Spring源码分析系列（二）ioc加载过程

  首先看一段代码，我们通过这段代码分析ioc的加载过程。

public static void main(String[] args) {
ApplicationContext applicatiOnContext= new AnnotationConfigApplicationContext( MainConfig.class );
Person bean = applicationContext.getBean(Person.class);
System.out.println(bean);
String[] namesForType = applicationContext.getBeanNamesForType( Person.class );
for (String name : namesForType) {
System.out.println(name);
}
}

  通过上面的代码，可以看到是通过ApplicationContext加载ioc容器的。下面我们来看一下AnnotationConfigApplicationContext执行的具体流程，主要分为下面几步：

• 初始化一个空容器，容器中不包含任何Bean信息。
• 为容器中注册一个要被处理的注解Bean
• 刷新容器

//创建ioc容器
//最常用的构造函数，通过将涉及到的配置类传递给该构造函数，以实现将相应配置类中的Bean自动注册到容器中
public AnnotationConfigApplicationContext(Class... annotatedClasses) {
//1.初始化一个空容器，容器不包含任何Bean信息，需要在稍后通过调用其register()方法注册配置类，并调用refresh()方法刷新容器，触发容器对注解Bean的载入、解析和注册过程
this();
//2.为容器中注册一个要被处理的注解Bean，新注册的Bean，必须手动调用容器的refresh()方法刷新容器，触发容器对新注册的Bean的处理
register(annotatedClasses);
//3.刷新容器
refresh();
}

附一张时序图，大家可以结合代码理解（图片来源网络）

//默认构造函数，初始化一个空容器，容器不包含任何Bean信息，需要在稍后通过调用其register()方法注册配置类，并调用refresh()方法刷新容器，触发容器对注解Bean的载入、解析和注册过程
public AnnotationConfigApplicationContext() {
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}2.为容器注册一个要被处理的注解Bean

//为容器中注册一个要被处理的注解Bean，新注册的Bean，必须手动调用容器的refresh()方法刷新容器，触发容器对新注册的Bean的处理
public void register(Class... annotatedClasses) {
Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
this.reader.register(annotatedClasses);
}

2.1注册自定义注解Bean

//注册多个注解Bean自定义类
public void register(Class... annotatedClasses) {
for (Class annotatedClass : annotatedClasses) {
registerBean(annotatedClass);
}
}
/**
* Register a bean from the given bean class, deriving its metadata from
* class-declared annotations.
* @param annotatedClass the class of the bean
*/
//注册一个注解Bean定义类
public void registerBean(Class annotatedClass) {
doRegisterBean(annotatedClass, null, null, null);
}
//Bean定义读取器向容器注册注解Bean定义类
void doRegisterBean(Class annotatedClass, @Nullable Supplier instanceSupplier, @Nullable String name,
@Nullable Class[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
//根据指定的注解Bean定义类，创建Spring容器中对注解Bean的封装的数据结构
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}
abd.setInstanceSupplier(instanceSupplier);
//解析注解Bean定义的作用域，若@Scope("prototype")，则Bean为原型类型；若@Scope("singleton")，则Bean为单例类型
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
//为注解Bean定义设置作用域
abd.setScope(scopeMetadata.getScopeName());
//为注解Bean定义生成Bean名称
String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
//处理注解Bean定义中的通用注解
AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
//如果在向容器注册注解Bean定义时，使用了额外的限定符注解，则解析限定符注解。主要是配置的关于autowiring自动依赖注入装配的限定条件，即@Qualifier注解
//Spring自动依赖注入装配默认是按类型装配，如果使用@Qualifier则按名称
if (qualifiers != null) {
for (Class qualifier : qualifiers) {
//如果配置了@Primary注解，设置该Bean为autowiring自动依赖注入装配时的首选
if (Primary.class == qualifier) {
abd.setPrimary(true);
}
//如果配置了@Lazy注解，则设置该Bean为非延迟初始化，如果没有配置，则该Bean为预实例化
else if (Lazy.class == qualifier) {
abd.setLazyInit(true);
}
//如果使用了除了@Primary和@Lazy以外的其他注解，则为该Bean添加一个autowiring自动依赖注入装配限定符，该Bean在进autowiring自动依赖注入装配时，根据名称装配限定符指定的Bean
else {
abd.addQualifier(new AutowireCandidateQualifier(qualifier));
}
}
}
for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
customizer.customize(abd);
}
//创建一个指定Bean名称的Bean定义对象，封装直接Bean定义类数据
BeanDefinitionHolder definitiOnHolder= new BeanDefinitionHolder(abd, beanName);
//根据注解Bean定义类中配置的作用域，创建响应的代理对象
definitiOnHolder= AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
//向IOC容器注册注解Bean类定义对象
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}3.刷新容器

