What is the difference between these four annotations in Java? Why are they mixed in the project?

Question

@Component：
@Controller
@Repository
@Service

Answer 1

are all used to define Bean

• @Component is the most versatile

• @Service, @Repository are also @Service，@Repository也是@Component, but they are given different semantics to facilitate code reading. In fact, it doesn’t matter if you use these three casually, Spring will not report an error.

• @ControllerSpecial, exclusively handled by Spring MVC and cannot be replaced by the other three.

Answer 2

@Service is used to annotate business layer components

@Controller is used to annotate control layer components (controller in spring)

@Repository is used to annotate data access components, namely DAO components

@Component generally refers to components. When components are difficult to classify, we can use this annotation to annotate them

Answer 3

@Controller is used in controller, @Service is used in service, @Repository is used in dao, and @Component is used in other unclear places.

Answer 4

It’s just that the semantics are different, but the functions are the same

Answer 5

The effect is the same**

Answer 6

These four annotations have the same operating effect on the machine. There is only a semantic difference, which tells people who read the code which level component this class is