spring annotations bean Spring has @Component annotation, what is the real purpose of the annotations @Repository, @Service, @Controller?

@service annotation in spring boot (1)

I've developed web applications for a few years with Spring framework. Recently, a fresher of my team asked me a question, Spring has @Component annotation, what is the real purpose of the annotations @Repository, @Service, @Controller? I tried to give him the answer that there is no difference among them, only for identifying types of java Bean. As you know, my explanation lacks of persuasion, he didn't buy it.

So I want to ask a question, what is the real purpose of the annotations @Repository, @Service, @Controller? what the real difference among these annotations?

Answer #1

This question's been asked before: What's the difference between @Component, @Repository & @Service annotations in Spring?

In Spring 2.0 and later, the @Repository annotation is a marker for any class that fulfills the role or stereotype (also known as Data Access Object or DAO) of a repository. Among the uses of this marker is the automatic translation of exceptions.

Spring 2.5 introduces further stereotype annotations: @Component, @Service, and @Controller. @Component is a generic stereotype for any Spring-managed component. @Repository, @Service, and @Controller are specializations of @Component for more specific use cases, for example, in the persistence, service, and presentation layers, respectively.

Therefore, you can annotate your component classes with @Component, but by annotating them with @Repository, @Service, or @Controller instead, your classes are more properly suited for processing by tools or associating with aspects. For example, these stereotype annotations make ideal targets for pointcuts.

Thus, if you are choosing between using @Component or @Service for your service layer, @Service is clearly the better choice. Similarly, as stated above, @Repository is already supported as a marker for automatic exception translation in your persistence layer.