Spring AOP是怎么回事？

spring 5.x版本

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
  http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
    <!-- 业务类 -->
    <bean id="queryService" class="com.sucl.blog.springaop.service.QueryService"/>
    <!-- 定义Aspect，aop:method 的来源  -->
    <bean id="logAspect" class="com.sucl.blog.springaop.aspect.LogAspect"/>
    
    <!-- 基于Aspect-->
    <aop:config>
        <aop:aspect ref="logAspect">
            <aop:pointcut id="pointcut" expression="execution(* com.sucl.blog.springaop.service..*(..))"/>

            <aop:before method="before" pointcut-ref="pointcut"/>
            <aop:after-returning method="afterReturning" pointcut-ref="pointcut" returning="result"/>
            <aop:after-throwing method="afterThrowing" pointcut-ref="pointcut" throwing="e"/>
            <aop:after method="after" pointcut-ref="pointcut"/>
            <aop:around method="around" pointcut-ref="pointcut"/>
        </aop:aspect>
    </aop:config>
</beans>

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
  http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">

    <bean id="queryService" class="com.sucl.blog.springaop.service.QueryService"/>
    <bean id="logAdvice" class="com.sucl.blog.springaop.advice.LogAdvice"/>

    <!-- 基于Advisor -->
    <aop:config>
        <aop:pointcut id="pointcut" expression="execution(* com.sucl.blog.springaop.service..*(..))"/>
        <aop:advisor advice-ref="logAdvice" pointcut-ref="pointcut"/>
    </aop:config>
</beans>

@Slf4j
@Aspect
public class LogAspect {

    @Pointcut("execution(* com.sucl.blog.springaop.service..*(..))")
    public void pointcut(){}

    /**
     * 方法执行前执行
     * @param joinPoint
     * @param arg1
     */
    @Before(value = "pointcut()")
    public void before(JoinPoint joinPoint){
        log.info(">>> 执行 before");
    }

    /**
     * 方法出现异常时执行
     * @param joinPoint
     */
    @AfterThrowing(value = "pointcut()", throwing = "e")
    public void afterThrowing(JoinPoint joinPoint, Exception e){
        log.info(">>> 执行 afterThrowing: {}", e.getMessage());
    }

    /**
     * 方法返回后执行，异常时不执行
     * @param joinPoint
     */
    @AfterReturning(value = "pointcut()", returning = "result")
    public void afterReturning(JoinPoint joinPoint, Object result){
        log.info(">>> 执行 afterReturning: {}" ,result);
    }

    /**
     * 方法执行完执行，不管是否发生异常
     * @param joinPoint
     */
    @After(value = "pointcut()")
    public void after(JoinPoint joinPoint){
        log.info(">>> 执行 after");
    }

    /**
     * 在after与 around 前后执行
     * @param pjp
     * @param jp
     */
    @Around(value = "pointcut()")
    public void around(ProceedingJoinPoint pjp){
        try {
            log.info(">>> 执行 around starting");
            pjp.proceed();
            log.info(">>> 执行 around finished");
        } catch (Throwable e) {
            log.info(">>> 执行 around 异常：{}", e.getMessage());
        }
    }
}

@Configuration
public class ProxyConfiguration {

    @Bean
    public ProxyFactoryBean printServiceProxy() {
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
        proxyFactoryBean.setTarget(new PrintService());
        proxyFactoryBean.setProxyTargetClass(true);
        addInterceptors(proxyFactoryBean);
        return proxyFactoryBean;
    }

    /**
     * 定义方法拦截器：（支持通配符）
     * org.springframework.aop.Advisor
     * org.aopalliance.intercept.Interceptor
     *
     * MethodBeforeAdvice
     * AfterReturningAdvice
     * ThrowsAdvice
     *
     * org.aopalliance.intercept.MethodInterceptor
     * org.aopalliance.aop.Advice
     *
     * @param proxyFactoryBean
     */
    private void addInterceptors(ProxyFactoryBean proxyFactoryBean) {
        proxyFactoryBean.setInterceptorNames("logAdvice");
    }

    @Bean
    public LogAdvice logAdvice() {
        return new LogAdvice();
    }
}

@Slf4j
public class LogAdvice implements MethodInterceptor {

    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        try {
            log.info(">>> before");
            Object result = invocation.proceed();
            log.info(">>> afterReturning : {}", result);
            return result;
        } catch (Throwable e) {
            log.info(">>> afterThrowing : {}", e.getMessage());
            throw e;
        } finally {
            log.info(">>> after");
        }
    }
}