Bean生命周期
Spring大致的生命周期如下图所示
Bean实例化
/**
* 该方法完成IOC容器创建以及初始化工作
* 该方法中最重要的是第二步和第十一步
*
*/
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
// STEP 1： 刷新预处理
//准备工作包括设置启动时间，是否激活标识位，初始化属性源(property,source)配置
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//用DefaultListableBeanFactory的子类得到的是DefaultListableBeanFactory
//可以理解为初始化bean工厂
// STEP 2：
// a） 创建IoC容器（DefaultListableBeanFactory）
// b） 加载解析XML文件（最终存储到Document对象中）
// c） 读取Document对象，并完成BeanDefinition的加载和注册工作
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//最重要的方法，准备bean工厂
// STEP 3： 对IoC容器进行一些预处理（设置一些公共属性）
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
//这个方法在当前版本的spring是没有任何代码的，可能spring期待在后面的版本中进行扩展
//空壳方法
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//比较重要的方法
//在spring的环境中去执行已经被注册的factory processors
//设置执行自定义的ProcessorFactory和spring内部自己定义的(ConfigutationClassPoetProcessor)
//ConfigurationClassPostProcessor就是spring内部自己维护的BeanFactoryPostProcessor
//下面的方法主要执行ConfigurationClassPostProcessor中的方法
// STEP 5： 调用BeanFactoryPostProcessor后置处理器对BeanDefinition处理
/**
* BeanFactoryPostProcessor是spring的扩展点之一
* 实现该接口，可以在spring的bean创建之前修改bean的定义属性
* spring允许BeanFactoryPostProcessor在容器实例化任何其他bean之前读取它配置的元数据
* 并可以根据需要进行修改，例如可以把bean的scope从singleton改为prototype,也可以把property的值给修改
* 可以同时配置多个BeanFactoryPostProcessor,并且通过设置'order'属性来控制各个BeanFactoryPostProcessor
* BeanFactoryPostProcessor是在spring容器加载了bean的定义文件之后，在bean实例化之前执行的
* 可以写一个例子来测试以下这个功能
*/
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
//上一行的代码已经将一些后置处理器放到bdMap中了，包括自定义的BeanPostProcessor
// 注册BeanPostProcessor,即后置处理器，一共是7个
//把bdMap中的所有后置处理器拿出来，
// 再直接new另外一些后置处理器，一起放到工厂的list中
// STEP 6： 注册BeanPostProcessor后置处理器
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
//不重要，国际化的处理
// STEP 7： 初始化一些消息源（比如处理国际化的i18n等消息源）
initMessageSource();
// Initialize event multicaster for this context.
//事件处理，用的比较少，不重要
// STEP 8： 初始化应用事件广播器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
//这是一个空壳方法，里面没有代码
// STEP 9： 初始化一些特殊的bean
onRefresh();
// Check for listener beans and register them.
//对一些监听器的注册，先放一放
// STEP 10： 注册一些监听器
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
//重点，重点
//完成bean的实例化
// STEP 11： 实例化剩余的单例bean（非懒加载方式）
// 注意事项：Bean的IoC、DI和AOP都是发生在此步骤
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// STEP 12： 完成刷新时，需要发布对应的事件
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.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
入口：org.springframework.context.support.AbstractApplicationContext#refresh方法的第十一步，即org.springframework.context.support.AbstractApplicationContext#finishBeanFactoryInitialization方法
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
//下面的if中只是spring的一个小知识点，不重要
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.
//不重要
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
/**
* Spring aop是动态织入的，而AspectJ是静态织入的，即编译时期织入
* 过，不重要
*/
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
//基本用不到，不重要
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
//spring基本一些配置，不重要
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
//最重要的代码
//这里调用的DefaultListableBeanFactory中的preInstantiateSingletons
//实例化所有的单例对象
beanFactory.preInstantiateSingletons();
}
接着：org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons方法
//真正调用这里，重点
@Override
public void preInstantiateSingletons() throws BeansException {
if (logger.isDebugEnabled()) {
logger.debug("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.
