一、背景
前一节我们研究了 《ApplicationContextAware 方法的调用时机》 ，对 IOC 容器最核心的方法 refresh 有了初步的了解。
这节，我们将借助 BeanNameAware 方法的调用时机对 Bean 的初始化进一步学习。
二、分析
2.1 代码示例
实现 BeanNameAware接口：
package org.example.aware.bean;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.stereotype.Component;
@Component
public class NameAwaredTestBean implements BeanNameAware {
@Override
public void setBeanName(String name) {
System.out.println("beanName:" + name);
}
}
编写配置：
package org.example.aware.config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("org.example.aware.bean")
public class AwareConfiguration {
}
执行：
package org.example.aware;
import org.example.aware.bean.NameAwaredTestBean;
import org.example.aware.config.AwareConfiguration;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class AwareApplication {
public static void main(String[] args) throws Exception {
ApplicationContext ctx = new AnnotationConfigApplicationContext(AwareConfiguration.class);
NameAwaredTestBean atBean = ctx.getBean(NameAwaredTestBean.class);
System.out.println(atBean);
}
}
2.2 由外到内
先猜想后验证法
按照“国际惯例” 我们先进行猜测：BeanNameAware 应该比前文的 ApplicationContextAware 的时机更早，因为在 setBeanName 里我们可以修改 bean 的名称，而 ApplicationContextAware#setApplicationContext 里面很可能会用到 bean 的名称来构造策略 Map。
接下来我们进行验证。按照“老传统” 在 setBeanName 方法上断点。 发现调用来自：
private void invokeAwareMethods(String beanName, Object bean) {
if (bean instanceof Aware) {
//1 设置 BeanName
if (bean instanceof BeanNameAware) {
// 调用来自这里
((BeanNameAware) bean).setBeanName(beanName);
}
//2 设置 BeanClassLoader
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
//3 设置 BeanFactory
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
从这里我们可以看出 BeanClassLoaderAware#setBeanClassLoader 和 BeanFactoryAware#setBeanFactory 都在 invokeAwareMethods 方法里一起调用。
再上追溯一层：
AbstractAutowireCapableBeanFactory#initializeBean
/**
* Initialize the given bean instance, applying factory callbacks
* as well as init methods and bean post processors.
* 初始化给定的 Bean 实例，应用 init 方法和 bean 后置处理器
* <p>Called from {@link #createBean} for traditionally defined beans,
* and from {@link #initializeBean} for existing bean instances.
* 调用来自 createBean
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @return the initialized bean instance (potentially wrapped)
* @see BeanNameAware
* @see BeanClassLoaderAware
* @see BeanFactoryAware
* @see #applyBeanPostProcessorsBeforeInitialization
* @see #invokeInitMethods
* @see #applyBeanPostProcessorsAfterInitialization
*/
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
//【重要】执行到这里
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 执行 BeanPostProcessorsBeforeInitialization
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 执行 Init 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()) {
// 执行 BeanPostProcessorsAfterInitialization
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
主要流程：
其中 invokeInitMethods 方法的源码如下：
/**
* Give a bean a chance to react now all its properties are set,
* and a chance to know about its owning bean factory (this object).
* This means checking whether the bean implements InitializingBean or defines
* a custom init method, and invoking the necessary callback(s) if it does.
* 检查当前 bean 是否实现了 InitializingBean 接口或者定义了 init 方法，如果有则执行调用
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the merged bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @throws Throwable if thrown by init methods or by the invocation process
* @see #invokeCustomInitMethod
*/
protected void invokeInitMethods(String beanName, Object bean, @Nullable RootBeanDefinition mbd)
throws Throwable {
// 检查是否实现了 InitializingBean 接口
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isTraceEnabled()) {
logger.trace("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 {
// 调用 InitializingBean#afterPropertiesSet 方法
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null && bean.getClass() != NullBean.class) {
// 获取 init 方法名 并执行调用
String initMethodName = mbd.getInitMethodName();
if (StringUtils.hasLength(initMethodName) &&
!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
可以看到这里先执行 InitializingBean#afterPropertiesSet 然后再执行自定义 init 方法。
再往上追溯和前一篇文章非常类似。
AbstractAutowireCapableBeanFactory#doCreateBean
/**
* Actually create the specified bean. Pre-creation processing has already happened
* at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
* <p>Differentiates between default bean instantiation, use of a
* factory method, and autowiring a constructor.
