spring中bean的初始化过程源码分析(包含解决循环依赖问题)
1.上篇文章讲spring的初始化，这篇文章主要讲spring中bean的初始化以及如果解决循环依赖问题，有些细节还需要研究，之后的文章上说明，
上篇文章地址：
spring初始化过程源码分析_LouD_dm的博客-CSDN博客
2.spring如何解决循环依赖
循环依赖：a依赖b,b依赖于a,这就是循环依赖，spring不支持构造方法的循环依赖
如何解决循环依赖
1） 首先实例化a,从一级缓存找a,这时a没在创建直接返回空
2） 之后开始创建a放在三级缓存提前暴露,之后给a注入属性发现a依赖b,开始创建b
3) 创建b发现b把b放在三级缓存，b依赖a,开始创建a,这时发现a正在创建，找二级缓存，二级缓存默认没有，开始找三级缓存，这时三级缓存中已经有a,开始从三级缓存获取a，a是一个工厂函数，调用工厂函数创建bean放入二级缓存
4)b从二级缓存中找到了a填充b的属性a,之后走下面的流程创建完毕放在一级缓存
5)b创建完毕，a这边就能获取到b,填充a的属性b,放入一级缓存
首先从一级缓存找，没有找到并且bean正在创建的话找二级缓存，二级缓存为空并且要提前创建早期引用，从三级缓存取出工厂函数创建bean,没有找到开始创建bean,
3.在spring初始化时执行的refresh方法中有实例化剩余的单例bean这个方法
// 实例化所有剩余的（非延迟初始化）单例。
finishBeanFactoryInitialization(beanFactory);/**
* 完成这个上下文的bean工厂的初始化，
* 初始化所有剩余的单例 bean。
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// 为此上下文初始化转换服务。
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 bean 后处理器，则注册一个默认的嵌入值解析器
//（例如PropertyPlaceholderConfigurer bean）之前注册过任何：
// 在这一点上，主要用于注释属性值的解析。
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// 尽早初始化 LoadTimeWeaverAware bean 以允许尽早注册它们的转换器。
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// 停止使用临时 ClassLoader 进行类型匹配。
beanFactory.setTempClassLoader(null);
// 允许缓存所有 bean 定义元数据，不需要进一步更改。
beanFactory.freezeConfiguration();
// 实例化所有剩余的（非延迟初始化）单例。
beanFactory.preInstantiateSingletons();
}主要方法beanFactory.preInstantiateSingletons()实例化所有剩余的单例bean,由于在spring初始化的时候实例化了对应的BeanFactoryPostProcessor，BeanPostProcessor，messageSource，applicationEventMulticaster类型的bean,这里实例化剩余的bean
4.实例化bean代码执行流程
1)在DefaultListableBeanFactory这个类实例化剩余的bean，spring容器启动会加载所有的beanDefinition，这里遍历beanDefinitionName之后创建对应的bean,判断是否是单例，多例，抽象，懒加载，FactoryBean，主要看的是单例bean,调用getBean方法获取bean，bean不存在创建bean
@Override
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// 迭代一个副本以允许 init 方法依次注册新的 bean 定义。
// 虽然这可能不是常规工厂引导程序的一部分，但它确实可以正常工作。
List beanNames = new ArrayList<>(this.beanDefinitionNames);
// 触发所有非惰性单例 bean 的初始化...
for (String beanName : beanNames) {
//bean如果存在继承，返回一个父的BeanDefinition
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//如果是单例，并且不是抽象和懒加载
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//处理FactoryBean类型
if (isFactoryBean(beanName)) {
//前缀增加&来获取bean
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)
((SmartFactoryBean) factory)::isEagerInit,
getAccessControlContext());
} else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
} else {
//默认单例执行当前代码
getBean(beanName);
}
}
}
// 为所有适用的 bean 触发初始化后回调...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
//在单例初始化后试过实现了SmartInitializingSingleton接口调用SmartInitializingSingleton的afterSingletonsInstantiated方法
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction 2)主要看常用单例bean的初始化，主要方法AbstractBeanFactory的getBean，我们在创建完一个上下文的时候通过getBean来获取IOC容器中的bean,初始化的时候调用的AbstractBeanFactory的getBean，AbstractApplicationContext中也有getBean方法，也就是AbstractApplicationContext使用装饰者设计模式，实际调用的是AbstractBeanFactory接口的getBean方法。
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}3)getBean实际调用doGetBean方法
1.考虑bean是否使用别名，获取真实的bean名称处理
2.调用getSingleton获取beanA,第一次获取为空，走else创建beanA，默认创建早期引用，也
就是创建对象工厂，添加到三级缓存，之后实例化依赖的beanB,如果依赖当前
beanA,getSingleton获取当前bean发现beanA正在创建中，从三级缓存拿到工厂函数
创建beanA放入二级缓存，之后实例化完毕放入一级缓存,这时beanB拿到beanA完成实例化
3.如果当前的BeanFactory是否有bean，如果没有去父BeanFactory找
4.如果bean加了@DependsOn注解,确保依赖的bean先被实例化
5.createBean主要方法创建bean
6.getSingleton从缓存获取bean
/**
* 返回指定 bean 的一个实例，该实例可以是共享的，也可以是独立的。
*
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@SuppressWarnings("unchecked")
protected T doGetBean(final String name, @Nullable final Class requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
//如果bean名称是别名，找到原始名称
final String beanName = transformedBeanName(name);
Object bean;
// 急切地检查单例缓存是否有手动注册的单例。
// 第一次获取是空的，会走创建的流程
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 {
// 如果我们已经在创建这个 bean 实例，则失败：
// 我们可能处于循环引用中。
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// 检查此工厂中是否存在 bean 定义。
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// 未找到 -> 检查父项。
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
} else if (args != null) {
// 使用显式参数委托给父母。
return (T) parentBeanFactory.getBean(nameToLookup, args);
} else if (requiredType != null) {
// 没有参数 -> 委托给标准的 getBean 方法。
return parentBeanFactory.getBean(nameToLookup, requiredType);
