new AnnotationConfigApplicationContext(MyBean.class)时，发生了什么？

当我们run一段代码，像下面这样两行。spring究竟做了什么些，让整个容器准备就绪，交付给用户直接可用的各种特性。为了弄清楚，默默梳理记录下来。

public static void main (String[] args) {
    AnnotationConfigApplicationContext c = new AnnotationConfigApplicationContext(MyBean.class);
    c.getBean(MyBean.class).getS();
}

首先来看下 Annotationconfigapplicationcontext 的uml图

涉及到几个比较关键的类：GenericApplicationContext，AbstractApplicationContext，DefaultResourceLoader

几个很重要的接口：ApplicationContext，ApplicationEventPubliser，BeanFactory，ListableBeanFactory，BeanDefinitionRegistory，ResourceLoader。好复杂是不是，没关系，先放一放。我们直接进入代码看看。

第一步当然是构造函数，AnnotationConfigApplication的初始化必然会先初始化父类，看看GenericApplication和AbstractApplicationContext初始化做了些什么。

0.AnnotationConfigApplication的构造函数。

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

先看 this() ：

同时初始化了 AnnotationBeanDefinitionReader
和 ClasspathBeanDefinitionScanner 这两个类各自去创建bean生成的环境。

public AnnotationConfigApplicationContext() {
   this.reader = new AnnotatedBeanDefinitionReader(this);
   this.scanner = new ClassPathBeanDefinitionScanner(this);
}

进入：AnnotatedBeanDefinitionReader

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
   this(registry, getOrCreateEnvironment(registry));//构造了 StandardEnvironment 

}

进入：ClassPathBeanDefinitionScanner

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry) {
   this(registry, true);
}

调用

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) {
   this(registry, useDefaultFilters, getOrCreateEnvironment(registry));
}

调用

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
      Environment environment, ResourceLoader resourceLoader) {

   Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
   this.registry = registry;

   if (useDefaultFilters) {
      registerDefaultFilters();//注册默认的过滤器 包括 component，jsr-250的ManageBean,jsr-330的Named
   }
   setEnvironment(environment);
   setResourceLoader(resourceLoader);
}

/**
 * Register the default filter for {@link Component @Component}.
 * <p>This will implicitly register all annotations that have the
 * {@link Component @Component} meta-annotation including the
 * {@link Repository @Repository}, {@link Service @Service}, and
 * {@link Controller @Controller} stereotype annotations.
 * <p>Also supports Java EE 6's {@link javax.annotation.ManagedBean} and
 * JSR-330's {@link javax.inject.Named} annotations, if available.
 *
 */
@SuppressWarnings("unchecked")
protected void registerDefaultFilters() {
   this.includeFilters.add(new AnnotationTypeFilter(Component.class));
   ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
   try {
      this.includeFilters.add(new AnnotationTypeFilter(
            ((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
      logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
   }
   catch (ClassNotFoundException ex) {
      // JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
   }
   try {
      this.includeFilters.add(new AnnotationTypeFilter(
            ((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
      logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
   }
   catch (ClassNotFoundException ex) {
      // JSR-330 API not available - simply skip.
   }
}

在看父类的构造函数。

1.进入 GenericApplicationContext
初始化了默认的beanfactory：DefaultListableBeanFactory

public GenericApplicationContext() {
   this.beanFactory = new DefaultListableBeanFactory();}

　2.进入抽象类  AbstractApplicationContext

先执行了静态块，目前还不知道干啥用的，从住上来看是为针对weblogic的补丁。

static {
   // Eagerly load the ContextClosedEvent class to avoid weird classloader issues
   // on application shutdown in WebLogic 8.1. (Reported by Dustin Woods.)
   ContextClosedEvent.class.getName();
}

无参的构造函数。初始化了资源解析器。

/**
 * Create a new AbstractApplicationContext with no parent.
 */
public AbstractApplicationContext() {
   this.resourcePatternResolver = getResourcePatternResolver();
}

