Spring在BeanFactory基础上提供了一些列具体容器的实现，其中AnnotationConfigApplicationContext是一个用来管理注解bean的容器，从AnnotationConfigApplicationContext的实现结构图中可以看出：
AnnotationConfigApplicationContext继承GenericApplicationContext这个通用应用上下文，GenericApplicationContext内部定义了一个DefaultListableBeanFactory实例，GenericApplicationContext实现了BeanDefinitionRegistry接口，所以可以通过AnnotationConfigApplicationContext实例注册bean defintion，然后调用refresh()方法来初始化上下文。
AnnotationConfigApplicationContext继承AbstractApplicationContext，AbstractApplicationContext提供了ApplicationContext的抽象实现。
下面通过一个示例分析AnnotationConfigApplicationContext的初始化过程：
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(ExtensionConfig.class);
构造函数：
1 //1. 初始化bean读取器和扫描器; 2 //调用父类GenericApplicationContext无参构造函数，初始化一个BeanFactory: DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory() 3 this(); 4 //2.注册bean配置类 5 register(annotatedClasses); 6 //3.刷新上下文 7 refresh(); 8 }
1. this() 初始化bean读取器和扫描器
1 public AnnotationConfigApplicationContext() { 2 //在IOC容器中初始化一个 注解bean读取器AnnotatedBeanDefinitionReader 3 this.reader = new AnnotatedBeanDefinitionReader(this); 4 //在IOC容器中初始化一个 按类路径扫描注解bean的 扫描器 5 this.scanner = new ClassPathBeanDefinitionScanner(this);GenericApplicationContext部分代码:
1 public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry { 2 private final DefaultListableBeanFactory beanFactory; 3 4 //初始化一个BeanFactory 5 public GenericApplicationContext() { 6 this.beanFactory = new DefaultListableBeanFactory(); 7 } 8 9 … 10 }
2. register(annotatedClasses)
注册bean配置类, AnnotationConfigApplicationContext容器通过AnnotatedBeanDefinitionReader的register方法实现注解bean的读取，具体源码如下：
AnnotationConfigApplicationContext.java中register方法
1 //按指定bean配置类读取bean 2 public void register(Class<?>... annotatedClasses) { 3 for (Class<?> annotatedClass : annotatedClasses) { 4 registerBean(annotatedClass); 5 } 6 } 7 8 public void registerBean(Class<?> annotatedClass) { 9 doRegisterBean(annotatedClass, null, null, null); 10 } 11 12 //核心实现逻辑 13 <T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name, 14 @Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) { 15 //将Bean配置类信息转成容器中AnnotatedGenericBeanDefinition数据结构, AnnotatedGenericBeanDefinition继承自BeanDefinition作用是定义一个bean的数据结构，下面的getMetadata可以获取到该bean上的注解信息 16 AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass); 17 //@Conditional装配条件判断是否需要跳过注册 18 if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) { 19 return; 20 } 21 //@param instanceSupplier a callback for creating an instance of the bean 22 //设置回调 23 abd.setInstanceSupplier(instanceSupplier); 24 //解析bean作用域(单例或者原型)，如果有@Scope注解，则解析@Scope，没有则默认为singleton 25 ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd); 26 //作用域写回BeanDefinition数据结构, abd中缺损的情况下为空，将默认值singleton重新赋值到abd 27 abd.setScope(scopeMetadata.getScopeName()); 28 //生成bean配置类beanName 29 String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry)); 30 //通用注解解析到abd结构中，主要是处理Lazy, primary DependsOn, Role ,Description这五个注解 31 AnnotationConfigUtils.processCommonDefinitionAnnotations(abd); 32 //@param qualifiers specific qualifier annotations to consider, if any, in addition to qualifiers at the bean class level 33 // @Qualifier特殊限定符处理， 34 if (qualifiers != null) { 35 for (Class<? extends Annotation> qualifier : qualifiers) { 36 if (Primary.class == qualifier) { 37 // 如果配置@Primary注解，则设置当前Bean为自动装配autowire时首选bean 38 abd.setPrimary(true); 39 } 40 else if (Lazy.class == qualifier) { 41 //设置当前bean为延迟加载 42 abd.setLazyInit(true); 43 } 44 else { 45 //其他注解，则添加到abd结构中 46 abd.addQualifier(new AutowireCandidateQualifier(qualifier)); 47 } 48 } 49 } 50 //自定义bean注册，通常用在applicationContext创建后，手动向容器中一lambda表达式的方式注册bean, 51 //比如：applicationContext.registerBean(UserService.class, () -> new UserService()); 52 for (BeanDefinitionCustomizer customizer : definitionCustomizers) { 53 //自定义bean添加到BeanDefinition 54 customizer.customize(abd); 55 } 56 //根据beanName和bean定义信息封装一个beanhold,heanhold其实就是一个 beanname和BeanDefinition的映射 57 BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName); 58 //创建代理对象 59 definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); 60 // BeanDefinitionReaderUtils.registerBeanDefinition 内部通过DefaultListableBeanFactory.registerBeanDefinition(String beanName, BeanDefinition beanDefinition)按名称将bean定义信息注册到容器中， 61 // 实际上DefaultListableBeanFactory内部维护一个Map<String, BeanDefinition>类型变量beanDefinitionMap，用于保存注bean定义信息（beanname 和 beandefine映射） 62 BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry); 63 }
