Spring IoC源码解析之getBean
- 2019 年 10 月 3 日
- 筆記
一、实例化所有的非懒加载的单实例Bean
从org.springframework.context.support.AbstractApplicationContext#refresh方法开发，进入到实例化所有的非懒加载的单实例Bean的finishBeanFactoryInitialization(beanFactory)的方法：
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // 为Bean工厂设置类型转化器 if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) && beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { beanFactory.setConversionService( beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)); } // Register a default embedded value resolver if no bean post-processor // (such as a PropertyPlaceholderConfigurer bean) registered any before: // at this point, primarily for resolution in annotation attribute values. if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(new StringValueResolver() { @Override public String resolveStringValue(String strVal) { return getEnvironment().resolvePlaceholders(strVal); } }); } // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early. 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); //冻结所有的Bean定义 ， 至此注册的Bean定义将不被修改或任何进一步的处理 beanFactory.freezeConfiguration(); //实例化剩下的单实例Bean beanFactory.preInstantiateSingletons(); }
进入实例化剩下的单实例Bean的beanFactory.preInstantiateSingletons()的方法：
public void preInstantiateSingletons() throws BeansException { if (logger.isDebugEnabled()) { logger.debug("Pre-instantiating singletons in " + this); } //获取我们容器中所有Bean定义的名称 List<String> beanNames = new ArrayList<>(this.beanDefinitionNames); //循环我们所有的bean定义名称 for (String beanName : beanNames) { //合并我们的bean定义 RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); //根据bean定义判断是不是抽象的 && 不是单例的 && 不是懒加载的 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //是否FactoryBean if (isFactoryBean(beanName)) { //是 给beanName+前缀 & 符号 Object bean = getBean(FACTORY_BEAN_PREFIX + beanName); if (bean instanceof FactoryBean) { final FactoryBean<?> factory = (FactoryBean<?>) bean; boolean isEagerInit; if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) { isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit, getAccessControlContext()); } else { isEagerInit = (factory instanceof SmartFactoryBean && ((SmartFactoryBean<?>) factory).isEagerInit()); } //调用真正的getBean if (isEagerInit) { getBean(beanName); } } } else {//非工厂Bean就是普通的bean getBean(beanName); } } } //获取所有的bean的名称 至此所有的单实例的bean已经加入到单实例Bean的缓存池中，所谓的单实例缓存池实际上就是一个ConcurrentHashMap for (String beanName : beanNames) { //从单例缓存池中获取所有的对象 Object singletonInstance = getSingleton(beanName); //判断当前的bean是否实现了SmartInitializingSingleton接口 if (singletonInstance instanceof SmartInitializingSingleton) { final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance; if (System.getSecurityManager() != null) { AccessController.doPrivileged((PrivilegedAction<Object>) () -> { smartSingleton.afterSingletonsInstantiated(); return null; }, getAccessControlContext()); } else { //触发实例化之后的方法afterSingletonsInstantiated smartSingleton.afterSingletonsInstantiated(); } } } }
前面多个地方涉及到getBean，接下来就分析下getBean（很重要）
二、getBean流程
进入getBean(beanName)的方法：
@Override public Object getBean(String name) throws BeansException { //真正的获取Bean的逻辑 return doGetBean(name, null, null, false); }
该方法啥没干，又交给了干活的doGetBean(name, null, null, false)方法：
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType, @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException { //在这里传入进来的name可能是别名、也有可能是工厂beanName,所以在这里需要转换 final String beanName = transformedBeanName(name); Object bean; //先尝试去缓存中获取对象 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 + "'"); } } /** * 如果sharedInstance是普通的单例bean，下面的方法会直接返回。但如果 * sharedInstance是FactoryBean类型的，则需调用getObject工厂方法获取真正的 * bean实例。如果用户想获取 FactoryBean 本身，这里也不会做特别的处理，直接返回 * 即可。毕竟 FactoryBean 的实现类本身也是一种 bean，只不过具有一点特殊的功能而已。 */ bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); } else { //Spring只能解决单例对象的setter注入的循环依赖,不能解决构造器注入，也不能解决多实例的循环依赖 if (isPrototypeCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException(beanName); } //判断是否有父工厂 BeanFactory parentBeanFactory = getParentBeanFactory(); //若存在父工厂,切当前的bean工厂不存在当前的bean定义,那么bean定义是存在于父beanFactory中 if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { //获取bean的原始名称 String nameToLookup = originalBeanName(name); //若为AbstractBeanFactory类型，委托父类处理 if (parentBeanFactory instanceof AbstractBeanFactory) { return ((AbstractBeanFactory) parentBeanFactory).doGetBean( nameToLookup, requiredType, args, typeCheckOnly); } else if (args != null) { // 委托给构造函数getBean()处理 return (T) parentBeanFactory.getBean(nameToLookup, args); } else { // 没有args，委托给标准的getBean()处理 return parentBeanFactory.getBean(nameToLookup, requiredType); } } /** * 方法参数typeCheckOnly ，是用来判断调用getBean(...) 方法时，表示是否为仅仅进行类型检查获取Bean对象 * 如果不是仅仅做类型检查，而是创建Bean对象，则需要调用markBeanAsCreated(String beanName) 方法，进行记录 */ if (!typeCheckOnly) { markBeanAsCreated(beanName); } try { //从容器中获取beanName相应的GenericBeanDefinition对象，并将其转换为RootBeanDefinition对象 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); //检查当前创建的bean定义是不是抽象的bean定义 checkMergedBeanDefinition(mbd, beanName, args); //处理dependsOn的依赖(这个不是我们所谓的循环依赖 而是bean创建前后的依赖) //依赖bean的名称 String[] dependsOn = mbd.getDependsOn(); if (dependsOn != null) { for (String dep : dependsOn) { //beanName是当前正在创建的bean,dep是正在创建的bean的依赖的bean的名称 if (isDependent(beanName, dep)) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'"); } //保存的是依赖beanName之间的映射关系：依赖beanName -> beanName的集合 registerDependentBean(dep, beanName); try { //获取dependsOn的bean getBean(dep); } catch (NoSuchBeanDefinitionException ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "'" + beanName + "' depends on missing bean '" + dep + "'", ex); } } } //是单例则创建单例Bean if (mbd.isSingleton()) { //把beanName和一个singletonFactory匿名内部类传入用于回调 sharedInstance = getSingleton(beanName, () -> { try { //创建bean的逻辑 return createBean(beanName, mbd, args); } catch (BeansException ex) { //创建bean的过程中发生异常,需要销毁关于当前bean的所有信息 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, () -> { 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 && !requiredType.isInstance(bean)) { try { T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType); if (convertedBean == null) { throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } return convertedBean; } 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; }
第一步：先尝试去缓存中获取对象
Object sharedInstance = getSingleton(beanName)，由于第一次肯定为空:
public Object getSingleton(String beanName) { //在这里系统一般是允许早期对象引用的allowEarlyReference通过这个参数可以控制解决循环依赖 return getSingleton(beanName, true); }
进入到getSingleton(beanName, true)方法，这里涉及到Spring的三级缓存，用它来解决循环依赖：
protected Object getSingleton(String beanName, boolean allowEarlyReference) { /** * 第一步:我们尝试去一级缓存(单例缓存池中去获取对象,一般情况从该map中获取的对象是直接可以使用的) * Spring IoC容器初始化加载单实例bean的时候第一次进来的时候 该map中一般返回空 */ Object singletonObject = this.singletonObjects.get(beanName); /** * 若在第一级缓存中没有获取到对象,并且singletonsCurrentlyInCreation正在创建的单实例的list包含该beanName * Spring IoC容器初始化加载单实例bean的时候第一次进来的时候 该list中一般返回空,但是循环依赖的时候可以满足该条件 */ if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) { synchronized (this.singletonObjects) { /** * 尝试去二级缓存中获取对象(二级缓存中的对象是一个早期对象) * 何为早期对象:就是bean刚刚调用了构造方法，还没给bean的属性进行赋值的对象就是早期对象 */ singletonObject = this.earlySingletonObjects.get(beanName); /** * 二级缓存中也没有获取到对象,allowEarlyReference为true(参数是有上一个方法传递进来的true) */ if (singletonObject == null && allowEarlyReference) { /** * 直接从三级缓存中获取ObjectFactory对象 这个对接就是用来解决循环依赖的关键所在 * 在getBean的过程中,当bean调用了构造方法的时候,把早期对象包裹成一个ObjectFactory暴露到三级缓存中 */ ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName); //从三级缓存中获取到对象不为空 if (singletonFactory != null) { /** * 在这里通过暴露的ObjectFactory包装对象中,通过调用他的getObject()来获取我们的早期对象 * 在这个环节中会调用到 getEarlyBeanReference()来进行后置处理 */ singletonObject = singletonFactory.getObject(); //把早期对象放置在二级缓存, this.earlySingletonObjects.put(beanName, singletonObject); //ObjectFactory 包装对象从三级缓存中删除掉 this.singletonFactories.remove(beanName); } } } } return singletonObject; }
第二步：走else逻辑
