spring AOP源码分析（二）

现在，我们将对代理对象的生成过程进行分析。

在springAOP源码分析（一）的例子中，将会生成哪些对象呢？

可以看到将会生成六个对象，对应的beanName分别是:

userDao:目标对象

logger:定义的切面

InternalAutoProxyCreator:用来生成代理对象的后置处理器，它实现了BeanPostProcessor，类型是AspectJAwareAdvisorAutoProxyCreator

AspectJPointcutAdvisor#0:定义的通知

AspectJPointcutAdvisor#1:定义的通知

updateUserMethod:切入点表达式

这里我们只要搞明白AspectJAwareAdvisorAutoProxyCreator和userDao这两个对象的生成过程，那么关于代理对象是如何生成的，也就清楚了。

一.AspectJAwareAdvisorAutoProxyCreator的实例化

AspectJAwareAdvisorAutoProxyCreator是一个后置处理器，它的作用是在bean对象实例化的前后可以进行一些操作。在这里，准确的说是在它的postProcessAfterInitialization方法中完成了对userDao目标对象生成了代理对象，这个方法是代理对象生成的地方，稍后再分析这个方法。现在需要思考的是对于AspectJAwareAdvisorAutoProxyCreator这个对象是什么时候生成的呢？其实它在registerBeanPostProcessors注册后置处理器的时候实例化的。进入refesh方法

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
　　　　　　　　　 //进入这个方法　
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                initMessageSource();

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

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

                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

进入registerBeanPostProcessors方法，然后可以追踪到以下方法

    public static void registerBeanPostProcessors(
            ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
　　　　　
        //获取所有的后置处理器　
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        // Register BeanPostProcessorChecker that logs an info message when
        // a bean is created during BeanPostProcessor instantiation, i.e. when
        // a bean is not eligible for getting processed by all BeanPostProcessors.
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

         //对这些后置处理器进行分类存储
        // Separate between BeanPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        //以下这些就是针对不同类型的后置处理器分别进行注册实例化
        // First, register the BeanPostProcessors that implement PriorityOrdered.
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // Next, register the BeanPostProcessors that implement Ordered.
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : orderedPostProcessorNames) {
            //AspectJAwareAdvisorAutoProxyCreator的实例化就是在这里进行的
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        sortPostProcessors(orderedPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);

        // Now, register all regular BeanPostProcessors.
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : nonOrderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

        // Finally, re-register all internal BeanPostProcessors.
        sortPostProcessors(internalPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, internalPostProcessors);

        // Re-register post-processor for detecting inner beans as ApplicationListeners,
        // moving it to the end of the processor chain (for picking up proxies etc).
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }

现在AspectJAwareAdvisorAutoProxyCreator对象已生成，那么对于其它bean实例化的时候它就可以起到后置处理器应有的作用了。

二.userDao的实例化过程

目标对象userDao的实例化过程，也包含了代理对象的生成过程，通过源码来一步步分析。

进入AbstractAutowireCapableBeanFactory类的initializeBean方法

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                @Override
                public Object run() {
                    invokeAwareMethods(beanName, bean);
                    return null;
                }
            }, getAccessControlContext());
        }
        else {
            invokeAwareMethods(beanName, bean);
        }

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
            //对该bean调用所有后置处理器的postProcessBeforeInitialization方法
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }

        try {
            //调用初始化方法
            invokeInitMethods(beanName, wrappedBean, mbd);
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    (mbd != null ? mbd.getResourceDescription() : null),
                    beanName, "Invocation of init method failed", ex);
        }
        if (mbd == null || !mbd.isSynthetic()) {
            //代理对象的生成在这个方法中进行的
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

进入applyBeanPostProcessorsAfterInitialization方法

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
            //获取所有的后置处理器对该bean进行操作 然后进入AbstractAutoProxyCreator的
            //postProcessAfterInitialization方法中
            result = beanProcessor.postProcessAfterInitialization(result, beanName);
            if (result == null) {
                return result;
            }
        }
        return result;
    }

进入AbstractAutoProxyCreator类的postProcessAfterInitialization方法中

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean != null) {
            Object cacheKey = getCacheKey(bean.getClass(), beanName);
            if (!this.earlyProxyReferences.contains(cacheKey)) {
                //进入这个方法
                return wrapIfNecessary(bean, beanName, cacheKey);
            }
        }
        return bean;
    }

