这个类的设计，和Spring ioc的结合，简直是吊炸天，实现了根据配置把spring ioc里面的bean替换为相应的代理对象，也为AspectJ的整合提供了支持，让我们来看看Spring是如何做到这种更高级的声明式Aop
1.类结构
这边的讲解线路分为2块
- Spring的Bean后处理器，SmartInstantiationAwareBeanPostProcessor->InstantiationAwareBeanPostProcessor->BeanPostProcessor
- DefaultAdvisorAutoProxyCreator的主继承线，DefaultAdvisorAutoProxyCreator->AbstractAdvisorAutoProxyCreator->AbstractAutoProxyCreator->ProxyProcessorSupport->ProxyConfig
讲解之前可以看下我写的这块的demo ,可以一边看解析，一边打断点调试
2.解析
2.1 Spring Bean后处理器
在讲这三个接口之前，我们先来看下Spring bean的生命周期，不知道这个流程，也很难理解这三个接口的作用
阅读AbstractAutowireCapableBeanFactory的doCreateBean和destroyBean方法，我们能清楚看到Spring bean创建的整个生命周期，具体如下
- 调用InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation(Class<?> beanClass, String beanName)
- bean实例化
- 调用InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation(Object bean, String beanName)
- 调用InstantiationAwareBeanPostProcessor的postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)
- bean注入properties
- 分别调用BeanNameAware,BeanClassLoaderAware,BeanFactoryAware中的方法
- 调用BeanPostProcessor的postProcessBeforeInitialization(Object bean, String beanName)
- 调用InitializingBean的afterPropertiesSet方法
- 调用自定义初始化方法
- 调用BeanPostProcessor的postProcessAfterInitialization(Object bean, String beanName)
- 调用DisposableBean的destroy()方法
- 调用自定义销毁方法
下面分别介绍这三个bean后处理器的功能
public interface BeanPostProcessor {
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}
从生命周期中可以看到，BeanPostProcessor中的这两个方法分别会在bean调用init方法前后回调，用于对已经注入properties的bean对象进行修改，把bean替换成代理对象会在postProcessAfterInitialization中执行
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;
boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;
PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException;
}
postProcessBeforeInstantiation和postProcessAfterInstantiation分别在bean实例化前后回调
postProcessPropertyValues将在注入properties之前触发，可以对整理好的properties进行修改
public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationAwareBeanPostProcessor {
Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException;
Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName) throws BeansException;
Object getEarlyBeanReference(Object bean, String beanName) throws BeansException;
}
predictBeanType用于提前给出postProcessBeforeInstantiation生成的bean的类型
determineCandidateConstructors用于bean初始化的时候决定调用哪一个构造函数，如果针对某个类型的bean设置了这个回调，会采用回调设置的构造函数初始化bean，具体逻辑代码如下
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
getEarlyBeanReference用于解决循环依赖的问题
这三个bean后处理器讲解好了 ，现在我们开始讲DefaultAdvisorAutoProxyCreator是怎么实现自动配置代理对象的
2.2 DefaultAdvisorAutoProxyCreator
从类结构图中可以看到主要的继承链，DefaultAdvisorAutoProxyCreator->AbstractAdivisorAutoProxyCreator->AbstractAutoProxyCreator->ProxyProcessorSupport->ProxyConfig
ProxyConfig就不多讲了，之前讲过，我们来分别介绍下其他4个类的作用
2.2.1 ProxyProcessorSupport
看名字就知道是一个为代理生成提供支持的工具类,主要提供evaluateProxyInterfaces方法用来根据BeanClass对ProxyFactory中的代理方式进行配置，方法如下
protected void evaluateProxyInterfaces(Class<?> beanClass, ProxyFactory proxyFactory) {
Class<?>[] targetInterfaces = ClassUtils.getAllInterfacesForClass(beanClass, getProxyClassLoader());
boolean hasReasonableProxyInterface = false;
for (Class<?> ifc : targetInterfaces) {
if (!isConfigurationCallbackInterface(ifc) && !isInternalLanguageInterface(ifc) &&
ifc.getMethods().length > 0) {
hasReasonableProxyInterface = true;
break;
}
}
if (hasReasonableProxyInterface) {
// Must allow for introductions; can't just set interfaces to the target's interfaces only.
for (Class<?> ifc : targetInterfaces) {
proxyFactory.addInterface(ifc);
}
}
else {
proxyFactory.setProxyTargetClass(true);
}
}
这里会判断是否可以代理接口，如果可以，用proxyFactory的addInterface方法把设置所有存在的接口类，如果不可以，那么调用setProxyTargetClass(true)，配置为代理类
同时我们可以注意到这个类实现了Ordered接口，并且设置order = Ordered.LOWEST_PRECEDENCE，这是为了让生成代理的后处理器最后一个执行(原因可能是在之前的后处理器可能也会把Advisor加进去，那样就会出现不生效的问题)
2.2.2 AbstractAutoProxyCreator
这个类是这个继承链中最核心的类，因为生成代理的逻辑封装在这里
它实现SmartInstantiationAwareBeanPostProcessor，在回调方法里封装了把bean对象替换为代理对象的逻辑，在getEarlyBeanReference，postProcessBeforeInstantiation，postProcessAfterInitialization均能产生代理，postProcessBeforeInstantiation需要在配置了TargetSourceCreator之后才能生效，目前没有遇到这个场景，所以忽略，getEarlyBeanReference是为了解决循环依赖重写的，用来提前长生代理类，postProcessAfterInitialization在getEarlyBeanReference没有生效的情况下会被调用，这两个方法都调用了wrapIfNecessary来生成代理，我们来看下这个方法
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.
