Spring——IOC源码解析下

Spring

refresh()

接上文：

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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;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

prepareBeanFactory()

现在回到最开始的 refresh() 方法 prepareBeanFactory() 这个方法主要会:

  • 设置 BeanFactory的类加载器
  • 添加几个 BeanPostProcessor、事件监听器
  • 手动注册几个特殊的bean

源码：

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protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {

   // 设置为加载当前ApplicationContext类的类加载器
   beanFactory.setBeanClassLoader(getClassLoader());

   // 设置 BeanExpressionResolver
   beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));

   beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

   // 这里是Spring的又一个扩展点
   //在所有实现了Aware接口的bean在初始化的时候，这个 processor负责回调，
   // 这个我们很常用，如我们会为了获取 ApplicationContext 而 implement ApplicationContextAware
   // 注意：它不仅仅回调 ApplicationContextAware，还会负责回调 EnvironmentAware、ResourceLoaderAware 等
   beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

   // 下面几行的意思就是，如果某个 bean 依赖于以下几个接口的实现类，在自动装配的时候忽略它们，Spring 会通过其他方式来处理这些依赖。
   beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
   beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
   beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
   beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

   //下面几行就是为特殊的几个 bean 赋值，如果有 bean 依赖了以下几个，会注入这边相应的值
   beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
   beanFactory.registerResolvableDependency(ResourceLoader.class, this);
   beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
   beanFactory.registerResolvableDependency(ApplicationContext.class, this);

   // 注册 事件监听器
   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

   // 如果存在bean名称为loadTimeWeaver的bean则注册一个BeanPostProcessor
   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()));
   }

   // 如果没有定义 "environment" 这个 bean，那么 Spring 会 "手动" 注册一个
   if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
      beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
   }
   // 如果没有定义 "systemProperties" 这个 bean，那么 Spring 会 "手动" 注册一个
   if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
      beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
   }
   // 如果没有定义 "systemEnvironment" 这个 bean，那么 Spring 会 "手动" 注册一个
   if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
      beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
   }
}

postProcessBeanFactory()

这个比较简单，又是Spring的一个扩展点

如果有Bean实现了BeanFactoryPostProcessor接口， 那么在容器初始化以后，Spring 会负责调用里面的 postProcessBeanFactory 方法。具体的子类可以在这步的时候添加一些特殊的 BeanFactoryPostProcessor 的实现类或做点什么事

invokeBeanFactoryPostProcessors()

调用 BeanFactoryPostProcessor 各个实现类的 postProcessBeanFactory(factory) 方法

我们加载.properties文件设计到的PreferencesPlaceholderConfigurer类，也是在这里完成解析的。

registerBeanPostProcessors()

又是一个扩展点

注册 BeanPostProcessor 的实现类，注意不是BeanFactoryPostProcessor 此接口有两个方法: postProcessBeforeInitialization 和 postProcessAfterInitialization 分别会在Bean初始化之前和初始化之后得到执行

initMessageSource()

初始化当前 ApplicationContext 的 MessageSource，有想了解国际化的相关知识可以深入研究一下

initApplicationEventMulticaster()

这个方法主要为初始化当前 ApplicationContext 的事件广播器

onRefresh()

又是一个扩展点，子类可以在这里来搞事情

11. registerListeners()

注册事件监听器

bean实例化

上文我们介绍了几个方法，几乎都是对于初始化前后的扩展，但注意我们还没有开始初始化，一直到 finishBeanFactoryInitialization() 方法才开始初始化Bean(单例)的工作。

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/**
 * 初始化所有剩余的单例bean
 */
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        // 为容器注册conversion service，用于转化属性值
		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));
		}

        /**
	 * 如果没有的话(比如PropertyPlaceholderConfigurer)，注册一个默认的嵌入值解析器(value resoler)。
	 * 用于解析通过注解导入的值。
	 */
		if (!beanFactory.hasEmbeddedValueResolver()) {
			beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
		}
        //先初始化 LoadTimeWeaverAware 类型的 Bean
		String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
		for (String weaverAwareName : weaverAwareNames) {
			getBean(weaverAwareName);
		}
       //停止使用用于类型匹配的临时类加载器
		beanFactory.setTempClassLoader(null);
      //冻结所有的bean定义，即已注册的bean定义将不会被修改或后处理
		beanFactory.freezeConfiguration();
      //初始化
		beanFactory.preInstantiateSingletons();
	}

我们先来看一下 ConversionService.

