Spring MVC 中的 @Named 注解

2022-01-13 00:00:00 annotations java spring-mvc jsr330

根据 Spring 3 文档，IoC容器，@Named注解是标准等价于@Component注解.

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

由于@Repository、@Service、@Controller都是@Component，所以我尝试使用@Named 用于我的 Spring MVC 应用程序中的所有这些.它工作正常.但我发现 @Controller 的替换似乎有一个错误.在控制器类中，原来是

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{
    ...
}

它工作正常.当我将 @Controller 更改为 @Named

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

@Named
public class MyController{
    ...
}

失败并出现错误:

没有为带有 URI ... 的 HTTP 请求找到映射".

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

但是如果我将 @RequestMapping 添加到类中，如下所示

But if I added @RequestMapping to the class as follow 

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

它会按预期工作.

对于 @Repository 和 @Service，我可以简单地用 @Named 替换它们，没有任何问题.但是 @Controller 的替换需要额外的工作.配置中有什么我遗漏的吗?

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?

推荐答案

@Named 与 @Component 的作用相同.但是，注释 @Controller、@Service 和 @Repository 更具体.

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

来自 Spring 文档:

From the Spring docs:

@Component 是任何 Spring 管理的组件的通用构造型.@Repository、@Service 和 @Controller 是@Component 用于更具体的用例，例如，在分别是持久层、服务层和表示层.

@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.

例如，这些原型注释是理想的目标切入点.@Repository、@Service 和@Controller 可能会在未来版本的春天框架.因此，如果您在使用 @Component 之间进行选择或 @Service 为您的服务层，@Service 显然更好选择.同样，如上所述，@Repository 已经被支持作为持久性中自动异常翻译的标记层.

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.

本部分解释了与 @Named 的区别.

This section explains the difference with @Named.

许多组件，例如 Spring 的 DispatcherServlet(WebApplicationContext 中的 MVC 配置)不是在寻找 Component，而是在寻找 @控制器.所以当它扫描你的类时，它不会在 @Named 中找到它.以类似的方式，使用 @Transactional 的事务管理查找 @Service 和 @Repository，而不是更通用的 @Component.

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.

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