解析Context 中refresh（）方法
- 前言
- 正文
- spring的基础特性
- FactoryBean 和 BeanFactory
- 后置处理器
- BeanPostProcessor
- BeanFactoryPostProcessor
- 解析源码
- 后话
前言
前文中解析Spring启动时注册的beanDefinition意义，这次讲其中核心的refresh()方法中的部分内容。
正文
介绍源码之前，先了解一些基础特性
spring的基础特性
FactoryBean 和 BeanFactory
BeanFactory接口是容器的顶级接口，定义了容器的一些基础行为，负责生产和管理Bean的一个工厂，具体使用它下面的子接口类型，比如ApplicationContext；此处我们重点分析FactoryBean
Spring中Bean有两种，一种是普通Bean，另一种是工厂Bean（FactoryBean），FactoryBean可以成某一个类型的Bean实例（返回给我们），也就是说我们可以借助于它自定义Bean的创建过程。
Bean创建的三种方式中的静态方法和实例化方法和FactoryBean作用类似，FactoryBean使用较多，尤其在Spring框架一些组件中会使用，还有其他框架和Spring框架整合时使用
// 可以让我们⾃定义Bean的创建过程（完成复杂Bean的定义）
public interface FactoryBean<T> {
@Nullable
// 返回FactoryBean创建的Bean实例，如果isSingleton返回true，则该实例会放到Spring容器
的单例对象缓存池中Map
T getObject() throws Exception;
@Nullable
// 返回FactoryBean创建的Bean类型
Class<?> getObjectType();
// 返回作⽤域是否单例
default boolean isSingleton() {
return true;
}
}后置处理器
Spring提供了两种后处理bean的扩展接口，分别为 BeanPostProcessor 和
BeanFactoryPostProcessor，两者在使用上是有所区别的
工厂初始化（BeanFactory）—> Bean对象
在BeanFactory初始化之后可以使用BeanFactoryPostProcessor进行后置处理做一些事情在Bean对象实例化（并不是Bean的整个生命周期完成）之后可以使用BeanPostProcessor进行后置处理做一些事情
注意：对象不一定是springbean，而springbean一定是个对象
BeanPostProcessor
BeanPostProcessor是针对Bean级别的处理，可以针对某个具体的Bean.
该接口提供了两个方法，分别在Bean的初始化方法前和初始化方法后执行，具体这个初始化方法指的是什么方法，类似我们在定义bean时，定义了init-method所指定的方法。
定义一个类实现了BeanPostProcessor，默认是会对整个Spring容器中所有的bean进行处理。如果要对具体的某个bean处理，可以通过方法参数判断，两个类型参数分别为Object和String，第一个参数是每个bean的实例，第二个参数是每个bean的name或者id属性的值。所以我们可以通过第二个参数，来判断我们将要处理的具体的bean。
注意：处理是发生在Spring容器的实例化和依赖注入之后。
BeanFactoryPostProcessor
BeanFactory级别的处理，是针对整个Bean的工厂进行处理，典型应用:PropertyPlaceholderConfigurer
此接口只提供了一个方法，方法参数为ConfigurableListableBeanFactory，该参数类型定义了一些方法
其中有个方法名为getBeanDefinition的方法，我们可以根据此方法，找到我们定义bean 的BeanDefinition对象。然后我们可以对定义的属性进行修改，以下是BeanDefinition中的方法
方法名字类似我们bean标签的属性，setBeanClassName对应bean标签中的class属性，所以当我们拿到BeanDefinition对象时，我们可以手动修改bean标签中所定义的属性值。
BeanDefinition对象：我们在 XML 中定义的 bean标签，Spring 解析 bean 标签成为一个 JavaBean，这个JavaBean 就是 BeanDefinition
注意：调用BeanFactoryPostProcessor 方法时，这时候bean还没有实例化，此时 bean 刚被解析成BeanDefinition对象
解析源码
首先，先概览一下refresh() 方法。
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
/**
* 准备工作，记录上下文的启动时间，状态，
* 以及初始化早期app监听set
*/
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
// 刷新内部bean factory
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 给bean factory的属性赋值
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 空方法，允许子类去扩展
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 执行已经被注册的factory processors
// 设置执行用户自定义以及spring内部定义的ProcessorBeanFactory
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 注册bean processors
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
// 初始化消息源
initMessageSource();
// Initialize event multicaster for this context.
