探究Spring的后置處理器
本次我們主要探究invokeBeanFactoryPostProcessors()；后面的代碼下次再做解析；
入口代碼refresh()
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(); // ...... applicationContext.refresh();
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
// 啟動前的準備工作：記錄啟動時間，活動標記為啟動以及環境屬性變量集合的初始化
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//還是一些準備工作，添加了兩個后置處理器：ApplicationContextAwareProcessor，ApplicationListenerDetector
//還設置了 忽略自動裝配 和 允許自動裝配 的接口
//對環境，系統環境，系統屬性三個Bean如果不存在某個bean的時候，spring就自動生成singleton bean（Not bd）
//還設置了bean表達式解析器 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.
//執行自定義的BeanFactoryProcessor和內置的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();
}
}
}
流程圖
prepareRefresh剖析
該方法主要做啟動前的準備工作：記錄啟動時間，活動標記為啟動以及環境屬性變量集合的初始化；
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
主要是獲取context上下文中的bean工廠；
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
// CAS保證同步
refreshBeanFactory();
// 返回beanFactory- DefaultListableBeanFactory.class
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
return beanFactory;
}
prepareBeanFactory刨析
做一些準備工作，添加了兩個后置處理器ApplicationContextAwareProcessor和ApplicationListenerDetector;
設置了bean表達式解析器等；
通過工廠的接口可以設置了忽略自動裝配，和允許自動裝配；
對環境、系統環境、系統屬性三個Bean如果不存在某個bean的時候，spring就自動生成singletonBean（Not bd）；
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
//設置bean表達式解析器
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
//屬性編輯器支持
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
//添加一個后置處理器：ApplicationContextAwareProcessor，此后置處理處理器實現了BeanPostProcessor接口
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
//以下接口，忽略自動裝配
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，允許自動裝配,第一個參數是自動裝配的類型，，第二個字段是自動裝配的值
// 這個接口僅會將注入的參數XXX.class注入為指定的值，但不影響XXX.class創建Bean對象；
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
// Register default environment beans.
// 環境，系統環境，系統屬性 因此通常情況下，這三個Bean是沒有bd的
//如果沒有注冊過bean名稱為XXX，spring就自己創建一個名稱為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
執行自定義的BeanFactoryProcessor和內置的BeanFactoryProcessor;
getBeanFactoryPostProcessors()方法是我們手動通過執行addBeanFactoryPostProcessor(XX)設置自定義的后置處理器。如果初始化執行到這，沒有手動增加后置處理器的話，那么此時List<BeanFactoryPostProcessor>的size()為empty；
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// getBeanFactoryPostProcessors是spring允許我們手動添加BeanFactoryPostProcessor
// 即：annotationConfigApplicationContext.addBeanFactoryPostProcessor(XXX);
// 未手動添加的話，getBeanFactoryPostProcessors()為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()));
}
}
我們通過委托PostProcessorRegistrationDelegate去調用invokeBeanFactoryPostProcessors()方法，從而去掃描并執行BeanFactoryProcessor和BeanDefinitionRegistryPostProcessor;
我們通過繼承關系看，BeanDefinitionRegistryPostProcessor實際上是繼承BeanFactoryProcessor接口的；
- BeanDefinitionRegistryPostProcessor:主要掃描類解析類;
- BeanFactoryProcessor:主要給配置類進行增強代理;
這里面需要看我們的BeanFactory的類型；初始時BeanFactory的類型是DefaultListableBeanFactory;因此，該bean工廠是實現BeanDefinitionRegistry;
該方法的具體流程如下（按初始化進入到這里描述）：
- 循環遍歷手動添加的后置處理器（并不排序）;
- 若該bfp是bdrp則直接執行bdrp. postProcessBeanDefinitionRegistry();
- 取出內置的bdrp，分為實現了PriorityOrdered,Ordered和都沒有實現的三類；
初始這里只有一個，就是我們在初始化reader()時，注冊了一個ConfigurationClassPostProcessor.class;
public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {}
將上面三類直接執行bdrp. postProcessBeanDefinitionRegistry();
然后將手動加入和內置的bdrp執行bfp.postProcessBeanFactory();
上面的已經執行完了：
- 手動添加的后置處理器的bdrf. postProcessBeanDefinitionRegistry()和bfp.postProcessBeanFactory();
- 內置的bdrp. postProcessBeanDefinitionRegistry()
取出內置的bfp，分為實現了PriorityOrdered, Ordered和都沒有實現的三類；
目前這里內置的有兩個。但其中config上面已經執行過了，此處只執行下方的一個；
將上面三類直接執行bfp. postProcessBeanDefinitionRegistry();
清除緩存中的bd，因為后處理器可能有修改了原始元數據，例如替換值中的占位符;
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
// 如果不是BeanDefinitionRegistry 則直接執行beanFactoryPostProcessors
// 剛啟動時傳入的beanFactory是DefaultListableBeanFactory，他是實現了BeanDefinitionRegistry 因此會走這里
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
// bf后置處理器集合（手動添加與bdr后置處理器集合【下面的那個集合】）：因為bdrp屬于bfp
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// bdr后置處理器集合（手動添加與spring自己的）
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
// 循環傳進來的beanFactoryPostProcessors，剛啟動時未手動增加的情況下beanFactoryPostProcessors肯定沒有數據
// 因為beanFactoryPostProcessors是獲得手動添加的，而不是spring掃描的
// 只有手動調用annotationConfigApplicationContext.addBeanFactoryPostProcessor(XXX)才會有數據
