@Component, @Service, @Repository, @Controller in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the primary role of the @Service annotation in Spring Boot?

Choose the option that best describes what @Service does in a Spring Boot application.

A Indicates a class is responsible for handling HTTP requests and returning responses.

B Marks a class as a service provider to hold business logic and be managed by Spring's container.

C Designates a class as a data access object that interacts with the database.

D Marks a class as a generic component without any specific role.

💡 Hint

Think about where you put your business rules and logic in a Spring app.

The @Service annotation marks a class as a service layer component. It holds business logic and is managed by Spring's container for dependency injection.

📝 Syntax

intermediate

Which annotation should you use to mark a class that directly accesses the database?

Select the correct Spring annotation for a class that handles database operations.

A @Repository

B @Service

C @Controller

D @Component

💡 Hint

This annotation also helps with exception translation for database errors.

The @Repository annotation marks a class as a data access object (DAO). It also enables Spring to translate database exceptions into Spring's data access exceptions.

❓ component_behavior

advanced

What happens if you annotate a class with @Component but also annotate it with @Controller in Spring Boot?

Choose the correct statement about the behavior of a class annotated with both @Component and @Controller.

A Spring treats it as a controller, and @Component is redundant but harmless.

B Spring throws a runtime error due to conflicting annotations.

C Spring treats it only as a generic component and ignores @Controller.

D The class will not be registered as a bean in the Spring container.

💡 Hint

Consider how Spring handles meta-annotations and specialization.

@Controller is a specialized form of @Component. Annotating a class with both is redundant but Spring treats it as a controller.

🔧 Debug

advanced

Why does Spring fail to inject a bean annotated only with @Component in a package outside the main application package?

Given a Spring Boot app, a class annotated with @Component is in a package not scanned by Spring. What is the cause of the injection failure?

A Spring requires explicit XML configuration to inject @Component beans.

B @Component beans cannot be injected unless also annotated with @Service.

C Spring only scans packages under the main application class package by default.

D The class must be annotated with @Repository to be injected.

💡 Hint

Think about how Spring Boot finds beans automatically.

By default, Spring Boot scans the package of the main application class and its subpackages. Classes outside these packages are not detected unless explicitly configured.

❓ lifecycle

expert

In what order does Spring instantiate and inject beans annotated with @Component, @Service, @Repository, and @Controller during application startup?

Select the correct order of bean instantiation and injection by Spring Boot for these annotations.

A @Component beans first, then @Repository, then @Service, then @Controller

B @Repository beans first, then @Component, then @Service, then @Controller

C @Controller beans first, then @Service, then @Repository, then @Component

D Spring does not guarantee a specific order; it instantiates beans as needed based on dependencies.

💡 Hint

Think about how Spring resolves dependencies and manages bean lifecycle.

Spring creates beans in an order based on dependency needs, not annotation type. It ensures dependencies are ready before injection but does not follow a fixed annotation order.