register方法重点完成了bean配置类本身的解析和注册，处理过程可以分为以下几个步骤：
根据bean配置类，使用BeanDefinition解析Bean的定义信息，主要是一些注解信息
Bean作用域的处理，默认缺少@Scope注解，解析成单例
借助AnnotationConfigUtils工具类解析通用注解
将bean定义信息已beanname，beandifine键值对的形式注册到ioc容器中
3. refresh()刷新上下文
refresh方法在AbstractApplicationContext容器中实现，refresh()方法的作用加载或者刷新当前的配置信息，如果已经存在spring容器，则先销毁之前的容器，重新创建spring容器，载入bean定义，完成容器初始化工作，所以可以看出AnnotationConfigApplicationContext容器是通过调用其父类AbstractApplicationContext的refresh()函数启动整个IoC容器完成对Bean定义的载入。
AbstractApplicationContext.java中refresh方法的实现代码如下：
1 public void refresh() throws BeansException, IllegalStateException { 2 synchronized (this.startupShutdownMonitor) { 3 //1.刷新前的预处理 4 prepareRefresh(); 5 6 //2.获取刷新后的内部Bean工厂 7 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); 8 9 //3.BeanFactory的预准备工作 10 prepareBeanFactory(beanFactory); 11 12 try { 13 // BeanFactory准备工作完成后，可以做一些后置处理工作， 14 // 4.空方法，用于在容器的子类中扩展 15 postProcessBeanFactory(beanFactory); 16 17 // 5. 执行BeanFactoryPostProcessor的方法，BeanFactory的后置处理器，在BeanFactory标准初始化之后执行的 18 invokeBeanFactoryPostProcessors(beanFactory); 19 20 // 6. 注册BeanPostProcessor（Bean的后置处理器）,用于拦截bean创建过程 21 registerBeanPostProcessors(beanFactory); 22 23 // 7. 初始化MessageSource组件（做国际化功能；消息绑定，消息解析） 24 initMessageSource(); 25 26 // 8. 初始化事件派发器 27 initApplicationEventMulticaster(); 28 29 // 9.空方法，可以用于子类实现在容器刷新时自定义逻辑 30 onRefresh(); 31 32 // 10. 注册时间监听器，将所有项目里面的ApplicationListener注册到容器中来 33 registerListeners(); 34 35 // 11. 初始化所有剩下的单实例bean,单例bean在初始化容器时创建，原型bean在获取时（getbean）时创建 36 finishBeanFactoryInitialization(beanFactory); 37 38 // 12. 完成BeanFactory的初始化创建工作，IOC容器就创建完成； 39 finishRefresh(); 40 } 41 42 catch (BeansException ex) { 43 if (logger.isWarnEnabled()) { 44 logger.warn("Exception encountered during context initialization - " + 45 "cancelling refresh attempt: " + ex); 46 } 47 48 // Destroy already created singletons to avoid dangling resources. 49 destroyBeans(); 50 51 // Reset 'active' flag. 52 cancelRefresh(ex); 53 54 // Propagate exception to caller. 55 throw ex; 56 } 57 58 finally { 59 // Reset common introspection caches in Spring's core, since we 60 // might not ever need metadata for singleton beans anymore... 61 resetCommonCaches(); 62 } 63 } 64 }
具体分析refresh中的函数逻辑：
1. 刷新预处理：
AbstractApplicationContext. prepareRefresh ()方法:
1 protected void prepareRefresh() { 2 //设置容器启动时间 3 this.startupDate = System.currentTimeMillis(); 4 //启动标识 5 this.closed.set(false); 6 this.active.set(true); 7 8 if (logger.isInfoEnabled()) { 9 logger.info("Refreshing " + this); 10 } 11 12 //空方法，用于子容器自定义个性化的属性设置方法 13 initPropertySources(); 14 //检验属性的合法等 15 getEnvironment().validateRequiredProperties(); 16 17 //保存容器中的一些早期的事件 18 this.earlyApplicationEvents = new LinkedHashSet<>(); 19 }
2. 获取刷新后的内部Bean工厂，obtainFreshBeanFactory方法为内部bean工厂重新生成id，并返回bean工厂
AbstractApplicationContext. obtainFreshBeanFactory()方法
1 protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { 2 //为beanfactory生成唯一序列化id，beanfactory已经在GenericApplicationContext构造函数中初始化了，refreshBeanFactory的逻辑在AbstractApplicationContext的实现类GenericApplicationContext中 3 refreshBeanFactory(); 4 //获取beanfactory 5 ConfigurableListableBeanFactory beanFactory = getBeanFactory(); 6 if (logger.isDebugEnabled()) { 7 logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); 8 } 9 return beanFactory; 10 }
GenericApplicationContext.refreshBeanFactory()实现代码
1 protected final void refreshBeanFactory() throws IllegalStateException { 2 if (!this.refreshed.compareAndSet(false, true)) { 3 throw new IllegalStateException( 4 "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once"); 5 } 6 //生成一个序列化id 7 this.beanFactory.setSerializationId(getId()); 8 }
这里使用AbstractApplicationContext. refreshBeanFactory()在不同实现容器中有点区别，如果是以xml方式配置bean，会使用AbstractRefreshableApplicationContext容器中的实现，该容器中实现xml配置文件定位，并通过BeanDefinition载入和解析xml配置文件。