ConversionService

类型转换器，这种类型的bean最实用的场景就是用来：
将前端传过来的参数和后端的controller方法上的参数格式转换的时候使用

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public class StringToDateConverter implements Converter<String, Date> {

    @Override
    public Date convert(String date) {
        try {
            return dateFormat.parse(date);
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("日期转换失败!");
            return null;
        }
        
    }
}

配置bean:

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<bean id="conversionService"
  class="org.springframework.context.support.ConversionServiceFactoryBean">
  <property name="converters">
    <list>
      <bean class="cn.shiyujun.utils.StringToDateConverter"/>
    </list>
  </property></bean>

EmbeddedValueResolver

利用EmbeddedValueResolver可以很方便的实现读取配置文件的属性

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@Component
public class PropertiesUtil implements EmbeddedValueResolverAware {

    private StringValueResolver resolver;

    @Override
    public void setEmbeddedValueResolver(StringValueResolver resolver) {
        this.resolver = resolver;
    }


    /**
     * 获取属性时直接传入属性名称即可
     */
    public String getPropertiesValue(String key) {
        StringBuilder name = new StringBuilder("${").append(key).append("}");
        return resolver.resolveStringValue(name.toString());
    }

}
preInstantiateSingletons()

真正开始初始化的方法，里面包括 getBean(),createBean()等方法，处理了循环依赖、别名、懒加载的问题。

这里关于bean的初始化我们要知道：

  1. 如果bean的scope是singleton的，并且lazy-init为false（默认是false，所以可以不用设置），则 ApplicationContext启动的时候就实例化该Bean，并且将实例化的Bean放在一个map结构的缓存中，下次再使 用该 Bean的时候，直接从这个缓存中取

  2. 如果bean的scope是singleton的，并且lazy-init为true，则该Bean的实例化是在第一次使用该Bean的时候进 行实例化

  3. 如果bean的scope是prototype的，则该Bean的实例化是在第一次使用该Bean的时候进行实例化 

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public void preInstantiateSingletons() throws BeansException {
   if (this.logger.isDebugEnabled()) {
      this.logger.debug("Pre-instantiating singletons in " + this);
   }
   // this.beanDefinitionNames 保存了所有的 beanNames
   List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);

   for (String beanName : beanNames) {

      // 合并父 Bean 中的配置，主意<bean id="" class="" parent="" /> 中的 parent属性
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);

      // 不是抽象类、是单例的且不是懒加载的
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
         // 处理 FactoryBean
         if (isFactoryBean(beanName)) {
            //在 beanName 前面加上“&” 符号
            final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
            // 判断当前 FactoryBean 是否是 SmartFactoryBean 的实现
            boolean isEagerInit;
            if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
               isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                  @Override
                  public Boolean run() {
                     return ((SmartFactoryBean<?>) factory).isEagerInit();
                  }
               }, getAccessControlContext());
            }
            else {
               isEagerInit = (factory instanceof SmartFactoryBean &&
                     ((SmartFactoryBean<?>) factory).isEagerInit());
            }
            if (isEagerInit) {

               getBean(beanName);
            }
         }
         else {
            // 不是FactoryBean的直接使用此方法进行初始化
            getBean(beanName);
         }
      }
   }