// 初始化事件监听器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 初始化上下文中已指定的bean
onRefresh();
// Check for listener beans and register them.
// 检查和注册监听器
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 实例化所有非懒加载的单例bean
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// 发布合适的事件
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.
// 销毁bean
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...
// 清除缓存
resetCommonCaches();
}
}
}前面几个方法都很简单，笔者就不多赘述，直接奔向第一个难点invokeBeanFactoryPostProcessors(beanFactory);这个方法简言会执行spring内部定义的BeanFactoryPostProcessors以及用户自定义实现BeanFactoryPostProcessor接口的postProcessors。也就是说在spring初始化bean的时候，是允许用户参与进来进行扩展。
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// 调用getBeanFactoryPostProcessors()获取上下文中的BeanFactoryPostProcessors，一般值为null
// 执行gBeanFactoryPostProcessors
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()));
}
}继续深挖
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
// 先执行BeanDefinitionRegistryPostProcessors
// 判断beanFactory 是否是 BeanDefinitionRegistry的实例， 因为BeanDefinitionRegistry实现了BeanFactoryPostProcessor接口
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;
// 执行postProcessBeanDefinitionRegistry方法
registryProcessor.postProcessBeanDefinitionRegistry(registry);
// 添加到regularPostProcessors(用于最后回调执行postProcessBeanFactory方法)
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<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
// 第一步，执行 实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessors
// 获取beanName
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 校验是否实现PriorityOrdered接口
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
// 获取ppName对应的bean实例, 添加到currentRegistryProcessors
// beanFactory.getBean从单例池中获取，没有则创建，放到后续篇章详细展开
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
// 进行排序(根据是否实现PriorityOrdered、Ordered接口和order值来排序)
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 添加到registryProcessors(用于最后回调执行postProcessBeanFactory方法
registryProcessors.addAll(currentRegistryProcessors);
// 执行BeanDefinitionRegistryPostProcessors
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
// 第二步，执行 实现Ordered接口的BeanDefinitionRegistryPostProcessors
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);
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 最后，执行 其他的BeanDefinitionRegistryPostProcessors
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.
// 执行回调注册好的BeanFactoryPostProcessors
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
// 执行回调常规BeanFactoryPostProcessors
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
// 执行 上下文中注册好的 factory processors
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!
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<>();
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<>();
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...
// 因为后处理器可能已经修改了原始元数据，例如， 替换值中的占位符.
beanFactory.clearMetadataCache();
}看着很长，整理一下很简单
第一个流程：
- 先执行BeanDefinitionRegistryPostProcessor中的postProcessBeanDefinitionRegistry方法
- 实例化实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessors并添加到processedBeans中
- 排序
- 注册到registryProcessors用于最后的回调
- 执行invokeBeanDefinitionRegistryPostProcessors
然后是 实例化实现Ordered接口的BeanDefinitionRegistryPostProcessors并添加到processedBeans中，重复3到5步。
第69行判断入参是注册的postProcessor 还是常规的postProcessor
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
// 判断入参是registry还是regular
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
// 执行postProcessBeanDefinitionRegistry方法
registryProcessor.postProcessBeanDefinitionRegistry(registry);
// 添加到regularPostProcessors(用于最后回调执行postProcessBeanFactory方法)
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}执行完入参中的beanFactoryPostProcessors后，开始执行spring自己的beanFactoryPostProcessors。流程和第一流程一样。
然后，在挖一下invokeBeanDefinitionRegistryPostProcessors 方法，继续debug会看到调用processConfigBeanDefinitions 获取的candidateNames数组
/**
* Build and validate a configuration model based on the registry of
* {@link Configuration} classes.
