如何进行Spring源码分析？

用户5155972636167
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目标

追踪下面一段代码的流程：

AnnotationConfigApplicationContextDemo

/**

  • description
  • date 2021-06-30 11:21 **/ public class AnnotationConfigApplicationContextDemo {

public static void main(String[] args) { final AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SimpleConfig.class); User user = applicationContext.getBean(User.class); System.out.println("user:" + user); } } Configuration public class SimpleConfig {

Bean public User user(){ return new User("xgimi", 10); } } public class User {

private String name; private Integer age;

...

流程

核心逻辑都在AnnotationConfigApplicationContext的带参构造器中：

public AnnotationConfigApplicationContext(Class<?>... componentClasses) { this(); register(componentClasses); refresh(); }

空构造器做了什么

先说答案： 两个事情，一是创建了BedefinitionReader、BeanDefinitionScanner，提供了扫描BeanDefinition的能力； 二是通过父类GenericApplicationContext的构造器创建了DefaultListableBeanFactory，提供底层的IOC能力。

初始化AnnotatedBeanDefinitionReader

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) { //注入registry，并且初始化Environment对象 this(registry, getOrCreateEnvironment(registry)); }

提供注册beanDefinition的能力

public AnnotationConfigApplicationContext() { StartupStep createAnnotatedBeanDefReader = this.getApplicationStartup().start("spring.context.annotated-bean-reader.create"); this.reader = new AnnotatedBeanDefinitionReader(this); createAnnotatedBeanDefReader.end(); this.scanner = new ClassPathBeanDefinitionScanner(this); }

我们会在后面探究BeanDefinitionRegistry注册BeanDefinition的本质

获取环境对象 getOrCreateEnvironment这个方法进行页游的内部环境的创建并获取：

private static Environment getOrCreateEnvironment(BeanDefinitionRegistry registry) { Assert.notNull(registry, "BeanDefinitionRegistry must not be null"); if (registry instanceof EnvironmentCapable) { return ((EnvironmentCapable) registry).getEnvironment(); } return new StandardEnvironment(); }

环境对象中包含了系统环境变量，自定义属性等内容。

通过构造器可以看到，AnnotatedBeanDefinitwww.sangpi.comionReader底层维护了一个BeanDefinitionRegistry。实际上，他就是通过BeanDefinitionRegistry提供的注册能力，而AnnotationConfigApplicationContext本身就是一个BeanDefinitionRegistry；所以在调用AnnotatedBeanDefinitionReader构造器时，我们传入的就是AnnotationConfigApplicationContext：

实际上是组合关系，AnnotationConfigApplicationContext中大部分的能力，包括注册beanDefinition，依赖查找，依赖注入，都是通过DefaultListableBeanFactory通过的底层能力支持。

如何将配置类注册为BeanDefinition

在AnnotationConfigApplicationContext中：

Override public void register(Class<?>... componentClasses) { Assert.notEmpty(componentClasses, "At least one component class must be specified"); StartupStep registerComponentClass = this.getApplicationStartup().start("spring.context.component-classes.register") .tag("classes", () -> Arrays.toString(componentClasses)); //注册配置类 this.reader.register(componentClasses); registerComponentClass.end(); }

从上面代码可以看出，主要是调用了reader的register方法完成的注册，来看下这个方法的实现逻辑

public void register(Class... componentClasses) { for (Class componentClass : componentClasses) { registerBean(componentClass); } } public void registerBean(Class<?> beanClass) { doRegisterBean(beanClass, null, null, null, null); } private void doRegisterBean(Class beanClass, @Nullable String name, @Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier supplier, @Nullable BeanDefinitionCustomizer[] customizers) { //进来就先把class对象转为一个BeanDefinition，此时这个BeanDefinition中只有class信息和注解类上注解信息 AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass); //处理@Conditional注解 if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) { return; } //supplier会优先于所有的构造器和工厂方法进行类的实例化，但是不会影响属性设置 abd.setInstanceSupplier(supplier); //处理scope，没有设置，默认返回singleton；@Scope("scopeName")会在这个方法中进行处理，获得scopeName ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd); abd.setScope(scopeMetadata.getScopeName()); //创建beanName AnnotationBeanNameGenerator提供能力，但以接口入参为优先 String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry)); //将以下几个注解标注的值设置到abd中 //1.@Lazy 2.@Primary 3.@Role 4.@DependesOn 5.@Description AnnotationConfigUtils.processCommonDefinitionAnnotations(abd); if (qualifiers != null) { for (Class<? extends Annotation> qualifier : qualifiers) { if (Primary.class == qualifier) { abd.setPrimary(true); } else if (Lazy.class == qualifier) { abd.setLazyInit(true); } else { abd.addQualifier(new AutowireCandidateQualifier(qualifier)); } } } if (customizers != null) { for (BeanDefinitionCustomizer customizer : customizers) { customizer.customize(abd); } } //definitionHolder 保存的是beanDefinition和beanName(还可以有别名) BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName); //如果@Scope设置了代理，这里将会返回一个代理对象 definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); //将definitionHolder中的beanDefinition注册到registry对象中 //DefaultListableBeanFactory.registerBeanDefinition(String beanName, BeanDefinition beanDefinition) //最后的结果：DefaultListableBeanFactory中的beanDefinitionMap中存入一个beanDefinition，beanDefinitionNames中存入beanName BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry); }