} else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {
//标注bean为已创建
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// 保证当前 bean 所依赖的 bean 的初始化。
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 + "'");
}
registerDependentBean(dep, beanName);
try {
getBean(dep);
} catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// 创建 bean 实例,
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
} catch (BeansException ex) {
//从单例缓存中显式删除实例：它可能已经放在那里
// 在创建过程中急切地允许循环引用解析。
// 同时删除接收到对 bean 的临时引用的所有 bean。
destroySingleton(beanName);
throw ex;
}
});
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);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
} else {
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;
}
}
// 检查所需类型是否与实际 bean 实例的类型匹配。
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;
} 4）doGetBean主要方法getSingleton，第一次获取为空，当前bean没在创建中，只有a依赖b,b依赖a,创建b时走获取a的流程发现a在创建中，之后走下面从三级缓存拿到a的工厂函数创建a放入二级缓存，之后实例化完成放入一级缓存
@Override
@Nullable
public Object getSingleton(String beanName) {
return getSingleton(beanName, true);
}
/**
* 返回在给定名称下注册的（原始）单例对象。
* 检查已经实例化的单例并允许提前
* 对当前创建的单例的引用（解析循环引用）。
*
* @param beanName 要查找的 bean 的名称
* @param allowEarlyReference 是否应创建早期引用
* 返回注册的单例对象，如果没有找到则返回 {code null}
*/
@Nullable
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
synchronized (this.singletonObjects) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
ObjectFactory singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return singletonObject;
}
5）主要方法createBean方法，createBean来创建bean
/**
* 这个类的中心方法：创建一个bean实例，
* 填充 bean 实例，应用后处理器等。
*
* @see #doCreateBean
*/
@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;
// 确保此时真正解析了 bean 类，并且
// 在动态解析类的情况下克隆 bean 定义
// 不能存储在共享的合并 bean 定义中。
Class resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// 准备方法覆盖。
try {
mbdToUse.prepareMethodOverrides();
} catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// 让 BeanPostProcessors 有机会返回一个代理而不是目标 bean 实例。
// BeanPostProcessors前置处理和后置处理
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 {
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);
}
}BeanPostProcessor前置处理，可能返回代理,注意这里是如果自定义target,可以提前生成代理
/**
* 应用实例化前的后处理器，解决是否存在
* 指定 bean 的实例化前快捷方式。
*
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @return the shortcut-determined bean instance, or {@code null} if none
*/
@Nullable
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// 确保此时实际解析了 bean 类。
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
Class targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}实际创建bean的是doCreateBean方法
1.通过根据bean名称等信息创建BeanWrapper，使用BeanWrapper来创建bean
2.判断是否要解决循环依赖，将一个工厂函数ObjectFactory添加到三级缓存，spring是在这里生成对应bean的代理，并从二级缓存移除bean初始化提前生成的代理，一般二级缓存默认是没有的，除非自定义target
3.使用BeanPostProcessor对bean进行处理
4.如果实现了initializeBean接口，调用afterPropertiesSet方法
5.填充属性，如果我们在实例化a,发现依赖的属性b没有，就开始重新创建b，创建b发现依赖a,而三级缓存有a,从三级缓存取出工厂函数创建a放入二级缓存返回，b拿到a填充属性，创建完放入一级缓存，这时a拿到了创建完的b,之后a实例化完成
/**
* 返回指定 bean 的一个实例，该实例可以是共享的，也可以是独立的。
*
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@SuppressWarnings("unchecked")
protected T doGetBean(final String name, @Nullable final Class requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
//如果bean名称是别名，找到原始名称
final String beanName = transformedBeanName(name);
Object bean;
// 急切地检查单例缓存是否有手动注册的单例。
// 第一次获取是空的，会走创建的流程
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 + "'");
}
}
//处理FactoryBean类型
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
} else {
// 如果我们已经在创建这个 bean 实例，则失败：
// 我们可能处于循环引用中。
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// 检查此工厂中是否存在 bean 定义。
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// 未找到 -> 检查父项。
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
} else if (args != null) {
// 使用显式参数委托给父母。
return (T) parentBeanFactory.getBean(nameToLookup, args);
} else if (requiredType != null) {
// 没有参数 -> 委托给标准的 getBean 方法。
return parentBeanFactory.getBean(nameToLookup, requiredType);
} else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {
//标注bean为已创建
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// 保证当前 bean 所依赖的 bean 的初始化。
// 如果加了@DependsOn注解，确保DependsOn注解配置的bean先被实例化
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 + "'");
}
registerDependentBean(dep, beanName);
try {
getBean(dep);
} catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// 创建 bean 实例,
