spring-系列
文章目录
前言
BeanFactoryPostProcessor是BeanFactory的一个钩子接口，更是一种扩展，也正是因为这个接口造就了spring加载Bean的方式变得多种多样。我相信大部分开发人员对这个接口可能还存在一些陌生，毕竟这个接口是属于一种底层扩展，如果你是一个spring插件开发者，那一定对这个接口很熟悉。本文从源码的角度来分析spring是如何通过BeanDefinitionRegistryPostProcessor来加载Bean。
BeanFactoryPostProcessor介绍
我们从源码查看BeanFactoryPostProcessor的层次结构，发现它还有一个子接口BeanDefinitionRegistryPostProcessor，代码结构如下：
BeanFactoryPostProcessor
@FunctionalInterface
public interface BeanFactoryPostProcessor {
/**
* Modify the application context's internal bean factory after its standard
* initialization. All bean definitions will have been loaded, but no beans
* will have been instantiated yet. This allows for overriding or adding
* properties even to eager-initializing beans.
* @param beanFactory the bean factory used by the application context
* @throws org.springframework.beans.BeansException in case of errors
*/
void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}
根据源码我们知道只有一个方法postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)，我们是通过这个BeanFactory来增强BeanFactory的功能。
BeanDefinitionRegistryPostProcessor
public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
/**
* Modify the application context's internal bean definition registry after its
* standard initialization. All regular bean definitions will have been loaded,
* but no beans will have been instantiated yet. This allows for adding further
* bean definitions before the next post-processing phase kicks in.
* @param registry the bean definition registry used by the application context
* @throws org.springframework.beans.BeansException in case of errors
*/
void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
}
根据源码我们知道只有一个方法postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)，这个方法很明显是为了Bean的注册而生了，BeanDefinitionRegistry 是BeanDefinition的注册器，而注册Bean的过程是将满足Bean条件的类解析为BeanDefinition对象然后注册到BeanDefinition注册器中。
小结
BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor都是扩展Bean的加载方式，当我们需要自定义自己的Bean加载方式时实现BeanDefinitionRegistryPostProcessor接口即可。@Configuration注解的实现就是基于BeanDefinitionRegistryPostProcessor接口完成。
BeanFactoryPostProcessor原理
看过spring源码的读者都很清楚AbstractApplicationContext类中refresh()是spring加载Bean的核心方法，大部分的处理逻辑都是在这个方法中完成，代码如下：
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// Prepare this context for refreshing.
/**
* 准备上下文刷新工作，如设置初始值
*/
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
/**
* 告诉子类刷新内部beanFactory，返回Bean工厂
*/
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
/**
* 准备beanFactory，以便于上下文中使用
*/
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
/**
* 允许在上下文子类中对bean工厂进行后处理。
*/
postProcessBeanFactory(beanFactory);
/**
* 开启处理PostProcessors步骤器
*/
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
/**
* 调用BeanFactory的后置处理器
*/
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
/**
*
* 注册拦截bean创建的bean处理器
*/
registerBeanPostProcessors(beanFactory);
/**
* 处理PostProcessors步骤器
*/
beanPostProcess.end();
// Initialize message source for this context.
/**
* 初始化MessageSource
*/
initMessageSource();
// Initialize event multicaster for this context.
/**
* 初始化Application监听器的管理Bean（ApplicationEventMulticaster）
*/
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
/**
* 模板模式，刷新Bean的操作，由子类实现具体逻辑
*/
onRefresh();
// Check for listener beans and register them.