  
   // 如果bean实现了 SmartInitializingSingleton 接口的，那么在这里得到回调
   for (String beanName : beanNames) {
      Object singletonInstance = getSingleton(beanName);
      if (singletonInstance instanceof SmartInitializingSingleton) {
         final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
         if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
               @Override
               public Object run() {
                  smartSingleton.afterSingletonsInstantiated();
                  return null;
               }
            }, getAccessControlContext());
         }
         else {
            smartSingleton.afterSingletonsInstantiated();
         }
      }
   }
}

bean初始化调用的是AbstractBeanFactory.getBean，最终调用的是AbstractBeanFactory.doGetBean：

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@Override
public Object getBean(String name) throws BeansException {
   return doGetBean(name, null, null, false);
}

protected <T> T doGetBean(
      final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
      throws BeansException {
   // 获取beanName，处理两种情况，一个是前面说的 FactoryBean(前面带 ‘&’)，再一个这个方法是可以根据别名来获取Bean的，所以在这里是要转换成最正统的BeanName
  //主要逻辑就是如果是FactoryBean就把&去掉如果是别名就把根据别名获取真实名称后面就不贴代码了
   final String beanName = transformedBeanName(name);

   //最后的返回值
   Object bean; 

   // 检查是否已初始化
   Object sharedInstance = getSingleton(beanName);
  //如果已经初始化过了，且没有传args参数就代表是get，直接取出返回
   if (sharedInstance != null && args == null) {
      if (logger.isDebugEnabled()) {
         if (isSingletonCurrentlyInCreation(beanName)) {
            logger.debug("...");
         }
         else {
            logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
         }
      }
      // 这里如果是普通Bean 的话，直接返回，如果是 FactoryBean 的话，返回它创建的那个实例对象
      bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
   }

   else {
	   // 如果存在prototype类型的这个bean
      if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
      }

      // 如果当前BeanDefinition不存在这个bean且具有父BeanFactory
      BeanFactory parentBeanFactory = getParentBeanFactory();
      if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
         String nameToLookup = originalBeanName(name);
		// 返回父容器的查询结果
         if (args != null) {
            return (T) parentBeanFactory.getBean(nameToLookup, args);
         }
         else {
            return parentBeanFactory.getBean(nameToLookup, requiredType);
         }
      }

      if (!typeCheckOnly) {
         // typeCheckOnly 为 false，将当前 beanName 放入一个 alreadyCreated 的 Set 集合中。
         markBeanAsCreated(beanName);
      }

      /*
       * 到这就要创建bean了
       */
      try {
         final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
         checkMergedBeanDefinition(mbd, beanName, args);

         // 先初始化依赖的所有 Bean， depends-on 中定义的依赖
         String[] dependsOn = mbd.getDependsOn();
         if (dependsOn != null) {
            for (String dep : dependsOn) {
               // 检查是不是有循环依赖
               if (isDependent(beanName, dep)) {
                  throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
               }
               // 注册一下依赖关系
               registerDependentBean(dep, beanName);
               // 先初始化被依赖项
               getBean(dep);
            }
         }

         // 如果是单例的
         if (mbd.isSingleton()) {
            sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
               @Override
               public Object getObject() throws BeansException {
                  try {
                     // 执行创建 Bean，下面说
                     return createBean(beanName, mbd, args);
                  }
                  catch (BeansException ex) {
                     destroySingleton(beanName);
                     throw ex;
                  }
               }
            });
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
         }

         // 如果是prototype
         else if (mbd.isPrototype()) {
            Object prototypeInstance = null;
            try {
               beforePrototypeCreation(beanName);
               // 执行创建 Bean
               prototypeInstance = createBean(beanName, mbd, args);
            }
            finally {
               afterPrototypeCreation(beanName);
            }
            bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
         }

         // 如果不是 singleton 和 prototype 那么就是自定义的scope、例如Web项目中的session等类型，这里就交给自定义scope的应用方去实现
         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 {
                        // 执行创建 Bean
                        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;
      }
   }

   //检查bean的类型
   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;
}

看了上方方法我们知道了原来Spring本身只定义了两种Scope，也知道了SpringMVC的几种Scope是如何实现的了。 然后发现一开始会先判断bean存不存在，如果存在就直接返回了。

