What is the usage of @pointcut in Spring?

在Spring中，@pointcut注解用于定义一个切入点（pointcut）。切入点是在程序中定义的一个条件表达式，用于确定哪些方法或类应该被织入（intercept）到横切逻辑（cross-cutting concerns）中。

The @pointcut annotation is usually used together with the @Aspect annotation. The @Aspect annotation identifies a class as an aspect, while the @pointcut annotation is used to define the pointcut. An aspect is a modular encapsulation of cross-cutting concerns, which can include one or more advices and pointcut definitions.

When using the @pointcut annotation, AspectJ pointcut expressions can be utilized to define the specific points where aspects will be applied. These expressions allow for the specification of various conditions such as method visibility, return type, method name, parameter types, and number of parameters, in order to match the desired methods for weaving. For example:

@Aspect
public class LoggingAspect {

    @Pointcut("execution(* com.example.service.*.*(..))")
    public void serviceMethods() {}
    
    @Before("serviceMethods()")
    public void beforeServiceMethods(JoinPoint joinPoint) {
        // 在匹配的方法执行之前执行的通知逻辑
    }
    
    // 其他通知方法...
}

In the above example, the @Pointcut annotation defines a pointcut named serviceMethods, which uses an AspectJ pointcut expression to specify all methods of all classes in the com.example.service package. Then, the beforeServiceMethods method, identified by the @Before annotation, uses the serviceMethods pointcut to specify the advice logic that will be executed before the matched methods.

By using the @Pointcut annotation, we are able to separate the definition of the join points from the definition of the advice, making the code more modular and maintainable. Additionally, it is possible to define multiple join points within one aspect and share these definitions among multiple advices.