而如果是注解的方式，则并没有解析项目包下的注解，而是通过在refresh()方法中执行ConfigurationClassPostProcessor后置处理器完成对bean的加载.
3.BeanFactory的预准备工作
prepareBeanFactory主要完成beanFactory的一些属性设置
1 protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) { 2 // Tell the internal bean factory to use the context's class loader etc. 3 beanFactory.setBeanClassLoader(getClassLoader()); //设置类加载器 4 beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader())); //bean表达式解析器 5 beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment())); 6 7 // Configure the bean factory with context callbacks. 8 beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); //添加一个BeanPostProcessor实现ApplicationContextAwareProcessor 9 //设置忽略的自动装配接口，表示这些接口的实现类不允许通过接口自动注入 10 beanFactory.ignoreDependencyInterface(EnvironmentAware.class); 11 beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class); 12 beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class); 13 beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class); 14 beanFactory.ignoreDependencyInterface(MessageSourceAware.class); 15 beanFactory.ignoreDependencyInterface(ApplicationContextAware.class); 16 17 // BeanFactory interface not registered as resolvable type in a plain factory. 18 // MessageSource registered (and found for autowiring) as a bean. 19 //注册可以自动装配的组件，就是可以在任何组件中允许自动注入的组件 20 beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory); 21 beanFactory.registerResolvableDependency(ResourceLoader.class, this); 22 beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this); 23 beanFactory.registerResolvableDependency(ApplicationContext.class, this); 24 25 // Register early post-processor for detecting inner beans as ApplicationListeners. 26 beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this)); 27 28 //添加编译时的AspectJ 29 if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { 30 beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); 31 // Set a temporary ClassLoader for type matching. 32 beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); 33 } 34 35 // 给beanfactory容器中注册组件ConfigurableEnvironment、systemProperties、systemEnvironment 36 if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) { 37 beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment()); 38 } 39 if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) { 40 beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties()); 41 } 42 if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) { 43 beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment()); 44 } 45 }
5.invokeBeanFactoryPostProcessors 执行bean工厂后置处理器
AbstractApplicationContext. invokeBeanFactoryPostProcessors方法实现：
1 protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) { 2 PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()); 3 4 // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime 5 // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor) 6 if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { 7 beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); 8 beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); 9 } 10 }
invokeBeanFactoryPostProcessors方法内部执行实现了BeanFactoryPostProcessor、BeanDefinitionRegistryPostProcessor这两个接口的Processor，先获取所有BeanDefinitionRegistryPostProcessor的实现，按优先级执行（是否实现PriorityOrdered优先级接口，是否实现Ordered顺序接口）；再以相同的策略执行所有BeanFactoryPostProcessor的实现。
PostProcessorRegistrationDelegate. invokeBeanFactoryPostProcessors实现:
1 public static void invokeBeanFactoryPostProcessors( 2 ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) { 3 4 // Invoke BeanDefinitionRegistryPostProcessors first, if any. 5 Set<String> processedBeans = new HashSet<>(); 6 7 if (beanFactory instanceof BeanDefinitionRegistry) { 8 BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; 9 List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>(); 10 List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>(); 11 12 for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { 13 if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { 14 BeanDefinitionRegistryPostProcessor registryProcessor = 15 (BeanDefinitionRegistryPostProcessor) postProcessor; 16 registryProcessor.postProcessBeanDefinitionRegistry(registry); 