// 執行手動添加的beanFactoryPostProcessors， 如果是BeanDefinitionRegistryPostProcessor，則執行其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);
}
}
//一個臨時變量，用來裝載BeanDefinitionRegistryPostProcessor為了排序
//BeanDefinitionRegistry繼承了PostProcessorBeanFactoryPostProcessor
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// 獲得實現BeanDefinitionRegistryPostProcessor接口的類
// 就是ConfigurationClassPostProcessor（Spring自己添加的-在reader()時增加的）
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
//獲得ConfigurationClassPostProcessor類，并且放到currentRegistryProcessors
//ConfigurationClassPostProcessor是很重要的一個類，它實現了BeanDefinitionRegistryPostProcessor接口
//BeanDefinitionRegistryPostProcessor接口又實現了BeanFactoryPostProcessor接口
//ConfigurationClassPostProcessor是極其重要的類
//里面執行了掃描Bean，Import，ImportResouce等各種操作
//用來處理配置類（有兩種情況 一種是傳統意義上的配置類，一種是普通的bean）的各種邏輯
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
//把name放到processedBeans，后續會根據這個集合來判斷處理器是否已經被執行過了
processedBeans.add(ppName);
}
}
//處理排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
//合并Processors，為什么要合并，因為registryProcessors是裝載BeanDefinitionRegistryPostProcessor的
//一開始的時候，spring只會執行BeanDefinitionRegistryPostProcessor獨有的方法
//而不會執行BeanDefinitionRegistryPostProcessor父類的方法，即BeanFactoryProcessor的方法
//所以這里需要把處理器放入一個集合中，后續統一執行父類的方法
registryProcessors.addAll(currentRegistryProcessors);
//可以理解為執行ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry方法
//Spring熱插播的體現，像ConfigurationClassPostProcessor就相當于一個組件，Spring很多事情就是交給組件去管理
//將spring提供的RegistryProcessors(就是這個ConfigurationClassPostProcessor)執行其postProcessBeanDefinitionRegistry
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
//清空臨時變量
currentRegistryProcessors.clear();
// 再次根據BeanDefinitionRegistryPostProcessor獲得BeanName，看這個BeanName是否已經被執行過了，有沒有實現Ordered接口
// 如果沒有被執行過，也實現了Ordered接口的話，把對象推送到currentRegistryProcessors，名稱推送到processedBeans
// 如果沒有實現Ordered接口的話，這里不把數據加到currentRegistryProcessors，processedBeans中，后續再做處理
// 這里才可以獲得我們定義的實現了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);
}
}
//處理排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
//合并Processors
registryProcessors.addAll(currentRegistryProcessors);
//執行有Ordered的BeanDefinitionRegistryPostProcessor
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
//清空臨時變量
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 下面的代碼就是執行沒有實現PriorityOrdered接口也沒有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集合裝載BeanDefinitionRegistryPostProcessor
//上面的代碼是執行bfr后置處理器子類獨有的方法，這里需要再把bfr后置處理器父類的方法也執行一次
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
//regularPostProcessors裝載BeanFactoryPostProcessor，執行BeanFactoryPostProcessor的方法
//但是regularPostProcessors一般情況下，是不會有數據的，只有在外面手動添加BeanFactoryPostProcessor，才會有數據
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
// 若bfp沒有繼承bdrp則直接執行手動增加bf后置處理器的后置處理器
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實現類的BeanName數組
// 處理Spring自己的bf后置處理器
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
// PriorityOrdered的bf后置處理器集合
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// Ordered的bf后置處理器集合
List<String> orderedPostProcessorNames = new ArrayList<>();
// 無PriorityOrdered無Ordered的bf后置處理器集合
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
//循環BeanName數組
for (String ppName : postProcessorNames) {
//如果這個Bean被執行過了，跳過
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
//如果實現了PriorityOrdered接口，加入到priorityOrderedPostProcessors
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
//如果實現了Ordered接口，加入到orderedPostProcessorNames
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
//如果既沒有實現PriorityOrdered，也沒有實現Ordered。加入到nonOrderedPostProcessorNames
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
//排序處理priorityOrderedPostProcessors，即實現了PriorityOrdered接口的BeanFactoryPostProcessor
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
//執行priorityOrderedPostProcessors
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
//執行實現了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.
// 執行既沒有實現PriorityOrdered接口，也沒有實現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()
// 清除緩存中的bd，因為后處理器可能有修改了原始元數據，例如替換值中的占位符
beanFactory.clearMetadataCache();
}
到此這篇關于Java 圖解Spring啟動時的后置處理器工作流程是怎樣的的文章就介紹到這了,更多相關Java Spring 后置處理器內容請搜索服務器之家以前的文章或繼續瀏覽下面的相關文章希望大家以后多多支持服務器之家！
原文鏈接：https://blog.csdn.net/qq_37419449/article/details/120879661
