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// 11. 初始化所有剩下的单例Bean
this.finishBeanFactoryInitialization(beanFactory);
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十一、 finishBeanFactoryInitialization: 初始化所有剩下的单例Bean
刷新容器-初始化剩余的单实例Bean
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
// 初始化ConversionService，这个ConversionService是用于类型转换的服务接口。
// 它的工作，是将配置文件/properties中的数据，进行类型转换，得到Spring真正想要的数据类型。
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.
// 嵌入式值解析器EmbeddedValueResolver的组件注册，它负责解析占位符和表达式
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
// 尽早初始化LoadTimeWeaverAware类型的bean，以允许尽早注册其变换器。
//与AspectJ有关
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
// 停用临时类加载器
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
// 允许缓存所有bean定义元数据
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
// 【初始化】实例化所有非延迟加载的单例Bean
beanFactory.preInstantiateSingletons();
}
实例化单例Bean
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// 获取所有的Bean定义信息
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// 这里面有一些Bean已经在之前的步骤中已经创建过了，这里只创建剩余的那些非延迟加载的单例Bean
for (String beanName : beanNames) {
// 11.4 合并BeanFactory中同名的BeanDefinition
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 这个Bean不是抽象Bean、是单例Bean、是非延迟加载的Bean
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
// 是否为工厂Bean（如果是工厂Bean，还需要实现FactoryBean接口）
if (isFactoryBean(beanName)) {
// 如果是工厂Bean：判断该工厂Bean是否需要被迫切加载，如果需要，则直接实例化该工厂Bean
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);
}
}
}// 如果不是工厂Bean，直接调用getBean方法
else {
getBean(beanName);
}
}
}
// 到这里，所有非延迟加载的单实例Bean都已经创建好。
// 如果有Bean实现了SmartInitializingSingleton接口，还会去回调afterSingletonsInstantiated方法
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();
}
}
}
}
获取Bean
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
创建Bean
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
// 处理Bean名称，如果有别名返回别名
String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
//11.1 获取单实例Bean
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 + "'");
}
}
// 11.2 返回Bean实例（处理FactoryBean）
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
// 校验是否是多例(Prototype)的Bean，多例的bean是不支持循环依赖的
// 为了避免循环依赖，遇到这种情况，直接抛出异常
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
// 检查父容器是否存在这个BeanDefinition（Web环境会存在父子容器现象）
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) {
//标记Bean即将创建，让Bean信息重新合并，防止数据发生变化
markBeanAsCreated(beanName);
}
try {
//11.3 合并BeanDefinition
RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
//处理依赖项
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
//存在循环应用的情况要抛出异常
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
//注册依赖关系
registerDependentBean(dep, beanName);
try {
//先创建被依赖项
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// Create bean instance.
//11.4 获取单例Bean
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
//11.5 创建单例Bean
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;
}
});
//11.2 返回Bean实例（处理FactoryBean）
bean = 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);
}
//11.2 返回Bean实例（处理FactoryBean）
bean = 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);
}
});
//11.2 返回Bean实例（处理FactoryBean）
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;
}
}
// Check if required type matches the type of the actual bean instance.
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;
}
11.1 getSingleton 获取单实例Bean（循环依赖）
//允许早期引用（解决循环依赖）
public Object getSingleton(String beanName) {
return getSingleton(beanName, true);
}
singletonObjects：一级缓存，存放**完全初始化好的Bean（填充属性完成，初始化完成）**的集合，从这个集合中取出来的Bean可以立马返回earlySingletonObjects：二级缓存，存放**半成品的单实例Bean(已实例化但未注入属性和初始化)**的集合，它用来解决循环依赖singletonFactories：三级缓存，存放**Bean工厂对象（仅仅只实例化完成）**的集合singletonsCurrentlyInCreation：存放正在被创建的Bean
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
// Quick check for existing instance without full singleton lock
//先从一级缓存获取
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
synchronized (this.singletonObjects) {
// Consistent creation of early reference within full singleton lock
//获取二级缓存
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null) {
//获取三级缓存
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
}
}
return singletonObject;
}
11.2 getObjectForBeanInstance：返回Bean实例（处理FactoryBean）
这里如果不是FactoryBean类型则会直接返回Bean,否则会返回由FactoryBean的getObject()方法得到的Bean对象
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
// Don't let calling code try to dereference the factory if the bean isn't a factory.
