In a typical Spring application, the architecture is often organized into distinct layers to promote separation of concerns and maintain a modular structure. These layers include data access, presentation, service, and business layers. Each layer serves a specific purpose and contributes to the overall functionality of the application.
To make easier the automatic detection and registration of beans (components) in the Spring application context, Spring Framework uses class-path scanning annotations. These annotations help Spring identify the classes that should be treated as Spring beans and automatically register them in the ApplicationContext.
And here is the nice diagram to explain the hierarchy of all these annotations in Spring Framework:
@Component: The most general stereotype annotation, which marks a class as a Spring component. It indicates that the class is a candidate for auto-detection and bean registration.
@Repository: This annotation is a specialization of @Component and is used to indicate that a class is a Spring repository. It is typically used for data access components that interact with the database.
@Service: This annotation is also a specialization of @Component and is used to indicate that a class is a Spring service. It represents the business logic components in the service layer.
@Controller: This annoatation is used to indicate class is a Spring MVC controller. It is an extension of the @Component annotation, so it inherits all the functionalities of @Component. This means that a class annotated with @Controller will also be automatically detected and registered as a bean in the ApplicationContext.
The controller's primary responsibility is to handle HTTP requests, process the data (if necessary), invoke appropriate business logic (usually located in service classes), and return a response to the client, often in the form of a view to render in the user's browser.
In the Spring Framework, the annotations @Component, @Controller, @Service, and @Repository all serve the purpose of automatically detecting and registering Spring beans when context scanning is enabled. While they share the common functionality of facilitating dependency injection, each annotation has a distinct purpose based on the layer and role of the class within the application architecture.
In conclusion, by using these annotations appropriately, developers can create a clearer and more organized architecture, effectively highlighting the role of each class in the application's different layers.
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