创建bean实例的方法为：AbstractAutowireCapableBeanFactory.createBean：

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

   // 确保 BeanDefinition 中的 Class 被加载
   Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
   if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
      mbdToUse = new RootBeanDefinition(mbd);
      mbdToUse.setBeanClass(resolvedClass);
   }

   // 准备方法覆写，如果bean中定义了 <lookup-method /> 和 <replaced-method />
   try {
      mbdToUse.prepareMethodOverrides();
   }
   catch (BeanDefinitionValidationException ex) {
      throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
            beanName, "Validation of method overrides failed", ex);
   }

   try {
      // 如果有代理的话直接返回
      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);
   }
   // 创建 bean
   Object beanInstance = doCreateBean(beanName, mbdToUse, args);
   if (logger.isDebugEnabled()) {
      logger.debug("Finished creating instance of bean '" + beanName + "'");
   }
   return beanInstance;
}

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

   BeanWrapper instanceWrapper = null;
   if (mbd.isSingleton()) {
	 //如果是.factoryBean则从缓存删除
      instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
   }
   if (instanceWrapper == null) {
      // 实例化 Bean，这个方法里面才是终点，下面说
      instanceWrapper = createBeanInstance(beanName, mbd, args);
   }
	//bean实例
   final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
	//bean类型
   Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
   mbd.resolvedTargetType = beanType;

   synchronized (mbd.postProcessingLock) {
      if (!mbd.postProcessed) {
         try {
            // 循环调用实现了MergedBeanDefinitionPostProcessor接口的postProcessMergedBeanDefinition方法
		   // Spring对这个接口有几个默认的实现，其中大家最熟悉的一个是操作@Autowired注解的
            applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
         }
         catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                  "Post-processing of merged bean definition failed", ex);
         }
         mbd.postProcessed = true;
      }
   }

 
   // 解决循环依赖问题
   boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
         isSingletonCurrentlyInCreation(beanName));
   if (earlySingletonExposure) {
      if (logger.isDebugEnabled()) {
         logger.debug("Eagerly caching bean '" + beanName +
               "' to allow for resolving potential circular references");
      }
	 //当正在创建A时，A依赖B，此时通过（8将A作为ObjectFactory放入单例工厂中进行early expose，此处B需要引用A，但A正在创建，从单例工厂拿到ObjectFactory，从而允许循环依赖
      addSingletonFactory(beanName, new ObjectFactory<Object>() {
         @Override
         public Object getObject() throws BeansException {
            return getEarlyBeanReference(beanName, mbd, bean);
         }
      });
   }

   Object exposedObject = bean;
   try {
      // 负责属性装配,很重要，下面说
      populateBean(beanName, mbd, instanceWrapper);
      if (exposedObject != null) {
         // 这里是处理bean初始化完成后的各种回调，例如init-method、InitializingBean 接口、BeanPostProcessor 接口
         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);
      }
   }
	//同样的，如果存在循环依赖
   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<String>(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 " +
                     "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
            }
         }
      }
   }

   // 把bean注册到相应的Scope中
   try {
      registerDisposableBeanIfNecessary(beanName, bean, mbd);
   }
   catch (BeanDefinitionValidationException ex) {
      throw new BeanCreationException(
            mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
   }

   return exposedObject;
}

createBean主要的函数为doCreateBean：

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

	// 实例化bean
	BeanWrapper instanceWrapper = null;
	if (mbd.isSingleton()) {
		instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
	}
	if (instanceWrapper == null) {
		instanceWrapper = createBeanInstance(beanName, mbd, args);
	}
	final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
	Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
	mbd.resolvedTargetType = beanType;

	// 调用MergedBeanDefinitionPostProcessor的postProcessMergedBeanDefinition来修改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;
		}
	}

