Declaration
可以通过在 Servlet 的 WebApplicationContext 中使用标准 Spring Bean 定义来定义 Controller Bean。@Controller 构造型允许自动检测，与 Spring 检测类路径中 @Component 类并自动注册 Bean 定义的通用支持相一致。它还可以作为标注类的构造型，表明其作为 Web 组件的角色。
You can define controller beans by using a standard Spring bean definition in the
Servlet’s WebApplicationContext. The @Controller stereotype allows for auto-detection,
aligned with Spring general support for detecting @Component classes in the classpath
and auto-registering bean definitions for them. It also acts as a stereotype for the
annotated class, indicating its role as a web component.
若要启用此类 @Controller Bean 的自动检测，可以向 Java 配置添加组件扫描，如下例所示：
To enable auto-detection of such @Controller beans, you can add component scanning to
your Java configuration, as the following example shows:
include-code::./WebConfiguration[tag=snippet,indent=0]
@RestController 是一个 composed annotation，它本身通过 @Controller 和 @ResponseBody 进行元注释，以指示一个控制器，其每个方法都继承类型级别的 @ResponseBody 注释，并且因此直接写入响应体，而不是视图分辨率，也不使用 HTML 模板进行渲染。
@RestController is a composed annotation that is
itself meta-annotated with @Controller and @ResponseBody to indicate a controller whose
every method inherits the type-level @ResponseBody annotation and, therefore, writes
directly to the response body versus view resolution and rendering with an HTML template.
AOP Proxies
在某些情况下，你可能需要在运行时使用 AOP 代理装饰 Controller。如果选择在 Controller 上直接使用 @Transactional 标注，则这是一个示例。当出现此类情况，特别是对于 Controller，我们建议使用基于类的代理。对于 Controller 上的此类标注，这种情况会自动发生。
In some cases, you may need to decorate a controller with an AOP proxy at runtime.
One example is if you choose to have @Transactional annotations directly on the
controller. When this is the case, for controllers specifically, we recommend
using class-based proxying. This is automatically the case with such annotations
directly on the controller.
如果 Controller 实现了某个接口并且需要 AOP 代理，你可能需要显式配置基于类的代理。例如，使用 @EnableTransactionManagement，可以更改为 @EnableTransactionManagement(proxyTargetClass = true)，使用 <tx:annotation-driven/>，可以更改为 <tx:annotation-driven proxy-target-class="true"/>。
If the controller implements an interface, and needs AOP proxying, you may need to
explicitly configure class-based proxying. For example, with @EnableTransactionManagement
you can change to @EnableTransactionManagement(proxyTargetClass = true), and with
<tx:annotation-driven/> you can change to <tx:annotation-driven proxy-target-class="true"/>.
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请记住，从 6.0 开始，在接口代理中，Spring MVC 不会再仅根据接口上的类型级 |
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Keep in mind that as of 6.0, with interface proxying, Spring MVC no longer detects
controllers based solely on a type-level |