation

C. @Repository cannot be used on classes

D. Method saveUser must return a value

Solution

1. Step 1: Understand typical repository pattern in Spring Boot

   Spring Data JPA repositories are usually interfaces extending JpaRepository or CrudRepository to get built-in methods.

2. Step 2: Identify the issue with the class declaration

   The class is a concrete class, not an interface extending JpaRepository, so it misses Spring Data JPA features.

3. Final Answer:

   Class should be an interface extending JpaRepository -> Option A

4. Quick Check:

   Repositories usually extend JpaRepository interface [OK]

Hint: Repositories are interfaces extending JpaRepository, not plain classes [OK]

Common Mistakes:

• Thinking @Repository cannot be on classes
• Assuming @Service is needed for repositories
• Believing saveUser must return a value

5. You have a Spring Boot application with these classes:

@Component
public class UtilityHelper { }

@Service
public class OrderService { }

@Repository
public interface OrderRepository extends JpaRepository { }

@Controller
public class OrderController { }

Which statement correctly describes the roles and how Spring manages these beans?

hard

A. @Component manages data access; @Service handles web requests; @Repository is for business logic; @Controller is a utility bean

B. @Component handles web requests; @Service manages data access; @Repository is for utility beans; @Controller handles business logic

C. All annotations are interchangeable and have the same role in Spring

D. @Component is for utility beans; @Service handles business logic; @Repository manages data access; @Controller handles web requests

Solution

1. Step 1: Recall the purpose of each annotation

   @Component is a general-purpose bean, often used for utilities. @Service is for business logic. @Repository is for data access layers. @Controller is for handling web requests.

2. Step 2: Match each class role to its annotation

   UtilityHelper is a utility bean, so @Component fits. OrderService contains business logic, so @Service fits. OrderRepository accesses data, so @Repository fits. OrderController handles HTTP requests, so @Controller fits.

3. Final Answer:

   @Component is for utility beans; @Service handles business logic; @Repository manages data access; @Controller handles web requests -> Option D

4. Quick Check:

   Annotations match roles: Component-utility, Service-logic, Repository-data, Controller-web [OK]

Hint: Match annotation to role: Component-utility, Service-logic, Repository-data, Controller-web [OK]

Common Mistakes:

• Mixing up @Service and @Controller roles
• Thinking all annotations are interchangeable
• Confusing @Component with @Repository