进到getResourcePatternResolver();

protected ResourcePatternResolver getResourcePatternResolver() {
   return new PathMatchingResourcePatternResolver(this);
}

将 PathMatchingResourcePatternResolver 作为默认的资源解析器。（对于ResourceLoader spring也定义了一套比较复杂的规则，后面再讲）

3.进到DefaultResourceLoader

/**
 * Create a new DefaultResourceLoader.
 * <p>ClassLoader access will happen using the thread context class loader
 * at the time of this ResourceLoader's initialization.
 * @see java.lang.Thread#getContextClassLoader()
 */
public DefaultResourceLoader() {
   this.classLoader = ClassUtils.getDefaultClassLoader();
}

进入ClassUtils中：

public static ClassLoader getDefaultClassLoader() {
   ClassLoader cl = null;
   try {
      cl = Thread.currentThread().getContextClassLoader();
   }
   catch (Throwable ex) {
      // Cannot access thread context ClassLoader - falling back...
   }
   if (cl == null) {
      // No thread context class loader -> use class loader of this class.
      cl = ClassUtils.class.getClassLoader();
      if (cl == null) {
         // getClassLoader() returning null indicates the bootstrap ClassLoader
         try {
            cl = ClassLoader.getSystemClassLoader();
         }
         catch (Throwable ex) {
            // Cannot access system ClassLoader - oh well, maybe the caller can live with null...
         }
      }
   }
   return cl;
}

能看到spring给DefaultResourceLoader持有了classloader 线程上下文类加载器 -- 当前类的类加载器 -- 系统类加载器（Appclassloader）

关于java的类加载器请拜读 深度好文： https://blog.csdn.net/javazejian/article/details/73413292

到此为止，spring的准备工作做好了。

1.GenericApplicationContext 创建了beanFactory -- DefaultListableBeanFactory

2.AbstractApplicationContext 构建了ResourceLoader
3.DefaultResourceLoader 准备好了ClassLoader
4.AnnotationConfigApplication 准备好BeanFactory 的 AnnotationBeanDefinitionReader 和 ClassPathBeanDefinitionScanner
5.AnnotationBeanDefinitionReader 准备好了conditionEvaluator 和 annotationprocessor
6.ClassPathBeanDefinitionScanner 注册了需要扫描的注解 如component 以及之下的 service，repository，controller等
7.DefaultListableBeanFactory 准备好了beanDefinitionMap存放 bean。

再看

register(annotatedClasses);方法

==调用==

@SuppressWarnings("unchecked")
public void registerBean(Class<?> annotatedClass, String name, Class<? extends Annotation>... qualifiers) {
   AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
   if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {//跳过处理
      return;
   }

   ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);//获取@scope注解
   abd.setScope(scopeMetadata.getScopeName());
   String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));//取得bean名字
   AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);//处理Lazy primary等注解，仅仅是设置属性。
   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));
         }
      }
   }

   BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
   definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);//进入
   BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}
static BeanDefinitionHolder applyScopedProxyMode(
      ScopeMetadata metadata, BeanDefinitionHolder definition, BeanDefinitionRegistry registry) {

   ScopedProxyMode scopedProxyMode = metadata.getScopedProxyMode();
   if (scopedProxyMode.equals(ScopedProxyMode.NO)) {//不需要代理直接返回
      return definition;
   }
   boolean proxyTargetClass = scopedProxyMode.equals(ScopedProxyMode.TARGET_CLASS);//默认是cglib的方式代理
   return ScopedProxyCreator.createScopedProxy(definition, registry, proxyTargetClass);
}

所以，register方法主要作用就是把bean上的注解扫描一遍。想是别名，懒加载，代理模式，scope等，将其注册到beanDefinitionRegistry（这个registry其实就是AnnotationConfigApplicationContext）中。

接下来看重头戏，refresh();方法，这是AbstractApplicationContext种定义的方法。所有的AbstractApplicationContext容器的子类初始化都会经过这条路。先上代码。

@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      // 1.Prepare this context for refreshing.
      prepareRefresh();