Spring只能解决单例对象的setter注入的循环依赖,不能解决构造器注入，也不能解决多实例的循环依赖，所以会抛Bean当前正在创建的异常，接着判断是否有父工厂，有就调用父工厂的getBean，如果不是仅仅做类型检查，而是创建Bean对象，则需要调用markBeanAsCreated方法进行标识
合并Bean定义信息
① 接着调用getMergedLocalBeanDefinition(beanName)进行Bean定义的合并方法如下：
protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException { // 快速从缓存中获取，如果不为空，则直接返回 RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName); if (mbd != null) { return mbd; } //获取 RootBeanDefinition 对象。若获取的 BeanDefinition 为子 BeanDefinition，则需要合并父类的相关属性. return getMergedBeanDefinition(beanName, getBeanDefinition(beanName)); }
② 进入到getMergedBeanDefinition(beanName, getBeanDefinition(beanName))方法：
protected RootBeanDefinition getMergedBeanDefinition(String beanName, BeanDefinition bd) throws BeanDefinitionStoreException { //调用重载的方法 return getMergedBeanDefinition(beanName, bd, null); }
③ 进入到getMergedBeanDefinition(beanName, bd, null)的方法：
protected RootBeanDefinition getMergedBeanDefinition( String beanName, BeanDefinition bd, @Nullable BeanDefinition containingBd) throws BeanDefinitionStoreException { //加锁 synchronized (this.mergedBeanDefinitions) { RootBeanDefinition mbd = null; // Check with full lock now in order to enforce the same merged instance. if (containingBd == null) { mbd = this.mergedBeanDefinitions.get(beanName); } if (mbd == null) { //bd.getParentName() == null，表明无父配置，这时直接将当前的BeanDefinition升级为RootBeanDefinition if (bd.getParentName() == null) { //直接把原始的bean定义升级为RootBeanDefinition if (bd instanceof RootBeanDefinition) { mbd = ((RootBeanDefinition) bd).cloneBeanDefinition(); } else { //包裹为RootBeanDefinition mbd = new RootBeanDefinition(bd); } } //有父定义 else { BeanDefinition pbd; try { /* * 判断父类beanName与子类beanName名称是否相同。若相同，则父类bean一定 * 在父容器中。原因也很简单，容器底层是用Map缓存<beanName, bean> 键值对 * 的。同一个容器下，使用同一个 beanName 映射两个bean实例显然是不合适的 */ String parentBeanName = transformedBeanName(bd.getParentName()); if (!beanName.equals(parentBeanName)) { pbd = getMergedBeanDefinition(parentBeanName); } else { /* * 这里再次调用getMergedBeanDefinition，只不过参数值变为了 * parentBeanName，用于合并父BeanDefinition 和爷爷辈的 * BeanDefinition。如果爷爷辈的BeanDefinition仍有父 * BeanDefinition，则继续合并 */ BeanFactory parent = getParentBeanFactory(); if (parent instanceof ConfigurableBeanFactory) { pbd = ((ConfigurableBeanFactory) parent).getMergedBeanDefinition(parentBeanName); } else { throw new NoSuchBeanDefinitionException(parentBeanName, "Parent name '" + parentBeanName + "' is equal to bean name '" + beanName + "': cannot be resolved without an AbstractBeanFactory parent"); } } } catch (NoSuchBeanDefinitionException ex) { throw new BeanDefinitionStoreException(bd.getResourceDescription(), beanName, "Could not resolve parent bean definition '" + bd.getParentName() + "'", ex); } //以父BeanDefinition的配置信息为基本创建RootBeanDefinition mbd = new RootBeanDefinition(pbd); //用子BeanDefinition中的属性覆盖父BeanDefinition中的属性 mbd.overrideFrom(bd); } // 如果用户未配置scope属性，则默认将该属性配置为singleton if (!StringUtils.hasLength(mbd.getScope())) { mbd.setScope(RootBeanDefinition.SCOPE_SINGLETON); } // A bean contained in a non-singleton bean cannot be a singleton itself. // Let's correct this on the fly here, since this might be the result of // parent-child merging for the outer bean, in which case the original inner bean // definition will not have inherited the merged outer bean's singleton status. if (containingBd != null && !containingBd.isSingleton() && mbd.isSingleton()) { mbd.setScope(containingBd.getScope()); } //缓存合并后的BeanDefinition if (containingBd == null && isCacheBeanMetadata()) { this.mergedBeanDefinitions.put(beanName, mbd); } } return mbd; } }
④ 然后检查当前创建的bean定义是不是抽象的bean定义，checkMergedBeanDefinition(mbd, beanName, args)方法：
protected void checkMergedBeanDefinition(RootBeanDefinition mbd, String beanName, @Nullable Object[] args) throws BeanDefinitionStoreException { //抽象的bean定义是不能够被实例化的 if (mbd.isAbstract()) { throw new BeanIsAbstractException(beanName); } }
处理dependsOn的依赖(这个不是我们所谓的循环依赖 而是bean创建前后的依赖)
① 进入到isDependent(beanName, dependentBeanName, null)的方法：
