SpringIOC源码解析(下)

待我称王封你为后i 2024-04-18 20:14 226阅读 0赞

注意，看完这篇文章需要很长很长很长时间。。。

本篇文章是SpringIOC源码解析（上）的续集，上一篇文章介绍了使用XML的方式启动Spring，然后追踪了BeanFactory容器的创建、配置文件的解析、Bean的注册等,本篇文章继续分析Bean的初始化流程

``

  1. `finishBeanFactoryInitialization()` 
  1. 前方超长篇幅预警。。。

刚才我们提到了bean还没有初始化。这个方法就是负责初始化所有的没有设置懒加载的singleton bean

  • protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { 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)); } 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(); }

    上方没有解释的代码往下看吧

conversionService

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

例如：前端要传一个String，后端使用Date接受的时候就可以这样操作

  • public class StringToDateConverter implements Converter { @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; } }}

再搞个bean

EmbeddedValueResolver

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

  • @Componentpublic 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()); } }

初始化
敲黑板了，重点来了。。。

这里分析`beanFactory.preInstantiateSingletons()`方法

  • 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 beanNames = new ArrayList(this.beanDefinitionNames); for (String beanName : beanNames) { // 合并父 Bean 中的配置，主意 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() { @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() { @Override public Object run() { smartSingleton.afterSingletonsInstantiated(); return null; } }, getAccessControlContext()); } else { smartSingleton.afterSingletonsInstantiated(); } } }}

    可以看到，不管是不是FactoryBean，最后都调用了`getBean(beanName)`，继续看这个方法吧

    • @Overridepublic Object getBean(String name) throws BeansException { return doGetBean(name, null, null, false);} protected T doGetBean( final String name, final Class 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() { @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() { @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。如果不存在那就要接着往下看`createBean`方法了

      • 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 和 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() { @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 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 “ + “‘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;}

        到这里第一次初始化的bean也返回了，你以为就这样结束了么。不，还有几个很重要的点

        创建bean实例`createBeanInstance ()`

        • protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) { // 确保已经加载了此 class Class<?> beanClass = resolveBeanClass(mbd, beanName); // 校验类的访问权限 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()); } if (mbd.getFactoryMethodName() != null) { // 采用工厂方法实例化 return instantiateUsingFactoryMethod(beanName, mbd, args); } //是否第一次 boolean resolved = false; //是否采用构造函数注入 boolean autowireNecessary = false; if (args == null) { synchronized (mbd.constructorArgumentLock) { if (mbd.resolvedConstructorOrFactoryMethod != null) { resolved = true; autowireNecessary = mbd.constructorArgumentsResolved; } } } if (resolved) { if (autowireNecessary) { return autowireConstructor(beanName, mbd, null, null); } else { // 无参构造函数 return instantiateBean(beanName, mbd); } } // 判断是否采用有参构造函数 Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); if (ctors != null || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { // 构造函数依赖注入 return autowireConstructor(beanName, mbd, ctors, args); } // 调用无参构造函数 return instantiateBean(beanName, mbd);}

        选一个无参的构造看一下吧

        • protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) { try { Object beanInstance; final BeanFactory parent = this; if (System.getSecurityManager() != null) { beanInstance = AccessController.doPrivileged(new PrivilegedAction() { @Override public Object run() { return getInstantiationStrategy().instantiate(mbd, beanName, parent); } }, getAccessControlContext()); } else { // 具体实例化的实现，往下看 beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent); } BeanWrapper bw = new BeanWrapperImpl(beanInstance); initBeanWrapper(bw); return bw; } catch (Throwable ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, “Instantiation of bean failed”, ex); }} public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner) { // 如果不存在方法覆写，那就使用 java 反射进行实例化，否则使用 CGLIB, if (bd.getMethodOverrides().isEmpty()) { Constructor<?> constructorToUse; synchronized (bd.constructorArgumentLock) { constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod; if (constructorToUse == null) { final Class<?> clazz = bd.getBeanClass(); if (clazz.isInterface()) { throw new BeanInstantiationException(clazz, “Specified class is an interface”); } try { if (System.getSecurityManager() != null) { constructorToUse = AccessController.doPrivileged(new PrivilegedExceptionAction>() { @Override public Constructor<?> run() throws Exception { return clazz.getDeclaredConstructor((Class[]) null); } }); } else { constructorToUse = clazz.getDeclaredConstructor((Class[]) null); } bd.resolvedConstructorOrFactoryMethod = constructorToUse; } catch (Throwable ex) { throw new BeanInstantiationException(clazz, “No default constructor found”, ex); } } } // 利用构造方法进行实例化 return BeanUtils.instantiateClass(constructorToUse); } else { // 存在方法覆写，利用 CGLIB 来完成实例化，需要依赖于 CGLIB 生成子类，这里就不展开了 return instantiateWithMethodInjection(bd, beanName, owner); }}