      // 2.Tell the subclass to refresh the internal bean factory.
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // 3.Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory);

      try {
         //4. Allows post-processing of the bean factory in context subclasses.
         postProcessBeanFactory(beanFactory);

         // 5.Invoke factory processors registered as beans in the context.
         invokeBeanFactoryPostProcessors(beanFactory);

         // 6.Register bean processors that intercept bean creation.
         registerBeanPostProcessors(beanFactory);

         // 7.Initialize message source for this context.
         initMessageSource();

         // 8.Initialize event multicaster for this context.
         initApplicationEventMulticaster();

         // 9.Initialize other special beans in specific context subclasses.
         onRefresh();

         // 10.Check for listener beans and register them.
         registerListeners();

         // 11.Instantiate all remaining (non-lazy-init) singletons.
         finishBeanFactoryInitialization(beanFactory);

         // 12.Last step: publish corresponding event.
         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...
         //13.
　　　　　　resetCommonCaches();
      }
   }
}

一共13步，这个过程比较难产和漫长，但结果是喜出望外的。分别来看下 每一步都干了什么。
注意这个方法是加锁的。

  // 1.Prepare this context for refreshing.
  prepareRefresh();
顾名思义，是准备工作，这个和前面初始化的准备工作不同。这个是进行参数配置的。placeholder解析和校验工作，但是主要针对web项目的。暂时先不看。

// 2.Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
得到beanfactory

 // 3.Prepare the bean factory for use in this context.
 prepareBeanFactory(beanFactory);

上代码：

/**
 * Configure the factory's standard context characteristics,
 * such as the context's ClassLoader and post-processors.
 * @param beanFactory the BeanFactory to configure
 */
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
   // Tell the internal bean factory to use the context's class loader etc.
　　首先，设置了类加载器
   beanFactory.setBeanClassLoader(getClassLoader());

　　添加对spel的支持，
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
　　添加一个默认的properties的处理工具
   beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

   // Configure the bean factory with context callbacks.
　　//设置需要忽略的类，这些类实现了如下的接口需要在bean创建的阶段在beanFactory的容器级别对自动装配进行忽略，而交由context容器进行callback注入。
   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 interface not registered as resolvable type in a plain factory.
   // MessageSource registered (and found for autowiring) as a bean.
　　设置扩展点，对于这些扩展点接口的实现bean需要走特殊的callback流程，特殊装备规则。
   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));

   // Detect a LoadTimeWeaver and prepare for weaving, if found.
   if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
      beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
      // Set a temporary ClassLoader for type matching.
      beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
   }

   // Register default environment beans.
注册特殊的基础bean 如 environment systemEnvironment，systemProperties

   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());
   }
}

  //4. Allows post-processing of the bean factory in context subclasses.  给web项目使用，通常不会与自定义产生交集。
  postProcessBeanFactory(beanFactory);

/* 5 .. 扩展点开始，调用BeanFactoryPostProcessors接口的 postProcessBeanFactory 方法。这里有些细节，会有处理的优先级。
首先处理 BeanDefinitionRegistryPostProcessor 中带有PriorityOrdered ，Ordered 这些接口的实现，
然后处理 实现了BeanDefinitionRegistryPostProcessor接口不带order的类。
再然后处理 实现了 BeanFactoryPostProcessor 中带有PriorityOrdered ，Ordered 这些接口的实现。
最后处理 实现了 BeanFactoryPostProcessor 但没有order 接口的实现类。

这里也会进入 beanFactory获取Bean的关键方法  doGetBean();方法位于AbstractBeanFactory中。
getbean的实现比较简单，检查依赖 getDependsOn ，检查是否有循环依赖，有依赖的话先load依赖，AbstractAutowireCapableFactory 的 createBean();方法进行bean的创建。
最后是在SimpleInstantiationStrategy 调用 Beanutils.instantiateClass()通过调用无参构造函数newinstance();创建得到bean实例。如果是单例会被缓存一份。