// 如果 BeanName 是 FactoryBean<?> 相关的 BeanName
if (BeanFactoryUtils.isFactoryDereference(name)) {
// BeanInstance 是 NullBean
if (beanInstance instanceof NullBean) {
// 直接返回 beanInstance
return beanInstance;
}
// 如果不是 FactoryBean<?> 类型的 Bean 实例
if (!(beanInstance instanceof FactoryBean)) {
// 抛出异常 : 当前 Bean 不是一个工厂
throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass());
}
// 如果 BeanName 与 FactoryBean<?> 相关 && beanInstance 不是 NullBean
// && beanInstance 是 FactoryBean<?> 类型 && RootBeanDefinition 不为空
if (mbd != null) {
// 当前 Bean 实例为 FactoryBean<?> 类型的 Bean
mbd.isFactoryBean = true;
}
// 直接返回当前 Bean 实例, 这也是为什么针对于一个 FactoryBean<?> 类型的 Bean 实例而言
// 使用 '&' + beanName 就能获取到 FactoryBean<?> 本身
return beanInstance;
}
// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
// 现在拥有了一个新的 BeanInstance, 这个实例可能是常规 Bean 也有可能是 FactoryBean<?>
// 如果是 FactoryBean<?> 则使用它创建实例, 但如果是开发者想要直接获取工厂实例而不是工厂的 getObject()
// 方法对应的实例, 那么传入的 BeanName 应该加入前缀 '&'
if (!(beanInstance instanceof FactoryBean)) {
// 如果不是 FactoryBean 直接返回当前 Bean 实例
return beanInstance;
}
// 如果是 FactoryBean
Object object = null;
if (mbd != null) {
mbd.isFactoryBean = true;
}
else {
// 从缓存中加载
object = getCachedObjectForFactoryBean(beanName);
}
// 激活 FactoryBean<?> 的 getObject() 方法
if (object == null) {
// Return bean instance from factory.
// 这里已经明确知道 beanInstance 一定是 FactoryBean<?> 类型
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
// 如果 mbd 为空 && 从 XML 配置文件中加载的 BeanDefinition 中包含 BeanName 对应的 Bean 定义信息
if (mbd == null && containsBeanDefinition(beanName)) {
// 将解析 XML 配置文件的 GenericBeanDefinition 转换为 RootBeanDefinition, 如果指定的 BeanName
// 是子 Bean 的话同时会合并父类的相关属性
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
// 如果是单例 Bean && Bean 实例已经创建过, 没有再次创建的必要, 要保证单例 Bean 全局唯一, 直接从缓存中获取
if (factory.isSingleton() && containsSingleton(beanName)) {
// 进入同步代码块
synchronized (getSingletonMutex()) {
// 从缓存中获取
Object object = this.factoryBeanObjectCache.get(beanName);
// 如果缓存中没有
if (object == null) {
// 激活 FactoryBean<?> 中的 getObject() 方法获取开发者
// 定制的初始化逻辑
object = doGetObjectFromFactoryBean(factory, beanName);
// Only post-process and store if not put there already during getObject() call above
// (e.g. because of circular reference processing triggered by custom getBean calls)
Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
if (alreadyThere != null) {
object = alreadyThere;
}
else {
if (shouldPostProcess) {
if (isSingletonCurrentlyInCreation(beanName)) {
// Temporarily return non-post-processed object, not storing it yet..