if (mbd.isSingleton()) {
//主要方法
//createBean创建bean实例
//getSingleton方法从缓存获取bean
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
} catch (BeansException ex) {
//从单例缓存中显式删除实例：它可能已经放在那里
// 在创建过程中急切地允许循环引用解析。
// 同时删除接收到对 bean 的临时引用的所有 bean。
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
} else if (mbd.isPrototype()) {
// 这是一个原型 -> 创建一个新实例。
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
} finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
} else {
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;
}
} 创建BeanWrapper实例化bean,选择对应的构造方法实例化
/**
* 使用适当的实例化策略为指定的 bean 创建一个新实例：
* 工厂方法、构造函数自动装配或简单实例化。
*
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a BeanWrapper for the new instance
* @see #obtainFromSupplier
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
* @see #instantiateBean
*/
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
Class beanClass = resolveBeanClass(mbd, beanName);
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
}
Supplier instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
return autowireConstructor(beanName, mbd, null, null);
} else {
return instantiateBean(beanName, mbd);
}
}
// 自动装配的候选构造函数？
Constructor[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
return instantiateBean(beanName, mbd);
} /**
* 使用其默认构造函数实例化给定的 bean。
*
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @return a BeanWrapper for the new instance
*/
protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
try {
Object beanInstance;
final BeanFactory parent = this;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged((PrivilegedAction这里调用BeanPostProcessor可以让bean被代理
/**
* 获取早期访问指定 bean 的参考，
* 通常用于解析循环引用。
*
* @param beanName the name of the bean (for error handling purposes)
* @param mbd the merged bean definition for the bean
* @param bean the raw bean instance
* @return the object to expose as bean reference
*/
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
Object exposedObject = bean;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
//调用SmartInstantiationAwareBeanPostProcessor的getEarlyBeanReference方法
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
}
}
}
return exposedObject;
}addSingletonFactory添加到三级缓存
/**
* 添加给定的单例工厂以构建指定的单例
* 如有必要。
* 被调用以急切注册单身人士，例如有能力去
* 解决循环引用。
*
* @param beanName the name of the bean
* @param singletonFactory the factory for the singleton object
*/
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);
}
}
}
填充属性执行BeanPostProcessor后置处理
/**
* 使用属性值填充给定 BeanWrapper 中的 bean 实例
* 来自 bean 定义。
*
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param bw the BeanWrapper with bean instance
*/
@SuppressWarnings("deprecation") // for postProcessPropertyValues
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
if (bw == null) {
if (mbd.hasPropertyValues()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
} else {
// Skip property population phase for null instance.
return;
}
}
// 给任何 InstantiationAwareBeanPostProcessors 机会修改
// 设置属性之前 bean 的状态。这可以用于，例如，
// 支持字段注入的样式。
boolean continueWithPropertyPopulation = true;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
continueWithPropertyPopulation = false;
break;
}
}
}
}
if (!continueWithPropertyPopulation) {
return;
}
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// 如果适用，根据名称添加基于自动装配的属性值。
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// 如果适用，根据类型添加基于自动装配的属性值。
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
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);
}
}5）主要方法getSingleton，
上一步的createBean方法返回的是一个工厂，singletonFactory.getObject()的时候调用createBean,这里通过工厂创建bean,添加到一级缓存,如果要解决循环依赖会放在二级缓存，这里是最后一步，从二三级缓存删除放在一级缓存。
/**
* 返回以给定名称注册的（原始）单例对象，
* 如果尚未注册，则创建并注册一个新的。
*
* @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) {
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 + "'");
}
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
singletonObject = singletonFactory.getObject();
newSingleton = true;
} catch (IllegalStateException ex) {
// 在此期间是否隐式出现了单例对象 ->
// 如果是，则继续执行，因为异常指示该状态。
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;
}
afterSingletonCreation(beanName);
}
if (newSingleton) {
//从二级,三级缓存移除，添加到一级缓存
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}