//从bdMap拿到所有需要初始化的类
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
//这行代码不重要，合并父类的bd，这种应用很少用
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//肯定会进到if中
//如果bean不是抽象的，而且是单例的，同时还不是懒加载的，则进行下面的操作
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//这里判断是不是FactoryBean
if (isFactoryBean(beanName)) {
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<Boolean>)
((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
//重点
getBean(beanName);
}
}
}
}
接着：org.springframework.beans.factory.support.AbstractBeanFactory#getBean方法
//重点
@Override
public Object getBean(String name) throws BeansException {
//获取Bean实例
return doGetBean(name, null, null, false);
}
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
//因为你的beanName有可能加了&,所以要将&移除
//这里用到的是FactoryBean的知识
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
//先从容器中拿beanName对应的对象，如果拿不到再new
/**
* 这个方法在初始化的时候会调用，在getBean的时候也会调用
* 为什么呢？
* 也就是说Spring在初始化的时候先获取这个对象
* 判断这个对象是狗被实例化过(普通情况下绝对为空，只有一种情况下不为空)
* 就是lazy的情况，lazy在调用getBean方法的时候才会初始化，
* 这里就是判断lazy的类之前是否new过，
* 所以你可以理解getSingleton(beanName)等于bdMap.get(beanName)
* 由于方法会在spring环境初始化的时候（就是对象被创建的调用一次）调用一次
* 还会在getBean的时候调用一次
* 所以在调试的时候特别重要，不能直接断点在这里
* 需要先进入annotationConfigApplicationContext.getBean(xxx.class)
* 之后再来断点，这样就确保了我峨嵋你是在获取这个bean的时候调用的
*/
//从三级缓存中获取bean对象，面试重点 spring三级缓存
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
//如果取出来的Bean实例是FactoryBean的Bean实例，则需要从FactoryBean实例中产生一个对象实例
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
//重点，容器中没有该对象的实例
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
/**
* 如果是原型，不应该在初始化的时候创建
* spring当中的标识CurrentlyInCreation标识该类正在创建
*/
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
//这里没有对spring进行改造，parentBeanFactory应该null
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 {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
//做了一个检查
if (!typeCheckOnly) {
//添加到alreadyCreated set集合当中，表示它已经创建过
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
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);
}
}
}
// Create bean instance.
//重点重点
if (mbd.isSingleton()) {
/**
* getSingleton相当于从缓存中根据beanName取出对象，
* 如果取不到，就回调下面的匿名内部类的createBean方法
*/
sharedInstance = getSingleton(beanName, () -> {
try {
//重点
//真正调用AbstractAutowireCapableBeanFactory中的createBean方法
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);
}
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;
}
}
// 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.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
接着：org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory<?>)方法
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 + "'");
}
//往正在创建的bean的标识的容器中添加该beanName
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
//这行代码是真正创建对象的，该对象已经是一个代理对象了，重点
/**
* 后置处理器就是再这里把原生的变成代理对象，去看匿名内部类中的createBean方法
* 这里其实就是调用外面的lamda表达式中的createBean方法
*/
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;
}
afterSingletonCreation(beanName);
}
if (newSingleton) {
//重点，三级缓存解决循环依赖问题
//实例化完成对象，并且对象设只属性和完成初始化之后
//及那个该对象放入到一级缓存中
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
接着：org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean方法
**
* Central method of this class: creates a bean instance,
* populates the bean instance, applies post-processors, etc.
* @see #doCreateBean
* 重点
* 真正调用该方法createBean
*/
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isDebugEnabled()) {
logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
try {
//处理lookup-method和replace-method配置，Spring将这两个配置统称为override methods
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.
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 {
//真正实例化bean（还有填充属性，初始化）的方法在这一行
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("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);
}
}
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
//BeanWrapper把真实对象包装了一层，该类中的getWrappedInstance返回真实对象
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//开始创建真实对象的包装类，利用反射
//默认调用无参构造实例化bean
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//这里从包装类中拿出的是原生对象，而不是代理对象，接着下面的操作把原生对象变成代理对象
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
//重要，牛逼
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.