*/
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();
//
for (String beanName : candidateNames) {
// 获取注册的BeanDefinition
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
// 是否是配置类
if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||
ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {
if (logger.isDebugEnabled()) {
logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
}
}
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
// Return immediately if no @Configuration classes were found
// 如果一个配置类没有找到就返回
if (configCandidates.isEmpty()) {
return;
}
// Sort by previously determined @Order value, if applicable
// 排序
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
// Detect any custom bean name generation strategy supplied through the enclosing application context
SingletonBeanRegistry sbr = null;
// 单例bean注册器
if (registry instanceof SingletonBeanRegistry) {
sbr = (SingletonBeanRegistry) registry;
// 判断是否存在localbean生成器，默认值是false
if (!this.localBeanNameGeneratorSet) {
// 从单例池获取，没有则生成
BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);
if (generator != null) {
this.componentScanBeanNameGenerator = generator;
this.importBeanNameGenerator = generator;
}
}
}
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// Parse each @Configuration class
// 解析配置类
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
do {
// 解析
parser.parse(candidates);
// 验证
parser.validate();
Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
// 移除解析过的
configClasses.removeAll(alreadyParsed);
// Read the model and create bean definitions based on its content
// 读取病创建其他的bean definitions基于上下文中
if (this.reader == null) {
this.reader = new ConfigurationClassBeanDefinitionReader(
registry, this.sourceExtractor, this.resourceLoader, this.environment,
this.importBeanNameGenerator, parser.getImportRegistry());
}
// 根据配置类加载本地的beanDefinitions
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);
candidates.clear();
// 判断注册器中的BeanDefinitionCount数量是否大于candidateName，正常来说都大于的
if (registry.getBeanDefinitionCount() > candidateNames.length) {
String[] newCandidateNames = registry.getBeanDefinitionNames();
Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));
Set<String> alreadyParsedClasses = new HashSet<>();
for (ConfigurationClass configurationClass : alreadyParsed) {
alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());
}
for (String candidateName : newCandidateNames) {
if (!oldCandidateNames.contains(candidateName)) {
// 创建大于旧的中的BeanDefinition
BeanDefinition bd = registry.getBeanDefinition(candidateName);
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
!alreadyParsedClasses.contains(bd.getBeanClassName())) {
candidates.add(new BeanDefinitionHolder(bd, candidateName));
}
}
}
// candidateNames值覆盖
candidateNames = newCandidateNames;
}
}
// 判断没有配置类或者其他引用注解标记的类
while (!candidates.isEmpty());
// Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes
// 扫描带@ipmort注解的注册器
if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
}
if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) {
// Clear cache in externally provided MetadataReaderFactory; this is a no-op
// for a shared cache since it'll be cleared by the ApplicationContext.
((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache();
}
}接下来在看一下postProcessBeanFactory
/**
* Prepare the Configuration classes for servicing bean requests at runtime
* by replacing them with CGLIB-enhanced subclasses.
*/
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// 获取beanFactory的hash值
int factoryId = System.identityHashCode(beanFactory);
// 判断工厂processed是否已经包含了beanFactory，没有则加入
if (this.factoriesPostProcessed.contains(factoryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + beanFactory);
}
this.factoriesPostProcessed.add(factoryId);
// 懒加载
if (!this.registriesPostProcessed.contains(factoryId)) {
// BeanDefinitionRegistryPostProcessor hook apparently not supported...
// Simply call processConfigurationClasses lazily at this point then.
processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
}
// 增强配置类，开启自动代理
enhanceConfigurationClasses(beanFactory);
// beanFactory 加入一个新的ImportAwareBeanPostProcessor
beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
}后话
本文介绍了执行invokeBeanFactoryPostProcessors(beanFactory);通过这个方法，也就是常说的后置处理器。通过这个方法，用户可以完成手动类的注册。
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