Advice通知

提示：为了理解advice，我们可以参考下面的例子：
http://www.mkyong.com/spring/spring-aop-examples-advice/

通知，制定在连接点做什么，在Sping中，他主要描述Spring围绕方法调用注入的额外的行为，Spring提供的通知类型有：
beforeadvice,AfterReturningAdvice,ThrowAdvice,MethodBeforeAdvice，这些都是Spring AOP定义的接口类，具体的动作实现需要用
户程序来完成。

public interface Advice {

}

public interface MethodBeforeAdvice extends BeforeAdvice {
    void before(Method method, Object[] args, Object target) throws Throwable;

}

public interface AfterReturningAdvice extends AfterAdvice {
    void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable;
}

Pointcut连接点

提示:为了理解Pointcut和Advisor，我们可以参考下面的例子：
http://www.mkyong.com/spring/spring-aop-example-pointcut-advisor/

切点，其决定一个advice应该应用于哪个连接点，也就是需要插入额外处理的地方的集合，例如，被某个advice作为目标的一组方法。Spring pointcut通常意味着标示方法，可以选择一组方法调用作为pointcut,Spring提供了具体的切点来给用户使用，比如正则表达式切点 JdkRegexpMethodPointcut通过正则表达式对方法名进行匹配，其通过使用 AbstractJdkRegexpMethodPointcut中的对MethodMatcher接口的实现来完成pointcut功能.

public interface Pointcut {

    /**
     * Return the ClassFilter for this pointcut.
     * @return the ClassFilter (never {@code null})
     */
    ClassFilter getClassFilter();

    /**
     * Return the MethodMatcher for this pointcut.
     * @return the MethodMatcher (never {@code null})
     */
    MethodMatcher getMethodMatcher();


    /**
     * Canonical Pointcut instance that always matches.
     */
    Pointcut TRUE = TruePointcut.INSTANCE;

}

AbstractRegexpMethodPointcut
public boolean matches(Method method, Class<?> targetClass) {
    return ((targetClass != null && matchesPattern(targetClass.getName() + "." + method.getName())) ||
            matchesPattern(method.getDeclaringClass().getName() + "." + method.getName()));
}

advisor通知器

当我们完成额外的动作设计（advice)和额外动作插入点的设计（pointcut)以后,我们需要一个对象把他们结合起来，这就是通知器 -advisor,定义应该在哪里应用哪个通知。Advisor的实现有：DefaultPointcutAdvisor他有两个属性advice和 pointcut来让我们配置advice
和pointcut。

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
     */
    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
     */
    boolean isPerInstance();

}

public interface PointcutAdvisor extends Advisor {

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

}

代理对象ProxyFactoryBean

ProxyFactoryBean
@Override
public Object getObject() throws BeansException {
    //初始化通知器(advisor)链
    initializeAdvisorChain();
    if (isSingleton()) {
        return getSingletonInstance();
    }
    else {
        if (this.targetName == null) {
            logger.warn("Using non-singleton proxies with singleton targets is often undesirable. " +
                    "Enable prototype proxies by setting the 'targetName' property.");
        }
        return newPrototypeInstance();
    }
}

/**
 * Create the advisor (interceptor) chain. Aadvisors that are sourced
 * from a BeanFactory will be refreshed each time a new prototype instance
 * is added. Interceptors added programmatically through the factory API
 * are unaffected by such changes.
 */
private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException {
    if (this.advisorChainInitialized) {
        return;
    }

    if (!ObjectUtils.isEmpty(this.interceptorNames)) {
        if (this.beanFactory == null) {
            throw new IllegalStateException("No BeanFactory available anymore (probably due to serialization) " +
                    "- cannot resolve interceptor names " + Arrays.asList(this.interceptorNames));
        }

        // Globals can't be last unless we specified a targetSource using the property...
        if (this.interceptorNames[this.interceptorNames.length - 1].endsWith(GLOBAL_SUFFIX) &&
                this.targetName == null && this.targetSource == EMPTY_TARGET_SOURCE) {
            throw new AopConfigException("Target required after globals");
        }

        // Materialize interceptor chain from bean names.
        for (String name : this.interceptorNames) {
            if (logger.isTraceEnabled()) {
                logger.trace("Configuring advisor or advice '" + name + "'");
            }

            if (name.endsWith(GLOBAL_SUFFIX)) {
                if (!(this.beanFactory instanceof ListableBeanFactory)) {
                    throw new AopConfigException(
                            "Can only use global advisors or interceptors with a ListableBeanFactory");
                }
                addGlobalAdvisor((ListableBeanFactory) this.beanFactory,
                        name.substring(0, name.length() - GLOBAL_SUFFIX.length()));
            }

            else {
                // If we get here, we need to add a named interceptor.
                // We must check if it's a singleton or prototype.
                Object advice;
                if (this.singleton || this.beanFactory.isSingleton(name)) {
                    // Add the real Advisor/Advice to the chain.
                    advice = this.beanFactory.getBean(name);
                }
                else {
                    // It's a prototype Advice or Advisor: replace with a prototype.
                    // Avoid unnecessary creation of prototype bean just for advisor chain initialization.
                    advice = new PrototypePlaceholderAdvisor(name);
                }
                addAdvisorOnChainCreation(advice, name);
            }
        }
    }

    this.advisorChainInitialized = true;
}

/**
 * Return the singleton instance of this class's proxy object,
 * lazily creating it if it hasn't been created already.
 * @return the shared singleton proxy
 */
private synchronized Object getSingletonInstance() {
    if (this.singletonInstance == null) {
        this.targetSource = freshTargetSource();
        if (this.autodetectInterfaces && getProxiedInterfaces().length == 0 && !isProxyTargetClass()) {
            // Rely on AOP infrastructure to tell us what interfaces to proxy.
            Class<?> targetClass = getTargetClass();
            if (targetClass == null) {
                throw new FactoryBeanNotInitializedException("Cannot determine target class for proxy");
            }
            setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, this.proxyClassLoader));
        }
        // Initialize the shared singleton instance.
        super.setFrozen(this.freezeProxy);
        this.singletonInstance = getProxy(createAopProxy());
    }
    return this.singletonInstance;
}

protected Object getProxy(AopProxy aopProxy) {
    return aopProxy.getProxy(this.proxyClassLoader);
}

protected final synchronized AopProxy createAopProxy() {
    if (!this.active) {
        activate();
    }
    return getAopProxyFactory().createAopProxy(this);
}


DefaultAopProxyFactory
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
    if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
        Class<?> targetClass = config.getTargetClass();
        if (targetClass == null) {
            throw new AopConfigException("TargetSource cannot determine target class: " +
                    "Either an interface or a target is required for proxy creation.");
        }
        if (targetClass.isInterface()) {
            return new JdkDynamicAopProxy(config);
        }
         Objenesis based extension of {@link CglibAopProxy} to create proxy instances without invoking the constructor of the class.
        return new ObjenesisCglibAopProxy(config);
    }
    else {
        return new JdkDynamicAopProxy(config);
    }
}