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Spring三级缓存解决循环依赖( 三 )

spring

  • 执行到B对象的属性填充时 ， 发现依赖了A对象 ， 执行AbstracBeanFactory.getBean方法 ， 尝试获取A对象 。
  • 在AbstracBeanFactory.doGetBean方法中执行DefaultSingletonBeanRegistry#getSingleton方法 ， 尝试从缓存中获取A对象的单例对象缓存 。到一级缓存singletonObjects中找 ， 未找到； 到二级缓存earlySingletonObjects中找 ， 未找到； 到三级缓存singletonFactories中找 ， 找到了 ， 并调用ObjectFactory的getObject方法获取A对象的引用 ， ObjectFactory内部调用了AbstractAutowireCapableBeanFactory#getEarlyBeanReference ， 获取到A的早期对象 ， 将A的早期对象放入二级缓存earlySingletonObjects中 ， 并将三级缓存singletonFactories中A对象移除；
  • 这样拿到A的对象之后 ， B的属性填充完毕 ， B初始化完成 ， 方法return到DefaultSingletonBeanRegistry#getSingleton的重载方法时 ， 调用DefaultSingletonBeanRegistry#addSingleton方法 ， 将B对象放入一级缓存 ， 并将B从二三级缓存中移除（虽然已经没有了） 。
  • 这样在return回A的流程 ， 第11步 ， 将A依赖的B属性填充完整 ， 此时A也填充完毕 ， 初始化完成 ， 方法继续return到A流程的DefaultSingletonBeanRegistry#getSingleton的重载方法时 ， 调用DefaultSingletonBeanRegistry#addSingleton方法 ， 将A对象放入一级缓存 ， 并将A从二三级缓存中移除（此时只有二级缓存中有） 。
  • 这样A和B就初始化完成了 。
  • 如果A或者B存在AOP ， 需要返回代理对象 ， 这操作是在第9步的AbstractAutowireCapableBeanFactory#getEarlyBeanReference中完成的 ， B尝试获取A的时候 ， 触发了这个方法 ， 如果A需要被代理 ， 则是在这个方法中执行的 ， 这个方法最终返回了一个代理对象 ， 并将这个对象以A的名义放入了二级缓存 。
  • 打完收工 。
    • 源码
    AbstractApplicationContext#refresh#finishBeanFactoryInitialization 入口类方法 刷新上下文 ， 初始化BeanFactory ， 完成工厂初始化 。
    DefaultListableBeanFactory#preInstantiateSingletons 准备实例化单例对象
    @Overridepublic void preInstantiateSingletons() throws BeansException {if (logger.isTraceEnabled()) {logger.trace("Pre-instantiating singletons in " + this);}// Iterate over a copy to allow for init methods which in turn register new bean definitions.// While this may not be part of the regular factory bootstrap, it does otherwise work fine.List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);// Trigger initialization of all non-lazy singleton beans...for (String beanName : beanNames) {RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {if (isFactoryBean(beanName)) {Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);if (bean instanceof FactoryBean) {FactoryBean<?> factory = (FactoryBean<?>) bean;boolean isEagerInit;if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,getAccessControlContext());}else {isEagerInit = (factory instanceof SmartFactoryBean &&((SmartFactoryBean<?>) factory).isEagerInit());}if (isEagerInit) {getBean(beanName);}}}else {getBean(beanName);}}}// Trigger post-initialization callback for all applicable beans...for (String beanName : beanNames) {Object singletonInstance = getSingleton(beanName);if (singletonInstance instanceof SmartInitializingSingleton) {StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize").tag("beanName", beanName);SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {smartSingleton.afterSingletonsInstantiated();return null;}, getAccessControlContext());}else {smartSingleton.afterSingletonsInstantiated();}smartInitialize.end();}}}AbstractBeanFactory#getBean(JAVA.lang.String) 获取bean对象
    @Overridepublic Object getBean(String name) throws BeansException {return doGetBean(name, null, null, false);}AbstractBeanFactory#doGetBean 实际执行获取bean对象
    /*** Return an instance, which may be shared or independent, of the specified bean.* @param name the name of the bean to retrieve* @param requiredType the required type of the bean to retrieve* @param args arguments to use when creating a bean instance using explicit arguments* (only applied when creating a new instance as opposed to retrieving an existing one)* @param typeCheckOnly whether the instance is obtained for a type check,* not for actual use* @return an instance of the bean* @throws BeansException if the bean could not be created*/@SuppressWarnings("unchecked")protected <T> T doGetBean(String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)throws BeansException {String beanName = transformedBeanName(name);Object beanInstance;// Eagerly check singleton cache for manually