private boolean isDependent(String beanName, String dependentBeanName, @Nullable Set<String> alreadySeen) { //alreadySeen已经检测的依赖bean if (alreadySeen != null && alreadySeen.contains(beanName)) { return false; } //获取原始beanName String canonicalName = canonicalName(beanName); //获取创建当前bean所依赖的bean的名称集合 Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName); //不依赖任何前置Bean直接返回 if (dependentBeans == null) { return false; } //存在，则证明存在已经注册的依赖 if (dependentBeans.contains(dependentBeanName)) { return true; } //递归检测依赖 for (String transitiveDependency : dependentBeans) { if (alreadySeen == null) { alreadySeen = new HashSet<>(); } //添加到alreadySeen 中 alreadySeen.add(beanName); //递归检查依赖 if (isDependent(transitiveDependency, dependentBeanName, alreadySeen)) { return true; } } return false; }
② 进入到保存的是依赖beanName之间的映射关系：依赖beanName -> beanName的集合registerDependentBean(dep, beanName)的方法：
public void registerDependentBean(String beanName, String dependentBeanName) { //获取原始的beanName String canonicalName = canonicalName(beanName); // 添加 <canonicalName, dependentBeanName> 到 dependentBeanMap 中 synchronized (this.dependentBeanMap) { Set<String> dependentBeans = this.dependentBeanMap.computeIfAbsent(canonicalName, k -> new LinkedHashSet<>(8)); if (!dependentBeans.add(dependentBeanName)) { return; } } // 添加 <dependentBeanName, canonicalName> 到 dependenciesForBeanMap 中 synchronized (this.dependenciesForBeanMap) { Set<String> dependenciesForBean = this.dependenciesForBeanMap.computeIfAbsent(dependentBeanName, k -> new LinkedHashSet<>(8)); dependenciesForBean.add(canonicalName); } }
③ 然后到获取dependsOn的Bean的getBean(dep)，就获取到了dependsOn的Bean了；
处理单实例Bean
① 把beanName和一个singletonFactory匿名内部类传入用于回调的getSingleton方法：
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) { Assert.notNull(beanName, "Bean name must not be null"); //加锁 synchronized (this.singletonObjects) { //尝试从单例缓存池中获取对象 Object singletonObject = this.singletonObjects.get(beanName); if (singletonObject == null) { if (this.singletonsCurrentlyInDestruction) { throw new BeanCreationNotAllowedException(beanName, "Singleton bean creation not allowed while singletons of this factory are in destruction " + "(Do not request a bean from a BeanFactory in a destroy method implementation!)"); } if (logger.isDebugEnabled()) { logger.debug("Creating shared instance of singleton bean '" + beanName + "'"); } /** * 标记当前的bean马上就要被创建了 * singletonsCurrentlyInCreation 在这里会把beanName加入进来，若第二次循环依赖（构造器注入会抛出异常） */ beforeSingletonCreation(beanName); boolean newSingleton = false; boolean recordSuppressedExceptions = (this.suppressedExceptions == null); if (recordSuppressedExceptions) { this.suppressedExceptions = new LinkedHashSet<>(); } try { //创建bean这个过程其实是调用 createBean() 方法 singletonObject = singletonFactory.getObject(); newSingleton = true; } catch (IllegalStateException ex) { //回调我们singletonObjects的get方法,进行正在的创建bean的逻辑 singletonObject = this.singletonObjects.get(beanName); if (singletonObject == null) { throw ex; } } catch (BeanCreationException ex) { if (recordSuppressedExceptions) { for (Exception suppressedException : this.suppressedExceptions) { ex.addRelatedCause(suppressedException); } } throw ex; } finally { if (recordSuppressedExceptions) { this.suppressedExceptions = null; } //后置处理主要做的事情就是把singletonsCurrentlyInCreation标记正在创建的bean从集合中移除 afterSingletonCreation(beanName); } if (newSingleton) { //加入缓存中 addSingleton(beanName, singletonObject); } } return singletonObject; } }
第一：先到单例缓存池中获取对象获取，有就返回没有就继续往下
第二：调用标记当前的bean马上就要被创建了beforeSingletonCreation(beanName)方法：
protected void beforeSingletonCreation(String beanName) { //若singletonsCurrentlyInCreation没有 则添加成功 if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) { throw new BeanCurrentlyInCreationException(beanName); }
第三：创建Bean的singletonFactory.getObject()其实是调用createBean()方法：
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; }
真正的创建我们的bean的实例对象的doCreateBean(beanName, mbdToUse, args)的方法：