17 registryProcessors.add(registryProcessor); 18 } 19 else { 20 regularPostProcessors.add(postProcessor); 21 } 22 } 23 24 // Do not initialize FactoryBeans here: We need to leave all regular beans 25 // uninitialized to let the bean factory post-processors apply to them! 26 // Separate between BeanDefinitionRegistryPostProcessors that implement 27 // PriorityOrdered, Ordered, and the rest. 28 List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>(); 29 30 // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered. 31 String[] postProcessorNames = 32 beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); 33 for (String ppName : postProcessorNames) { 34 if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { 35 currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); 36 processedBeans.add(ppName); 37 } 38 } 39 sortPostProcessors(currentRegistryProcessors, beanFactory); 40 registryProcessors.addAll(currentRegistryProcessors); 41 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); 42 currentRegistryProcessors.clear(); 43 44 // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered. 45 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); 46 for (String ppName : postProcessorNames) { 47 if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) { 48 currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); 49 processedBeans.add(ppName); 50 } 51 } 52 sortPostProcessors(currentRegistryProcessors, beanFactory); 53 registryProcessors.addAll(currentRegistryProcessors); 54 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); 55 currentRegistryProcessors.clear(); 56 57 // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear. 58 boolean reiterate = true; 59 while (reiterate) { 60 reiterate = false; 61 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); 62 for (String ppName : postProcessorNames) { 63 if (!processedBeans.contains(ppName)) { 64 currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); 65 processedBeans.add(ppName); 66 reiterate = true; 67 } 68 } 69 sortPostProcessors(currentRegistryProcessors, beanFactory); 70 registryProcessors.addAll(currentRegistryProcessors); 71 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); 72 currentRegistryProcessors.clear(); 73 } 74 75 // Now, invoke the postProcessBeanFactory callback of all processors handled so far. 76 invokeBeanFactoryPostProcessors(registryProcessors, beanFactory); 77 invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory); 78 } 79 80 else { 81 // Invoke factory processors registered with the context instance. 82 invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory); 83 } 84 85 // Do not initialize FactoryBeans here: We need to leave all regular beans 86 // uninitialized to let the bean factory post-processors apply to them! 87 String[] postProcessorNames = 88 beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false); 89 90 // Separate between BeanFactoryPostProcessors that implement PriorityOrdered, 91 // Ordered, and the rest. 92 List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); 93 List<String> orderedPostProcessorNames = new ArrayList<>(); 94 List<String> nonOrderedPostProcessorNames = new ArrayList<>(); 95 for (String ppName : postProcessorNames) { 96 if (processedBeans.contains(ppName)) { 97 // skip - already processed in first phase above 98 } 99 else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { 100 priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class)); 101 } 102 else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { 103 orderedPostProcessorNames.add(ppName); 104 } 105 else { 106 nonOrderedPostProcessorNames.add(ppName); 107 } 108 } 109 110 // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered. 111 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); 112 invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); 113 114 // Next, invoke the BeanFactoryPostProcessors that implement Ordered. 