探究Spring的后置处理器
本次我们主要探究invokeBeanFactoryPostProcessors()；后面的代码下次再做解析；
入口代码refresh()
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(); // ...... applicationContext.refresh();
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
// 启动前的准备工作：记录启动时间，活动标记为启动以及环境属性变量集合的初始化
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//还是一些准备工作，添加了两个后置处理器：ApplicationContextAwareProcessor，ApplicationListenerDetector
//还设置了 忽略自动装配 和 允许自动装配 的接口
//对环境，系统环境，系统属性三个Bean如果不存在某个bean的时候，spring就自动生成singleton bean（Not bd）
//还设置了bean表达式解析器 等
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 空方法
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//执行自定义的BeanFactoryProcessor和内置的BeanFactoryProcessor
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();
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
流程图
prepareRefresh剖析
该方法主要做启动前的准备工作：记录启动时间，活动标记为启动以及环境属性变量集合的初始化；
protected void prepareRefresh() {
// Switch to active.
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
// Initialize any placeholder property sources in the context environment.
// 空方法
initPropertySources();
// Validate that all properties marked as required are resolvable:
// see ConfigurablePropertyResolver#setRequiredProperties
getEnvironment().validateRequiredProperties();
// Store pre-refresh ApplicationListeners...
if (this.earlyApplicationListeners == null) {
this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
}
else {
// Reset local application listeners to pre-refresh state.
this.applicationListeners.clear();
this.applicationListeners.addAll(this.earlyApplicationListeners);
}
// Allow for the collection of early ApplicationEvents,
// to be published once the multicaster is available...
this.earlyApplicationEvents = new LinkedHashSet<>();
}
obtainFreshBeanFactory刨析
主要是获取context上下文中的bean工厂；
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
// CAS保证同步
refreshBeanFactory();
// 返回beanFactory- DefaultListableBeanFactory.class
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
return beanFactory;
}
prepareBeanFactory刨析
做一些准备工作，添加了两个后置处理器ApplicationContextAwareProcessor和ApplicationListenerDetector;
设置了bean表达式解析器等；
通过工厂的接口可以设置了忽略自动装配，和允许自动装配；
对环境、系统环境、系统属性三个Bean如果不存在某个bean的时候，spring就自动生成singletonBean（Not bd）；
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
//设置bean表达式解析器
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
//属性编辑器支持
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
//添加一个后置处理器：ApplicationContextAwareProcessor，此后置处理处理器实现了BeanPostProcessor接口
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
//以下接口，忽略自动装配
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
// .....
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
//以下接口，允许自动装配,第一个参数是自动装配的类型，，第二个字段是自动装配的值
// 这个接口仅会将注入的参数XXX.class注入为指定的值，但不影响XXX.class创建Bean对象；
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
// Register default environment beans.
// 环境，系统环境，系统属性 因此通常情况下，这三个Bean是没有bd的
//如果没有注册过bean名称为XXX，spring就自己创建一个名称为XXX的singleton bean
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
invokeBeanFactoryPostProcessors剖析
执行自定义的BeanFactoryProcessor和内置的BeanFactoryProcessor;
getBeanFactoryPostProcessors()方法是我们手动通过执行addBeanFactoryPostProcessor(XX)设置自定义的后置处理器。如果初始化执行到这，没有手动增加后置处理器的话，那么此时List<BeanFactoryPostProcessor>的size()为empty；
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// getBeanFactoryPostProcessors是spring允许我们手动添加BeanFactoryPostProcessor
// 即：annotationConfigApplicationContext.addBeanFactoryPostProcessor(XXX);
// 未手动添加的话，getBeanFactoryPostProcessors()为empty
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
我们通过委托PostProcessorRegistrationDelegate去调用invokeBeanFactoryPostProcessors()方法，从而去扫描并执行BeanFactoryProcessor和BeanDefinitionRegistryPostProcessor;
我们通过继承关系看，BeanDefinitionRegistryPostProcessor实际上是继承BeanFactoryProcessor接口的；
- BeanDefinitionRegistryPostProcessor:主要扫描类解析类;
- BeanFactoryProcessor:主要给配置类进行增强代理;
这里面需要看我们的BeanFactory的类型；初始时BeanFactory的类型是DefaultListableBeanFactory;因此，该bean工厂是实现BeanDefinitionRegistry;
该方法的具体流程如下（按初始化进入到这里描述）：
- 循环遍历手动添加的后置处理器（并不排序）;
- 若该bfp是bdrp则直接执行bdrp. postProcessBeanDefinitionRegistry();
- 取出内置的bdrp，分为实现了PriorityOrdered,Ordered和都没有实现的三类；
初始这里只有一个，就是我们在初始化reader()时，注册了一个ConfigurationClassPostProcessor.class;
public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {}
将上面三类直接执行bdrp. postProcessBeanDefinitionRegistry();
然后将手动加入和内置的bdrp执行bfp.postProcessBeanFactory();
上面的已经执行完了：
- 手动添加的后置处理器的bdrf. postProcessBeanDefinitionRegistry()和bfp.postProcessBeanFactory();
- 内置的bdrp. postProcessBeanDefinitionRegistry()
取出内置的bfp，分为实现了PriorityOrdered, Ordered和都没有实现的三类；
目前这里内置的有两个。但其中config上面已经执行过了，此处只执行下方的一个；
将上面三类直接执行bfp. postProcessBeanDefinitionRegistry();
清除缓存中的bd，因为后处理器可能有修改了原始元数据，例如替换值中的占位符;
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
// 如果不是BeanDefinitionRegistry 则直接执行beanFactoryPostProcessors
// 刚启动时传入的beanFactory是DefaultListableBeanFactory，他是实现了BeanDefinitionRegistry 因此会走这里
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