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args) throws BeanCreationException { //BeanWrapper是对Bean的包装，其接口中所定义的功能很简单包括设置获取被包装的对象，获取被包装bean的属性描述器 BeanWrapper instanceWrapper = null; if (mbd.isSingleton()) { //从没有完成的FactoryBean中移除 instanceWrapper = this.factoryBeanInstanceCache.remove(beanName); } if (instanceWrapper == null) { //使用合适的实例化策略来创建新的实例：工厂方法、构造函数自动注入、简单初始化 比较复杂也很重要 instanceWrapper = createBeanInstance(beanName, mbd, args); } //从beanWrapper中获取我们的早期对象 final 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 { //进行后置处理@AutoWired的注解的预解析 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", ex); } mbd.postProcessed = true; } } /** * 该对象进行判断是否能够暴露早期对象的条件 * 单实例 this.allowCircularReferences 默认为true * isSingletonCurrentlyInCreation(表示当前的bean对象正在创建singletonsCurrentlyInCreation包含当前正在创建的bean) */ boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName)); //上述条件满足，允许中期暴露对象 if (earlySingletonExposure) { if (logger.isDebugEnabled()) { logger.debug("Eagerly caching bean '" + beanName + "' to allow for resolving potential circular references"); } //把我们的早期对象包装成一个singletonFactory对象 该对象提供了一个getObject方法,该方法内部调用getEarlyBeanReference方法 addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); } // Initialize the bean instance. Object exposedObject = bean; try { //给我们的属性进行赋值(调用set方法进行赋值) populateBean(beanName, mbd, instanceWrapper); //进行对象初始化操作(在这里可能生成代理对象) 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); } } //允许早期对象的引用 if (earlySingletonExposure) { /** * 去缓存中获取到我们的对象 由于传递的allowEarlyReference 是false 要求只能在一级二级缓存中去获取 * 正常普通的bean(不存在循环依赖的bean) 创建的过程中，压根不会把三级缓存提升到二级缓存中 */ Object earlySingletonReference = getSingleton(beanName, false); //能够获取到 if (earlySingletonReference != null) { //经过后置处理的bean和早期的bean引用还相等的话(表示当前的bean没有被代理过) if (exposedObject == bean) { exposedObject = earlySingletonReference; } //处理依赖的bean 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 " + "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example."); } } } } // Register bean as disposable. try { //注册销毁的bean的销毁接口 registerDisposableBeanIfNecessary(beanName, bean, mbd); } catch (BeanDefinitionValidationException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); } return exposedObject; }
① 实例化：使用合适的实例化策略来创建新的实例：工厂方法、构造函数自动注入、简单初始化的createBeanInstance方法：
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) { //从bean定义中解析出当前bean的class对象 Class<?> beanClass = resolveBeanClass(mbd, beanName); //检测类的访问权限。默认情况下，对于非 public 的类，是允许访问的。若禁止访问，这里会抛出异常 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()); } Supplier<?> instanceSupplier = mbd.getInstanceSupplier(); if (instanceSupplier != null) { return obtainFromSupplier(instanceSupplier, beanName); } //工厂方法,我们通过配置类来进行配置的话 采用的就是工厂方法 if (mbd.getFactoryMethodName() != null) { return instantiateUsingFactoryMethod(beanName, mbd, args); } //判断当前构造函数是否被解析过 boolean resolved = false; //有没有必须进行依赖注入 boolean autowireNecessary = false; /** * 通过getBean传入进来的构造函数是否来指定需要推断构造函数 * 若传递进来的args不为空，那么就可以直接选出对应的构造函数 */ if (args == null) { synchronized (mbd.constructorArgumentLock) { //判断我们的bean定义信息中的resolvedConstructorOrFactoryMethod(用来缓存我们的已经解析的构造函数或者工厂方法) if (mbd.resolvedConstructorOrFactoryMethod != null) { //修改已经解析过的构造函数的标志 resolved = true; //修改标记为ture 标识构造函数或者工厂方法已经解析过 autowireNecessary = mbd.constructorArgumentsResolved; } } } //若被解析过 if (resolved) { if (autowireNecessary) { //通过有参的构造函数进行反射调用 return autowireConstructor(beanName, mbd, null, null); } else { //调用无参数的构造函数进行创建对象 return instantiateBean(beanName, mbd); } } //通过bean的后置处理器进行选举出合适的构造函数对象 Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); //通过后置处理器解析出构造器对象不为null或获取bean定义中的注入模式是构造器注入或bean定义信息ConstructorArgumentValues或获取通过getBean的方式传入的构造器函数参数类型不为null if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { //通过构造函数创建对象 return autowireConstructor(beanName, mbd, ctors, args); } //使用无参数的构造函数调用创建对象 return instantiateBean(beanName, mbd); }
判断是否暴露早期对象条件满足就暴露早期对象，把我们的早期对象包装成一个singletonFactory对象 该对象提供了一个getObject方法,该方法内部调用getEarlyBeanReference方法：