          bean属性注入`populateBean ()`

          • protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) { // bean的所有属性 PropertyValues pvs = mbd.getPropertyValues(); if (bw == null) { if (!pvs.isEmpty()) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, “Cannot apply property values to null instance”); } else { return; } } boolean continueWithPropertyPopulation = true; if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; // 如果返回 false，代表不需要进行后续的属性设值，也不需要再经过其他的 BeanPostProcessor 的处理 if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) { continueWithPropertyPopulation = false; break; } } } } if (!continueWithPropertyPopulation) { return; } if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { MutablePropertyValues newPvs = new MutablePropertyValues(pvs); // 通过名字找到所有属性值，如果是 bean 依赖，先初始化依赖的 bean。记录依赖关系 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) { autowireByName(beanName, mbd, bw, newPvs); } // 通过类型装配。复杂一些 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; // 这里就是上方曾经提到过得对@Autowired处理的一个BeanPostProcessor了 // 它会对所有标记@Autowired、@Value 注解的属性进行设值 pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName); if (pvs == null) { return; } } } } if (needsDepCheck) { checkDependencies(beanName, mbd, filteredPds, pvs); } } // 设置 bean 实例的属性值 applyPropertyValues(beanName, mbd, bw, pvs);}

          getBean这一块就搞完了

          13. `finishRefresh()`

          • 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); }

          14. `resetCommonCaches()`
          最后一步还是清除缓存

          15. `refresh()`总结
          上方以及之前的一篇文章，用了这么长的篇幅把整个`refresh()`方法的细节给梳理清楚，这里再把刚开始看的懵懵的`refresh() `方法贴一下
          ```

          • public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // 记录容器的启动时间、标记“已启动”状态、检查环境变量 prepareRefresh(); // 初始化BeanFactory容器、注册BeanDefinition ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // 设置 BeanFactory 的类加载器，添加几个 BeanPostProcessor，手动注册几个特殊的 bean prepareBeanFactory(beanFactory); try { // 扩展点 postProcessBeanFactory(beanFactory); // 调用 BeanFactoryPostProcessor 各个实现类的 postProcessBeanFactory(factory) 方法 invokeBeanFactoryPostProcessors(beanFactory); // 注册 BeanPostProcessor 的实现类 registerBeanPostProcessors(beanFactory); // 初始化MessageSource initMessageSource(); // 初始化事件广播器 initApplicationEventMulticaster(); // 扩展点 onRefresh(); // 注册事件监听器 registerListeners(); // 初始化所有的 singleton beans finishBeanFactoryInitialization(beanFactory); // 广播事件 finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn(“Exception encountered during context initialization - “ + “cancelling refresh attempt: “ + ex); } // 销毁已经初始化的的Bean destroyBeans(); // 设置 ‘active’ 状态 cancelRefresh(ex); throw ex; } finally { // 清除缓存 resetCommonCaches(); } }}

          总结

          至此，本文到此结束。鉴于XML方式比较简单、通俗易懂，所以本文基于XML的方式大致介绍了SpringIOC的启动流程、稍微深入的讲解了Bean容器的创建以及Bean的初始化过程。这也是作者第一次阅读开源框架的源码，如文章有错误之处还请您费心指出。

          鉴于现在比较流行SpringBoot和SpringCloud，下篇文章将会从基于注解的方向分析SpringIOC

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