/**
* 检查和注册监听器
*/
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
/**
* 实例化所有（非惰性初始化）单例
*/
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
/**
* 发布相应的事件
*/
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();
contextRefresh.end();
}
}
}
根据源码发现spring在invokeBeanFactoryPostProcessors(beanFactory)方法中是实现BeanFactoryPostProcessors的具体逻辑，下面根据这个方法来分析处理逻辑。
invokeBeanFactoryPostProcessors
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
/**
* 执行BeanFactoryPostProcessor，是该方法的处理核心
*/
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)
/**
* 检查和赋初始值
*/
if (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
逻辑处理核心是PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors())方法，下面分析：
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
Set<String> processedBeans = new HashSet<>();
/**
* 首先调用BeanDefinitionRegistryPostProcessors（如果有）。
*/
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
/**
* 用于存放BeanFactoryPostProcessor的对象
*/
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
/**
* 用户存放BeanDefinitionRegistryPostProcessor对象
*/
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
/********************************* 下面处理BeanDefinitionRegistryPostProcessor逻辑 *************************************/
/**
* 遍历最原始的BeanFactoryPostProcessor列表，找出BeanDefinitionRegistryPostProcessor和 BeanFactoryPostProcessor
* BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口
*/
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
/**
* 执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry
*/
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
/**
* 定义当前找到的BeanDefinitionRegistryPostProcessor临时存储
*/
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
// 首先，调用实现PriorityOrdered的BeanDefinitionRegistryPostProcessor。
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, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
// 接下来，调用实现Ordered的BeanDefinitionRegistryPostProcessor。
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, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
// 最后，调用所有其他BeanDefinitionRegistryPostProcessor，直到不再出现其他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, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
}
/**
* 批量执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry
*/
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
/**
* 批量执行BeanFactoryPostProcessor（最开始的BeanFactoryPostProcessor）
*/
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
/********************************* 下面处理BeanFactoryPostProcessor逻辑（可能执行上面步骤产生新的BeanFactoryPostProcessor），执行逻辑和BeanDefinitionRegistryPostProcessor一致 *************************************/
// 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
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
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();
}
/**
* 排序BeanFactoryPostProcessor
* @param postProcessors
* @param beanFactory
*/
private static void sortPostProcessors(List<?> postProcessors, ConfigurableListableBeanFactory beanFactory) {
// Nothing to sort?
if (postProcessors.size() <= 1) {
return;
}
Comparator<Object> comparatorToUse = null;
if (beanFactory instanceof DefaultListableBeanFactory) {
comparatorToUse = ((DefaultListableBeanFactory) beanFactory).getDependencyComparator();
}
if (comparatorToUse == null) {
comparatorToUse = OrderComparator.INSTANCE;
}
postProcessors.sort(comparatorToUse);
}
/**
* 执行 BeanDefinitionRegistryPostProcessor
* @param postProcessors
* @param registry
* @param applicationStartup
*/
private static void invokeBeanDefinitionRegistryPostProcessors(
Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {
for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
.tag("postProcessor", postProcessor::toString);
postProcessor.postProcessBeanDefinitionRegistry(registry);
postProcessBeanDefRegistry.end();
}
}
/**
* 执行invokeBeanFactoryPostProcessors
* @param postProcessors
* @param beanFactory
*/
private static void invokeBeanFactoryPostProcessors(
Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {
for (BeanFactoryPostProcessor postProcessor : postProcessors) {
StartupStep postProcessBeanFactory = beanFactory.getApplicationStartup().start("spring.context.bean-factory.post-process")
.tag("postProcessor", postProcessor::toString);
postProcessor.postProcessBeanFactory(beanFactory);
postProcessBeanFactory.end();
}
}
上面是spring执行BeanFactoryPostProcessor的具体逻辑，执行流程非常清晰，执行步骤如下：
-
第一步 ：遍历最原始的BeanFactoryPostProcessor，找到BeanDefinitionRegistryPostProcessor和BeanFactoryPostProcessor，且执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry(registry)方法加载Bean。
-
第二步 ：从BeanFactory中寻找BeanDefinitionRegistryPostProcessor的PriorityOrdered（最高优先级的排序）类型Bean，排序后执行postProcessBeanDefinitionRegistry(registry)方法加载Bean。
-
第三步 ：从BeanFactory中寻找BeanDefinitionRegistryPostProcessor未被加载的Ordered（排序）类型Bean，排序后执行postProcessBeanDefinitionRegistry(registry)方法加载Bean。
-
第四步 ：从BeanFactory中寻找出未被加载的BeanDefinitionRegistryPostProcessor类型Bean，然后执行postProcessBeanDefinitionRegistry(registry)方法加载Bean，这一步目的就是处理加载新的BeanDefinitionRegistryPostProcessor的Bean。
-
第五步 ：从BeanFactory中寻找BeanFactoryPostProcessor的PriorityOrdered（最高优先级的排序）类型Bean，排序后执行postProcessBeanFactory(beanFactory)方法加载Bean。
-
第六步 ：从BeanFactory中寻找BeanFactoryPostProcessor未被加载的Ordered（排序）的类型Bean，排序后执行postProcessBeanFactory(beanFactory)方法加载Bean。
-
第七步 ：从BeanFactory中寻找出未排序的BeanFactoryPostProcessor类型Bean，然后执行postProcessBeanFactory(beanFactory)方法加载Bean。
总结
BeanFactoryPostProcessor是执行最早的后置处理器，了解其原理对我们开发spring插件有很大的帮助，特别是BeanDefinitionRegistryPostProcessor接口对外扩展spring加载Bean的多样化。希望通过源码的角度帮助读者知其然更知其所以然。