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) { Object exposedObject = bean; //判读我们容器中是否有InstantiationAwareBeanPostProcessors类型的后置处理器 if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { //获取我们所有的后置处理器 for (BeanPostProcessor bp : getBeanPostProcessors()) { //判断我们的后置处理器是不是实现了SmartInstantiationAwareBeanPostProcessor接口 if (bp instanceof SmartInstantiationAwareBeanPostProcessor) { //进行强制转换 SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp; //挨个调用SmartInstantiationAwareBeanPostProcessor的getEarlyBeanReference exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName); } } } return exposedObject; }
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean))方法：
/** * 该方法用于把早期对象包装成一个ObjectFactory 暴露到三级缓存中 用于将解决循环依赖 * @param beanName the name of the bean * @param singletonFactory the factory for the singleton object */ protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) { Assert.notNull(singletonFactory, "Singleton factory must not be null"); //加锁 synchronized (this.singletonObjects) { //单例缓存池中没有包含当前的bean if (!this.singletonObjects.containsKey(beanName)) { //加入到三级缓存中 暴露早期对象用于解决循环依赖 this.singletonFactories.put(beanName, singletonFactory); this.earlySingletonObjects.remove(beanName); this.registeredSingletons.add(beanName); } } }
②属性赋值：给我们的属性进行赋值(调用set方法进行赋值)populateBean(beanName, mbd, instanceWrapper)方法：
/** *给我们的对象BeanWrapper属性赋值 * @param beanName bean的名称 * @param mbd bean的定义 * @param bw bean实例包装对象 */ protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) { //若bw为null的话,则说明对象没有实例化 if (bw == null) { //进入if说明对象有属性，bw为空,不能为他设置属性，那就在下面就执行抛出异常 if (mbd.hasPropertyValues()) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance"); } else { // Skip property population phase for null instance. return; } } /** * 在属性被填充前，给 InstantiationAwareBeanPostProcessor 类型的后置处理器一个修改 * bean 状态的机会。官方的解释是：让用户可以自定义属性注入。比如用户实现一 * 个 InstantiationAwareBeanPostProcessor 类型的后置处理器，并通过 * postProcessAfterInstantiation 方法向 bean 的成员变量注入自定义的信息。 *当时我们发现系统中的的InstantiationAwareBeanPostProcessor.postProcessAfterInstantiationM没有进行任何处理， *若我们自己实现了这个接口 可以自定义处理.....spring 留给我们自己扩展接口的 *特殊需求，直接使用配置中的信息注入即可。 */ boolean continueWithPropertyPopulation = true; //是否持有 InstantiationAwareBeanPostProcessor if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { //获取容器中的所有的BeanPostProcessor for (BeanPostProcessor bp : getBeanPostProcessors()) { //判断我们的后置处理器是不是InstantiationAwareBeanPostProcessor if (bp instanceof InstantiationAwareBeanPostProcessor) { //进行强制转化 InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; //若存在后置处理器给我们属性赋值了，那么返回false 可以来修改我们的开关变量，就不会走下面的逻辑了 if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) { // 返回值为是否继续填充 bean // postProcessAfterInstantiation：如果应该在 bean上面设置属性则返回 true，否则返回 false // 一般情况下，应该是返回true 。 // 返回 false 的话，将会阻止在此 Bean 实例上调用任何后续的 InstantiationAwareBeanPostProcessor 实 continueWithPropertyPopulation = false; break; } } } } // 如果后续处理器发出停止填充命令，则终止后续操作 if (!continueWithPropertyPopulation) { return; } //获取bean定义的属性 PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null); /** * 判断我们的bean的属性注入模型 * AUTOWIRE_BY_NAME 根据名称注入 * AUTOWIRE_BY_TYPE 根据类型注入 */ if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_NAME || mbd.getResolvedAutowireMode() == AUTOWIRE_BY_TYPE) { //把PropertyValues封装成为MutablePropertyValues MutablePropertyValues newPvs = new MutablePropertyValues(pvs); //根据bean的属性名称注入 if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_NAME) { autowireByName(beanName, mbd, bw, newPvs); } //根据bean的类型进行注入 if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_TYPE) { autowireByType(beanName, mbd, bw, newPvs); } //把处理过的 属性覆盖原来的 pvs = newPvs; } /** * 这里又是一种后置处理，用于在 Spring 填充属性到 bean 对象前，对属性的值进行相应的处理， * 比如可以修改某些属性的值。这时注入到 bean 中的值就不是配置文件中的内容了， * 而是经过后置处理器修改后的内容 */ boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors(); //判断是否需要检查依赖 boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE); if (hasInstAwareBpps || needsDepCheck) { if (pvs == null) { pvs = mbd.getPropertyValues(); } //提出当前正在创建的beanWrapper 依赖的对象 PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching); if (hasInstAwareBpps) { //获取所有的后置处理器 for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; //对依赖对象进行后置处理 pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName); if (pvs == null) { return; } } } } //判断是否检查依赖 if (needsDepCheck) { checkDependencies(beanName, mbd, filteredPds, pvs); } } /** * 其实，上面只是完成了所有注入属性的获取，将获取的属性封装在 PropertyValues 的实例对象 pvs 中， * 并没有应用到已经实例化的 bean 中。而 #applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) 方法， * 则是完成这一步骤的 */ if (pvs != null) { applyPropertyValues(beanName, mbd, bw, pvs); } }