return object;
}
beforeSingletonCreation(beanName);
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Post-processing of FactoryBean's singleton object failed", ex);
}
finally {
afterSingletonCreation(beanName);
}
}
if (containsSingleton(beanName)) {
this.factoryBeanObjectCache.put(beanName, object);
}
}
}
return object;
}
}
else {
// 直接获取
Object object = doGetObjectFromFactoryBean(factory, beanName);
if (shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
}
}
return object;
}
}
直接获取Bean
private Object doGetObjectFromFactoryBean(FactoryBean<?> factory, String beanName) throws BeanCreationException {
Object object;
try {
if (System.getSecurityManager() != null) {
AccessControlContext acc = getAccessControlContext();
try {
object = AccessController.doPrivileged((PrivilegedExceptionAction<Object>) factory::getObject, acc);
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
// 激活 FactoryBean<?> 中的 getObject() 方法调用
// 开发者定制化的的 Bean 注册逻辑
object = factory.getObject();
}
}
catch (FactoryBeanNotInitializedException ex) {
throw new BeanCurrentlyInCreationException(beanName, ex.toString());
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
}
// Do not accept a null value for a FactoryBean that's not fully
// initialized yet: Many FactoryBeans just return null then.
if (object == null) {
if (isSingletonCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(
beanName, "FactoryBean which is currently in creation returned null from getObject");
}
object = new NullBean();
}
return object;
}
11.3 getMergedLocalBeanDefinition：合并BeanDefinition
这里如果有需要合并的BeanDefinition先进行合并
11.4 获取单例Bean
if (mbd.isSingleton()) {
//11.4.1 获取单例Bean
sharedInstance = getSingleton(beanName, () -> {
11.4.1 获取单例Bean
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 + "'");
}
//11.4.1.1 标记单例Bean正在被创建
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
//11.5 创建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;
}
// 11.4.1.2 标记单例Bean已创建完成
afterSingletonCreation(beanName);
}
if (newSingleton) {
// 11.4.1.3将Bean添加进一级缓存中
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
这里会先执行11.5创建Bean,因为比较关键所以放入大标题中
11.4.1.1 标记单例Bean正在被创建
单例Bean正在被创建会被放入singletonsCurrentlyInCreation集合中，在11.1中
protected void beforeSingletonCreation(String beanName) {
if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
}
11.4.1.2 标记单例Bean创建完成
单例Bean创建完成会从singletonsCurrentlyInCreation集合中移除，在11.1中
protected void afterSingletonCreation(String beanName) {
if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.remove(beanName)) {
throw new IllegalStateException("Singleton '" + beanName + "' isn't currently in creation");
}
}
11.4.1.3将Bean添加进一级缓存中
这里会将Bean放入一级缓存中（singletonObjects）并将其从二级缓存中移除
protected void addSingleton(String beanName, Object singletonObject) {
synchronized (this.singletonObjects) {
this.singletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
11.5 创建单例Bean
singletonFactory.getObject();这里会跳到外层的匿名方法中
{
try {
//11.5 创建Bean
return createBean(beanName, mbd, args);
}
}
注意跳转到的类：AbstractAutowireCapableBeanFactory，创建bean前的一些准备
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.
// 先拿到这个Bean的定义信息，获取Bean的类型
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
// 方法重写的准备工作
// 利用反射，对该Bean对应类及其父类的方法定义进行获取和加载，确保能够正确实例化出该对象
try {
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.
//11.5.1 确保可以创建的是被增强的代理对象而不是原始对象（AOP）
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 {
// 11.5.2 doCreateBean 如果不需要创建代理对象 则执行此方法
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);
}
}
11.5.1 resolveBeforeInstantiation （AOP）
确保可以创建的是被增强的代理对象而不是原始对象（AOP）
11.5.2 doCreateBean （创建Bean的流程）
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
// 实例化Bean，并创建一个BeanWrapper，对Bean进行包装
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
// 确保已经实例化的Bean中没有当前要创建的bean，而且不是工厂Bean，才可以开始创建
if (instanceWrapper == null) {
// 11.5.2.1 createBeanInstance：实例化Bean
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 {
// 这个方法只允许MergedBeanDefinitionPostProcessor执行
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.