   /**
    * 缓存单例，用于解决循环引用的问题。
    * lifecycle接口比如BeanFactoryAware可能会引发循环引用
    */
	boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName));
	if (earlySingletonExposure) {
		if (logger.isDebugEnabled()) {
			logger.debug("Eagerly caching bean '" + beanName +
					"' to allow for resolving potential circular references");
		}
		addSingletonFactory(beanName, new ObjectFactory<Object>() {
			@Override
			public Object getObject() throws BeansException {
				return getEarlyBeanReference(beanName, mbd, bean);
			}
		});
	}

	// 初始化bean实例
	Object exposedObject = bean;
	try {
		// 注入成员以及属性
		populateBean(beanName, mbd, instanceWrapper);
		if (exposedObject != null) {
			// 初始化实例
			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<String>(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 " +
							"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
				}
			}
		}
	}

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

	return exposedObject;
}

实例化bean调用的是AbstractAutowireCapableBeanFactory.createBeanInstance：

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protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
	// 解析bean的定义
	Class<?> beanClass = resolveBeanClass(mbd, beanName);

   // 判断bean是否是public
	if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
		throw new BeanCreationException(mbd.getResourceDescription(), beanName,
				"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
	}
   
   // 如果bean有工厂方法，则使用工厂方法来实例化，然后直接返回
	if (mbd.getFactoryMethodName() != null)  {
		return instantiateUsingFactoryMethod(beanName, mbd, args);
	}

	// 如果显式指定了构造函数则调用`autowireConstructor`，否则调用`instantiateBean`
	boolean resolved = false;
	boolean autowireNecessary = false;
	if (args == null) {
		synchronized (mbd.constructorArgumentLock) {
			if (mbd.resolvedConstructorOrFactoryMethod != null) {
				resolved = true;
				autowireNecessary = mbd.constructorArgumentsResolved;
			}
		}
	}
	// 如果可以确定构造函数，则直接实例化bean
	if (resolved) {
		if (autowireNecessary) {
			return autowireConstructor(beanName, mbd, null, null);
		}
		else {
			return instantiateBean(beanName, mbd);
		}
	}

	// 如果不能确定构造函数，则尝试从BeanPostProcessor中获取构造函数
	Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
	if (ctors != null ||
			mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
			mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
		return autowireConstructor(beanName, mbd, ctors, args);
	}

	// 如果还是无法确定构造函数，则使用默认的无参构造函数
	return instantiateBean(beanName, mbd);
}

在构造函数中注入相应的参数:

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protected BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd, Constructor<?>[] ctors, Object[] explicitArgs) {

	return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
}

autowireConstructor实际的工作在于寻找构造函数、参数，然后调用InstantiationStrategy.instantiate来实例化bean。

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beanInstance = this.beanFactory.getInstantiationStrategy().instantiate(mbd, beanName, this.beanFactory, constructorToUse, argsToUse);
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public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner, final Constructor<?> ctor, Object... args) {
    /**
     * 如果bean中有被容器重写的方法，则调用instantiateWithMethodInjection实例化bean
     * 否则，调用BeanUtils.instantiateClass实例化bean
     */
    if (bd.getMethodOverrides().isEmpty()) {
        if (System.getSecurityManager() != null) {
				// use own privileged to change accessibility (when security is on)
				AccessController.doPrivileged(new PrivilegedAction<Object>() {
					@Override
					public Object run() {
						ReflectionUtils.makeAccessible(ctor);
						return null;
					}
				});
		  }
		  /**
		   * 调用ctor.newInstance(args)来实例化
		   */
	     return BeanUtils.instantiateClass(ctor, args);
    }
    else {
        /**
         * 使用cglib来生成一个子类
         */
        return instantiateWithMethodInjection(bd, beanName, owner, ctor, args);
    }
}

bean实例化完成之后，调用AbstractAutowireCapableBeanFactory.populateBean注入其中的成员以及变量：

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protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
	PropertyValues pvs = mbd.getPropertyValues();

	if (bw == null) {
		if (!pvs.isEmpty()) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
		}
		else {
			// 如果bean为null，则跳过填充的阶段
			return;
		}
	}