在创建bean的同时，调用aware接口。通常只会用BeanNameAware 接口来更改名字。

private void invokeAwareMethods(final String beanName, final Object bean) {
   if (bean instanceof Aware) {
      if (bean instanceof BeanNameAware) {
         ((BeanNameAware) bean).setBeanName(beanName);
      }
      if (bean instanceof BeanClassLoaderAware) {
         ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
      }
      if (bean instanceof BeanFactoryAware) {
         ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
      }
   }
}

private boolean isDependent(String beanName, String dependentBeanName, Set<String> alreadySeen) {
        if (alreadySeen != null && alreadySeen.contains(beanName)) {
            return false;
        }
        String canonicalName = canonicalName(beanName);
        Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName);
        if (dependentBeans == null) {
            return false;
        }
        if (dependentBeans.contains(dependentBeanName)) {
            return true;
        }
        for (String transitiveDependency : dependentBeans) {
            if (alreadySeen == null) {
                alreadySeen = new HashSet<String>();
            }
            alreadySeen.add(beanName);
            if (isDependent(transitiveDependency, dependentBeanName, alreadySeen)) {
                return true;
            }
        }
        return false;
    }

protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating instance of bean '" + beanName + "'");
        }
        RootBeanDefinition mbdToUse = mbd;

        // Make sure bean class is actually resolved at this point, and
        // clone the bean definition in case of a dynamically resolved Class
        // which cannot be stored in the shared merged bean definition.
        Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }

        // Prepare method overrides.
        try {
            mbdToUse.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }

        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
            if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }

public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
        Assert.notNull(ctor, "Constructor must not be null");
        try {
            ReflectionUtils.makeAccessible(ctor);
            return ctor.newInstance(args);
        }
        catch (InstantiationException ex) {
            throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
        }
        catch (IllegalAccessException ex) {
            throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
        }
        catch (IllegalArgumentException ex) {
            throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
        }
        catch (InvocationTargetException ex) {
            throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
        }
    }

再然后调用BeanPostProcessor的 postProcessBeforeInitialization方法。

然后调用 InitializingBean接口的 afterPropertiesSet();此时bean已经被初始化，可对属性进行更改。

再然后调用 BeanPostProcessor接口的 postProcessAfterInitialization 此时可以对bean进行进一步的修饰。

最后将 单例缓存起来

然后 BeanFactoryPostProcessor 调用 postProcessBeanFactory方法

*/

 // 5.Invoke factory processors registered as beans in the context.

invokeBeanFactoryPostProcessors(beanFactory);  
代码如下：

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

        // Invoke BeanDefinitionRegistryPostProcessors first, if any.
        Set<String> processedBeans = new HashSet<String>();

        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
            List<BeanDefinitionRegistryPostProcessor> registryProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();

            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<BeanDefinitionRegistryPostProcessor>();

            // 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<BeanFactoryPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        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<BeanFactoryPostProcessor>();
        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<BeanFactoryPostProcessor>();
        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();
    }

protected <T> T doGetBean(
            final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
            throws BeansException {

        final String beanName = transformedBeanName(name);
        Object bean;

        // Eagerly check singleton cache for manually registered singletons.
        Object sharedInstance = getSingleton(beanName);
        if (sharedInstance != null && args == null) {
            if (logger.isDebugEnabled()) {
                if (isSingletonCurrentlyInCreation(beanName)) {
                    logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                            "' that is not fully initialized yet - a consequence of a circular reference");
                }
                else {
                    logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
                }
            }
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
        }

        else {
            // Fail if we're already creating this bean instance:
            // We're assumably within a circular reference.
            if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            // Check if bean definition exists in this factory.
            BeanFactory parentBeanFactory = getParentBeanFactory();
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                // Not found -> check parent.
                String nameToLookup = originalBeanName(name);
                if (args != null) {
                    // Delegation to parent with explicit args.
                    return (T) parentBeanFactory.getBean(nameToLookup, args);
                }
                else {
                    // No args -> delegate to standard getBean method.
                    return parentBeanFactory.getBean(nameToLookup, requiredType);
                }
            }

            if (!typeCheckOnly) {
                markBeanAsCreated(beanName);
            }

            try {
                final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                checkMergedBeanDefinition(mbd, beanName, args);

