Spring源码解析 – AnnotationConfigApplicationContext容器创建过程

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. 初始化bean读取器和扫描器;
    //调用父类GenericApplicationContext无参构造函数，初始化一个BeanFactory: DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory()
   this();
//2.注册bean配置类
   register(annotatedClasses);
//3.刷新上下文
   refresh();
} 

1. this() 初始化bean读取器和扫描器

public AnnotationConfigApplicationContext() {
    //在IOC容器中初始化一个 注解bean读取器AnnotatedBeanDefinitionReader
   this.reader = new AnnotatedBeanDefinitionReader(this);
   //在IOC容器中初始化一个 按类路径扫描注解bean的 扫描器
   this.scanner = new ClassPathBeanDefinitionScanner(this);

父类GenericApplicationContext部分代码:

public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry {
private final DefaultListableBeanFactory beanFactory;

//初始化一个BeanFactory
public GenericApplicationContext() {
      this.beanFactory = new DefaultListableBeanFactory();
    }

    …
}

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

//按指定bean配置类读取bean
public void register(Class<?>... annotatedClasses) {
   for (Class<?> annotatedClass : annotatedClasses) {
      registerBean(annotatedClass);
   }
}

public void registerBean(Class<?> annotatedClass) {
   doRegisterBean(annotatedClass, null, null, null);
}

//核心实现逻辑
<T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name,
      @Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
    //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
   AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
    //@Conditional装配条件判断是否需要跳过注册
   if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
      return;
   }
   //@param instanceSupplier a callback for creating an instance of the bean
   //设置回调
   abd.setInstanceSupplier(instanceSupplier);
   //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 
   ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
　　//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
   abd.setScope(scopeMetadata.getScopeName());
　　//生成bean配置类beanName
   String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
   //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
   AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
　　//@param qualifiers specific qualifier annotations to consider, if any, in addition to qualifiers at the bean class level
　　// @Qualifier特殊限定符处理，
   if (qualifiers != null) {
      for (Class<? extends Annotation> qualifier : qualifiers) {
         if (Primary.class == qualifier) {
    // 如果配置@Primary注解，则设置当前Bean为自动装配autowire时首选bean
            abd.setPrimary(true);
         }
　　else if (Lazy.class == qualifier) {
　　//设置当前bean为延迟加载
            abd.setLazyInit(true);
         }
         else {
　　　　　　//其他注解，则添加到abd结构中
            abd.addQualifier(new AutowireCandidateQualifier(qualifier));
         }
      }
   }
　　//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, 
　　//比如：applicationContext.registerBean(UserService.class, () -> new UserService());
   for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
53　　　　 //自定义bean添加到BeanDefinition
      customizer.customize(abd);
   }
   //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
   BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
　　//创建代理对象
   definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
　　// 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，
　　// 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）
   BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}

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：

1. 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
2. Bean作用域的处理，默认缺少@Scope注解，解析成单例
3. 借助AnnotationConfigUtils工具类解析通用注解
4. 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，debug进源码可以看出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：

public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      //1.刷新上下文前的预处理
      prepareRefresh();

      //2.获取刷新后的内部Bean工厂
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      //3.BeanFactory的预准备工作
      prepareBeanFactory(beanFactory);

      try {
         // BeanFactory准备工作完成后，可以做一些后置处理工作，
　　　　  // 4.空方法，用于在容器的子类中扩展
         postProcessBeanFactory(beanFactory);

         // 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
         invokeBeanFactoryPostProcessors(beanFactory);

         // 6. 注册BeanPostProcessor（Bean的后置处理器）,用于拦截bean创建过程
         registerBeanPostProcessors(beanFactory);

         // 7. 初始化MessageSource组件（做国际化功能；消息绑定，消息解析）
         initMessageSource();

         // 8. 初始化事件派发器
         initApplicationEventMulticaster();

         // 9.空方法，可以用于子类实现在容器刷新时自定义逻辑
         onRefresh();

         // 10. 注册时间监听器，将所有项目里面的ApplicationListener注册到容器中来
         registerListeners();

         // 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
         finishBeanFactoryInitialization(beanFactory);

         // 12. 完成BeanFactory的初始化创建工作，IOC容器就创建完成；
         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.
         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...
         resetCommonCaches();
      }
   }
}

具体分析refresh中的函数逻辑：

1.   刷新上线文前的预处理 prepareRefresh()：

AbstractApplicationContext. prepareRefresh ()方法:

protected void prepareRefresh() {
　　//设置容器启动时间
   this.startupDate = System.currentTimeMillis();
　　//启动标识
   this.closed.set(false);
   this.active.set(true);

   if (logger.isInfoEnabled()) {
      logger.info("Refreshing " + this);
   }

   //空方法，用于子容器自定义个性化的属性设置方法
   initPropertySources();
   //检验属性的合法等
   getEnvironment().validateRequiredProperties();