// bf后置处理器集合（手动添加与bdr后置处理器集合【下面的那个集合】）：因为bdrp属于bfp
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// bdr后置处理器集合（手动添加与spring自己的）
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
// 循环传进来的beanFactoryPostProcessors，刚启动时未手动增加的情况下beanFactoryPostProcessors肯定没有数据
// 因为beanFactoryPostProcessors是获得手动添加的，而不是spring扫描的
// 只有手动调用annotationConfigApplicationContext.addBeanFactoryPostProcessor(XXX)才会有数据
// 执行手动添加的beanFactoryPostProcessors， 如果是BeanDefinitionRegistryPostProcessor，则执行其postProcessBeanDefinitionRegistry再加到list中
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
//一个临时变量，用来装载BeanDefinitionRegistryPostProcessor为了排序
//BeanDefinitionRegistry继承了PostProcessorBeanFactoryPostProcessor
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// 获得实现BeanDefinitionRegistryPostProcessor接口的类
// 就是ConfigurationClassPostProcessor（Spring自己添加的-在reader()时增加的）
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
//获得ConfigurationClassPostProcessor类，并且放到currentRegistryProcessors
//ConfigurationClassPostProcessor是很重要的一个类，它实现了BeanDefinitionRegistryPostProcessor接口
//BeanDefinitionRegistryPostProcessor接口又实现了BeanFactoryPostProcessor接口
//ConfigurationClassPostProcessor是极其重要的类
//里面执行了扫描Bean，Import，ImportResouce等各种操作
//用来处理配置类（有两种情况 一种是传统意义上的配置类，一种是普通的bean）的各种逻辑
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
//把name放到processedBeans，后续会根据这个集合来判断处理器是否已经被执行过了
processedBeans.add(ppName);
}
}
//处理排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
//合并Processors，为什么要合并，因为registryProcessors是装载BeanDefinitionRegistryPostProcessor的
//一开始的时候，spring只会执行BeanDefinitionRegistryPostProcessor独有的方法
//而不会执行BeanDefinitionRegistryPostProcessor父类的方法，即BeanFactoryProcessor的方法
//所以这里需要把处理器放入一个集合中，后续统一执行父类的方法
registryProcessors.addAll(currentRegistryProcessors);
//可以理解为执行ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry方法
//Spring热插播的体现，像ConfigurationClassPostProcessor就相当于一个组件，Spring很多事情就是交给组件去管理
//将spring提供的RegistryProcessors(就是这个ConfigurationClassPostProcessor)执行其postProcessBeanDefinitionRegistry
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
//清空临时变量
currentRegistryProcessors.clear();
// 再次根据BeanDefinitionRegistryPostProcessor获得BeanName，看这个BeanName是否已经被执行过了，有没有实现Ordered接口
// 如果没有被执行过，也实现了Ordered接口的话，把对象推送到currentRegistryProcessors，名称推送到processedBeans
// 如果没有实现Ordered接口的话，这里不把数据加到currentRegistryProcessors，processedBeans中，后续再做处理
// 这里才可以获得我们定义的实现了BeanDefinitionRegistryPostProcessor的Bean
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);
}
}
//处理排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
//合并Processors
registryProcessors.addAll(currentRegistryProcessors);
//执行有Ordered的BeanDefinitionRegistryPostProcessor
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
//清空临时变量
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 下面的代码就是执行没有实现PriorityOrdered接口也没有Ordered的BeanDefinitionRegistryPostProcessor
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();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
//registryProcessors集合装载BeanDefinitionRegistryPostProcessor
//上面的代码是执行bfr后置处理器子类独有的方法，这里需要再把bfr后置处理器父类的方法也执行一次
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
//regularPostProcessors装载BeanFactoryPostProcessor，执行BeanFactoryPostProcessor的方法
//但是regularPostProcessors一般情况下，是不会有数据的，只有在外面手动添加BeanFactoryPostProcessor，才会有数据
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
// 若bfp没有继承bdrp则直接执行手动增加bf后置处理器的后置处理器
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// 找到BeanFactoryPostProcessor实现类的BeanName数组
// 处理Spring自己的bf后置处理器
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
// PriorityOrdered的bf后置处理器集合
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// Ordered的bf后置处理器集合
List<String> orderedPostProcessorNames = new ArrayList<>();
// 无PriorityOrdered无Ordered的bf后置处理器集合
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
//循环BeanName数组
for (String ppName : postProcessorNames) {
//如果这个Bean被执行过了，跳过
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
//如果实现了PriorityOrdered接口，加入到priorityOrderedPostProcessors
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
//如果实现了Ordered接口，加入到orderedPostProcessorNames
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
//如果既没有实现PriorityOrdered，也没有实现Ordered。加入到nonOrderedPostProcessorNames
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
//排序处理priorityOrderedPostProcessors，即实现了PriorityOrdered接口的BeanFactoryPostProcessor
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
//执行priorityOrderedPostProcessors
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
//执行实现了Ordered接口的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
// 执行既没有实现PriorityOrdered接口，也没有实现Ordered接口的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
// 清除了allBeanNamesByType&singletonBeanNamesByType()
// 清除缓存中的bd，因为后处理器可能有修改了原始元数据，例如替换值中的占位符
beanFactory.clearMetadataCache();
}
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原文链接：https://blog.csdn.net/qq_37419449/article/details/120879661
