[Java知识库]001.spring源码分析-bean创建流程

首先创建ClassPathXmlApplicationContext

public ClassPathXmlApplicationContext(
      String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
      throws BeansException {

   super(parent);
   setConfigLocations(configLocations);
   if (refresh) {
      refresh();
   }
}

会调用到refresh方法。

refresh()方法

AbstractApplicationContext中的refresh方法中的步骤。

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

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

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

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

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

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

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

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

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

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

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

         // 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;
      }
   }
}

prepareRefresh();

initPropertySources();

替换配置中的占位符，默认什么都不做

protected void initPropertySources() {
   // For subclasses: do nothing by default.
}

getEnvironment().validateRequiredProperties();

createEnvironment();
->new StandardEnvironment(); //调用父类的构造方法

public StandardEnvironment() {
}

–>AbstractEnvironment() //父类构造器

/**
 * Create a new {@code Environment} instance, calling back to
 * {@link #customizePropertySources(MutablePropertySources)} during construction to
 * allow subclasses to contribute or manipulate {@link PropertySource} instances as
 * appropriate.
 * @see #customizePropertySources(MutablePropertySources)
 */
public AbstractEnvironment() {
   this(new MutablePropertySources());
}

—> this(new MutablePropertySources());

protected AbstractEnvironment(MutablePropertySources propertySources) {
   this.propertySources = propertySources;
   this.propertyResolver = createPropertyResolver(propertySources);
   customizePropertySources(propertySources);
}

—>customizePropertySources(propertySources);//这里是个空实现，真正实现该方法在子类里。

protected void customizePropertySources(MutablePropertySources propertySources) {
}

—>调用StandardEnvironment的customizePropertySources方法

/**
 * Customize the set of property sources with those appropriate for any standard
 * Java environment:
 * <ul>
 * <li>{@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME}
 * <li>{@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}
 * </ul>
 * <p>Properties present in {@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME} will
 * take precedence over those in {@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}.
 * @see AbstractEnvironment#customizePropertySources(MutablePropertySources)
 * @see #getSystemProperties()
 * @see #getSystemEnvironment()
 */
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
   propertySources.addLast(
         new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
   propertySources.addLast(
         new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
}

获取环境后，调用validateRequiredProperties();验证资源。（略）

存储预刷新监听器的集合，为了做扩展，springboot中有个多个listener，这里创建一些集合。

// Store pre-refresh ApplicationListeners...
if (this.earlyApplicationListeners == null) {
   this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
}
else {
   // Reset local application listeners to pre-refresh state.
   this.applicationListeners.clear();
   this.applicationListeners.addAll(this.earlyApplicationListeners);
}

prepareRefresh();总结

设置spring启动时间
更改关闭/开启状态标志位
获取并初始化环境
初始化监听器和发布事件集合

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

获取bean工厂，重要子接口：ListableBeanFactory，ConfigurableBeanFactory
实现类：DefaultListableBeanFactory类继承结构及重要接口：

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

父子容器，先找当前容器，再去找父容器。springmvc中会有很多父子容器的使用。

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

refreshBeanFactory()

销毁已经存在的bean工厂，创建新的DefaultListableBeanFactory

@Override
protected final void refreshBeanFactory() throws BeansException {
   if (hasBeanFactory()) {
      //如果已经存在bean工厂，先销毁
      destroyBeans();
      closeBeanFactory();
   }
   try {
      //创建一个DefaultListableBeanFactory
      DefaultListableBeanFactory beanFactory = createBeanFactory();
      beanFactory.setSerializationId(getId());
      customizeBeanFactory(beanFactory);
      loadBeanDefinitions(beanFactory);
      this.beanFactory = beanFactory;
   }
   catch (IOException ex) {
      throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
   }
}

-> createBeanFactory()

protected DefaultListableBeanFactory createBeanFactory() {
   return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}

getInternalParentBeanFactory()方法返回的是个null。到这里，DefaultListableBeanFactory 就创建好了。
->beanFactory.setSerializationId(getId()); 设置个id
->customizeBeanFactory(beanFactory);
->setAllowBeanDefinitionOverriding
->setAllowCircularReferences
-> loadBeanDefinitions(beanFactory);