@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//刷新前的预处理
//1、调用容器准备刷新的方法，获取容器的当前时间，同时给容器设置同步标识
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//初始化BeanFactory
//2.告诉子类启动refreshBeanFactory()方法，Bean定义资源文件的载入从子类的refreshBeanFactory()方法启动
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//BeanFactory的预准备工作
//3、为BeanFactory配置容器特性，例如类加载器、事件处理器等
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
//BeanFactory的后置处理器
//4、为容器的某些子类指定特殊的BeanPost事件处理器
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//5、调用所有注册的BeanFactoryPostProcessor的Bean
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
//Bean的后置处理器
//6、为BeanFactory注册BeanPost事件处理器
//BeanPostProcessor是Bean后置处理器，用于监听容器触发的事件
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
//7、初始化信息源，和国际化相关
initMessageSource();
// Initialize event multicaster for this context.
//8、初始化容器事件传播器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
//9、调用子类的某些特殊Bean初始化方法
onRefresh();
// Check for listener beans and register them.
//10、为事件传播器注册事件监听器
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
//11、初始化所有剩余的单例Bean
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
//12、初始化容器的生命周期事件处理器，并发布容器的声明周期事件
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.
//13、销毁已创建的Bean
destroyBeans();
// Reset 'active' flag.
//14、取消refresh操作，重置容器的同步标识
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...
//15、重设公共缓存
resetCommonCaches();
}
}
}

3.1调用容器准备刷新的方法，获取容器的当前时间，同时给容器设置同步标识（刷新前的预处理）

protected void prepareRefresh() {
// Switch to active.
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
if (logger.isDebugEnabled()) {
if (logger.isTraceEnabled()) {
logger.trace("Refreshing " + this);
}
else {
logger.debug("Refreshing " + getDisplayName());
}
}
// Initialize any placeholder property sources in the context environment.
//初始化一些属性设置，子类自定义个性化的属性设置方法
initPropertySources();
// Validate that all properties marked as required are resolvable:
// see ConfigurablePropertyResolver#setRequiredProperties
//检查属性的合法性等
getEnvironment().validateRequiredProperties();
// Store pre-refresh ApplicationListeners...
if (this.earlyApplicatiOnListeners== null) {
//保存容器中的一些早期的事件
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<>();
}

3.2告诉子类启动refreshBeanFactory()方法，Bean定义资源文件的载入从子类的refreshBeanFactory()方法启动

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//刷新【创建】BeanFactory
//这里使用了委派设计模式，父类定义了抽象的refreshBeanFactory()方法，具体实现调用子类容器的refreshBeanFactory()方法
refreshBeanFactory();
//返回刚才GenericApplicationContext创建的BeanFactory对象
//将创建的BeanFactory【DefaultListableBeanFactory】返回
return getBeanFactory();
}

3.2.1刷新（创建）BeanFactory

@Override
protected final void refreshBeanFactory() throws IllegalStateException {
if (!this.refreshed.compareAndSet(false, true)) {
throw new IllegalStateException(
"GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
}
this.beanFactory.setSerializationId(getId());
}

3.2.2返回刚才GenericApplicationContext创建的BeanFactory对象

@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
return this.beanFactory;
}

3.3为BeanFactory配置容器特性，例如类加载器、事件处理器等（BeanFactory的预准备工作）

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
//1、设置BeanFactory的类加载器、支持表达式解析器
beanFactory.setBeanClassLoader(getClassLoader());
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
//2、添加部分BeanPostProcessor【ApplicationContextAwareProcessor】
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
//3、设置忽略的自动装配的接口EnvironmentAware、EmbeddedValueResolverAware、xxx
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
//4、注册可以解析的自动装配：我们能直接在任何组件中自动注入：BeanFactory、ResourceLoader、ApplicationEventPublisher、ApplicationContext
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Register early post-processor for detecting inner beans as ApplicationListeners.
//5、添加BeanPostProcessor【ApplicationListenerDetector】
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// Register default environment beans.
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());
}
}

