refresh中的postProcessBeanFactory和invokeBeanFactoryPostProcessors
废话不多说，直接开始主题，今天我们讲解refresh的postProcessBeanFactory和invokeBeanFactoryPostProcessors方法。
老规矩，贴上代码：
@Override
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.
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();
}
}
}
1.postProcessBeanFactory
此方法允许子类在所有的bean尚未初始化之前注册BeanPostProcessor。空实现且没有子类覆盖。
对，这个方法就是这么的简单，不要觉得它干了什么大事情，所以这篇文章，我们要讲解refresh的两个方法，当然重点就在下面讲解的方法中。
2.invokeBeanFactoryPostProcessors
这个是spring对这个方法的一个定义，说大白话其实就是BeanFactoryPostProcessor接口允许我们在bean正是初始化之前改变其值。此接口只有一个方法:
void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory);
有两种方式可以向Spring添加此对象:
- 通过代码的方式
context.addBeanFactoryPostProcessor
- 通过xml配置的方式:
<bean class="base.SimpleBeanFactoryPostProcessor" />
这里需要注意BeanFactory此时尚未进行bean的初始化工作，初始化是在后面的finishBeanFactoryInitialization进行的，所以在BeanFactoryPostProcessor对象中获取bean会导致提前初始化。
此方法的关键源码:
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory,
getBeanFactoryPostProcessors());
}
getBeanFactoryPostProcessors获取的就是AbstractApplicationContext的成员beanFactoryPostProcessors(ArrayList)，但是很有意思，只有通过context.addBeanFactoryPostProcessor这种方式添加的才会出现在这个List里，所以对于xml配置方式，此List其实没有任何元素。玄机就在PostProcessorRegistrationDelegate里。
核心思想就是使用BeanFactory的getBeanNamesForType方法获取相应的BeanDefinition的name数组，之后逐一调用getBean方法获取到bean(初始化)，getBean方法后面再说。
注意此处有一个优先级的概念，如果你的BeanFactoryPostProcessor同时实现了Ordered或者是PriorityOrdered接口，那么会被首先执行。这其实在代码中就有体现
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
//首先，调用实现了PriorityOrdered接口的BeanDefinitionRegistryPostProcessors
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
//然后，调用实现了Ordered接口的BeanDefinitionRegistryPostProcessors
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 最后调用其他的BeanDefinitionRegistryPostProcessors
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
}
其中registryProcessor.postProcessBeanDefinitionRegistry(registry);这里需要稍微关注一下，这个跟spring-context中的ConfigurationClassPostProcessor等类有着紧密的联系。这里以后可以专门出一个专栏去讲解一下spring-context。
好了，这两个方法已经讲解完毕，其中稍微提醒一下invokeBeanFactoryPostProcessors中很多的代码细节需要大家自己去琢磨，这里博主只讲解一个大概。
