spring源码篇(3)——bean的加载和创建

spring-framework 版本：v5.3.19

bean的加载

beanFactory的genBean最常用的一个实现就是AbstractBeanFactory.getBean()。
以ApplicationContext为例，流程是: ApplicationContext.getBean()----》BeanFactory.getBean()----》AbstractBeanFactory.getBean()

而真正做事情的是deGetBean方法

protected <T> T doGetBean(String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)throws BeansException {//获取beanNameString beanName = transformedBeanName(name);Object beanInstance;//无论是什么作用域都先尝试从单例池获取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 + "'");}}//有时候并不是放回实例本身，而是返回其映射的实例。如：BeanFactory情况下返回指定方法返回的实例beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);}else {//当原型模式下有循环依赖时，抛异常（原型模式下若存在循环依赖会导致内存泄漏）if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);}//尝试从父beanFactory加载beanBeanFactory parentBeanFactory = getParentBeanFactory();if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {String nameToLookup = originalBeanName(name);if (parentBeanFactory instanceof AbstractBeanFactory) {return ((AbstractBeanFactory) parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);}else if (args != null) {return (T) parentBeanFactory.getBean(nameToLookup, args);}else if (requiredType != null) {return parentBeanFactory.getBean(nameToLookup, requiredType);}else {return (T) parentBeanFactory.getBean(nameToLookup);}}//如果不是仅仅做类型检查则是创建bean，这里进行记录if (!typeCheckOnly) {markBeanAsCreated(beanName);}StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate").tag("beanName", name);try {if (requiredType != null) {beanCreation.tag("beanType", requiredType::toString);}//得到合并后的beanDefinitionRootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);//检查beanDefinition，抽象的beanDefinition会报错checkMergedBeanDefinition(mbd, beanName, args);//先加载dependsOn标注的beanString[] dependsOn = mbd.getDependsOn();if (dependsOn != null) {for (String dep : dependsOn) {//dePendsOn引起的循环依赖，抛异常if (isDependent(beanName, dep)) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");}//注册dependentBeanMap（dependsOn 于哪些bean）和注册dependenciesForBeanMap（被哪些bean dependOn）registerDependentBean(dep, beanName);try {getBean(dep);}catch (NoSuchBeanDefinitionException ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,"'" + beanName + "' depends on missing bean '" + dep + "'", ex);}}}//-----------------------------------开始创建bean-----------------------------------------------//单例模式if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, () -> {try {return createBean(beanName, mbd, args);}catch (BeansException ex) {destroySingleton(beanName);throw ex;}});beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);}//原型模式else if (mbd.isPrototype()) {Object prototypeInstance = null;try {beforePrototypeCreation(beanName);prototypeInstance = createBean(beanName, mbd, args);}finally {afterPrototypeCreation(beanName);}beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);}//其他模式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();}}//必要时进行类型转换return adaptBeanInstance(name, beanInstance, requiredType);}

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bean的创建

从bean的加载中得知，当一个从缓存中获取不到的时候就会调用createBean方法去创建一个bean。而在AbstractBeanFactory中这是一个抽象方法，具体的创建逻辑由具体的beanFactory类自行实现。至少目前为止，spring内置的实现只有AbstractAutowireCapableBeanFactory.createBean()。无论是AnnotationConfigApplicationContext还是ClassPathXmlApplicationContext创建bean的逻辑最终都会来到这个方法。

虽然AnnotationConfigApplicationContext和ClassPathXmlApplicationContext并不直接继承AbstractAutowireCapableBeanFactory。但是都维护了一个DefaultListableBeanFactory成员变量，而这个成员变量继承自AbstractAutowireCapableBeanFactory。

createBean

doCreateBean

protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)throws BeanCreationException {//如果是单例，factoryBeanCache.removeBeanWrapper instanceWrapper = null;if (mbd.isSingleton()) {instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);}//实例化beanif (instanceWrapper == null) {instanceWrapper = createBeanInstance(beanName, mbd, args);}Object bean = instanceWrapper.getWrappedInstance();Class<?> beanType = instanceWrapper.getWrappedClass();if (beanType != NullBean.class) {mbd.resolvedTargetType = beanType;}//MergedBeanDefinitionPostProcessor的应用（如：AutowiredAnnotationBeanPostProcessor）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;}}//提前暴露bean，循环依赖处理boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&isSingletonCurrentlyInCreation(beanName));if (earlySingletonExposure) {if (logger.isTraceEnabled()) {logger.trace("Eagerly caching bean '" + beanName +"' to allow for resolving potential circular references");}addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));}Object exposedObject = bean;try {//属性填充//填充属性之前会调用 InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation//填充属性之后会调用 InstantiationAwareBeanPostProcessor.postProcessProperties --如果返回null--> postProcessPropertyValuespopulateBean(beanName, mbd, instanceWrapper);//初始化bean（是指据配置自定义的初始化bean如：@PostConstruct，而不是指构造方法的初始化）//初始化之前会调用 PostProcessors.postProcessBeforeInitialization//初始化之后会调用 PostProcessors.postProcessAfterInstantiationexposedObject = 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);}}//循环依赖检查，判断是否需要抛出异常if (earlySingletonExposure) {Object earlySingletonReference = getSingleton(beanName, false);if (earlySingletonReference != null) {if (exposedObject == bean) {exposedObject = earlySingletonReference;}else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {String[] dependentBeans = getDependentBeans(beanName);Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);for (String dependentBean : dependentBeans) {if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {actualDependentBeans.add(dependentBean);}}if (!actualDependentBeans.isEmpty()) {throw new BeanCurrentlyInCreationException(beanName,"Bean with name '" + beanName + "' has been injected into other beans [" +StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +"] in its raw version as part of a circular reference, but has eventually been " +"wrapped. This means that said other beans do not use the final version of the " +"bean. This is often the result of over-eager type matching - consider using " +"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");}}}}//注册DisposableBean，如果配置了destroy-methoy，这里需要注册以便于在销毁的时候调用try {registerDisposableBeanIfNecessary(beanName, bean, mbd);}catch (BeanDefinitionValidationException ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);}return exposedObject;}

initializeBean

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总结

getBean流程

1：transformedBeanName(name) 转换为对应的beanName
2：getSingleton(beanName) 尝试从缓存中加载单例
3：isPrototypeCurrentlyIncreation(beanName) 原型模式的依赖检查
4：检测父BeanFactory
5：getMergedLocalBeanDefinition(beanName) GernericBeanDefinition转换为RootBeanDefinition
6：依赖检测
7：根据不同的模式创建bean
8：getObjectForBeanInstance(prototypeInstance, name, beanName, mbd) 根据得到的Bean获取真正对象
9：如果需要则做类型转换

createBean流程

1：锁定class
2：指定方法的覆盖
3：InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation
4：doCreateBean

doCreateBean流程

1：若为单例，移除factoryBeanCache内的缓存
2：实例化Bean
3：MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition（如：AutowiredAnnotationBeanPostProcessor）
4：提前暴露bean，循环依赖处理

(populateBean)
5：InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation
6：属性填充
7：InstantiationAwareBeanPostProcessor.postProcessProperties --如果返回null–> postProcessPropertyValues

(initializeBean)
8：aware方法的执行（beanNameAware，beanClassLoaderAware，beanFactoryAware）
9：PostProcessors.postProcessBeforeInitialization
10：自定义初始化bean（如：InitializingBean.afterPropertiesSet，@PostConstruct，init-method）
11：PostProcessors.postProcessAfterInstantiation

12：循环依赖检查，判断是否需要抛出异常
13：注册DisposableBean