115 List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(); 116 for (String postProcessorName : orderedPostProcessorNames) { 117 orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); 118 } 119 sortPostProcessors(orderedPostProcessors, beanFactory); 120 invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); 121 122 // Finally, invoke all other BeanFactoryPostProcessors. 123 List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(); 124 for (String postProcessorName : nonOrderedPostProcessorNames) { 125 nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); 126 } 127 invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory); 128 129 // Clear cached merged bean definitions since the post-processors might have 130 // modified the original metadata, e.g. replacing placeholders in values... 131 beanFactory.clearMetadataCache(); 132 }
这里面在处理BeanDefinitionRegistryPostProcessors时有一个非常重要的过程，AnnotationConfigApplicationContext构造函数在初始化reader时为内部beanFactory容器初始化了一个id为org.springframework.context.annotation.internalConfigurationAnnotationProcessor的组件，这是一个ConfigurationClassPostProcessor组件，用来处理添加@Configuration注解的类，并将Bean定义注册到BeanFactory中。
6.注册BeanPostProcessor（Bean的后置处理器）,用于拦截bean创建过程
注册后置处理器的大致逻辑是：
1.获取所有的 BeanPostProcessor
2.根据处理器实现的接口区分出4中类型：
a.实现PriorityOrdered接口的处理器
b.实现Ordered接口的处理器，
c.实现MergedBeanDefinitionPostProcessor接口的处理器，
d.普通后置处理器
3.按这个4中类型依次注册到容器中
4.注册一个特殊的后置处理器ApplicationListenerDetector，ApplicationListenerDetector本身也实现了MergedBeanDefinitionPostProcessor接口，有个问题，这个为什么没有在上面c,d之间注册，而是放到最后？
AbstractApplicationContext .registerBeanPostProcessors(beanFactory);实现逻辑：
1 protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) { 2 PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this); 3 }
1 public static void registerBeanPostProcessors( 2 ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) { 3 4 String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false); 5 6 // Register BeanPostProcessorChecker that logs an info message when 7 // a bean is created during BeanPostProcessor instantiation, i.e. when 8 // a bean is not eligible for getting processed by all BeanPostProcessors. 9 int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length; 10 beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)); 11 12 // Separate between BeanPostProcessors that implement PriorityOrdered, 13 // Ordered, and the rest. 14 //按优先级分类 15 List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); 16 List<BeanPostProcessor> internalPostProcessors = new ArrayList<>(); 17 List<String> orderedPostProcessorNames = new ArrayList<>(); 18 List<String> nonOrderedPostProcessorNames = new ArrayList<>(); 19 for (String ppName : postProcessorNames) { 20 if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { 21 BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); 22 priorityOrderedPostProcessors.add(pp); 23 if (pp instanceof MergedBeanDefinitionPostProcessor) { 24 internalPostProcessors.add(pp); 25 } 26 } 27 else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { 28 orderedPostProcessorNames.add(ppName); 29 } 30 else { 31 nonOrderedPostProcessorNames.add(ppName); 32 } 33 } 34 35 //先注册实现PriorityOrdered接口的处理器，添加到beanfactory容器中beanFactory.addBeanPostProcessor(postProcessor); 36 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); 37 registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors); 38 39 //注册实现Ordered接口的处理器 40 List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(); 41 for (String ppName : orderedPostProcessorNames) { 42 BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); 43 orderedPostProcessors.add(pp); 44 if (pp instanceof MergedBeanDefinitionPostProcessor) { 45 internalPostProcessors.add(pp); 46 } 47 } 48 sortPostProcessors(orderedPostProcessors, beanFactory); 49 registerBeanPostProcessors(beanFactory, orderedPostProcessors); 50 51 // 注册没有实现Ordered或PriorityOrdered的处理器（nonOrderedPostProcessors） 52 List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(); 53 for (String ppName : nonOrderedPostProcessorNames) { 54 BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); 55 nonOrderedPostProcessors.add(pp); 56 if (pp instanceof MergedBeanDefinitionPostProcessor) { 57 internalPostProcessors.add(pp); 58 } 59 } 60 registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors); 61 62 // Finally, re-register all internal BeanPostProcessors. 63 //最后，重新注册所有internal BeanPostProcessors（实现MergedBeanDefinitionPostProcessor接口的后置处理器 64 65 sortPostProcessors(internalPostProcessors, beanFactory); 66 registerBeanPostProcessors(beanFactory, internalPostProcessors); 67 68 //注册ApplicationListenerDetector，用于Bean创建完时检查是否是ApplicationListener 69 beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext)); 70 }
