使用注解开发AspectJ，已在java代码中加入@Aspect,为什么在配置中再次定义切面

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

       xmlns:aop="http://www.springframework.org/schema/aop" 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">

    <!--开启AspectJ的注解开发，自动代理=====================-->

    <aop:aspectj-autoproxy/>

    <!--目标类===================-->

    <bean id="productDao" class="com.imooc.aspectJ.demo1.ProductDao"/>

    <!--定义切面-->

    <bean class="com.imooc.aspectJ.demo1.MyAspectAnno"/>

</beans>

@Aspect
public class MyAspectAnno {

    @Before(value="myPointcut1()")
    public void before(JoinPoint joinPoint){
        System.out.println("前置通知=================="+joinPoint);
    }

    @AfterReturning(value="myPointcut2()",returning = "result")
    public void afterReturing(Object result){
        System.out.println("后置通知=================="+result);
    }

    @Around(value="myPointcut3()")
    public Object around(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("环绕前通知================");
        Object obj = joinPoint.proceed(); // 执行目标方法
        System.out.println("环绕后通知================");
        return obj;
    }

    @AfterThrowing(value="myPointcut4()",throwing = "e")
    public void afterThrowing(Throwable e){
        System.out.println("异常抛出通知=============="+e.getMessage());
    }

    @After(value="myPointcut5()")
    public void after(){
        System.out.println("最终通知==================");
    }


    @Pointcut(value="execution(* com.imooc.aspectJ.demo1.ProductDao.save(..))")
    private void myPointcut1(){}

    @Pointcut(value="execution(* com.imooc.aspectJ.demo1.ProductDao.update(..))")
    private void myPointcut2(){}

    @Pointcut(value="execution(* com.imooc.aspectJ.demo1.ProductDao.delete(..))")
    private void myPointcut3(){}

    @Pointcut(value="execution(* com.imooc.aspectJ.demo1.ProductDao.findOne(..))")
    private void myPointcut4(){}

    @Pointcut(value="execution(* com.imooc.aspectJ.demo1.ProductDao.findAll(..))")
    private void myPointcut5(){}
}