bean的生命周期的几个后置接口都是在这个方法里面调用，所以单独开一篇该方法的源码阅读
下面从两个点来阅读：
1.何时调用（只看容器启动）
2.梳理这个方法的流程（跟上一节对应上）
先贴上源码：
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
// factoryBeanObjectCache：存的是beanName对应的FactoryBean.getObject()所返回的对象
// factoryBeanInstanceCache：存的是beanName对应的FactoryBean实例对象
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
// 2、实例化
if (instanceWrapper == null) {
// 创建bean实例 new USerSerive()
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
// 原始对象
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 {
// 运行修改合并好了的BeanDefinition
// 这里会查找@Autowired的注入点(InjectedElement)，并把这些注入点添加到mbd的属性externallyManagedConfigMembers中
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.
// 如果当前创建的是单例bean，并且允许循环依赖，并且还在创建过程中，那么则提早暴露
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");
}
// 此时的bean还没有完成属性注入，是一个非常简单的对象
// 构造一个对象工厂添加到singletonFactories中
// 第四次调用后置处理器
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); // AService
}
// Initialize the bean instance.
// 对象已经暴露出去了
Object exposedObject = bean;
try {
// 3、填充属性 @Autowired
populateBean(beanName, mbd, instanceWrapper); //
// 4、 初始化 和 BeanPostProcessor 正常AOP BeanPostProcessor
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);
}
}
if (earlySingletonExposure) {
// 在解决循环依赖时，当AService的属性注入完了之后，从getSingleton中得到AService AOP之后的代理对象
Object earlySingletonReference = getSingleton(beanName, false); // earlySingletonObjects
if (earlySingletonReference != null) {
// 如果提前暴露的对象和经过了完整的生命周期后的对象相等，则把代理对象赋值给exposedObject
// 最终会添加到singletonObjects中去
if (exposedObject == bean) { //
exposedObject = earlySingletonReference;
}
// 如果提前暴露的对象和经过了完整的生命周期后的对象不相等
// allowRawInjectionDespiteWrapping表示在循环依赖时，只能
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()) {
// AService的原始对象被注入给了其他bean，但是AService最后被包装了
// 也就是说其他bean没有用到AService的最终版本
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 {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}咱们现在只看UserService 这个类的创建，其余的后续在分析。
还是一样，咱们打上条件断点：
启动测试代码：
由上面可以看到，先执行实例化的后置处理器TestInstantiationAwareBeanPostProcessor的前置方法，查看调用栈针可以看到是在创建AnnotationConfigApplicationContext时候在refresh（）里
// Instantiate all remaining (non-lazy-init) singletons.
// 完成beanFactory的初始化（实例化非懒加载的单例bean）
finishBeanFactoryInitialization(beanFactory);createBean（）方法，源码如下：@Override
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;
// 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 {
// 对通过XML定义的bean中的look-up方法进行预处理
// 对于@Lookup注解标注的方法不在这里进行处理，@AutowiredAnnotationBeanPostProcessor会处理@Lookup注解
// 不研究了
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.
// 1、实例化前 null
Object bean = resolveBeforeInstantiation(beanName, mbdToUse); // 对象
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
// 创建bean Spring自带的创建bean的方法
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);
}
}该方法也是抽象工厂类的方法：
简单分析下该方法的流程：
1.对传过来的RootBeanDefinition进行一些处理
2.然后调用实例化前的方法
3.最后去调用doCreateBean方法生成一个object 对象
所以UserService创建的时候会createBean（）方法，然后按上面的流程调用到doCreateBean方法。
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
// factoryBeanObjectCache：存的是beanName对应的FactoryBean.getObject()所返回的对象
// factoryBeanInstanceCache：存的是beanName对应的FactoryBean实例对象
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}（1）判断是否单例，清除掉工厂缓存池factoryBeanInstanceCache的实例的包装器
// 2、实例化
if (instanceWrapper == null) {
// 创建bean实例 new USerSerive()
instanceWrapper = createBeanInstance(beanName, mbd, args);
}（2）实例化：这里面会推断构造方法，如果没有就按无参构造方法实例
// 原始对象
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 {
// 运行修改合并好了的BeanDefinition
// 这里会查找@Autowired的注入点(InjectedElement)，并把这些注入点添加到mbd的属性externallyManagedConfigMembers中
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}（3）这个点是接口MergedBeanDefinitionPostProcessor的扩展点：在BeanPostProcessor的基础上增加了在实例化和实例化后之间的扩展点，也是继承BeanPostProcessor接口。
接口源码：
public interface MergedBeanDefinitionPostProcessor extends BeanPostProcessor {
/**
* Post-process the given merged bean definition for the specified bean.
