BeanPostProcessor 接口类型实例是针对某种特定功能的埋点，在这个点会根据接口类型来过滤掉不关注这个点的其他类，只有真正关注的类才会在这个点进行相应的功能实现。
前言
Spring 初始化核心流程
spring容器初始化的核心方法AbstractApplicationContext#refresh，
- refresh Spring 初始化核心流程入口
- prepareRefresh ① 准备此上下文用于刷新，设置启动时间和active标志，初始化属性
- obtainFreshBeanFactory ② 创建 BeanFactory 已经跟踪过的源码流程
- prepareBeanFactory ③ 设置 BeanFactory 的基本属性
- postProcessBeanFactory ④ 子类处理自定义的BeanFactoryPostProcess
- invokeBeanFactoryPostProcessors ⑤ 调用所有的BeanFactoryPostProcessor 本节主要跟踪的源码流程
- registerBeanPostProcessors ⑥ 注册，把实现了BeanPostProcessor接口的类实例化，加到BeanFactory 本节主要跟踪的源码流程
- initMessageSource ⑦ 初始化上下文中的资源文件，如国际化文件的处理等
- initApplicationEventMulticaster ⑧ 初始化上下文的事件传播器
- onRefresh ⑨ 给子类扩展初始化其他Bean，springboot 中用来做内嵌 tomcat 启动
- registerListeners ⑩ 在所有bean中查找监听 bean，然后注册到广播器中
- finishBeanFactoryInitialization ⑪ 初始化所有的单例Bean、ioc、BeanPostProcessor的执行、Aop入口
- finishRefresh ⑫ 完成刷新过程，发布相应的事件
一、invokeBeanFactoryPostProcessors()
1.作用
invokeBeanFactoryPostProcessors方法，负责激活各种 BeanFactory 处理器，以及两个核心接口的调用：
BeanDefinitionRegistryPostProcessor
实际完成了对其实现类中postProcessBeanDefinitionRegistry方法的调用，完成对BeanDefinition的新增、修改BeanFactoryPostProcessor
实际完成了对其实现类中postProcessBeanFactory方法的调用；
2.源码跟踪
2.1.AbstractApplicationContext.invokeBeanFactoryPostProcessors()
//AbstractApplicationContext
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
//委派给PostProcessorRegistrationDelegate去处理
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()));
}
}2.2.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors()
public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// Separate between BeanDefinitionRegistryPostProcessors that implement
// PriorityOrdered, Ordered, and the rest.
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
//获取实现了BeanDefinitionRegistryPostProcessor接口的所有类的BeanDefinition对象的beanName
// 1、最先调用的是实现了 PriorityOrdered 接口的所有BeanDefinitionRegistryPostProcessor
// 中的 postProcessBeanDefinitionRegistry的方法
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 判断是否实现了排序接口 PriorityOrdered
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
//排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
//调用过程
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// 2、其次调用的是实现了 Ordered 接口的所有BeanDefinitionRegistryPostProcessor
// 中的 postProcessBeanDefinitionRegistry的方法
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
//判断是否是实现的Ordered接口
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();
// 3、最后调用的是没实现排序接口的所有实现BeanDefinitionRegistryPostProcessor接口
// 中的 postProcessBeanDefinitionRegistry的方法
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
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();
}
//调用postProcessBeanFactory方法
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
//获取实现了BeanFactoryPostProcessor接口的类，获取beanDefinition的名称
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
//实现了PriorityOrdered接口的
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
//实现了Ordered接口的
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
//没实现接口的
nonOrderedPostProcessorNames.add(ppName);
}
}
//排序
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
//调用
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
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...
beanFactory.clearMetadataCache();
}2.3.invokeBeanDefinitionRegistryPostProcessors()
调用BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry()方法，完成对BeanDefinition的新增、修改
private static void invokeBeanDefinitionRegistryPostProcessors(
Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {
for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
postProcessor.postProcessBeanDefinitionRegistry(registry);
}
}2.4.invokeBeanFactoryPostProcessors()
调用BeanFactoryPostProcessor的postProcessBeanFactory()方法，完成对BeanFactory的修改
private static void invokeBeanFactoryPostProcessors(
Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {
for (BeanFactoryPostProcessor postProcessor : postProcessors) {
postProcessor.postProcessBeanFactory(beanFactory);
}
}二、registerBeanPostProcessors()
registerBeanPostProcessors方法主要把实现了BeanPostProcessor接口的类实例化，并且加入到BeanFactory中
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
//拿到工程里面所有实现了BeanPostProcessor接口的类，获取到BeanDefinition的名称
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.
