Question:
In Spring there are 3 class notes @Component , @Service , @Controller and @Repository .
I know @Component is the only one that can be used in all cases ( Controller , Service and Repository ).
But what are the advantages and disadvantages of using this annotation which is more generic?
Answer:
Unlike the generic @Component annotation, specific annotations mark classes with stereotypes, just like in the UML.
This way, if a class is annotated with @Service you can assume that it contains business rules, if the annotation is @Repository is obvious that the class implements the Respository pattern (it is not the same as DAO, but it is similar) and if the annotation is @Controller you can also bind directly to a controller from the MVC model.
Although at first it looks like just an ornament, it is possible to list some advantages:
- Aids in application layer separation.
- It facilitates the use of POA (AOP – Aspect Oriented Programming), as in the case of the Spring Data JPA module, which dynamically "generates" the implementation of annotated interfaces with Repository.
- Allows the specific handling of exceptions thrown by specific layers, where we have again the example of the data access layer (
Repository), where Spring will translate specific exceptions from a database into standardized classes. - You can create any functionality that needs general treatment by layer, just use a little imagination. 🙂
Honestly, I didn't find any disadvantages in using specific annotations compared to generic annotation. The only caveat is regarding the performance of component-scan , which finds the annotations automatically (regardless of which one you are using), as it can delay the application's startup. Mapping beans to XML improves startup time if this is critical.