1.是什么？

面向切面编程，横切关注点被模块化为特殊的类，这些类被称为切面

2.为什么？

解耦；让一组类共享相同的行为（在OOP开发模式中只能通过继承和实现接口来实现，单继承，阻碍了更多的行为添加到一组类中）

3.怎么用？

3.1声明切面 @Aspect

3.2定义建言（advice） @After @Before @Around

4.demo

4.1在spring工程中创建如下几个文件

4.1.1编写拦截规则的注解

import java.lang.annotation.*;

@Target(ElementType.METHOD)

@Retention(RetentionPolicy.RUNTIME)

@Documented

public @interface Action {

Stringname();

}

4.1.2编写一个使用注解的被拦截类

import org.springframework.stereotype.Service;

@Service

public class DemoAnnotationService {

@Action(name ="注解式拦截的add操作")

public void add() {

System.out.println("我就是那个需要被拦截的方法！！！");

    }
}

4.1.3编写切面

import org.aspectj.lang.JoinPoint;

import org.aspectj.lang.annotation.After;

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.Pointcut;

import org.aspectj.lang.reflect.MethodSignature;

import org.springframework.stereotype.Component;

import java.lang.reflect.Method;

@Aspect

@Component

public class LogAspect {

@Pointcut("@annotation(com.dxj.springboot.springbootdemo.Action)")

public void annotationPointCut(){};

@Before("annotationPointCut()")

public void before(JoinPoint joinPoint){

MethodSignature signature = (MethodSignature)joinPoint.getSignature();

    Method method = signature.getMethod();

    Action action = method.getAnnotation(Action.class);

    System.out.println("我是Before!注解式拦截" + action.name());

}

@After("annotationPointCut()")

public void after(JoinPointjoinPoint){

MethodSignature signature = (MethodSignature)joinPoint.getSignature();

        Method method = signature.getMethod();

        Action action = method.getAnnotation(Action.class);

        System.out.println("我是AFTER!注解式拦截" + action.name());

    }

}

4.1.4 配置类

import org.springframework.context.annotation.ComponentScan;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.EnableAspectJAutoProxy;

@Configuration

**@ComponentScan("com.xxx.springboot.springbootdemo")**

**@EnableAspectJAutoProxy**

public class AopConfig {

}

4.1.5 运行

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

@SpringBootApplication

public class SpringbootDemoApplication {

public static void main(String[] args) {

AnnotationConfigApplicationContext context =new AnnotationConfigApplicationContext(AopConfig.class);

      DemoAnnotationService demoAnnotationService = context.getBean(DemoAnnotationService.class);

      demoAnnotationService.add();

      context.close();

  }

}

4.1.6结果