Spring源码之BeanFactoryPostProcessor(后置处理器)。
有点程度的Spring开发人员想必都晓得BeanFactoryPostProcessor也就是常说的后置管理器，这是Spirng生命周期中的一个接口，实现这个接口能够在beanFactory初始化前做一些事。
咱们熟知的Spring和Mybatis的联合，正是因为Mybatis实现了BeanFactoryPostProcessor，它的重要性显而易见，深刻了解他对于切入Mybatis源码有着粗浅的意义。
如下图是简略的利用：
还是先贴上refresh()的源码
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//1、刷新前的筹备
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//2、将会初始化 BeanFactory、加载 Bean、注册 Bean
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//3、设置 BeanFactory 的类加载器，增加几个 BeanPostProcessor，手动注册几个非凡的 bean
prepareBeanFactory(beanFactory);
try {
//4、模板办法
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//执行BeanFactory后置处理器
invokeBeanFactoryPostProcessors(beanFactory);
// 5、Register bean processors that intercept bean creation.
//注册bean后置处理器
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
//国际化
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
//6、模板办法--springboot实现了这个办法
onRefresh();
// Check for listener beans and register them.
//7、注册监听器
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
//8、实现bean工厂的初始化**办法**********************************************
finishBeanFactoryInitialization(beanFactory);
//9、 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();
}
}
}benafactory源码的解决位于第三个地位。
次要波及到两个办法postProcessBeanFactory(beanFactory);
和invokeBeanFactoryPostProcessors(beanFactory);
postProcessBeanFactory(beanFactory)点进去发现是一个空办法，具体的执行在invokeBeanFactoryPostProcessors(beanFactory);中
咱们在invokeBeanFactoryPostProcessors办法上打断点一探到底。第一次看的时候感觉这是什么玩意，这么长，耐住性子一步步的往下看。
办法虽长大略总结一下就是，判断beanFactory类型，而后将注册的BeanPostFactory放入、排好程序、执行。
invokeBeanFactoryPostProcessors 办法的内容其实比拟少，大部分过程在正文都曾经写分明，这边在略微总结一下。
整个 invokeBeanFactoryPostProcessors 办法围绕两个接口，BeanDefinitionRegistryPostProcessor 和 BeanFactoryPostProcessor，其中 BeanDefinitionRegistryPostProcessor 继承了 BeanFactoryPostProcessor 。
BeanDefinitionRegistryPostProcessor 次要用来在惯例 BeanFactoryPostProcessor 检测开始之前注册其余 Bean 定义，说的简略点，就是 BeanDefinitionRegistryPostProcessor 具备更高的优先级，执行程序在 BeanFactoryPostProcessor 之前。
具体的过程看正文吧
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
// 1.判断beanFactory是否为BeanDefinitionRegistry，beanFactory为DefaultListableBeanFactory,
// 而DefaultListableBeanFactory实现了BeanDefinitionRegistry接口，因而这边为true
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
// 用于寄存一般的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// 用于寄存BeanDefinitionRegistryPostProcessor
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
// 2.首先解决入参中的beanFactoryPostProcessors
// 遍历所有的beanFactoryPostProcessors, 将BeanDefinitionRegistryPostProcessor和一般BeanFactoryPostProcessor辨别开
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
// 2.1 如果是BeanDefinitionRegistryPostProcessor
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
// 2.1.1 间接执行BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry办法
registryProcessor.postProcessBeanDefinitionRegistry(registry);
// 2.1.2 增加到registryProcessors(用于最初执行postProcessBeanFactory办法)
registryProcessors.add(registryProcessor);
}
else {
// 2.2 否则，只是一般的BeanFactoryPostProcessor
// 2.2.1 增加到regularPostProcessors(用于最初执行postProcessBeanFactory办法)
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.