③初始化：进行对象初始化操作调用initializeBean，这里会进行Aware接口进行方法的回调，然后调用Bean的后置处理器的Before方法（postProcessorsBeforeInitialization），然后Bean的初始化方法，最后调用Bean的后置处理器的After方法（PostProcessorsAfterInitialization）
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) { if (System.getSecurityManager() != null) { AccessController.doPrivileged((PrivilegedAction<Object>) () -> { invokeAwareMethods(beanName, bean); return null; }, getAccessControlContext()); } else { //若我们的Bean实现了Aware接口进行方法的回调 invokeAwareMethods(beanName, bean); } Object wrappedBean = bean; if (mbd == null || !mbd.isSynthetic()) { //调用我们的bean的后置处理器的postProcessorsBeforeInitialization方法 wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName); } try { //调用初始化方法 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()) { //调用我们bean的后置处理器的PostProcessorsAfterInitialization方法 动态代理就是在这里实现的 wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName); } return wrappedBean; }
进入调用初始化方法invokeInitMethods(beanName, wrappedBean, mbd)方法：
protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd) throws Throwable { //判断我们的容器中是否实现了InitializingBean接口 boolean isInitializingBean = (bean instanceof InitializingBean); if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) { if (logger.isDebugEnabled()) { logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'"); } if (System.getSecurityManager() != null) { try { AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> { ((InitializingBean) bean).afterPropertiesSet(); return null; }, getAccessControlContext()); } catch (PrivilegedActionException pae) { throw pae.getException(); } } else { //回调InitializingBean的afterPropertiesSet()方法 ((InitializingBean) bean).afterPropertiesSet(); } } if (mbd != null && bean.getClass() != NullBean.class) { //我们beanClass中看是否有自己定义的init方法 String initMethodName = mbd.getInitMethodName(); //判断自定义的init方法名称不叫afterPropertiesSet if (StringUtils.hasLength(initMethodName) && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) && !mbd.isExternallyManagedInitMethod(initMethodName)) { //调用我们自己的初始化方法 invokeCustomInitMethod(beanName, bean, mbd); } } }
至此doCreateBean创建完成然后返回
接下来bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd)，为什么不直接等于sharedInstance，原因可能刚刚创建的Bean是FactoryBean类型的Bean，如果是就要调用getObject方法来获取真正的Bean，运用场景就是那些创建Bean的逻辑比较复杂的情况下可以用这个，比如Spring整合Mybatis的SqlSessionFactoryBean
getObjectForBeanInstance(sharedInstance, name, beanName, mbd)方法：
protected Object getObjectForBeanInstance( Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) { // 如果name以&开头，但beanInstance却不是FactoryBean，则认为有问题。 if (BeanFactoryUtils.isFactoryDereference(name)) { if (beanInstance instanceof NullBean) { return beanInstance; } if (!(beanInstance instanceof FactoryBean)) { throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass()); } } /** * 如果上面的判断通过了，表明 beanInstance 可能是一个普通的 bean，也可能是一个 * FactoryBean。如果是一个普通的 bean，这里直接返回 beanInstance 即可。如果是 * FactoryBean，则要调用工厂方法生成一个 bean 实例。 */ if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) { return beanInstance; } Object object = null; if (mbd == null) { /** * 如果 mbd 为空，则从缓存中加载 bean。FactoryBean 生成的单例 bean 会被缓存 * 在 factoryBeanObjectCache 集合中，不用每次都创建 */ object = getCachedObjectForFactoryBean(beanName); } if (object == null) { // 经过前面的判断，到这里可以保证beanInstance是 FactoryBean类型的，所以可以进行类型转换 FactoryBean<?> factory = (FactoryBean<?>) beanInstance; // 如果 mbd 为空，则判断是否存在名字为 beanName 的 BeanDefinition if (mbd == null && containsBeanDefinition(beanName)) { mbd = getMergedLocalBeanDefinition(beanName); } //synthetic 字面意思是"合成的"。通过全局查找，我发现在 AOP 相关的类中会将该属性设为 true。 //所以我觉得该字段可能表示某个 bean 是不是被 AOP 增强过，也就是 AOP 基于原始类合成了一个新的代理类。 //不过目前只是猜测，没有深究 boolean synthetic = (mbd != null && mbd.isSynthetic()); //调用 getObjectFromFactoryBean 方法继续获取实例 object = getObjectFromFactoryBean(factory, beanName, !synthetic); } return object; }
