spring aop实现过程之一代理对象的生成

AOP实现中，可以看到三个主要的步骤，一个是代理对象的生成，然后是拦截器的作用，然后是Aspect编织的实现。

 1.ProxyFactoryBean生成AopProxy

ProxyFactoryBean生成AOP proxy

    /**
     * Return a proxy. Invoked when clients obtain beans from this factory bean.
     * Create an instance of the AOP proxy to be returned by this factory.
     * The instance will be cached for a singleton, and create on each call to
     * <code>getObject()</code> for a proxy.
     * @return a fresh AOP proxy reflecting the current state of this factory
     */
    public Object getObject() throws BeansException {
 9         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();
        }
    }

初始化Advisor chain

    /**
     * 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 (int i = 0; i < this.interceptorNames.length; i++) {
                String name = this.interceptorNames[i];
                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 = null;
                    if (this.singleton || this.beanFactory.isSingleton(this.interceptorNames[i])) {
                        // Add the real Advisor/Advice to the chain.
                        advice = this.beanFactory.getBean(this.interceptorNames[i]);
                    }
                    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(this.interceptorNames[i]);
                    }
53                     addAdvisorOnChainCreation(advice, this.interceptorNames[i]);
                }
            }
        }

        this.advisorChainInitialized = true;
    }

增加advisor chain（AdvisedSupport.java）

    private void addAdvisorInternal(int pos, Advisor advisor) throws AopConfigException {
        Assert.notNull(advisor, "Advisor must not be null");
        if (isFrozen()) {
            throw new AopConfigException("Cannot add advisor: Configuration is frozen.");
        }
        if (pos > this.advisors.size()) {
            throw new IllegalArgumentException(
                    "Illegal position " + pos + " in advisor list with size " + this.advisors.size());
        }
        this.advisors.add(pos, advisor);
        updateAdvisorArray();
        adviceChanged();
    }