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获取bean

获取bean

在进行获取bean的时候使用getBean方法来进行获取,那么就从getBean来作为入口,看一下获取bean的流程

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ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
Car car = (Car) context.getBean("car");
System.out.println(car);
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// org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String)
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}

doGetBean方法

这个方法比较长,分为很多步

  • transformedBeanName方法,对传入的beanName进行转换,因为传入的name不一定是beanName,也可能是FactoryBean,检查name的前缀是不是&,如果是别名的话,从aliasMap中获取真正的beanName
  • getSingleton方法,从缓存singletonObjects中加载单例,如果加载不成功尝试从singletonFactories中加载
  • getObjectForBeanInstance方法,进行bean的实例化,缓存中记录的是最原始的bean状态,对于FactoryBean需要再次进行处理
  • isPrototypeCurrentlyInCreation方法,原型的依赖检查
  • parentBeanFactory != null && !containsBeanDefinition(beanName),如果parentBeanFactory不为null,且当前加载的XML配置文件中不包含beanName,则会去parentBeanFactory中进行尝试获取
  • mbd.getDependsOn(),寻找依赖
  • 针对不同的scope的bean来进行创建
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// org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
// 实际获取Bean的方法
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
// 获取对应的beanName,可能是FactoryBean,可能是使用别名的
final String beanName = transformedBeanName(name);
Object bean;

// Eagerly check singleton cache for manually registered singletons.
// 检查缓存中或者实例工厂中是否存在该bean,处理已经被创建过的单例bean,这种bean不需要重复创建
// 在创建单例bean的时候会存在依赖注入的情况,为了避免循环依赖,spring创建bean的原则是不等bean创建完成就会将创建bean的ObjectFactory提前曝光,将ObjectFactory加入到缓存中,一旦下一个bean创建时需要依赖上一个bean则直接使用ObjectFactory
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {

// 返回对应的bean,如果是FactoryBean的话是通过指定方法来创建bean
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}

else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
// 只有单例才会解决循环依赖,原型如果存在循环依赖的话就会抛出异常
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}

// Check if bean definition exists in this factory.
// 检查ioc容器中是否存在BeanDefinition,检查是否能在当前的BeanFactory中取得需要的bean
BeanFactory parentBeanFactory = getParentBeanFactory();
// 如果当前的工厂中取不到,则到双亲BeanFactory中去取
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
// 如果不仅仅做类型检查,则是需要创建bean
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}

try {
// 根据bean的名字取得BeanDefinition
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);

// Guarantee initialization of beans that the current bean depends on.
// 获取当前Bean所依赖的Bean
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
// 递归查找依赖的bean
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
// 缓存依赖调用
registerDependentBean(dep, beanName);
getBean(dep);
}
}

// Create bean instance.
// 创建单例bean
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
try {
// 创建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;
}
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
// 创建prototype bean
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 {
// 其他scope的bean
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, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
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;
}
}

// Check if required type matches the type of the actual bean instance.
// 检查需要的类型是否符合bean的实际类型
if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
catch (TypeMismatchException ex) {

throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}

getSingleton方法

从缓存singletonObjects中加载单例,如果加载不成功尝试从singletonFactories中加载

三级缓存解决循环依赖

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// allowEarlyReference是true,表示允许早期依赖
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
// 从singletonObjects缓存中取
// singletonObjects中存的是beanName和bean实例
// singletonObjects是一级缓存
Object singletonObject = this.singletonObjects.get(beanName);
// 缓存中没有
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
// 锁定全局变量进行处理
synchronized (this.singletonObjects) {
// 如果该bean正在进行加载则不进行处理,直接返回
// earlySingletonObjects中存的是beanName和bean实例,但是与singletonObjects不同的是,存储的是还没进行属性注入操作的Bean的实例,,目的是为了监测循环引用
// earlySingletonObjects是二级缓存
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
// 从singletonFactories中获取,对于某些方法需要提前进行初始化时则会调用addSingletonFactory方法将对应的ObjectFactory初始化策略存在singletonFactories中
// singletonFactories中存的是beanName和创建bean的ObjectFactory工厂
// singletonFactories是三级缓存
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
// 调用ObjectFactory的getObject方法
singletonObject = singletonFactory.getObject();
// 记录在缓存earlySingletonObjects中,earlySingletonObjects和singletonFactories互斥
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}

getObjectForBeanInstance获取bean实例

主要是为了解决FactoryBean的情况

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protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

// Don't let calling code try to dereference the factory if the bean isn't a factory.
// 如果指定的name是以&为前缀,但是却不是FactoryBean实例,则抛出异常
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}