进入wrapIfNecessary方法

    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
            return bean;
        }
        if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
            return bean;
        }
        if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
            this.advisedBeans.put(cacheKey, Boolean.FALSE);
            return bean;
        }

        // Create proxy if we have advice.
　　　　 // 为目标bean查找匹配的通知器
        Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
        if (specificInterceptors != DO_NOT_PROXY) {
            this.advisedBeans.put(cacheKey, Boolean.TRUE);
            //如果通知器的数组specificInterceptors不为空，那么生成代理对象

            Object proxy = createProxy(
                    bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
            this.proxyTypes.put(cacheKey, proxy.getClass());
            //把生成的代理对象放到容器中，此时beanName对应的对象不再是目标对象，而是代理对象。
            return proxy;
        }

        this.advisedBeans.put(cacheKey, Boolean.FALSE);
        return bean;
    }

接下来我们去分析两个方法：为目标bean查询匹配的通知器getAdvicesAndAdvisorsForBean和代理对象的生成方法createProxy

1.查询匹配的通知器，进入getAdvicesAndAdvisorsForBean方法

protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource) {
        //进入该方法
        List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
        if (advisors.isEmpty()) {
            return DO_NOT_PROXY;
        }
        return advisors.toArray();
    }

进入getAdvicesAndAdvisorsForBean方法

    protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
        //查找所有的通知器
        List<Advisor> candidateAdvisors = findCandidateAdvisors();
        //然后筛选匹配出可应用在beanClass上的通知器
        List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
        extendAdvisors(eligibleAdvisors);
        if (!eligibleAdvisors.isEmpty()) {
            eligibleAdvisors = sortAdvisors(eligibleAdvisors);
        }
        return eligibleAdvisors;
    }

2.代理对象的生成过程，有JDK动态代理和cglib两种生成方式，默认是JDK动态代理

进入createProxy方法，这个方法是代理对象生成的地方

/**
     * Create an AOP proxy for the given bean.
     * @param beanClass the class of the bean
     * @param beanName the name of the bean
     * @param specificInterceptors the set of interceptors that is
     * specific to this bean (may be empty, but not null)
     * @param targetSource the TargetSource for the proxy,
     * already pre-configured to access the bean
     * @return the AOP proxy for the bean
     * @see #buildAdvisors
     */
    protected Object createProxy(
            Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {

        if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
            AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
        }

        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.copyFrom(this);

        if (!proxyFactory.isProxyTargetClass()) {
            if (shouldProxyTargetClass(beanClass, beanName)) {
                proxyFactory.setProxyTargetClass(true);
            }
            else {
                evaluateProxyInterfaces(beanClass, proxyFactory);
            }
        }
        // 获取所有的通知器，并给ProxyFactory配置通知器，目标对象
        Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
        proxyFactory.addAdvisors(advisors); // 当调用目标方法时，这些配置好的通知器就会起作用
        proxyFactory.setTargetSource(targetSource);
        customizeProxyFactory(proxyFactory);

        proxyFactory.setFrozen(this.freezeProxy);
        if (advisorsPreFiltered()) {
            proxyFactory.setPreFiltered(true);
        }
        // 此处生成代理对象，进入ProxyFactory的getProxy方法
        return proxyFactory.getProxy(getProxyClassLoader());
    }

进入getProxy方法，由于ProxyFactory继承ProxyCreatorSupport类，所以进入该方法后可知，真正的实现在ProxyCreatorSupport类中，调用的方法是ProxyCreatorSupport类中的方法，而ProxyFactory只是做了一层封装。

    /**
     * Create a new proxy according to the settings in this factory.
     * <p>Can be called repeatedly. Effect will vary if we've added
     * or removed interfaces. Can add and remove interceptors.
     * <p>Uses the given class loader (if necessary for proxy creation).
     * @param classLoader the class loader to create the proxy with
     * (or {@code null} for the low-level proxy facility's default)
     * @return the proxy object
     */
    public Object getProxy(ClassLoader classLoader) {
        // 下面的createAopProxy()方法是ProxyCreatorSupport类中的方法
        return createAopProxy().getProxy(classLoader);
    }

好了，接下来是重点部分 ：

createAopProxy()方法返回的是AopProxy接口类型，它有两个实现类分别是CglibAopProxy(通过cglib方式生成代理对象)和JdkDynamicAopProxy(通过JDK动态代理方式生成对象)，AopProxy的作用是用于生成代理对象的，稍后将会分析这两种不同的实现方式。