/**
* 解决循环依赖的关键步骤
*/
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
//如果要提前暴露单理bean，则将该bean加入到三级缓存中
if (earlySingletonExposure) {
if (logger.isDebugEnabled()) {
logger.debug("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
//重要，一定要进去看看
//把创建出来的对象放入相应的map中
//将刚创建的bean放入到三级缓存中 singleFactories(key是besnName,value是FactoryBean)
//singletonFactory是通过lamda表达式获取得到的
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//赋值属性的，重要
//主要借助Common和Autowired两个后置处理器来填充属性
//bean初始化第二步：填充属性（DI依赖注入发生在此步骤）
populateBean(beanName, mbd, instanceWrapper);
/**
* 重点，这里就是把原生对象变成代理对象的地方
* bean初始化第三步：调用初始化方法，完成bean的初始化，aop发生在此步骤
* 例如<besn init-method=""></besn>中的init-method方法就是在这里调用的
*/
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);
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 " +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
/**
* 重点，在该方法中创建bean的实例
*/
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);
//检测一个类的访问权限
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);
}
/**
* 如果工厂方法不为空，则通过工厂方法创建bean对象
* 这种构建bean的方式可以自己写个demo去试试
* 源码就不深入分析了
*/
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
/**
* 当一个对象被实例化多次时
* 当创建对象时，是使用默认的构造方法，还是自定义的构造方法，
* spring通过autowireNecessary值来记录
*/
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 {
//通过默认的无参构造方法
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
//由后置处理器返回哪些构造方法，然后决定使用哪个构造方法来创建bean的实例
/**
* 在spring中如果你类中的构造方法跟默认的构造方法一样的话，
* spring就认为相当于没有勾走方法，所以这里会返回null;
* 而如果你在类中重写了构造方法，并且与默认构造方法有区别，例如方法参数不一样
* 或者有方法体，这里就会返回你重写的构造方法
*/
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// No special handling: simply use no-arg constructor.
//使用默认的无参构造方法
return instantiateBean(beanName, mbd);
}
/**
* 使用默认的构造方法进行创建对象
*/
protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
try {
Object beanInstance;
final BeanFactory parent = this;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
getInstantiationStrategy().instantiate(mbd, beanName, parent),
getAccessControlContext());
}
else {
//getInstantiationStrategy得到类的实例化策略
//默认情况下得到一个反射的实例化策略
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}
接着：org.springframework.beans.factory.support.SimpleInstantiationStrategy#instantiate方法
//重点，该方法通过默认的构造方法完成创建对象
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
if (!bd.hasMethodOverrides()) {
Constructor<?> constructorToUse;
synchronized (bd.constructorArgumentLock) {
constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {
final Class<?> clazz = bd.getBeanClass();
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
if (System.getSecurityManager() != null) {
constructorToUse = AccessController.doPrivileged(
(PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
}
else {
//获取构造方法
//constructorToUse表示spring使用哪个构造方法实例化对象的
constructorToUse = clazz.getDeclaredConstructor();
}
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
//重点 创建bean实例
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// Must generate CGLIB subclass.
return instantiateWithMethodInjection(bd, beanName, owner);
}
}
接着：org.springframework.beans.BeanUtils#instantiateClass方法
/**
* 通过ctor.newInstance(args)完成创建对象，利用的是反射技术
*/
public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
ReflectionUtils.makeAccessible(ctor);
//通过ctor.newInstance(args)完成创建对象，利用的是反射技术
return (KotlinDetector.isKotlinType(ctor.getDeclaringClass()) ?
KotlinDelegate.instantiateClass(ctor, args) : ctor.newInstance(args));
}
catch (InstantiationException ex) {
throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {
throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
}
}
总结
从DefaultListableBeanFactory中beanDefinitionMap中获取到对应的BeanDefinition，然后获取到Bean的Class，接着通过反射获取到构造函数，然后调用newInstance方法创建出对象实例，具体如下：
//获取到构造函数
Constructor<?> constructorToUse = clazz.getDeclaredConstructor();
//通过newInstance方法创建出对象，args为构造函数参数
constructorToUse.newInstance(args)
填充属性
参照上面的创建bean实例
入口：org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean方法
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
//BeanWrapper把真实对象包装了一层，该类中的getWrappedInstance返回真实对象
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//开始创建真实对象的包装类，利用反射
//默认调用无参构造实例化bean
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//这里从包装类中拿出的是原生对象，而不是代理对象，接着下面的操作把原生对象变成代理对象
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
//重要，牛逼
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.
