Declaring an Aspect

如果启用了 @AspectJ 支持，应用程序上下文中的任何 bean 都采用了带有 @Aspect 批注（带有 @Aspect 批注）的 @AspectJ 方面类的 bean，Spring 会自动检测到它们，并可用于配置 Spring AOP。以下两个示例显示并非十分有用的方面所需的最小步骤。

With @AspectJ support enabled, any bean defined in your application context with a class that is an @AspectJ aspect (has the @Aspect annotation) is automatically detected by Spring and used to configure Spring AOP. The next two examples show the minimal steps required for a not-very-useful aspect.

这两个示例中，第一个示例显示应用程序上下文中带有常规定义的 bean，它指向用 @Aspect 做批注的 bean 类：

The first of the two examples shows a regular bean definition in the application context that points to a bean class that is annotated with @Aspect:

  • Java

  • Kotlin

  • Xml

public class ApplicationConfiguration {

	@Bean
	public NotVeryUsefulAspect myAspect() {
		NotVeryUsefulAspect myAspect = new NotVeryUsefulAspect();
		// Configure properties of the aspect here
		return myAspect;
	}
}
class ApplicationConfiguration {

	@Bean
	fun myAspect() = NotVeryUsefulAspect().apply {
		// Configure properties of the aspect here
	}
}
<bean id="myAspect" class="org.springframework.docs.core.aop.ataspectj.aopataspectj.NotVeryUsefulAspect">
	<!-- configure properties of the aspect here -->
</bean>

这两个示例中，第二个示例显示带有 @Aspect 做批注的 NotVeryUsefulAspect 类定义：

The second of the two examples shows the NotVeryUsefulAspect class definition, which is annotated with @Aspect:

  • Java

  • Kotlin

@Aspect
public class NotVeryUsefulAspect {
}
@Aspect
class NotVeryUsefulAspect

（带有 @Aspect 做批注的）方面（类）可以具有与任何其他类相同的方法和字段。它们还可以包含切入点、建议和引入（中间类型）声明。

Aspects (classes annotated with @Aspect) can have methods and fields, the same as any other class. They can also contain pointcut, advice, and introduction (inter-type) declarations.

Autodetecting aspects through component scanning

您可以在Spring XML配置中将aspect类注册为常规bean，通过`@Configuration`类中的`@Bean`方法注册，或者让Spring通过类路径扫描自动检测它们，就像其他Spring托管的bean一样。但是，请注意，@Aspect`注释不足以在类路径中进行自动检测。为此，您需要添加一个单独的@Component`注释（或者，一个自定义的stereotype注释，根据Spring组件扫描程序的规则进行限定）。
Autodetecting aspects through component scanning

You can register aspect classes as regular beans in your Spring XML configuration, via @Bean methods in @Configuration classes, or have Spring autodetect them through classpath scanning — the same as any other Spring-managed bean. However, note that the @Aspect annotation is not sufficient for autodetection in the classpath. For that purpose, you need to add a separate @Component annotation (or, alternatively, a custom stereotype annotation that qualifies, as per the rules of Spring’s component scanner).
Advising aspects with other aspects?

在Spring AOP中，aspect本身不能成为其他aspect的advice目标。类上的`@Aspect`注释将其标记为aspect，因此，将其排除在自动代理之外。
Advising aspects with other aspects?

In Spring AOP, aspects themselves cannot be the targets of advice from other aspects. The @Aspect annotation on a class marks it as an aspect and, hence, excludes it from auto-proxying.