7.初始化MessageSource组件（做国际化功能；消息绑定，消息解析）
AbstractApplicationContext .initMessageSource()方法实现代码：
1 protected void initMessageSource() { 2 //获取beanFactory 3 ConfigurableListableBeanFactory beanFactory = getBeanFactory(); 4 //判断是否已经存在id为MESSAGE_SOURCE_BEAN_NAME的组件 5 if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) { 6 this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class); 7 // Make MessageSource aware of parent MessageSource. 8 if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) { 9 HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource; 10 if (hms.getParentMessageSource() == null) { 11 // Only set parent context as parent MessageSource if no parent MessageSource 12 // registered already. 13 hms.setParentMessageSource(getInternalParentMessageSource()); 14 } 15 } 16 if (logger.isDebugEnabled()) { 17 logger.debug("Using MessageSource [" + this.messageSource + "]"); 18 } 19 } 20 else { 21 // Use empty MessageSource to be able to accept getMessage calls. 22 DelegatingMessageSource dms = new DelegatingMessageSource(); 23 dms.setParentMessageSource(getInternalParentMessageSource()); 24 this.messageSource = dms; 25 beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource); 26 if (logger.isDebugEnabled()) { 27 logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME + 28 "': using default [" + this.messageSource + "]"); 29 } 30 } 31 }
8.初始化事件派发器
AbstractApplicationContext .initApplicationEventMulticaster()方法实现逻辑
1 protected void initApplicationEventMulticaster() { 2 //获取BeanFactory 3 ConfigurableListableBeanFactory beanFactory = getBeanFactory(); 4 //如果有配置beanName为applicationEventMulticaster的事件派发器，则将其赋给容器中的applicationEventMulticaster对象 5 if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) { 6 this.applicationEventMulticaster = 7 beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class); 8 if (logger.isDebugEnabled()) { 9 logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]"); 10 } 11 } 12 else { 13 //不存在，则创建一个SimpleApplicationEventMulticaster事件派发器，并注册到beanfactory中 14 this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory); 15 beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster); 16 if (logger.isDebugEnabled()) { 17 logger.debug("Unable to locate ApplicationEventMulticaster with name '" + 18 APPLICATION_EVENT_MULTICASTER_BEAN_NAME + 19 "': using default [" + this.applicationEventMulticaster + "]"); 20 } 21 } 22 }
10. 注册时间监听器，将项目里面的ApplicationListener注册到容器中来
registerListeners方法主要实现将事件监听器添加到IOC容器中的事件派发器中，并在最后做了一个事件发布的逻辑(如果之前的步骤有产生事件，则将earlyApplicationEvents中保存的事件逐一发布)
AbstractApplicationContext .registerListeners()方法实现逻辑：
1 protected void registerListeners() { 2 // Register statically specified listeners first. 3 for (ApplicationListener<?> listener : getApplicationListeners()) { 4 getApplicationEventMulticaster().addApplicationListener(listener); 5 } 6 7 // Do not initialize FactoryBeans here: We need to leave all regular beans 8 // uninitialized to let post-processors apply to them! 9 String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false); 10 for (String listenerBeanName : listenerBeanNames) { 11 getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName); 12 } 13 14 // Publish early application events now that we finally have a multicaster... 15 Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents; 16 this.earlyApplicationEvents = null; 17 if (earlyEventsToProcess != null) { 18 for (ApplicationEvent earlyEvent : earlyEventsToProcess) { 19 getApplicationEventMulticaster().multicastEvent(earlyEvent); 20 } 21 } 22 }
11. 初始化所有剩下的单实例bean,单例bean在初始化容器时创建，原型bean在获取时（getbean）时创建
AbstractApplicationContext.finishBeanFactoryInitialization(beanFactory);方法实现代码：