接着调用object = getObjectFromFactoryBean(factory, beanName, !synthetic)方法：
protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) { /** * FactoryBean 也有单例和非单例之分，针对不同类型的 FactoryBean，这里有两种处理方式： * 1. 单例 FactoryBean 生成的 bean 实例也认为是单例类型。需放入缓存中，供后续重复使用 * 2. 非单例 FactoryBean 生成的 bean 实例则不会被放入缓存中，每次都会创建新的实例 **/ if (factory.isSingleton() && containsSingleton(beanName)) { synchronized (getSingletonMutex()) { //从缓存中取bean实例，避免多次创建bean实例 Object object = this.factoryBeanObjectCache.get(beanName); if (object == null) { //使用工厂对象中创建实例 object = doGetObjectFromFactoryBean(factory, beanName); // Only post-process and store if not put there already during getObject() call above // (e.g. because of circular reference processing triggered by custom getBean calls) Object alreadyThere = this.factoryBeanObjectCache.get(beanName); if (alreadyThere != null) { object = alreadyThere; } else { if (shouldPostProcess) { //判断当地的bean是否正在创建 if (isSingletonCurrentlyInCreation(beanName)) { // Temporarily return non-post-processed object, not storing it yet.. return object; } beforeSingletonCreation(beanName); try { object = postProcessObjectFromFactoryBean(object, beanName); } catch (Throwable ex) { throw new BeanCreationException(beanName, "Post-processing of FactoryBean's singleton object failed", ex); } finally { afterSingletonCreation(beanName); } } // 这里的beanName对应于FactoryBean的实现类，FactoryBean的实现类也会被实例化，并被缓存在singletonObjects中 if (containsSingleton(beanName)) { // 这里的beanName对应于FactoryBean的实现类，FactoryBean的实现类也会被实例化，并被缓存在singletonObjects中 this.factoryBeanObjectCache.put(beanName, object); } } } return object; } } else { Object object = doGetObjectFromFactoryBean(factory, beanName); if (shouldPostProcess) { try { object = postProcessObjectFromFactoryBean(object, beanName); } catch (Throwable ex) { throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex); } } return object; } }
使用工厂对象中创建实例object = doGetObjectFromFactoryBean(factory, beanName)方法：
private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName) throws BeanCreationException { Object object; try { if (System.getSecurityManager() != null) { AccessControlContext acc = getAccessControlContext(); try { object = AccessController.doPrivileged((PrivilegedExceptionAction<Object>) factory::getObject, acc); } catch (PrivilegedActionException pae) { throw pae.getException(); } } else { //真正的调用工厂bean的getObject()方法 object = factory.getObject(); } } catch (FactoryBeanNotInitializedException ex) { throw new BeanCurrentlyInCreationException(beanName, ex.toString()); } catch (Throwable ex) { throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex); } // Do not accept a null value for a FactoryBean that's not fully // initialized yet: Many FactoryBeans just return null then. if (object == null) { if (isSingletonCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException( beanName, "FactoryBean which is currently in creation returned null from getObject"); } object = new NullBean(); } return object; }
处理多实例Bean
mbd.isPrototype()，每次使用的时候再创建，因为不会加入到单实例缓冲池中，也就无法解决循环依赖问题。
至此doGetBean创建完成，返回，getBean创建完成
最后获取所有的bean的名称（至此所有的单实例的bean已经加入到单实例Bean的缓存池中，所谓的单实例缓存池实际上就是一个ConcurrentHashMap），遍历所有的bean名称，根据beanName从单例缓存池中获取所有的对象，然后判断是否是SmartInitializingSingleton类型，是再触发实例化之后的方法afterSingletonsInstantiated；
完整的Spring IoC源码解析见：Spring系列（三）：Spring IoC源码解析
三、getBean流程图
① getBean流程图：
② @AutoWired注入属性和set方法注入流程图：
总结：通过对Spring IoC的getBean流程分析，了解了Bean的创建过程，先到单实例缓存池(ConcurrentHashMap)中获取，取不到就调用createBean创建，创建成功后加入到单实例缓存池(ConcurrentHashMap)中，下次获取的时候直接从JVM级别的缓存中获取，Bean的生命周期，以及如何用三级缓存解决循环依赖，还有就是多实例为什么不能解决循环依赖问题。