综合上述代码，整理以下doRegisterBean的大致逻辑：

创建一个配置类对象的AnnotationBeanDefinition 通过AnnotationBeanDefinition解析类上面是否存在Conditional注解，并判断是否满足注册的条件，如果不满足，则不进行注册 向abd中注册方法入参传入的 Supplier，后续可通过该接口实现bean的实例化 解析Scope属性并注册到abd中 创建beanName

创建一个beanDefinitionHolder保存abd和beanName，alias之间的对应关系 处理非单例Scope，返回一个代理，详见Scope的处理过程 BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);

我们来看下第9步，究竟是如何注册的：

BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);

public static void registerBeanDefinition( BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException { // Register bean definition under primary name. String beanName = definitionHolder.getBeanName(); registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); // Register aliases for bean name, if any. String[] aliases = definitionHolder.getAliases(); if (aliases != null) { for (String alias : aliases) { //TODO registry.registerAlias(beanName, alias); } } }

可以看到，实际进行了两部分注册：

注册beanName 注册别名

结果发现还是使用的DefaultListableBeanFactory进行注册的，这也论证了我们上面关于DefaultListableBeanFactory和AnnotationConfigApplicationContext之间关系的结论。来看看DefaultListableBeanFactory中究竟是怎么实现的吧：

@Override

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException { Assert.hasText(beanName, "Bean name must not be empty"); Assert.notNull(beanDefinition, "BeanDefinition must not be null"); if (beanDefinition instanceof AbstractBeanDefinition) { try { ((AbstractBeanDefinition) beanDefinition).validate(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", ex); } } BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName); if (existingDefinition != null) { if (!isAllowBeanDefinitionOverriding()) { throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition); } else if (existingDefinition.getRole() < beanDefinition.getRole()) { // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE if (logger.isInfoEnabled()) { logger.info("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]"); } } else if (!beanDefinition.equals(existingDefinition)) { if (logger.isDebugEnabled()) { logger.debug("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]"); } } else { if (logger.isTraceEnabled()) { logger.trace("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]"); } } this.beanDefinitionMap.put(beanName, beanDefinition); } else { if (hasBeanCreationStarted()) { // Cannot modify startup-time collection elements anymore (for stable iteration) synchronized (this.beanDefinitionMap) { this.beanDefinitionMap.put(beanName, beanDefinition); List updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1); updatedDefinitions.addAll(this.beanDefinitionNames); updatedDefinitions.add(beanName); this.beanDefinitionNames = updatedDefinitions; removeManualSingletonName(beanName); } } else { // Still in startup registration phase // 主要看这里

        this.beanDefinitionMap.put(beanName, beanDefinition);
        this.beanDefinitionNames.add(beanName);
        removeManualSingletonName(beanName);
    }
    this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
    resetBeanDefinition(beanName);
}
else if (isConfigurationFrozen()) {
    clearByTypeCache();
}

}

上述的代码，先检查了容器中是否已经注册过了该bd，再检查了是否正在注册该db；而我们是第一次注册，所以走的核心分支就是第59行开始的else分支。做了下面几件事情：

向beanDefinitionMap中放入了beanName为key的beanDefinition 向beanDefinitionNames中放入了beanName 如果manualSingletonNames中存在beanName，将其移除

为什么要单独维护一个beanDefinitionNames？主要是因为beanDefinitionMap是无序的，而beanDefinitionNames是一个ArrayList，是有序的，可以保存bd的注册顺序

refresh方法都做了什么 1.prepareRefresh

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. //非web环境下默认是空的实现 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<>(); } 预刷新阶段主要做了一下几件事情：

提供initPropertySources()扩展方法供容器进行外部资源加载，在AnnotationContextApplicationContext中默认是空实现

getEnvironment().validateRequiredProperties();进行必填属性的校验，是AbstractPropertyResolver这个接口提供的能力，Environment对象是这个接口的实现。