registered singletons.Object sharedInstance = getSingleton(beanName);if (sharedInstance != null && args == null) {if (logger.isTraceEnabled()) {if (isSingletonCurrentlyInCreation(beanName)) {logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +"' that is not fully initialized yet - a consequence of a circular reference");}else {logger.trace("Returning cached instance of singleton bean '" + beanName + "'");}}beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);}else {// Fail if we're already creating this bean instance:// We're assumably within a circular reference.if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);}// Check if bean definition exists in this factory.BeanFactory parentBeanFactory = getParentBeanFactory();if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {// Not found -> check parent.String nameToLookup = originalBeanName(name);if (parentBeanFactory instanceof AbstractBeanFactory) {return ((AbstractBeanFactory) parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);}else if (args != null) {// Delegation to parent with explicit args.return (T) parentBeanFactory.getBean(nameToLookup, args);}else if (requiredType != null) {// No args -> delegate to standard getBean method.return parentBeanFactory.getBean(nameToLookup, requiredType);}else {return (T) parentBeanFactory.getBean(nameToLookup);}}if (!typeCheckOnly) {markBeanAsCreated(beanName);}StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate").tag("beanName", name);try {if (requiredType != null) {beanCreation.tag("beanType", requiredType::toString);}RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);checkMergedBeanDefinition(mbd, beanName, args);// Guarantee initialization of beans that the current bean depends on.String[] dependsOn = mbd.getDependsOn();if (dependsOn != null) {for (String dep : dependsOn) {if (isDependent(beanName, dep)) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");}registerDependentBean(dep, beanName);try {getBean(dep);}catch (NoSuchBeanDefinitionException ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,"'" + beanName + "' depends on missing bean '" + dep + "'", ex);}}}// Create bean instance.if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, () -> {try {return createBean(beanName, mbd, args);}catch (BeansException ex) {// Explicitly remove instance from singleton cache: It might have been put there// eagerly by the creation process, to allow for circular reference resolution.// Also remove any beans that received a temporary reference to the bean.destroySingleton(beanName);throw ex;}});beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);}else if (mbd.isPrototype()) {// It's a prototype -> create a new instance.Object prototypeInstance = null;try {beforePrototypeCreation(beanName);prototypeInstance = createBean(beanName, mbd, args);}finally {afterPrototypeCreation(beanName);}beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);}else {String scopeName = mbd.getScope();if (!StringUtils.hasLength(scopeName)) {throw new IllegalStateException("No scope name defined for bean ´" + beanName + "'");}Scope scope = this.scopes.get(scopeName);if (scope == null) {throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");}try {Object scopedInstance = scope.get(beanName, () -> {beforePrototypeCreation(beanName);try {return createBean(beanName, mbd, args);}finally {afterPrototypeCreation(beanName);}});beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);}catch (IllegalStateException ex) {throw new ScopeNotActiveException(beanName, scopeName, ex);}}}catch (BeansException ex) {beanCreation.tag("exception", ex.getClass().toString());beanCreation.tag("message", String.valueOf(ex.getMessage()));cleanupAfterBeanCreationFailure(beanName);throw ex;}finally {beanCreation.end();}}return adaptBeanInstance(name, beanInstance, requiredType);}


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