这里有不同的实现，每个实现都有一堆重载方法，最终都是通过流将配置文件加载进来。
-> this.beanFactory = beanFactory;

getBeanFactory()

这里返回的就是上一步创建的beanFactory

@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
   DefaultListableBeanFactory beanFactory = this.beanFactory;
   if (beanFactory == null) {
      throw new IllegalStateException("BeanFactory not initialized or already closed - " +
            "call 'refresh' before accessing beans via the ApplicationContext");
   }
   return beanFactory;
}

prepareBeanFactory(beanFactory);

这里主要是给BeanFactory设置一些属性，做初始化操作

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
   // Tell the internal bean factory to use the context's class loader etc.
   beanFactory.setBeanClassLoader(getClassLoader());
   if (!shouldIgnoreSpel) {
      //SPEL表达式解析
      beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
   }
   beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

   // Configure the bean factory with context callbacks.
   //beanFactory添加PostProcessor
   beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
   //ignore系列：忽略这些接口实现
   beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
   beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
   beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
   beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationStartupAware.class);

   // BeanFactory interface not registered as resolvable type in a plain factory.
   // MessageSource registered (and found for autowiring) as a bean.
   beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
   beanFactory.registerResolvableDependency(ResourceLoader.class, this);
   beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
   beanFactory.registerResolvableDependency(ApplicationContext.class, this);

   // Register early post-processor for detecting inner beans as ApplicationListeners.
   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

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

   // Register default environment beans.
   if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
      beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
   }
   if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
      beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
   }
   if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
      beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
   }
   if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {
      beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());
   }
}

postProcessBeanFactory(beanFactory);

空实现，交给子类实现

protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
}

invokeBeanFactoryPostProcessors(beanFactory);

初始化并调用BeanFactoryPostProcessors

/**
 * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
 * respecting explicit order if given.
 * <p>Must be called before singleton instantiation.
 */
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
   PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

   // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
   // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
   if (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
      beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
      beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
   }
}

registerBeanPostProcessors(beanFactory);

注册这些BeanPostProcessor本身作为bean

initMessageSource();

国际化相关（略）

initApplicationEventMulticaster();

初始化ApplicationEventMulticaster.，默认的实现类是SimpleApplicationEventMulticaster

onRefresh();

留给子类做扩展工作，比如spring boot就是在这里做tomcat的启动

registerListeners();

注册监听器。

finishBeanFactoryInitialization(beanFactory);

这个方法很重要，很多bean实例化方法都在这里面：

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
   // Initialize conversion service for this context.
   //设置类型转换操作
   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 BeanFactoryPostProcessor
   // (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
   // at this point, primarily for resolution in annotation attribute values.
   //内置的值处理器
   if (!beanFactory.hasEmbeddedValueResolver()) {
      beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
   }

   // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
   //织入
   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();

   // Instantiate all remaining (non-lazy-init) singletons.
   //实例化所有的对象
   beanFactory.preInstantiateSingletons();
}

beanFactory.preInstantiateSingletons();

@Override
public void preInstantiateSingletons() throws BeansException {
   if (logger.isTraceEnabled()) {
      logger.trace("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.
   List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

   // Trigger initialization of all non-lazy singleton beans...
   for (String beanName : beanNames) {
      //bean定义信息
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
      //非抽象，单例，非懒加载，则实例化
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
         //是否类是否实现了FactoryBean这个接口
         if (isFactoryBean(beanName)) {
            Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
            if (bean instanceof FactoryBean) {
               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 {
            //一般没有实现的话，直接到这里
            getBean(beanName);
         }
      }
   }

getBean(beanName); -> doGetBean(name, null, null, false);

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

   String beanName = transformedBeanName(name);
   Object beanInstance;