                // Guarantee initialization of beans that the current bean depends on.
                String[] dependsOn = mbd.getDependsOn();
                if (dependsOn != null) {
                    for (String dep : dependsOn) {
                        if (isDependent(beanName, dep)) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                    "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                        }
                        registerDependentBean(dep, beanName);
                        getBean(dep);
                    }
                }

                // Create bean instance.
                if (mbd.isSingleton()) {
                    sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                        @Override
                        public Object getObject() throws BeansException {
                            try {
                                return createBean(beanName, mbd, args);
                            }
                            catch (BeansException ex) {
                                // Explicitly remove instance from singleton cache: It might have been put there
                                // eagerly by the creation process, to allow for circular reference resolution.
                                // Also remove any beans that received a temporary reference to the bean.
                                destroySingleton(beanName);
                                throw ex;
                            }
                        }
                    });
                    bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                }

                else if (mbd.isPrototype()) {
                    // It's a prototype -> create a new instance.
                    Object prototypeInstance = null;
                    try {
                        beforePrototypeCreation(beanName);
                        prototypeInstance = createBean(beanName, mbd, args);
                    }
                    finally {
                        afterPrototypeCreation(beanName);
                    }
                    bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                }

                else {
                    String scopeName = mbd.getScope();
                    final Scope scope = this.scopes.get(scopeName);
                    if (scope == null) {
                        throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
                    }
                    try {
                        Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                            @Override
                            public Object getObject() throws BeansException {
                                beforePrototypeCreation(beanName);
                                try {
                                    return createBean(beanName, mbd, args);
                                }
                                finally {
                                    afterPrototypeCreation(beanName);
                                }
                            }
                        });
                        bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                    }
                    catch (IllegalStateException ex) {
                        throw new BeanCreationException(beanName,
                                "Scope '" + scopeName + "' is not active for the current thread; consider " +
                                "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
                                ex);
                    }
                }
            }
            catch (BeansException ex) {
                cleanupAfterBeanCreationFailure(beanName);
                throw ex;
            }
        }

        // Check if required type matches the type of the actual bean instance.
        if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
            try {
                return getTypeConverter().convertIfNecessary(bean, requiredType);
            }
            catch (TypeMismatchException ex) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Failed to convert bean '" + name + "' to required type '" +
                            ClassUtils.getQualifiedName(requiredType) + "'", ex);
                }
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
        }
        return (T) bean;
    }

 // 6.Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);

第6步和第5步相似，也是根据 带有PriorityOrdered ，Ordered 这些接口的实现的实现判断优先级，这一步仅仅是注册BeanPostProcessor。并不做处理。

 // 7.Initialize message source for this context. 注册messagesource
 initMessageSource();

//8.注册一个SimpleApplicationEventMulticaster到beanFactory中，同时abstractapplicationcontext也持有这个类。 作为spring事件发布机制。这个后面专门讲spring的事件机制。

this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);

 // 8.Initialize event multicaster for this context.
         initApplicationEventMulticaster();

//9. 这也是为web服务使用的，主要是加载主体 initThemeSource

// 9.Initialize other special beans in specific context subclasses.
         onRefresh();

//10. 从bean工厂中 找到ApplicationListener.class 的实现类，并加入到第8步中的SimpleApplicationEventMulticaster 中。

// 10.Check for listener beans and register them.
registerListeners();

 // 11.Instantiate all remaining (non-lazy-init) singletons. 主要工作注册placeholder，初始化不需要懒加载的bean。
 finishBeanFactoryInitialization(beanFactory);

// 12.Last step: publish corresponding event. 发布各种event事件。
 finishRefresh();

//13.  清理工作 。清理metadata 缓存，classloader缓存。
resetCommonCaches();

至此，spring 启动完毕。

下期开始看spring中的事件处理，后期梳理spring用到的设计模式。