   //保存容器中的一些早期的事件
   this.earlyApplicationEvents = new LinkedHashSet<>();
}

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

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
　　//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
 refreshBeanFactory();
 4　　 //获取beanfactory
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   if (logger.isDebugEnabled()) {
      logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
   }
   return beanFactory;
}

GenericApplicationContext.refreshBeanFactory()实现代码

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");
   }
　　//生成一个序列化id
   this.beanFactory.setSerializationId(getId());
}

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(beanFactory):

 prepareBeanFactory主要完成beanFactory的一些属性设置

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
   // Tell the internal bean factory to use the context's class loader etc.
   beanFactory.setBeanClassLoader(getClassLoader());  //设置类加载器
   beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader())); //bean表达式解析器
   beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

   // Configure the bean factory with context callbacks.
   beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));  //添加一个BeanPostProcessor实现ApplicationContextAwareProcessor
//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
   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.
//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
   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.
   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

   //添加编译时的AspectJ
   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()));
   }

   // 给beanfactory容器中注册组件ConfigurableEnvironment、systemProperties、systemEnvironment
   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());
   }
}

5.执行bean工厂的后置处理器 invokeBeanFactoryPostProcessors（beanFactory）

    IOC容器初始化过程中有三个重要的步骤，

          1：资源定位，2：bean定义的载入，3：将bean名称、bean定义以key-value形式注册到容器，这三个步骤都将在此完成。

 AbstractApplicationContext. invokeBeanFactoryPostProcessors方法实现：

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()));
   }
}

invokeBeanFactoryPostProcessors（beanFactory，getBeanFactoryPostProcessors()）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:

public static void invokeBeanFactoryPostProcessors(
      ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

   // 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);
      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);
      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);
         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<>();
   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...
   beanFactory.clearMetadataCache();
}

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。

invokeBeanFactoryPostProcessors的实现过程是较复杂，一路debug可以发现最终在org.springframework.context.annotation.ComponentScanAnnotationParser#parse方法完成第一步：【资源文件的定位】，其实就是拿到配置类的所在的包名：

 继续查看doScan方法源码：

    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        Assert.notEmpty(basePackages, "At least one base package must be specified");
        Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
        for (String basePackage : basePackages) {
            //从指定的包中扫描需要装载的类（bean）
            Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
            for (BeanDefinition candidate : candidates) {
                ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
                candidate.setScope(scopeMetadata.getScopeName());
                String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
                if (candidate instanceof AbstractBeanDefinition) {
                    postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
                }
                if (candidate instanceof AnnotatedBeanDefinition) {
                    AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
                }
                if (checkCandidate(beanName, candidate)) {
                    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                    definitionHolder =
                            AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                    beanDefinitions.add(definitionHolder);
                    //将扫描出的bean定义注册到IOC容器的beanDefinitionMap中
                    registerBeanDefinition(definitionHolder, this.registry);
                }
            }
        }
        return beanDefinitions;
    }

可以看到这个方法完成了第二和第三步，findCandidateComponents（basePackages）根据指定的扫描路径扫描并解析成beandefine, 后面通过registerBeanDefinition(definitionHolder,this.regsistry)将这些beandefine注册到IOC容器，及添加到IOC容器的beanDefinitionMap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：

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

public static void registerBeanPostProcessors(
      ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

   String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

   // Register BeanPostProcessorChecker that logs an info message when
   // a bean is created during BeanPostProcessor instantiation, i.e. when
   // a bean is not eligible for getting processed by all BeanPostProcessors.
   int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
   beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

   // Separate between BeanPostProcessors that implement PriorityOrdered,
   // Ordered, and the rest.
//按优先级分类
   List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
   List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
   List<String> orderedPostProcessorNames = new ArrayList<>();
   List<String> nonOrderedPostProcessorNames = new ArrayList<>();
   for (String ppName : postProcessorNames) {
      if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
         BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
         priorityOrderedPostProcessors.add(pp);
         if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
         }
      }
      else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
         orderedPostProcessorNames.add(ppName);
      }
      else {
         nonOrderedPostProcessorNames.add(ppName);
      }
   }

   //先注册实现PriorityOrdered接口的处理器，添加到beanfactory容器中beanFactory.addBeanPostProcessor(postProcessor);
   sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

   //注册实现Ordered接口的处理器
   List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
   for (String ppName : orderedPostProcessorNames) {
      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
      orderedPostProcessors.add(pp);
      if (pp instanceof MergedBeanDefinitionPostProcessor) {
         internalPostProcessors.add(pp);
      }
   }
   sortPostProcessors(orderedPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, orderedPostProcessors);