* @param beanName the name of the bean
* @param mbd the merged bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a new instance of the bean
* @throws BeanCreationException if the bean could not be created
* @see #instantiateBean
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
*/
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
// 实例化 bean
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
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 {
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");
}
addSingletonFactory(beanName, () ->
// 构造 早期暴漏的 bean 引用，来解决循环依赖问题
getEarlyBeanReference(beanName, mbd, bean));
}
// 初始化 bean 实例.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
// 【重要】 执行到这里（ bean 初始化)
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);
}
}
// 省略部分代码
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
再往上层回溯到 DefaultSingletonBeanRegistry#getSingleton 这里：
/**
* Return the (raw) singleton object registered under the given name,
* creating and registering a new one if none registered yet.
* @param beanName the name of the bean
* @param singletonFactory the ObjectFactory to lazily create the singleton
* with, if necessary
* @return the registered singleton object
*/
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
// 先通过 bean 名称从单例 bean 缓存中获取 bean 实例
Object singletonObject = this.singletonObjects.get(beanName);
// 如果没有执行创建
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 + "'");
}
// 执行单例bean 创建的前置逻辑
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
//【重要】执行到这里
// 创建单例 bean
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;
}
// 执行单例bean 创建的后置逻辑
afterSingletonCreation(beanName);
}
// 如果是新创建的单例 Bean ,则添加到 beanName 到 单例 bean 的缓存中
if (newSingleton) {
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
再往上一层：
/**
* Return an instance, which may be shared or independent, of the specified bean.
*/
@SuppressWarnings("unchecked")
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
// 省略部分代码
//1 如果是单例，创建单例 bean
// Create bean instance.
if (mbd.isSingleton()) {
// 底层
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
// 2 prototype
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
// 由于是 prototype -> 每次都新建一个实例
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
// 省略部分代码
return (T) bean;
}
再往上追溯：
/**
* Finish the initialization of this context's bean factory,
* initializing all remaining singleton beans.
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
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(strVal -> 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);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
//【重要】从这里进入
// 初始化所有非懒加载的单例 bean
beanFactory.preInstantiateSingletons();
}
再往上追溯：
@Override
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.
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) {
SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
再往上追溯：
/**
* Finish the initialization of this context's bean factory,
* initializing all remaining singleton beans.
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
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(strVal -> 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);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
//【重要】从这里进入
// 初始化所有单例 bean
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}
再往上追溯又回到上节讲到的 IOC 容器初始化核心方法 refresh:
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//1 初始化前的准备
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//2 获取 BeanFactory，加载所有 bean 的定义信息（未实例化）
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 3 BeanFactory 的预处理配置
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 4. 准备 BeanFactory 完成后进行的后置处理
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 5. 执行 BeanFactory 创建后的后置处理器
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 6. 注册 Bean 的后置处理器
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
// 7. 初始化MessageSource
initMessageSource();
// Initialize event multicaster for this context.
// 8. 初始化事件派发器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 9. 子类的多态 onRefresh
onRefresh();
// Check for listener beans and register them.
// 10. 监听器检查和注册
registerListeners();
// ------- BeanFactory已创建完成 --------
// Instantiate all remaining (non-lazy-init) singletons.
// 11. 初始化所有剩下的单例Bean（非懒加载的）
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// 12. 完成容器的创建工作（发布相应的事件)
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
// 销毁已经创建的单例避免浪费资源
destroyBeans();
// Reset 'active' flag.
// 重置 active 标记
cancelRefresh(ex);
// Propagate exception to caller.
// 异常抛给调用方
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
//13 清理缓存
resetCommonCaches();
}
}
}
三、总结
通过本文的分析，我们知道 BeanNameAware#setBeanName 在 refresh 的 finishBeanFactoryInitialization 环节被执行。
而且 BeanClassLoaderAware#setBeanClassLoader 和 BeanFactoryAware#setBeanFactory 也会在 BeanNameAware#setBeanName 执行之后一起调用。
BeanNameAware#setBeanName 在 BeanPostProcessorsBeforeInitialization 和 init 方法执行之前被执行。
强烈建议大家在整个链路感兴趣的地方断点调试，反复执行，才能对源码有进一步了解。
强烈建议先猜想后验证，以便对源码有更深刻地印象。
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