那么，CglibAopProxy或者JdkDynamicAopProxy又是如何生成的呢？进入createAopProxy方法，该方法就是获取AopProxy的地方，由方法可知，这里使用了AopProxyFactory来创建AopProxy，而AopProxyFactory使用的是DefaultAopProxyFactory类。

    /**
     * Subclasses should call this to get a new AOP proxy. They should <b>not</b>
     * create an AOP proxy with {@code this} as an argument.
     */
    protected final synchronized AopProxy createAopProxy() {
        if (!this.active) {
            activate();
        }
        return getAopProxyFactory().createAopProxy(this);
    }

进入DefaultAopProxyFactory类的createAopProxy方法：

    @Override
    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.");
            }
            // 如果targetClass是接口类，那么使用JDK来生成代理对象，返回JdkDynamicAopProxy类型的对象
            if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
                return new JdkDynamicAopProxy(config);
            }
            // 否则，返回ObjenesisCglibAopProxy类型的对象，它是使用cglib的方式生成代理对象的
            return new ObjenesisCglibAopProxy(config);
        }
        else {
            return new JdkDynamicAopProxy(config);
        }
    }

到这里，我们已经清楚AopProxy是如何生成的了，那么接下来我们介绍CglibAopProxy和JdkDynamicAopProxy又是如何生成代理对象的？

JDK动态代理的方式生成代理对象，进入JdkDynamicAopProxy的getProxy方法

    @Override
    public Object getProxy(ClassLoader classLoader) {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
        }
        // 取得代理对象的所有代理接口
        Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
        findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
        // 使用JDK的Proxy类来生成代理对象
        return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
    }

cglib的方式生成代理对象，进入CglibAopProxy类的getProxy方法：

@Override
    public Object getProxy(ClassLoader classLoader) {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating CGLIB proxy: target source is " + this.advised.getTargetSource());
        }

        try {
            //获取目标对象
            Class<?> rootClass = this.advised.getTargetClass();
            Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");

            Class<?> proxySuperClass = rootClass;
            if (ClassUtils.isCglibProxyClass(rootClass)) {
                proxySuperClass = rootClass.getSuperclass();
                Class<?>[] additionalInterfaces = rootClass.getInterfaces();
                for (Class<?> additionalInterface : additionalInterfaces) {
                    this.advised.addInterface(additionalInterface);
                }
            }

            // Validate the class, writing log messages as necessary.
            validateClassIfNecessary(proxySuperClass, classLoader);

            // 创建并配置Enhancer，它是cglib主要的操作类，用于代理对象的生成
            // Configure CGLIB Enhancer...
            Enhancer enhancer = createEnhancer();
            if (classLoader != null) {
                enhancer.setClassLoader(classLoader);
                if (classLoader instanceof SmartClassLoader &&
                        ((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
                    enhancer.setUseCache(false);
                }
            }
            // 配置enhancer对象，比如 代理接口，父类，回调方法等
            enhancer.setSuperclass(proxySuperClass);
            enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
            enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
            enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));

            Callback[] callbacks = getCallbacks(rootClass);
            Class<?>[] types = new Class<?>[callbacks.length];
            for (int x = 0; x < types.length; x++) {
                types[x] = callbacks[x].getClass();
            }
            // fixedInterceptorMap only populated at this point, after getCallbacks call above
            enhancer.setCallbackFilter(new ProxyCallbackFilter(
                    this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
            enhancer.setCallbackTypes(types);
            // 通过enhancer来生成代理对象
            // Generate the proxy class and create a proxy instance.
            return createProxyClassAndInstance(enhancer, callbacks);
        }
        catch (CodeGenerationException ex) {
            throw new AopConfigException("Could not generate CGLIB subclass of " + this.advised.getTargetClass() +
                    ": Common causes of this problem include using a final class or a non-visible class",
                    ex);
        }
        catch (IllegalArgumentException ex) {
            throw new AopConfigException("Could not generate CGLIB subclass of " + this.advised.getTargetClass() +
                    ": Common causes of this problem include using a final class or a non-visible class",
                    ex);
        }
        catch (Throwable ex) {
            // TargetSource.getTarget() failed
            throw new AopConfigException("Unexpected AOP exception", ex);
        }
    }

好了，现在代理对象已经生成，并且已经设置好了拦截器(通知)，当代理对象调用目标方法时，就会触发这些拦截器，在下一篇文章中我们就介绍，当调用目标方法时，拦截器（通知）是如何起作用的，整个过程是怎样的。

《springAOP源码分析一》

《springAOP源码分析三》