AOP-Advisor-笔记

一、Advisor接口

这个接口是一个通知者的顶层接口。它实现类持有一个通知(advice)和一个过滤器的引用。用过滤器来决定通知是否合适目标对象。

这个接口只有两个方法，所以将整个代码贴上来。

/**
 * Base interface holding AOP <b>advice</b> (action to take at a joinpoint)
 * and a filter determining the applicability of the advice (such as
 * a pointcut). <i>This interface is not for use by Spring users, but to
 * allow for commonality in support for different types of advice.</i>
 *
 * <p>Spring AOP is based around <b>around advice</b> delivered via method
 * <b>interception</b>, compliant with the AOP Alliance interception API.
 * The Advisor interface allows support for different types of advice,
 * such as <b>before</b> and <b>after</b> advice, which need not be
 * implemented using interception.
 *
 * @author Rod Johnson
 */
public interface Advisor {

    /**
     * Return the advice part of this aspect. An advice may be an
     * interceptor, a before advice, a throws advice, etc.
     * @return the advice that should apply if the pointcut matches
     * @see org.aopalliance.intercept.MethodInterceptor
     * @see BeforeAdvice
     * @see ThrowsAdvice
     * @see AfterReturningAdvice
     *///返回切面中的一个通知，这个通知有可能是个拦截器。
    Advice getAdvice();

    /**
     * Return whether this advice is associated with a particular instance
     * (for example, creating a mixin) or shared with all instances of
     * the advised class obtained from the same Spring bean factory.
     * <p><b>Note that this method is not currently used by the framework.</b>
     * Typical Advisor implementations always return {@code true}.
     * Use singleton/prototype bean definitions or appropriate programmatic
     * proxy creation to ensure that Advisors have the correct lifecycle model.
     * @return whether this advice is associated with a particular target instance
     *///返回一个通知是与一个实例关联还是的与多个实例关联，如果只与一个实例关联，那么就返回true.
    boolean isPerInstance();

}

二、 Advisor的子接口PointcutAdvisor

这个接口几乎是所有通知者的父接口，除了引入通知者之外。可以在方法级别上判断通知是否适用。

/**
 * Superinterface for all Advisors that are driven by a pointcut.
 * This covers nearly all advisors except introduction advisors,
 * for which method-level matching doesn't apply.
 *
 * @author Rod Johnson
 */
public interface PointcutAdvisor extends Advisor {

    /**
     * Get the Pointcut that drives this advisor.
     */
    Pointcut getPointcut();

}

 三、AspectJPointcutAdvisor

一）、这个类的属性

这个类的属性很少，只有三个。分别是通知、切点、顺序。Advisor就是用来将通知和切点结合在一起的。

    private final AbstractAspectJAdvice advice;//通知

    private final Pointcut pointcut;//切点

    private Integer order;//顺序，值越小优先级越高。如：值为1的优先级高于值为5的优先级。看Ordered接口。

二）、这个类的方法

这个类的方法也很简单，主要是一个构造方法，和若干个setter、getter方法，用来设置和获取以上的三个属性的。

①、构造方法

构造方法初始化通知和切点。

    /**
     * Create a new AspectJPointcutAdvisor for the given advice
     * @param advice the AbstractAspectJAdvice to wrap
     */
    public AspectJPointcutAdvisor(AbstractAspectJAdvice advice) {
        Assert.notNull(advice, "Advice must not be null");
        this.advice = advice;
        this.pointcut = advice.buildSafePointcut();//
    }

其他setter和getter方法就不列举了，可以想象的到。

所以现在如果提起Advisor，要能想象到这个Advisor具体是什么样子的。一个Advisor由通知、切点、顺序组成。

还有一个知识点，Advisor是什么实例化的？

根据的我的debug，发现它是在SpringIOC容器初始化或者刷新的时候初始化的。具体来说是在AbstractApplicationContext.refresh()方法中。因为Advisor都是非懒加载单例对象。

refresh()方法中的代码:

                // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);

就是上面这句代码执行了对Advisor的初始化。