* @param beanDefinition the merged bean definition for the bean
* @param beanType the actual type of the managed bean instance
* @param beanName the name of the bean
* @see AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors
*/
void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName);
/**
* A notification that the bean definition for the specified name has been reset,
* and that this post-processor should clear any metadata for the affected bean.
* <p>The default implementation is empty.
* @param beanName the name of the bean
* @since 5.1
* @see DefaultListableBeanFactory#resetBeanDefinition
*/
default void resetBeanDefinition(String beanName) {
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
// 如果当前创建的是单例bean，并且允许循环依赖，并且还在创建过程中，那么则提早暴露
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");
}
// 此时的bean还没有完成属性注入，是一个非常简单的对象
// 构造一个对象工厂添加到singletonFactories中
// 第四次调用后置处理器
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); // AService
}（4）这部分也是在实例化的一些操纵，设计到AbstractAutowireCapableBeanFactory的一些属性操做，总之为之后做准备（没有深入去了解）
// Initialize the bean instance.
// 对象已经暴露出去了
Object exposedObject = bean;
try {
// 3、填充属性 @Autowired
populateBean(beanName, mbd, instanceWrapper); //
// 4、 初始化 和 BeanPostProcessor 正常AOP BeanPostProcessor
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);
}
}（5）这部分就是属性填充和初始化了
populateBean(beanName, mbd, instanceWrapper);里面会调用实例化后InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation方法
// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of the bean before properties are set. This can be used, for example,
// to support styles of field injection.
// 可以提供InstantiationAwareBeanPostProcessor，控制对象的属性注入
// 我们可以自己写一个InstantiationAwareBeanPostProcessor，然后重写postProcessAfterInstantiation方法返回false,那么则不会进行属性填充了
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
return;
}
}
}
}这里判断执行的该方法返回是True 和false 如果false 就直接结束，后续不再进行属性填充，反之就会去执行InstantiationAwareBeanPostProcessor.postProcessProperties方法。
属性填充完了，再看初始化initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
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 {
// 4.1、执行Aware
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 4.2、初始化前
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 4.3、初始化
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()) {
// 4.4、初始化后 AOP （）
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
// 4.1、执行Aware
invokeAwareMethods(beanName, bean);
}进来就开始执行前置Aware：
BeanNameAwareBeanClassLoaderAwareBeanFactoryAwareObject wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 4.2、初始化前
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}然后初始化前的代码BeanPostProcessor.postProcessBeforeInitialization
首先AnnotationConfigApplicationContext.postProcessBeforeInitialization
@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
return bean;
}
AccessControlContext acc = null;
if (System.getSecurityManager() != null) {
acc = this.applicationContext.getBeanFactory().getAccessControlContext();
}
if (acc != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareInterfaces(bean);
return null;
}, acc);
}
else {
invokeAwareInterfaces(bean);
}
return bean;
}执行了上一节后续的几个Aware
后续还有很多BeanPostProcessor的处理暂时不分析
最后执行我们自己的BeanPostProcessor.postProcessBeforeInitialization（跟排序有关，暂时没测试）
然后是初始化：
try {
// 4.3、初始化
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}这里面会执行InitializingBean.afterPropertiesSet方法；
最后是初始化后的BeanPostProcessor.postProcessAfterInitialization:
if (mbd == null || !mbd.isSynthetic()) {
// 4.4、初始化后 AOP （）
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}到这一不可以看到上一节的bean生命周期的流程都执行完了
（6）后面的暂时先不分析，循环依赖问题。
根据上一节的生命周期的内容分析createBean里面的doCreateBean内容。总而言之：
1.doCreateBean是在createBean后面调用的，在createBean方法会执行InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation
2.然后在执行doCreateBean方法，首先先实例化
3.然后在属性填充的那里首选会执行InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation
4.属性填充完，马上就开始初始化，进来就开始执行前置Aware：
BeanNameAwareBeanClassLoaderAwareBeanFactoryAware5.利用AnnotationConfigApplicationContext.postProcessBeforeInitialization的前置方法执行后续的Aware，如果有
6.执行自己的BeanPostProcessor.postProcessBeforeInitialization（跟排序有关，暂时先这样分析）
7.初始化，这里面会执行InitializingBean.afterPropertiesSet方法；
8.最后是初始化后的BeanPostProcessor.postProcessAfterInitialization