// 用于保留本次要执行的BeanDefinitionRegistryPostProcessor
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
// 3.调用所有实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessor实现类
// 3.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的Bean的beanName
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
// 3.2 遍历postProcessorNames
for (String ppName : postProcessorNames) {
// 3.3 校验是否实现了PriorityOrdered接口
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
// 3.4 获取ppName对应的bean实例, 增加到currentRegistryProcessors中,
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
// 3.5 将要被执行的退出processedBeans，防止后续反复执行
processedBeans.add(ppName);
}
}
// 3.6 进行排序(依据是否实现PriorityOrdered、Ordered接口和order值来排序)
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 3.7 增加到registryProcessors(用于最初执行postProcessBeanFactory办法)
registryProcessors.addAll(currentRegistryProcessors);
// 3.8 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry办法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
// 3.9 执行结束后, 清空currentRegistryProcessors
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
// 4.调用所有实现了Ordered接口的BeanDefinitionRegistryPostProcessor实现类（过程跟下面的步骤3根本一样）
// 4.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的类, 这边反复查找是因为执行完下面的BeanDefinitionRegistryPostProcessor,
// 可能会新增了其余的BeanDefinitionRegistryPostProcessor, 因而须要从新查找
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 校验是否实现了Ordered接口，并且还未执行过
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);
// 4.2 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry办法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 5.最初, 调用所有剩下的BeanDefinitionRegistryPostProcessors
boolean reiterate = true;
while (reiterate) {
reiterate = false;
// 5.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的类
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 5.2 跳过曾经执行过的
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
// 5.3 如果有BeanDefinitionRegistryPostProcessor被执行, 则有可能会产生新的BeanDefinitionRegistryPostProcessor,
// 因而这边将reiterate赋值为true, 代表须要再循环查找一次
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
// 5.4 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry办法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
// 6.调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory办法(BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor)
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
// 7.最初, 调用入参beanFactoryPostProcessors中的一般BeanFactoryPostProcessor的postProcessBeanFactory办法
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
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!
// 到这里 , 入参beanFactoryPostProcessors和容器中的所有BeanDefinitionRegistryPostProcessor曾经全副处理完毕,
// 上面开始解决容器中的所有BeanFactoryPostProcessor
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// 8.找出所有实现BeanFactoryPostProcessor接口的类
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
// 用于寄存实现了PriorityOrdered接口的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// 用于寄存实现了Ordered接口的BeanFactoryPostProcessor的beanName
List<String> orderedPostProcessorNames = new ArrayList<>();
// 用于寄存一般BeanFactoryPostProcessor的beanName
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 8.1 遍历postProcessorNames, 将BeanFactoryPostProcessor按实现PriorityOrdered、实现Ordered接口、一般三种辨别开
for (String ppName : postProcessorNames) {
// 8.2 跳过曾经执行过的
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
// 8.3 增加实现了PriorityOrdered接口的BeanFactoryPostProcessor
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
// 8.4 增加实现了Ordered接口的BeanFactoryPostProcessor的beanName
orderedPostProcessorNames.add(ppName);
}
else {
// 8.5 增加剩下的一般BeanFactoryPostProcessor的beanName
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
// 9.调用所有实现PriorityOrdered接口的BeanFactoryPostProcessor
// 9.1 对priorityOrderedPostProcessors排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 9.2 遍历priorityOrderedPostProcessors, 执行postProcessBeanFactory办法
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
// 10.调用所有实现Ordered接口的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String postProcessorName : orderedPostProcessorNames) {
// 10.1 获取postProcessorName对应的bean实例, 增加到orderedPostProcessors, 筹备执行
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
// 10.2 对orderedPostProcessors排序
sortPostProcessors(orderedPostProcessors, beanFactory);
// 10.3 遍历orderedPostProcessors, 执行postProcessBeanFactory办法
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
// 11.调用所有剩下的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
// 11.1 获取postProcessorName对应的bean实例, 增加到nonOrderedPostProcessors, 筹备执行
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
// 11.2 遍历nonOrderedPostProcessors, 执行postProcessBeanFactory办法
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
// 12.革除元数据缓存（mergedBeanDefinitions、allBeanNamesByType、singletonBeanNamesByType），
// 因为后处理器可能曾经批改了原始元数据，例如， 替换值中的占位符...
beanFactory.clearMetadataCache();
}
发表回复