Difference between @Component, @Controller, @Service, and @Repository Spring Annotations - Java

Hello guys if you are wondering what is the difference between @Component, @Controller, @Service, and @Reposistory annotation in Spring Framework then you have come to the right place. In the past, I have shared 15 Spring Boot Interview Questions and 30 Spring MVC questions and in this article, I am going to answer the fundamental and popular Spring questions about @Component, @Service, and @Repository annotation, but before we go into differences, let’s understand the similarity first. All three of them are used to make a Java class a Spring bean, something which is managed by Spring Framework. 

Spring 2.0 has @Repository annotation, which is used as marker annotation. Currently a bean marked by @Component is also a Spring bean and a bean marked by @Service is also a spring bean, but they can be differentiated in future to associated Service level responsibility like transaction to a bean which is annotated by @Service, while @Component is a general purpose annotation to mark a Java object as Spring managed bean.

An example of @Component, @Service and @Repository annotation in Spring

As I said, you can use any of these annotation to mark a Java class as Spring managed bean, but using them in right context  is what you need. Annotating a Service class with @Service gives Spring flexibility to do some automation, which is needed by Service classes e.g. transaction management. Currently Spring provides  

Similar to @Repository annotated bean, which provides automatic exception translation for DAO classes.

Here is a simple example to see, where to use @Component, @Controller, @Service and @Repository annotation is Spring based Java applications. 

In our example, we have a class called TradeServiceImpl, which is a Service class, is annotated by @Service annotation. Our DAO class TradeDAOImpl is annotated by @Repository and our Domain object or POJO is annotated by @Component.

@Servicepublic class TradeServiceImpl implements TradeService{  @Autowired  private TradeDAO tradeDAO;   }@Repositorypublic class TradeDAOImple implements TradeDAO{  }@Componentpublic class Trade{   }

In short,

@Component is used to indicate that a class is a component. These classes are used for auto detection and configured as bean, when annotation based configurations are used.

@Controller is a specific type of component, used in MVC applications and mostly used with @RequestMapping annotation.

@Repository annotation is used to indicate that a component is used as repository and a mechanism to store/retrieve/search data. We can apply this annotation with DAO pattern implementation classes.

@Service is used to indicate that a class is a Service. Usually the business facade classes that provide some services are annotated with this.

We can use any of the above annotations for a class for auto-detection but different types are provided so that you can easily distinguish the purpose of the annotated classes.

That’s all about the difference between @Component, @Service, and @Repository Spring Annotations. The key thing is when to use which annotation. So for general purpose just use @Component annotation to mark a Java class as bean but if its part of Service layer then use @Service to allow Spring do some magic for you and if its part of persistence layer then use @Repository for similarly purpose. 

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