3.4为容器的某些子类指定特殊的BeanPost事件处理器

@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
if (this.servletContext != null) {
beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
}
WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext);
}

3.5调用所有注册的BeanFactoryPostProcessor的Bean

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
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()));
}
}

3.6为BeanFactory注册BeanPost事件处理器（Bean的后置处理器）

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}

3.7初始化信息，和国际化相关

protected void initMessageSource() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
// Make MessageSource aware of parent MessageSource.
if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
if (hms.getParentMessageSource() == null) {
// Only set parent context as parent MessageSource if no parent MessageSource
// registered already.
hms.setParentMessageSource(getInternalParentMessageSource());
}
}
if (logger.isTraceEnabled()) {
logger.trace("Using MessageSource [" + this.messageSource + "]");
}
}
else {
// Use empty MessageSource to be able to accept getMessage calls.
DelegatingMessageSource dms = new DelegatingMessageSource();
dms.setParentMessageSource(getInternalParentMessageSource());
this.messageSource = dms;
beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
if (logger.isTraceEnabled()) {
logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");
}
}
}

3.8初始化容器事件传播器

protected void initApplicationEventMulticaster() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
this.applicatiOnEventMulticaster=
beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
if (logger.isTraceEnabled()) {
logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
}
}
else {
this.applicatiOnEventMulticaster= new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
if (logger.isTraceEnabled()) {
logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
}
}
}

3.9调用子类的某些特殊Bean初始化方法

@Override
protected void onRefresh() {
this.themeSource = UiApplicationContextUtils.initThemeSource(this);
}

3.10为事件传播器注册事件监听器

protected void registerListeners() {
// Register statically specified listeners first.
for (ApplicationListener listener : getApplicationListeners()) {
getApplicationEventMulticaster().addApplicationListener(listener);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let post-processors apply to them!
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
for (String listenerBeanName : listenerBeanNames) {
getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}
// Publish early application events now that we finally have a multicaster...
Set earlyEventsToProcess = this.earlyApplicationEvents;
this.earlyApplicatiOnEvents= null;
if (earlyEventsToProcess != null) {
for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
getApplicationEventMulticaster().multicastEvent(earlyEvent);
}
}
}

3.11初始化所有剩余的单例Bean

//对配置了lazy-init属性的Bean进行预实例化处理
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
//这是Spring3以后新加的代码，为容器指定一个转换服务(ConversionService)
//在对某些Bean属性进行转换时使用
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
// Register a default embedded value resolver if no bean post-processor
// (such as a PropertyPlaceholderConfigurer bean) registered any before:
// at this point, primarily for resolution in annotation attribute values.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
//为了类型匹配，停止使用临时的类加载器
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
//缓存容器中所有注册的BeanDefinition元数据，以防被修改
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
//对配置了lazy-init属性的单态模式Bean进行预实例化处理
beanFactory.preInstantiateSingletons();
}

3.12初始化容器的生命周期事件处理器，并发布容器的声明周期事件

protected void finishRefresh() {
// Clear context-level resource caches (such as ASM metadata from scanning).
clearResourceCaches();
// Initialize lifecycle processor for this context.
initLifecycleProcessor();
// Propagate refresh to lifecycle processor first.
getLifecycleProcessor().onRefresh();
// Publish the final event.
publishEvent(new ContextRefreshedEvent(this));
// Participate in LiveBeansView MBean, if active.
LiveBeansView.registerApplicationContext(this);
}

3.13销毁已创建的Bean

protected void destroyBeans() {
getBeanFactory().destroySingletons();
}

3.14取消refresh操作，充值容器的同步标识

@Override
protected void cancelRefresh(BeansException ex) {
this.beanFactory.setSerializationId(null);
super.cancelRefresh(ex);
}

3.15重设公共缓存

protected void resetCommonCaches() {
ReflectionUtils.clearCache();
AnnotationUtils.clearCache();
ResolvableType.clearCache();
CachedIntrospectionResults.clearClassLoader(getClassLoader());
}