1 protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { 2 //组件转换器相关 3 if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) && 4 beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { 5 beanFactory.setConversionService( 6 beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)); 7 } 8 9 // Register a default embedded value resolver if no bean post-processor 10 // (such as a PropertyPlaceholderConfigurer bean) registered any before: 11 // at this point, primarily for resolution in annotation attribute values. 12 if (!beanFactory.hasEmbeddedValueResolver()) { 13 beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal)); 14 } 15 16 //aspectj相关. 17 String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); 18 for (String weaverAwareName : weaverAwareNames) { 19 getBean(weaverAwareName); 20 } 21 22 // Stop using the temporary ClassLoader for type matching. 23 beanFactory.setTempClassLoader(null); 24 25 // Allow for caching all bean definition metadata, not expecting further changes. 26 beanFactory.freezeConfiguration(); 27 28 // 初始化后剩下的单实例bean 29 beanFactory.preInstantiateSingletons(); 30 }
DefaultListableBeanFactory. preInstantiateSingletons()方法实现逻辑：
1 public void preInstantiateSingletons() throws BeansException { 2 if (logger.isDebugEnabled()) { 3 logger.debug("Pre-instantiating singletons in " + this); 4 } 5 6 // Iterate over a copy to allow for init methods which in turn register new bean definitions. 7 // While this may not be part of the regular factory bootstrap, it does otherwise work fine. 8 //容器中所有bean名称 9 List<String> beanNames = new ArrayList<>(this.beanDefinitionNames); 10 11 // Trigger initialization of all non-lazy singleton beans... 12 for (String beanName : beanNames) { 13 //获取Bean的定义信息；RootBeanDefinition 14 RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); 15 //非抽象，单例，非延迟加载 16 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { 17 //是否是FactoryBean 18 if (isFactoryBean(beanName)) { 19 // 通过"&beanName"获取工厂Bean实例 20 Object bean = getBean(FACTORY_BEAN_PREFIX + beanName); 21 if (bean instanceof FactoryBean) { 22 final FactoryBean<?> factory = (FactoryBean<?>) bean; 23 boolean isEagerInit; 24 if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) { 25 isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>) 26 ((SmartFactoryBean<?>) factory)::isEagerInit, 27 getAccessControlContext()); 28 } 29 else { 30 isEagerInit = (factory instanceof SmartFactoryBean && 31 ((SmartFactoryBean<?>) factory).isEagerInit()); 32 } 33 if (isEagerInit) { 34 getBean(beanName); 35 } 36 } 37 } 38 else { 39 //不是FactoryBean,则利用getBean(beanName)实例化bean 40 getBean(beanName); 41 } 42 } 43 } 44 45 // Trigger post-initialization callback for all applicable beans... 46 for (String beanName : beanNames) { 47 Object singletonInstance = getSingleton(beanName); 48 if (singletonInstance instanceof SmartInitializingSingleton) { 49 final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance; 50 if (System.getSecurityManager() != null) { 51 AccessController.doPrivileged((PrivilegedAction<Object>) () -> { 52 smartSingleton.afterSingletonsInstantiated(); 53 return null; 54 }, getAccessControlContext()); 55 } 56 else { 57 smartSingleton.afterSingletonsInstantiated(); 58 } 59 } 60 } 61 }
12. 完成BeanFactory的初始化创建工作，IOC容器就创建完成
AbstractApplicationContext.finishRefresh()实现逻辑：
1 protected void finishRefresh() { 2 // Clear context-level resource caches (such as ASM metadata from scanning). 3 clearResourceCaches(); 4 5 //初始化和生命周期有关的后置处理器LifecycleProcessor，默认DefaultLifecycleProcessor 6 initLifecycleProcessor(); 7 8 // 回调生命周期处理器 9 getLifecycleProcessor().onRefresh(); 10 11 //发布容器刷新完成事件：ContextRefreshedEvent 12 publishEvent(new ContextRefreshedEvent(this)); 13 14 LiveBeansView.registerApplicationContext(this); 15 }
以上基本分析了AnnotationConfigApplicationContext容器的初始化过程， Spring容器在启动过程中，会先保存所有注册进来的Bean的定义信息；Spring容器根据条件创建Bean实例，区分单例，还是原型，后置处理器等（后置处理器会在容器创建过程中通过getBean创建，并执行相应的逻辑）；Spring容器在创建bean实例后，会使用多种后置处理器来增加bean的功能，比如处理自动注入，AOP，异步，这种后置处理器机制也丰富了bean的功能。
原文出处：https://www.cnblogs.com/ashleyboy/p/9662119.html
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