   // Eagerly check singleton cache for manually registered singletons.
   //获取实例对象,三级缓存里获取，这里还没有创建
   //sharedInstance是FactoryBean
   //beanInstance是实际的对象
   Object sharedInstance = getSingleton(beanName);
   if (sharedInstance != null && args == null) {
      if (logger.isTraceEnabled()) {
         if (isSingletonCurrentlyInCreation(beanName)) {
            logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
                  "' that is not fully initialized yet - a consequence of a circular reference");
         }
         else {
            logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
         }
      }
      beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);
   }

   else {
      // Fail if we're already creating this bean instance:
      // We're assumably within a circular reference.
      //如果不是单例的，不给解决循环依赖问题，直接抛出异常
      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 (parentBeanFactory instanceof AbstractBeanFactory) {
            return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
                  nameToLookup, requiredType, args, typeCheckOnly);
         }
         else if (args != null) {
            // Delegation to parent with explicit args.
            return (T) parentBeanFactory.getBean(nameToLookup, args);
         }
         else if (requiredType != null) {
            // No args -> delegate to standard getBean method.
            return parentBeanFactory.getBean(nameToLookup, requiredType);
         }
         else {
            return (T) parentBeanFactory.getBean(nameToLookup);
         }
      }

      if (!typeCheckOnly) {
         //哪些对象创建了
         markBeanAsCreated(beanName);
      }

      StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate")
            .tag("beanName", name);
      try {
         if (requiredType != null) {
            beanCreation.tag("beanType", requiredType::toString);
         }
         RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
         checkMergedBeanDefinition(mbd, beanName, args);

         // Guarantee initialization of beans that the current bean depends on.
         String[] dependsOn = mbd.getDependsOn();
         //是否有依赖的bean，在使用@DependsOn其他的bean，则被依赖的先创建
         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);
               try {
                  getBean(dep);
               }
               catch (NoSuchBeanDefinitionException ex) {
                  throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
               }
            }
         }

         // Create bean instance.
         if (mbd.isSingleton()) {
            //todo 参数ObjectFactory<?> singletonFactory就是这个lambda表达式，实现的是T getObject() 方法
            //这个表达式本身就是getObject的实现， 通过这里创建的bean
            sharedInstance = getSingleton(beanName, () -> {
               try {
                   //这里创建bean
                  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;
               }
            });
            //todo enter
            beanInstance = 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);
            }
            beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
         }

         else {
            String scopeName = mbd.getScope();
            if (!StringUtils.hasLength(scopeName)) {
               throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
            }
            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, () -> {
                  beforePrototypeCreation(beanName);
                  try {
                     return createBean(beanName, mbd, args);
                  }
                  finally {
                     afterPrototypeCreation(beanName);
                  }
               });
               beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
            }
            catch (IllegalStateException ex) {
               throw new ScopeNotActiveException(beanName, scopeName, ex);
            }
         }
      }
      catch (BeansException ex) {
         beanCreation.tag("exception", ex.getClass().toString());
         beanCreation.tag("message", String.valueOf(ex.getMessage()));
         cleanupAfterBeanCreationFailure(beanName);
         throw ex;
      }
      finally {
         beanCreation.end();
      }
   }

   return adaptBeanInstance(name, beanInstance, requiredType);
}

这里getSingleton(beanName, () -> {} 第二个参数是个函数式接口，里面的方法是：T getObject()，所以在调用它的getObject的时候调用的就是这个lambda表达式里的
createBean(beanName, mbd, args);
调用->Object beanInstance = doCreateBean(beanName, mbdToUse, args);

protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
      throws BeanCreationException {

   // Instantiate the bean.
   BeanWrapper instanceWrapper = null;
   if (mbd.isSingleton()) {
      instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
   }
   if (instanceWrapper == null) {
      //todo enter 这里实例化了对象，但是对象值都是初始值
      instanceWrapper = createBeanInstance(beanName, mbd, args);
   }
   Object bean = instanceWrapper.getWrappedInstance();
   Class<?> beanType = instanceWrapper.getWrappedClass();
   if (beanType != NullBean.class) {
      mbd.resolvedTargetType = beanType;
   }

   // Allow post-processors to modify the merged bean definition.
   synchronized (mbd.postProcessingLock) {
      if (!mbd.postProcessed) {
         try {
            applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
         }
         catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                  "Post-processing of merged bean definition failed", ex);
         }
         mbd.postProcessed = true;
      }
   }

