Spring MVC，我的bean如何在控制器中自动接线？

Question

I'm new to spring and spring mvc. I have configured a dataSource and mvc by follwing a video tutorial. I have added a context file offers-servlet.xml in the WEB-INF where i'm scanning my controllers package where my controller.java is located. i created another context service-context.xml where i'm component-scanning service.java classes. i'm creating the instance of service.java in my controller.java with setService method which i annotated with @Autowired . And my doubt here is how the service.java is getting autowired in my controller.java where each of these are in different packages and different context.xml files with different component-scan .

Answer 1

This link here explains Component scanning in the case of Annotations. In your case you have configured component scanning through XML. Every XML definition in spring has its corresponding annotation definition. Although this link exmplains the case when component scan is configured through annotations, it is completly valid in your case as well:

How to understand Spring @ComponentScan

Answer 2

The fact that the beans are located in different packages is not important, if they are known to the spring container. By enabling the component scan in both packages, you make available all beans in both packages globally in the current execution context of the application.

You can think of spring IoC as a global map, that given a (previously registered) key it can give you the instance related to that key.

Answer 3

When you mentioned component-scan packages, it indicates the spring-container to find the annotated classes in those mentioned package and then beans (objects of classes which would have @Component or related annotation like @Service, @Controller, @Repository) would be managed (whole life-cycle from creation to destroy) by Spring. So, in your application, whenever you would need one such bean, rather than creating, it would be provided by container. On the other hand, if you wouldn't have specified 'component-scan', You will have to identify your classes (using either xml or javaConfig) whose beans you want Spring-container to manage. Now this part was identifying which beans would be managed by Spring-container.

Next comes wiring these beans where it is needed. To do so, you mentioned @Autowired on setter method. As Spring-container encounters this annotation, it will look for that bean (service bean in your case) in container. Since, that bean is managed by container (from previous step) and is available when needed (in controller class in your case), container will provide (auto-wire) service bean into the setter method.