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
wrapIfNecessary首先会通过getAdvicesAndAdvisorsForBean得到拦截器集合，这个会交给子类实现，子类可以设计不同的策略来获取拦截器集合，如果getAdvicesAndAdvisorsForBean返回的集合不为空，就调用createProxy生成代理
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);
}
}
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
proxyFactory.addAdvisors(advisors);
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
return proxyFactory.getProxy(getProxyClassLoader());
}
createProxy还是比较熟悉的，在上节铺垫过，使用了ProxyFactory的编程式Aop生成代理
通过这几个回调，巧妙的在spring生命周期内把我们生成代理bean的行为注入了
2.2.3 AbstractAdivisorAutoProxyCreator
AbstractAdivisorAutoProxyCreator主要实现了AbstractAutoProxyCreator提供的扩展点方法getAdvicesAndAdvisorsForBean,用来设置拦截器集合
protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource) {
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}
getAdvicesAndAdvisorsForBean中会通过findEligibleAdvisors来获取拦截器集合，如果不存在返回DO_NOT_PROXY，来看下findEligibleAdvisors
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
List<Advisor> candidateAdvisors = findCandidateAdvisors();
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
protected List<Advisor> findCandidateAdvisors() {
return this.advisorRetrievalHelper.findAdvisorBeans();
}
在findEligibleAdvisors中，通过findCandidateAdvisors来获取候选的adivisors，内部使用了advisorRetrievalHelper.findAdvisorBeans，其实就是从beanfactory获取实现Advisor接口的bean，然后可以在这个方法里面看到
public List<Advisor> findAdvisorBeans() {
// Determine list of advisor bean names, if not cached already.
String[] advisorNames = null;
synchronized (this) {
advisorNames = this.cachedAdvisorBeanNames;
if (advisorNames == null) {
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the auto-proxy creator apply to them!
advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Advisor.class, true, false);
this.cachedAdvisorBeanNames = advisorNames;
}
}
if (advisorNames.length == 0) {
return new LinkedList<Advisor>();
}
List<Advisor> advisors = new LinkedList<Advisor>();
for (String name : advisorNames) {
if (isEligibleBean(name)) {
if (this.beanFactory.isCurrentlyInCreation(name)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping currently created advisor '" + name + "'");
}
}
else {
try {
advisors.add(this.beanFactory.getBean(name, Advisor.class));
}
catch (BeanCreationException ex) {
Throwable rootCause = ex.getMostSpecificCause();
if (rootCause instanceof BeanCurrentlyInCreationException) {
BeanCreationException bce = (BeanCreationException) rootCause;
if (this.beanFactory.isCurrentlyInCreation(bce.getBeanName())) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping advisor '" + name +
"' with dependency on currently created bean: " + ex.getMessage());
}
// Ignore: indicates a reference back to the bean we're trying to advise.
// We want to find advisors other than the currently created bean itself.
continue;
}
}
throw ex;
}
}
}
}
return advisors;
}
注意到有一个isEligibleBean方法，在AbstractAdivisorAutoProxyCreator使用了BeanFactoryAdvisorRetrievalHelper扩展子类，重定义了isEligibleBean方法，如下
private class BeanFactoryAdvisorRetrievalHelperAdapter extends BeanFactoryAdvisorRetrievalHelper {
public BeanFactoryAdvisorRetrievalHelperAdapter(ConfigurableListableBeanFactory beanFactory) {
super(beanFactory);
}
@Override
protected boolean isEligibleBean(String beanName) {
return AbstractAdvisorAutoProxyCreator.this.isEligibleAdvisorBean(beanName);
}
}
把BeanFactoryAdvisorRetrievalHelper中的isEligibleBean委托给了AbstractAdvisorAutoProxyCreator实现，AbstractAdvisorAutoProxyCreator中默认实现如下
protected boolean isEligibleAdvisorBean(String beanName) {
return true;
}
这个实现默认为不过滤，可以让子类去实现
2.2.4 DefaultAdvisorAutoProxyCreator
DefaultAdvisorAutoProxyCreator实现AbstractAdivisorAutoProxyCreator开放的扩展点isEligibleAdvisorBean，逻辑很简单，如下
protected boolean isEligibleAdvisorBean(String beanName) {
return (!isUsePrefix() || beanName.startsWith(getAdvisorBeanNamePrefix()));
}
通过配置的prefix来过滤adivisor bean
2.3 InfrastructureAdvisorAutoProxyCreator
InfrastructureAdvisorAutoProxyCreator也实现了AbstractAdivisorAutoProxyCreator开放的扩展点isEligibleAdvisorBean
@Override
protected boolean isEligibleAdvisorBean(String beanName) {
return (this.beanFactory.containsBeanDefinition(beanName) &&
this.beanFactory.getBeanDefinition(beanName).getRole() == BeanDefinition.ROLE_INFRASTRUCTURE);
}
可以看到，这个过滤条件是，只选择框架级别(beanDefinitiod的role为ROLE_INFRASTRUCTURE)的Adivisor来进行对符合条件的对象进行织入，生成代理
3.总结
DefaultAdvisorAutoProxyCreator主要实现的功能为使用bean后处理器的回调函数，根据ioc容器配置的advisor，来对ioc 容器中的其他bean生成相应代理