//beanFactory.getBeanPostProcessorCount()会得到默认容器中注册的 BeanPostProcessor 个数，实际就是调用 List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>()的size()方法，默认的容器注册的 BeanPostProcessor 有：
//ApplicationContextAwarePostProcessor
//ApplicationListenerDetector
//ConfigurationClassPostProcessor
//PostProcessorRegistrationDelegate
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
// Separate between BeanPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
//提前实例化BeanPostProcessor类型的bean，然后bean进行排序
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
//getBean是实例化方法，后面我们在讲bean实例化过程是会着重讲到
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
//判断类型是否是MergedBeanDefinitionPostProcessor，如果是则代码是内部使用的
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
//注册到BeanFactory中
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String ppName : orderedPostProcessorNames) {
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<>(nonOrderedPostProcessorNames.size());
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));
}进入registerBeanPostProcessors()方法，注册过程
/**
* 注册当前的 BeanPostProcessor
*/
private static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
for (BeanPostProcessor postProcessor : postProcessors) {
// 添加到List<BeanPostProcessor> beanPostProcessors
beanFactory.addBeanPostProcessor(postProcessor);
}
}三、总结
invokeBeanFactoryPostProcessors和registerBeanPostProcessors两个方法的处理流程基本一致，都分别对实现接口的类实例化调用：
- 首先对实现 PriorityOrdered 接口的 beanPostProcessors 排序调用
- 其次对实现 Ordered 接口的 beanPostProcessors 排序调用
- 最后对没有实现排序接口的 beanPostProcessors 调用
1.BeanPostProcessor
BeanPostProcessor有两个方法，
- postProcessBeforeInitialization
- postProcessAfterInitialization。
它们分别在任何bean初始化回调之前或之后执行（例如InitializingBean的afterPropertiesSet方法或自定义init-method方法之前或者之后）， 在这个时候该bean的属性值已经填充完成了，并且我们返回的bean实例可能已经是原始实例的包装类型了。例如返回一个FactoryBean。
在本章开头，我们也说过，BeanPostProcessor 接口类型的实例是针对某种特定功能的埋点，在这个点会根据接口类型来过滤掉不关注这个点的其他类，只有真正关注的类才会在这个点进行相应的功能实现。现在来总结下这些埋点。
1.1.获取有@Autowired 注解的构造函数埋点
- 过滤的接口类型是：SmartInstantiationAwareBeanPostProcessor
- 调用的方法是：determineCandidateConstructors
//AbstractAutowireCapableBeanFactory
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
//......省略部分代码
//寻找当前正在实例化的bean中有@Autowired注解的构造函数
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
//如果ctors不为空，就说明构造函数上有@Autowired注解
return autowireConstructor(beanName, mbd, ctors, args);
}
//......省略部分代码
}
protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName)
throws BeansException {
if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
// 拿到 BeanPostProcessor 的所有接口，遍历
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
// 获取到有@Autowired注解信息的构造函数
Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
if (ctors != null) {
return ctors;
}
}
}
}
return null;
}而这个SmartInstantiationAwareBeanPostProcessor智能实例化Bean的后处理器，主要提供了三个方法：
- predictBeanType：预测从此处理器的postProcessBeforeInstantiation回调最终返回的bean的类型。
- determineCandidateConstructors：确定合适的实例化Bean的构造函数。
- getEarlyBeanReference：获取提早暴露的Bean的引用，提早暴露的Bean就是只完成了实例化，还未完成属性赋值和初始化的Bean。
1.2.收集@Resource@Autowired@Value@PostConstruct，@PreDestroy 注解的方法和属性埋点
- 过滤的接口类型是：MergedBeanDefinitionPostProcessor
- 调用的方法是：postProcessMergedBeanDefinition
//AbstractAutowireCapableBeanFactory
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {
//......省略部分代码
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
//CommonAnnotationBeanPostProcessor 支持了@PostConstruct，@PreDestroy,@Resource注解
//AutowiredAnnotationBeanPostProcessor 支持 @Autowired,@Value注解
//BeanPostProcessor接口的典型运用，这里要理解这个接口
//对类中注解的装配过程
//重要程度5，必须看
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
//......省略部分代码
}
protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof MergedBeanDefinitionPostProcessor) {
MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
}
}
}1.3.循环依赖解决中bean 的提前暴露埋点
- 过滤的接口类型是：SmartInstantiationAwareBeanPostProcessor
- 调用的方法是：getEarlyBeanReference
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
Object exposedObject = bean;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
}
}
}
return exposedObject;
}1.4.阻止依赖注入埋点
- 过滤的接口类型是：InstantiationAwareBeanPostProcessor
- 调用的方法是：postProcessAfterInstantiation
//AbstractAutowireCapableBeanFactory
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
//......省略部分代码
//这里很有意思，写接口可以让所有类都不能依赖注入
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
return;
}
}
}
}
//......省略部分代码
}1.5.IOC/DI 依赖注入埋点
- 过滤的接口类型是：InstantiationAwareBeanPostProcessor
- 调用的方法是：postProcessProperties(新版本)
//AbstractAutowireCapableBeanFactory
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
//......省略部分代码
//重点看这个if代码块，重要程度 5
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
//依赖注入过程，@Resource @Autowired的支持
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
//老版本用这个完成依赖注入过程，@Autowired的支持
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
//......省略部分代码
}