// 缓存单例对象，以便能够解析循环引用，甚至在生命周期接口(如BeanFactoryAware)触发时也是如此
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");
}
// 11.5.2.2 addSingletonFactory：将实例化的Bean放入三级缓存中
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
// 给Bean赋值
Object exposedObject = bean;
try {
// 11.5.2.3 populateBean：属性赋值和自动注入
populateBean(beanName, mbd, instanceWrapper);
// 11.5.2.4 initializeBean：初始化Bean
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);
}
}
// 又获取那个单例Bean，前面已经创建好了，但还没有缓存到IOC容器中，所以这里仍然返回null，故这部分是会跳过的
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.");
}
}
}
}
// Register bean as disposable.
try {
// 注册Bean的销毁方法，销毁方法在IOC容器关闭后再销毁
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
11.5.2.1 createBeanInstance：实例化Bean
11.5.2.2 addSingletonFactory：将实例化的Bean放入三级缓存中
将实例化的Bean放入三级缓存中（singletonFactories）
protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(singletonFactory, "Singleton factory must not be null");
synchronized (this.singletonObjects) {
if (!this.singletonObjects.containsKey(beanName)) {
this.singletonFactories.put(beanName, singletonFactory);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
}
11.5.2.3 populateBean：属性赋值和自动注入
11.5.2.4 initializeBean：初始化Bean
执行初始化方法
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 {
// 11.5.2.4.1 接口回调Aware方法
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 11.5.2.4.2 执行Bean初始化前的后置处理器
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 11.5.2.4.3 执行初始化Bean操作
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()) {
// 11.5.2.4.4 执行Bean初始化后的后置处理器
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
11.5.2.4.1 接口回调Aware方法
通过接口回调设置BeanName、BeanClassLoader、BeanFactory
private void invokeAwareMethods(final String beanName, final Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
11.5.2.4.2 执行Bean初始化前的后置处理器
执行BeanPostProcessor后置处理器的postProcessBeforeInitialization方法
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
11.5.2.4.3 执行初始化Bean操作
如果Bean是InitializingBean的实现类则会回调执行afterPropertiesSet方法
protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
throws Throwable {
// 不是InitializiingBean，而且也没声明afterPropertiesSet方法，则不执行下面的逻辑
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isDebugEnabled()) {
logger.debug("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 {
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null && bean.getClass() != NullBean.class) {
//获取初始化方法名称
String initMethodName = mbd.getInitMethodName();
if (StringUtils.hasLength(initMethodName) &&
!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
//执行初始化方法
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
如果Bean中设置了初始化方法，则通过反射调用初始化方法
protected void invokeCustomInitMethod(String beanName, Object bean, RootBeanDefinition mbd)
throws Throwable {
String initMethodName = mbd.getInitMethodName();
Assert.state(initMethodName != null, "No init method set");
Method initMethod = (mbd.isNonPublicAccessAllowed() ?
BeanUtils.findMethod(bean.getClass(), initMethodName) :
ClassUtils.getMethodIfAvailable(bean.getClass(), initMethodName));
//如果初始化方法为空
if (initMethod == null) {
if (mbd.isEnforceInitMethod()) {
throw new BeanDefinitionValidationException("Could not find an init method named '" +
initMethodName + "' on bean with name '" + beanName + "'");
}
else {
if (logger.isTraceEnabled()) {
logger.trace("No default init method named '" + initMethodName +
"' found on bean with name '" + beanName + "'");
}
// Ignore non-existent default lifecycle methods.
return;
}
}
if (logger.isTraceEnabled()) {
logger.trace("Invoking init method '" + initMethodName + "' on bean with name '" + beanName + "'");
}
Method methodToInvoke = ClassUtils.getInterfaceMethodIfPossible(initMethod);
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
ReflectionUtils.makeAccessible(methodToInvoke);
return null;
});
try {
AccessController.doPrivileged((PrivilegedExceptionAction<Object>)
() -> methodToInvoke.invoke(bean), getAccessControlContext());
}
catch (PrivilegedActionException pae) {
InvocationTargetException ex = (InvocationTargetException) pae.getException();
throw ex.getTargetException();
}
}
else {
try {
//通过反射调用初始化方法
ReflectionUtils.makeAccessible(methodToInvoke);
methodToInvoke.invoke(bean);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
}
11.5.2.4.4 执行Bean初始化后的后置处理器
执行BeanPostProcessor后置处理器的applyBeanPostProcessorsAfterInitialization方法
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
