finishBeanFactoryInitialization(beanFactory)：初始化不需要延迟实例化的单例bean
/* org/springframework/context/support/AbstractApplicationContext.java:870 */
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {//初始化容器的conversionService
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));
}
//如果没有任何一个类似PropertyPlaceholderConfigurer bean处理器
//默认一个嵌入式值解析器，主要是为了解析属性值例如数据库连接中${password}等属性解析
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// 先实例化LoadTimeWeaverAware相关的beans，以便尽早转换，AOP相关
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
//删除临时类加载器，停止临时类加载器进行类型匹配
beanFactory.setTempClassLoader(null);
//拷贝beandefinitionNames到frozenBeanDefinitionNames
beanFactory.freezeConfiguration();
// 实例化所有不需要延迟初始化的单例bean
beanFactory.preInstantiateSingletons();
}
beanFactory.preInstantiateSingletons()：实例化所有不需要延迟初始化的单例bean
/* org/springframework/beans/factory/support/DefaultListableBeanFactory.java:885 */
public 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.
//拷贝beanDefinitionNames副本，考虑到遍历中其他线程可能修改beandefinitionNames
// ArrayList类型遍历时规避fast-fail，实现fast-safe
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
//当bean存在parentBean时的继承关系
//① bean不存在parentBean时，创建一个new RootBeanDefinition(beandefinition)返回。
//② bean存在parentBean时，支持继承关系
// 需要先创建parentBean的new RootBeanDefinition(parentBeanDefinition)
// 然后用beandefinition覆盖parentBean的RootBeanDefinition的相关属性并返回。superBean.overrideFrom(subBean);
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//用mergedLocalBeanDefinition判断是否需要初始化
//筛选不是抽象类且不是延迟实例化的单例进行初始化
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
//工厂Bean beanName=&beanName
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());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
//不是工厂bean 直接初始化
getBean(beanName);
}
}
}
//SmartInitializingSingleton类型的单例初始化后的回调
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
getBean(beanName):Bean初始化
/* org/springframework/beans/factory/support/AbstractBeanFactory.java:414 */
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
//如果是aliaName，解析成beanName
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
//检查单例缓存中是否存在bean的实例化对象、初始化对象 （涉及循环依赖解决，需要先分清出Bean的两个阶段实例化、初始化）
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 + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
if (isPrototypeCurrentlyInCreation(beanName)) {
//多例bean正在初始化时抛出异常
//由于多例bean，每调用一次getBean就会创建一个实例，
//所以通过ThreadLocal打标，来避免单个线程的重复创建
throw new BeanCurrentlyInCreationException(beanName);
}
BeanFactory parentBeanFactory = getParentBeanFactory();
//父容器不为空，用父容器初始化
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) {
//alreadyCreated容器记录已经被实例化的beanName，
//这里将beanName添加到alreadyCreated
markBeanAsCreated(beanName);
}
try {
//重新获取mergedLocalBeanDefinition（bean与parentBean合并）
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
//检查mbd不是抽象类
checkMergedBeanDefinition(mbd, beanName, args);
//创建bean单例之前，需要保证先bean所依赖的Bean单例已创建，
//这里的依赖对应@dependsOn声明的依赖，这个注解不常用，这里也会出现一种循环依赖场景，与我们平常讨论的引用循环依赖不同
//@dependsOn(value = "b") class A;@dependsOn(value = "a") class B
//如果出现这种循环依赖 会直接抛出异常 启动失败
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 + "'");
}
//保存依赖关系到dependentBeanMap容器中
registerDependentBean(dep, beanName);
try {
//实例化依赖的bean 这里就是常见循环依赖地点 A依赖B B依赖A
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// Create bean instance.