// 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.
// 正常bean则直接返回
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
// 到这里就都是FactoryBean
Object object = null;
if (mbd == null) {
// 从缓存中加载bean
object = getCachedObjectForFactoryBean(beanName);
}
// 缓存中没有
if (object == null) {
// Return bean instance from factory.
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
// 判断是用户自定义的还是应用程序本身的
boolean synthetic = (mbd != null && mbd.isSynthetic());
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
getObjectFromFactoryBean
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protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
if (factory.isSingleton() && containsSingleton(beanName)) {
synchronized (getSingletonMutex()) {
Object object = this.factoryBeanObjectCache.get(beanName);
if (object == null) {
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 (object != null && shouldPostProcess) {
try {
// 调用ObjectFactory的后置处理器
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Post-processing of FactoryBean's singleton object failed", ex);
}
}
this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
}
}
return (object != NULL_OBJECT ? object : null);
}
}
else {
Object object = doGetObjectFromFactoryBean(factory, beanName);
if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
}
}
return object;
}
}
doGetObjectFromFactoryBean
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private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
throws BeanCreationException {

Object object;
try {
// 权限验证
if (System.getSecurityManager() != null) {
AccessControlContext acc = getAccessControlContext();
try {
object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
@Override
public Object run() throws Exception {
// 直接调用getObject方法
return factory.getObject();
}
}, acc);
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
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 && isSingletonCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(
beanName, "FactoryBean which is currently in creation returned null from getObject");
}
return object;
}
postProcessObjectFromFactoryBean
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// org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#postProcessObjectFromFactoryBean
protected Object postProcessObjectFromFactoryBean(Object object, String beanName) {
return applyBeanPostProcessorsAfterInitialization(object, beanName);
}

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {

Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessAfterInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}

createBean创建bean

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protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {

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.
// 根据设置的className来解析class
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}

// Prepare method overrides.
// 准备方法覆盖
// 在配置bean的时候配置lookup-method或者replace-method则会进行方法覆盖
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.
// BeanPostProcessors来返回代理代替真正的实例
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);
}

// 创建bean
Object beanInstance = doCreateBean(beanName, mbdToUse, args);

return beanInstance;
}
resolveBeforeInstantiation

后置处理器

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protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
// mbd.beforeInstantiationResolved为false
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
// 实例化前处理
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
// 实例化后处理
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}
applyBeanPostProcessorsBeforeInstantiation
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protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
if (result != null) {
return result;
}
}
}
return null;
}
applyBeanPostProcessorsAfterInitialization
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public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {

Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessAfterInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}
doCreateBean
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protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
throws BeanCreationException {

// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 创建bean实例
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
mbd.resolvedTargetType = beanType;

// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// 处理@Value、@Autowried 调用AutowiredAnnotationBeanPostProcessor#postProcessMergedBeanDefinition处理@Autowried和@Value
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.
// 是否需要提前曝光 是单例 && 允许循环依赖 && 当前bean正在创建
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {

// 在bean初始化完成前将创建实例的ObjectFactory加入singletonFactories中,以便于后期循环依赖使用bean
addSingletonFactory(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
// 对bean进行BeanPostProcessor后置处理 SmartInstantiationAwareBeanPostProcessor
// AOP中的advice就是在这里处理的
return getEarlyBeanReference(beanName, mbd, bean);
}
});
}

// Initialize the bean instance.
Object exposedObject = bean;
try {
// 对bean进行属性注入,在这里如果依赖于其他bean的话,会进行递归创建依赖bean
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
// 调用初始化方法,如BeanNameAware#setBeanName,BeanClassLoaderAware#setBeanClassLoader,BeanFactoryAware#setBeanFactory,BeanPostProcessor处理器,InitializingBean#afterPropertiesSet, init-method
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) {
Object earlySingletonReference = getSingleton(beanName, false);
// 在检测到有循环依赖的情况下earlySingletonReference不为null
if (earlySingletonReference != null) {
// exposedObject == bean表示没有在初始化方法中被改变
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
// bean创建后其所依赖的bean是已经被创建的,actualDependentBeans不为空表示当前bean创建后其所依赖的bean没有完全创建完,存在循环依赖
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 {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}

return exposedObject;
}
populateBean属性注入

依赖注入是在这里进行的

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protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
PropertyValues pvs = mbd.getPropertyValues();

if (bw == null) {
if (!pvs.isEmpty()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
// 没有可填充的属性
return;
}
}

// 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.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
return;
}
}
}
}

int resolvedAutowireMode = mbd.getResolvedAutowireMode();
// 解析autowired
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
// 根据名称自动注入
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
// 根据类型自动注入
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}

boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);

if (hasInstAwareBpps || needsDepCheck) {
PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
if (hasInstAwareBpps) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
checkDependencies(beanName, mbd, filteredPds, pvs);
}
}
// 将属性应用到bean中
applyPropertyValues(beanName, mbd, bw, pvs);
}