@Override public void validateRequiredProperties() { MissingRequiredPropertiesException ex = new MissingRequiredPropertiesException(); for (String key : this.requiredProperties) { if (this.getProperty(key) == null) { ex.addMissingRequiredProperty(key); } } if (!ex.getMissingRequiredProperties().isEmpty()) { throw ex; } } 默认容器中是没有必须存在的属性的，如果需要添加该校验，则通过beanFactory获取到Environment，然后再进行设置：

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
applicationContext.register(SimpleConfig.class);
applicationContext.getEnvironment().setRequiredProperties("system");
applicationContext.refresh();

实际上是调用的AbstractPropertyResolver类的下面方法

//设置必须存在的属性 @Override public void setRequiredProperties(String... requiredProperties) { Collections.addAll(this.requiredProperties, requiredProperties); } requiredProperties是一个LinkedHashSet

private final Set requiredProperties = new LinkedHashSet<>();

在容器中创建earlyApplicationListeners、earlyApplicationEvents 2.obtainFreshBeanFactory

通过该方法的返回值可以判断他就是获取了容器中内置的ConfigurableListableBeanFactory，我们来看他具体是怎么获取的：

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { refreshBeanFactory(); return getBeanFactory(); }

其中：getBeanFactory()方法是很好理解的，他就是把GenericApplicationContext中保存的DefaultListableBeanFactory返回，这个DefaultListableBeanFactor是在GenericApplicationContext的空构造器中实例化的。 我们看下refreshBeanFactory()中做了什么：

@Override protected final void refreshBeanFactory() throws IllegalStateException { //内部容器只允许refresh一次 if (!this.refreshed.compareAndSet(false, true)) { throw new IllegalStateException( "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once"); } this.beanFactory.setSerializationId(getId()); }

主要是对refreshed进行了cas修改，以保证容器只会被刷新一次

3.prepareBeanFactory(beanFactory)

容器的准备阶段

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {

// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
if (!shouldIgnoreSpel) {
    //设置el表达式解析器（#{...}）
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
}
//设置属性解析器PropertyEditorRegistrar
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
//为容器中添加一个ApplicationContextAwareProcessor，这是容器中添加的第一个BeanPostProcessor
//ApplicationContextAwareProcessor的作用：
//判断bean是否实现了下面的Aware接口，如果实现了，这把相应的内建bean或单例对象赋给该bean
//1.EnvironmentAware  -> applicationContext.getEnvironment()
//2.EmbeddedValueResolverAware -> embeddedValueResolver
//3.ResourceLoaderAware -> applicationContext
//4.ApplicationEventPublisherAware -> applicationContext
//5.MessageSourceAware -> applicationContext
//6.ApplicationContextAware -> applicationContext
//7.ApplicationStartupAware -> applicationContext.getApplicationStartup()
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
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.ignoreDependencyInterface(ApplicationStartupAware.class);
//添加容器内建依赖
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
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.
// 处理实现了ApplicationListener接口的bean
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (!NativeDetector.inNativeImage() && 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.
// 在beanFactory中注入下面的单例对象
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());
}
if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {
    beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());
}

} 设置ClassLoader 设置el表达式解析器 设置PropertyEditorRegistrar 添加一个ApplicationContextAwareProcessor判断bean是否实现了下面的Aware接口，如果实现了，这把相应的内建bean或单例对象赋给该bean 1.EnvironmentAware -> applicationContext.getEnvironment() 2.EmbeddedValueResolverAware -> embeddedValueResolver 3.ResourceLoaderAware -> applicationContext 4.ApplicationEventPublisherAware -> applicationContext 5.MessageSourceAware -> applicationContext 6.ApplicationContextAware -> applicationContext 7.ApplicationStartupAware -> applicationContext.getApplicationStartup() ignoreDependencyInterface：在自动装配时忽略下面这些接口，实现了下述接口，可以通过set方法接受aware回调传入的值进行装配如果相对electron有更多直观理解的, 也可以参考其格式如下:

页游：www.sangpi.com

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.ignoreDependencyInterface(ApplicationStartupAware.class);

添加容器内建依赖。容器的内建依赖会保存在resolvableDependencies，支持通过类型进行依赖注入，主要解决的问题是同一种类型存在多个依赖对象，spring在自动装配的时候会报错，但是如果在resolvableDependencies中指定了具体类型的装配对象，则直接可以使用指定对象。spring容器中存在多个BeanFactory等类型的对歌对象，所以这里将其依赖对象指定，避免报错。我们也可以通过自定义BeanFahttp://www.sangpi.com/ctoryPostProcessor获取Beanfactory，然后指定自己的类型-依赖对象关系。

beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);

添加ApplicationListenerDetector，DestructionAwareBeanPostProcessor：bean曝光前回调，在对外提供bean实例之前，可以返回代理对象替换beanMergedBeanDefinitionPostProcessor class ApplicationListenerDetector implements DestructionAwareBeanPostProcessor, MergedBeanDefinitionPostProcessor {