if (mbd.isSingleton()) {
//单例Bean创建 先取缓存，没有才createBean
sharedInstance = getSingleton(beanName, () -> {
try {
//创建Bean实例
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
//多例Bean创建 直接createbean
Object prototypeInstance = null;
try {
//正在创建bean打标prototypesCurrentlyInCreation
//与上面isPrototypeCurrentlyInCreation()联合
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
//正在创建bean打标prototypesCurrentlyInCreation删除标记
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
//自定义scope初始化、scope.get()
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;
}
}
//getBean(beanName,requiredType)时检查创建的实例是否需要的类型，容器初始化时不会走进里面
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.isTraceEnabled()) {
logger.trace("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
sharedInstance = getSingleton(beanName, () -> {try {return createBean(beanName, mbd, args);}:单例初始化，这个方法比较简单，主要关注下和循坏依赖相关的逻辑
/* org/springframework/beans/factory/support/DefaultSingletonBeanRegistry.java:201 */
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
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 + "'");
}
//循环依赖相关：初始化前先singletonsCurrentlyInCreation.add(beanName)
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
//lamda表达式：其实是调用createBean(beanName, mbd, args):Bean初始化
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
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;
}
//循环依赖相关：初始化后singletonsCurrentlyInCreation.remove(beanName)
afterSingletonCreation(beanName);
}
if (newSingleton) {
//初始化完后
//this.singletonObjects.put(beanName, singletonObject);放入到单例容器中
//this.singletonFactories.remove(beanName);清空循环依赖相关的两个打标
//this.earlySingletonObjects.remove(beanName);
//this.registeredSingletons.add(beanName);放入单例beanName容器中
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
createBean(beanName, mbd, args)：初始化实例,这个表方法注意一下，初始化实例前，留机会给BeanPostProcessor初始化代理类直接返回代理类初始化实例
/* org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java:467 */
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isTraceEnabled()) {
logger.trace("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
//确保beanclass确实被解析了，若合并出错，重新定义bean定义
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
try {
//校验需要重写方法是否全部重写，并且会给重写方法是否重载打标
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
//resolveBeforeInstantiation方法是调用BeanPostProcessor处理器
//后续研究一下BeanPostProcessor
//这里是给AOP相关BeanPostProcessor处理器生成代理类实例的机会，直接生成初始化代理类实例返回
//会面研究AOP时发现，proxy object不是在这里初始化，这里只是提供一个机会
//proxy object具体是在的下面doCreateBean时里先创建target object
//然后通过后置处理器的后置方法初始化的
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);
}
try {
//初始化实例
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isTraceEnabled()) {
logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
doCreateBean(beanName,mbdToUse,args):beanClass实例化（即earlysingleton，注意不是初始化）然后DI完成初始化
/* org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java:549 */
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//反射调用beanClass的构造方法创建实例并包装成beanwrapper--
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
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.
//允许MergedBeanDefinitionPostProcessors后置管理器修改rootBeandefinition
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;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
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");
}
//循环依赖相关逻辑：
//this.singletonFactories.put(beanName, singletonFactory);
//将实例化bean、beanName组装成singletonFactory装入singletonFactories容器
//this.earlySingletonObjects.remove(beanName);
//删除earlySingletonObjects中beanName
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
//创建实例
Object exposedObject = bean;
try {
//实例初始化 就是在这里面实现依赖注入DI的:
//具体是调用AutowiredAnnotationBeanPostProcessor.postProcessProperties
populateBean(beanName, mbd, instanceWrapper);//调用Bean后置管理器前置方法BeanPostProcessor.postProcessBeforeInitialization
//instanceof aware接口，setBeanName setBeanClassLoader setBeanFactory
//调用Bean后置管理器后置方法BeanPostProcessor.postProcessAfterInitialization
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);
}
}
//...
return exposedObject;
}
populateBean(beanName, mbd, instanceWrapper)：依赖注入DI执行时机
/* org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java:1381 */
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
//...
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
//这里调用AutowiredAnnotationBeanPostProcessor.postProcessProperties()
//完成注解自动注入（DI）
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
if (needsDepCheck) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
if (pvs != null) {
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
DI结束，bean初始化基本结束了。然后就是bean初始化的BeanPostProcessor执行前置后置方法
BeanPostProcessor前置后置方法：一些很重要架构都需要依靠实现，例如AOP动态代理产生代理对象
AnnotationAwareAspectJAutoProxyCreator.postProcessAfterInitialization
/* org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition) */
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 {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//调用所有BeanPostProcessor前置方法BeanPostProcessor.postProcessBeforeInitialization
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
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()) {
//调用所有BeanPostProcessor前置方法BeanPostProcessor.postProcessAfterInitialization
//例如AOP代理对象就是这里初始化的,AnnotationAwareAspectJAutoProxyCreator.postProcessAfterInitialization
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持呐喊教程。
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