   // Eagerly cache singletons to be able to resolve circular references
   // even when triggered by lifecycle interfaces like BeanFactoryAware.
   //这一块解决循环依赖问题
   //构造器循环依赖没法解决，set依赖可以解决，因为实例化和初始化分开了
   boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
         isSingletonCurrentlyInCreation(beanName));
   if (earlySingletonExposure) {
      if (logger.isTraceEnabled()) {
         logger.trace("Eagerly caching bean '" + beanName +
               "' to allow for resolving potential circular references");
      }
      //todo enter addSingletonFactory将bean加入到三级缓存里
      //为什么使用三级缓存：
      //todo enter getEarlyBeanReference 三级缓存解决循环依赖问题，getEarlyBeanReference实现的是getObject方法
      addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
   }

   // Initialize the bean instance.
   Object exposedObject = bean;
   try {
      //todo enter populate：填充属性，完成属性值的注入
      populateBean(beanName, mbd, instanceWrapper);
      //todo enter 执行aware，beforePostProcessor，init方法，afterPostProcessor类方法 -》初始化完成
      exposedObject = initializeBean(beanName, exposedObject, mbd);
   }
   catch (Throwable ex) {
      if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
         throw (BeanCreationException) ex;
      }
      else {
         throw new BeanCreationException(
               mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
      }
   }

   if (earlySingletonExposure) {
      Object earlySingletonReference = getSingleton(beanName, false);
      if (earlySingletonReference != null) {
         if (exposedObject == bean) {
            exposedObject = earlySingletonReference;
         }
         else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
            String[] dependentBeans = getDependentBeans(beanName);
            Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
            for (String dependentBean : dependentBeans) {
               if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                  actualDependentBeans.add(dependentBean);
               }
            }
            if (!actualDependentBeans.isEmpty()) {
               throw new BeanCurrentlyInCreationException(beanName,
                     "Bean with name '" + beanName + "' has been injected into other beans [" +
                     StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                     "] in its raw version as part of a circular reference, but has eventually been " +
                     "wrapped. This means that said other beans do not use the final version of the " +
                     "bean. This is often the result of over-eager type matching - consider using " +
                     "'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
            }
         }
      }
   }

   // Register bean as disposable.
   try {
      //todo enter 钩子函数
      registerDisposableBeanIfNecessary(beanName, bean, mbd);
   }
   catch (BeanDefinitionValidationException ex) {
      throw new BeanCreationException(
            mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
   }

   return exposedObject;
}

这段代码做了非常重要的几件事：

（1）instanceWrapper = createBeanInstance(beanName, mbd, args);

创建bean对象，但是此时创建的只是一个空对象，属性值还是默认值。

（2）populateBean(beanName, mbd, instanceWrapper);

填充属性，完成属性值的注入

（3）initializeBean(beanName, exposedObject, mbd);

这个方法又包含了几个非常重要的步骤：

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
   if (System.getSecurityManager() != null) {
      AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
         invokeAwareMethods(beanName, bean);
         return null;
      }, getAccessControlContext());
   }
   else {
      //todo enter 执行实现了自定义的aware相关的方法
      invokeAwareMethods(beanName, bean);
   }

   Object wrappedBean = bean;
   if (mbd == null || !mbd.isSynthetic()) {
      //todo enter 执行PostProcessorsBefore方法
      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   }

   try {
      //todo enter 执行指定的init方法
      invokeInitMethods(beanName, wrappedBean, mbd);
   }
   catch (Throwable ex) {
      throw new BeanCreationException(
            (mbd != null ? mbd.getResourceDescription() : null),
            beanName, "Invocation of init method failed", ex);
   }
   if (mbd == null || !mbd.isSynthetic()) {
      //todo enter 执行PostProcessorsAfter方法
      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
   }

   return wrappedBean;
}

①执行实现了自定义的aware相关的方法
②执行PostProcessorsBefore方法
③执行指定的init方法
④执行PostProcessorsAfter方法

finishRefresh();

做一些完成操作。

到此为止，创建bean的步骤就大体完成了。

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