直接注册四个单例对象

// Register default environment beans.
// 在beanFactory中注入下面的单例对象
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());
}
if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {
    beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());
}

4.postProcessBeanFactory

预留的扩展方法，默认没有实现

5.invokeBeanFactoryPostProcessors(beanFactory)

关于BeanFactoryPostProcesso，我们先了解下面两点：

注册BeanFactoryPostProcessor：ConfigurableApplicationContext#addBeanFactoryPostProcessor

BeanFactoryPostProcessor的作用：

@FunctionalInterface public interface BeanFactoryPostProcessor {

/**

  • 在所有beanDefinition已经加载，且没有Bean实例化之前，修改application的内置beanFactory
  • 该方法可以支持修改beanDefinition的属性配置，甚至可以提前初始化bean
  • 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; }

简而言之，就是在第3步将内置beanfactory准备完毕之后。给用户一次机会再获取到beanFactory 接下来我们研究invokeBeanFactoryPostProcessors的流程，这里默认容器中是不会注册BeanFactoryPostProcessor的，但是这个方法还有其他的作用

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 (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); } } getBeanFactoryPostProcessors()

public List getBeanFactoryPostProcessors() { return this.beanFactoryPostProcessors; } PostProcessorRegistrationDelegate

public static void invokeBeanFactoryPostProcessors(

    ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// WARNING: Although it may appear that the body of this method can be easily
// refactored to avoid the use of multiple loops and multiple lists, the use
// of multiple lists and multiple passes over the names of processors is
// intentional. We must ensure that we honor the contracts for PriorityOrdered
// and Ordered processors. Specifically, we must NOT cause processors to be
// instantiated (via getBean() invocations) or registered in the ApplicationContext
// in the wrong order.
//
// Before submitting a pull request (PR) to change this method, please review the
// list of all declined PRs involving changes to PostProcessorRegistrationDelegate
// to ensure that your proposal does not result in a breaking change:
// %3Aclosed+label%3A%22status%3A+declined%22
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
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;
            registryProcessor.postProcessBeanDefinitionRegistry(registry);
            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.
    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();
    // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
    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();
    // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
    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();
    }
    // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
    invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
    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!
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();

} 主要流程：

创建两个list分别保存BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor 将自定义注册的BeanFactoryPostProcessor按照类型分别存入regularPostProcessors或者registryProcessors，并且：如果是BeanDefinitionRegistryPostProcessor，则直接调用其postProcessBeanDefinitionRegistry方法 创建一个新的列表来保存容器内置的BeanDefinitionRegistryPostProcessor 通过BeanDefinitionRegistryPostProcessor类型以及PriorityOrdered获取容器中对对应的bean，放入currentRegistryProcessors，并将名字放入processedBeans，表示已经执行。这里会得到一个：org.springframework.context.annotation.internalConfigurationAnnotationProcessor 将currentRegistryProcessors排序，并且放入registryProcessors 遍历执行currentRegistryProcessors中的BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法 这里会执行internalConfigurationAnnotationProcessor的回调方法，这个类后续会专项研究，其结果就是把配置类中Bean方法对应的类加载到容器中注册为bd 清空currentRegistryProcessors 重复4-8，调用的是实现了Ordered接口的BeanDefinitionRegistryPostProcessor 重复4-8，调用没有实现排序接口的BeanDefinitionRegistryPostProcessor 通过上面的操作，所有的BeanDefinitionRegistryPostProcessor都加入了registryProcessors，所有的自定义BeanFactoryPostProcessor都加入了regularPostProcessors。执行他们的postProcessBeanFactory方法 现在还有容器内置的BeanFactoryPostProcessor没有处理，也按照PriorityOrdered，Ordered，nonOrdered的顺序依次加载并调用他们的postProcessBeanFactory方法 6.initMessageSource

MessageSource列为专题讨论

7.initApplicationEventMulticaster()

事件广播机制列为专题讨论

8.onRefresh

截止到这里，整个beanfactory已经准备就绪了。剩下的就是容器中的bean的处理了，再此之前，可以通过onFresh方法执行回调。例如在SpringBoot中，就是通过这个方法进行的嵌入式web容器启动

9.registerListeners()

注册容器内置的listener 注册实现了ApplicationListener接口的类 10.inishBeanFactoryInitialization(beanFactory)

实例化所有非懒加载的单例bean 这个流程又是非常复杂的逻辑，我们放在第二章进行讨论

总结

经过上述的步骤，spring容器已经初始化完成，beanFactory准备就绪。ApplicatiionContext提供的扩展特性：事件机制，资源，AOP等能力也已经初始化完成

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