	/**
	 * 调用InstantiationAwareBeanPostProcessor来修改bean的状态。可以用于支持字段注入
	 */
	boolean continueWithPropertyPopulation = true;

	if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
		for (BeanPostProcessor bp : getBeanPostProcessors()) {
			if (bp instanceof InstantiationAwareBeanPostProcessor) {
				InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
				if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
					continueWithPropertyPopulation = false;
					break;
				}
			}
		}
	}

   // 如果调用InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation返回false，则跳过填充阶段。表示不再需要继续填充
	if (!continueWithPropertyPopulation) {
		return;
	}

   // 如果自动装配的类型有AUTOWIRE_BY_NAME和AUTOWIRE_BY_TYPE，则分别尝试根据名称自动装配、根据类型自动装配
	if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
			mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
		MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

		// Add property values based on autowire by name if applicable.
		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
			autowireByName(beanName, mbd, bw, newPvs);
		}

		// Add property values based on autowire by type if applicable.
		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
			autowireByType(beanName, mbd, bw, newPvs);
		}

		pvs = newPvs;
	}

	boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
	boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

	if (hasInstAwareBpps || needsDepCheck) {
		PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
		if (hasInstAwareBpps) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					/**
					 * 调用InstantiationAwareBeanPostProcessor的具体子类的ibp.postProcessPropertyValues方法注入属性。
					 * 当我们使用@Resource注解的时候，具体的子类是CommonAnnotationBeanPostProcessor，
					 * 如果使用的是@Autowired注解，则具体的子类是AutowiredAnnotationBeanPostProcessor。
					 */
					pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
					if (pvs == null) {
						return;
					}
				}
			}
		}
		if (needsDepCheck) {
			checkDependencies(beanName, mbd, filteredPds, pvs);
		}
	}

	applyPropertyValues(beanName, mbd, bw, pvs);
}

finishRefresh()

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protected void finishRefresh() {
		//看名字就知道了，清理刚才一系列操作使用到的资源缓存
		clearResourceCaches();

		// 初始化LifecycleProcessor
		initLifecycleProcessor();

		// 这个方法的内部实现是启动所有实现了Lifecycle接口的bean
		getLifecycleProcessor().onRefresh();

		//发布ContextRefreshedEvent事件
		publishEvent(new ContextRefreshedEvent(this));

		// 检查spring.liveBeansView.mbeanDomain是否存在，有就会创建一个MBeanServer
		LiveBeansView.registerApplicationContext(this);
	}

resetCommonCaches()

最后还是一步还是清除缓存

参考文档

SpringIOC源码解析（上）

SpringIOC源码解析（下）

本文标题:Spring——IOC源码解析下

文章作者:南有乔木

发布时间:2020-04-20, 15:26:44

最后更新:2020-04-24, 10:20:39

原始链接:http://yoursite.com/2020/04/20/Spring%E2%80%94%E2%80%94IOC%E6%BA%90%E7%A0%81%E8%A7%A3%E6%9E%90%E4%B8%8B/

许可协议: "署名-非商用-相同方式共享 4.0" 转载请保留原文链接及作者。

文章目录
  1. 1. refresh()
    1. 1.1. prepareBeanFactory()
    2. 1.2. postProcessBeanFactory()
    3. 1.3. invokeBeanFactoryPostProcessors()
    4. 1.4. registerBeanPostProcessors()
    5. 1.5. initMessageSource()
    6. 1.6. initApplicationEventMulticaster()
    7. 1.7. onRefresh()
    8. 1.8. 11. registerListeners()
    9. 1.9. bean实例化
      1. 1.9.1. ConversionService
      2. 1.9.2. EmbeddedValueResolver
        1. 1.9.2.0.1. preInstantiateSingletons()
  2. 1.10. finishRefresh()
  3. 1.11. resetCommonCaches()
  • 2. 参考文档
    • |