   // 注册没有实现Ordered或PriorityOrdered的处理器（nonOrderedPostProcessors）
   List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
   for (String ppName : nonOrderedPostProcessorNames) {
      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
      nonOrderedPostProcessors.add(pp);
      if (pp instanceof MergedBeanDefinitionPostProcessor) {
         internalPostProcessors.add(pp);
      }
   }
   registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

   // Finally, re-register all internal BeanPostProcessors.
　　//最后，重新注册所有internal BeanPostProcessors（实现MergedBeanDefinitionPostProcessor接口的后置处理器
65    sortPostProcessors(internalPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, internalPostProcessors);

   //注册ApplicationListenerDetector，用于Bean创建完时检查是否是ApplicationListener
   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

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：

protected void initMessageSource() {
//获取beanFactory
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
//判断是否已经存在id为MESSAGE_SOURCE_BEAN_NAME的组件
   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.isDebugEnabled()) {
         logger.debug("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.isDebugEnabled()) {
         logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
               "': using default [" + this.messageSource + "]");
      }
   }
}

8.初始化事件派发器

 AbstractApplicationContext .initApplicationEventMulticaster()方法实现逻辑

protected void initApplicationEventMulticaster() {
//获取BeanFactory
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
//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
   if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
      this.applicationEventMulticaster =
            beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
      if (logger.isDebugEnabled()) {
         logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
      }
   }
   else {
//不存在，则创建一个SimpleApplicationEventMulticaster事件派发器，并注册到beanfactory中
      this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
      beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
      if (logger.isDebugEnabled()) {
         logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
               APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
               "': using default [" + this.applicationEventMulticaster + "]");
      }
   }
}

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：

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<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
   this.earlyApplicationEvents = null;
   if (earlyEventsToProcess != null) {
      for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
         getApplicationEventMulticaster().multicastEvent(earlyEvent);
      }
   }
}

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：

 

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
   //组件转换器相关
   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));
   }

   //aspectj相关.
   String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
   for (String weaverAwareName : weaverAwareNames) {
      getBean(weaverAwareName);
   }

   // Stop using the temporary ClassLoader for type matching.
   beanFactory.setTempClassLoader(null);

   // Allow for caching all bean definition metadata, not expecting further changes.
   beanFactory.freezeConfiguration();

   // 初始化后剩下的单实例bean
   beanFactory.preInstantiateSingletons();
}

DefaultListableBeanFactory. preInstantiateSingletons()方法实现逻辑：

public void preInstantiateSingletons() throws BeansException {
   if (logger.isDebugEnabled()) {
      logger.debug("Pre-instantiating singletons in " + this);
   }

   // Iterate over a copy to allow for init methods which in turn register new bean definitions.
   // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
　　//容器中所有bean名称
   List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

   // Trigger initialization of all non-lazy singleton beans...
   for (String beanName : beanNames) {
　　//获取Bean的定义信息；RootBeanDefinition
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
　　//非抽象，单例，非延迟加载
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
　　//是否是FactoryBean
         if (isFactoryBean(beanName)) {
    // 通过"&beanName"获取工厂Bean实例
            Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
            if (bean instanceof FactoryBean) {
               final FactoryBean<?> factory = (FactoryBean<?>) bean;
               boolean isEagerInit;
               if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                  isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
                              ((SmartFactoryBean<?>) factory)::isEagerInit,
                        getAccessControlContext());
               }
               else {
                  isEagerInit = (factory instanceof SmartFactoryBean &&
                        ((SmartFactoryBean<?>) factory).isEagerInit());
               }
               if (isEagerInit) {
                  getBean(beanName);
               }
            }
         }
         else {
　　　　　　//不是FactoryBean,则利用getBean(beanName)实例化bean 
            getBean(beanName);
         }
      }
   }

   // Trigger post-initialization callback for all applicable beans...
   for (String beanName : beanNames) {
      Object singletonInstance = getSingleton(beanName);
      if (singletonInstance instanceof SmartInitializingSingleton) {
         final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
         if (System.getSecurityManager() != null) {
            AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
               smartSingleton.afterSingletonsInstantiated();
               return null;
            }, getAccessControlContext());
         }
         else {
            smartSingleton.afterSingletonsInstantiated();
         }
      }
   }
}

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：

protected void finishRefresh() {
   // Clear context-level resource caches (such as ASM metadata from scanning).
   clearResourceCaches();

   //初始化和生命周期有关的后置处理器LifecycleProcessor，默认DefaultLifecycleProcessor
   initLifecycleProcessor();

   // 回调生命周期处理器
   getLifecycleProcessor().onRefresh();

   //发布容器刷新完成事件：ContextRefreshedEvent
   publishEvent(new ContextRefreshedEvent(this));

   LiveBeansView.registerApplicationContext(this);
}

　　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。