@Named annotation in Spring MVC

问题

Per Spring 3 document, The IoC container, the @Named annotation is a standard equivalent to the @Component annotation.

Since @Repository, @Service, and @Controller are all @Component, I tried to used @Named for all of them in my Spring MVC application. It works fine. But I found the replacement of @Controller seems to have a bug. In the controller class, originally, it was

@Controller
public class MyController{
    ...
}

It works fine. When I changed @Controller to @Named

@Named
public class MyController{
    ...
}

It failed with error:

"No mapping found for HTTP request with URI ...".

But if I added @RequestMapping to the class as follow

@Named
@RequestMapping
public class MyController{
     ...
 }

It would work as expected.

For @Repository and @Service, I can simply replace them with @Named with no issue. But the replacement of @Controller needs extra work. Is there anything I am missing in the configuration?

回答1:

@Named works the same as @Component. However, the annotations @Controller, @Service, and @Repository are more specific.

From the Spring docs:

@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.

For example, these stereotype annotations make ideal targets for pointcuts. It is also possible that @Repository, @Service, and @Controller may carry additional semantics in future releases of the Spring Framework. 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.

This section explains the difference with @Named.

Many components, like Spring's DispatcherServlet (MVC configuration in WebApplicationContext) aren't looking for Component, they are looking for @Controller. So when it scans your class, it won't find it in @Named. In a similar fashion, transaction management with @Transactional looks for @Service and @Repository, not for the more generic @Component.

回答2:

All @Repository, @Service and @Controller are mainly for declaring Spring beans, apart from that it gives extra information to Spring about the type of bean like controller, dao etc

来源：https://stackoverflow.com/questions/18540696/named-annotation-in-spring-mvc