/**
* 解决循环依赖的关键步骤
*/
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
//如果要提前暴露单理bean，则将该bean加入到三级缓存中
if (earlySingletonExposure) {
if (logger.isDebugEnabled()) {
logger.debug("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
//重要，一定要进去看看
//把创建出来的对象放入相应的map中
//将刚创建的bean放入到三级缓存中 singleFactories(key是besnName,value是FactoryBean)
//singletonFactory是通过lamda表达式获取得到的
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//赋值属性的，重要
//主要借助Common和Autowired两个后置处理器来填充属性
//bean初始化第二步：填充属性（DI依赖注入发生在此步骤）
populateBean(beanName, mbd, instanceWrapper);
/**
* 重点，这里就是把原生对象变成代理对象的地方
* bean初始化第三步：调用初始化方法，完成bean的初始化，aop发生在此步骤
* 例如<besn init-method=""></besn>中的init-method方法就是在这里调用的
*/
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);
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 " +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
/**
* 重要 利用两个后置处理器来填充属性
* Commonxxx后置处理器主要处理@Resurce,@PostConstruct等等
* Autowiredxxx处理器主要处理@Autowired注解的
*/
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;
}
}
// 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;
}
}
}
}
//获取出所有的property属性值，因为在组装BeanDefinition对象时，将类的属性放入到了PropertyValues中
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
//一般情况下不会进入if里面，因为spring默认的是AUTOWIRED_NO
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
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) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
//拿到所有set和get方法
PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
if (hasInstAwareBpps) {
//重点重点在这里
//通过后置处理器处理
/**
* 1.ImportAwareBeanPostProcessor 不重要
* 2.CommonAnnotationBeanPostProcessor重要
* 主要处理@Resource,@PostConstruct等
* 3.AutowiredAnnotationBeanPostProcessor重要
* 主要处理@Autowired
*/
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
//这行代码完成属性赋值
//重点看这两个后置处理器的postProcessPropertyValues方法
//CommonAnnotationBeanPostProcessor
//AutowiredAnnotationBeanPostProcessor
pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
checkDependencies(beanName, mbd, filteredPds, pvs);
}
}
if (pvs != null) {
//基于xml方式
//完成依赖注入
//PropertyValues pvs:待依赖的属性值集合
//BeanWrapper bw:实例化后的Bean的包装对象
//xml方式的属性注入在这里
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
/**
* 真正调用该方法完成基于xml方式的依赖注入
*/
protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
if (pvs.isEmpty()) {
return;
}
if (System.getSecurityManager() != null && bw instanceof BeanWrapperImpl) {
((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
}
MutablePropertyValues mpvs = null;
List<PropertyValue> original;
if (pvs instanceof MutablePropertyValues) {
mpvs = (MutablePropertyValues) pvs;
if (mpvs.isConverted()) {
// Shortcut: use the pre-converted values as-is.
try {
bw.setPropertyValues(mpvs);
return;
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}
original = mpvs.getPropertyValueList();
}
else {
original = Arrays.asList(pvs.getPropertyValues());
}
TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
// Create a deep copy, resolving any references for values.
List<PropertyValue> deepCopy = new ArrayList<>(original.size());
boolean resolveNecessary = false;
for (PropertyValue pv : original) {
if (pv.isConverted()) {
deepCopy.add(pv);
}
else {
String propertyName = pv.getName();
Object originalValue = pv.getValue();
//循环依赖重点
//！！！！重点
//一位属性中的对象还没有创建，所以不能直接设置属性值，必须先创建属性对象
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
boolean convertible = bw.isWritableProperty(propertyName) &&
!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
// Possibly store converted value in merged bean definition,
// in order to avoid re-conversion for every created bean instance.
if (resolvedValue == originalValue) {
if (convertible) {
pv.setConvertedValue(convertedValue);
}
deepCopy.add(pv);
}
else if (convertible && originalValue instanceof TypedStringValue &&
!((TypedStringValue) originalValue).isDynamic() &&
!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
pv.setConvertedValue(convertedValue);
deepCopy.add(pv);
}
else {
resolveNecessary = true;
deepCopy.add(new PropertyValue(pv, convertedValue));
}
}
}
if (mpvs != null && !resolveNecessary) {
mpvs.setConverted();
}
// Set our (possibly massaged) deep copy.
try {
//重点
//完成依赖注入
bw.setPropertyValues(new MutablePropertyValues(deepCopy));
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}
接着：org.springframework.beans.AbstractPropertyAccessor#setPropertyValues方法
@Override
public void setPropertyValues(PropertyValues pvs) throws BeansException {
//依赖注入 继续跟
setPropertyValues(pvs, false, false);
}
//真正嗲用该方法
//完成依赖注入
@Override
public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
throws BeansException {
List<PropertyAccessException> propertyAccessExceptions = null;
List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
//遍历
for (PropertyValue pv : propertyValues) {
try {
// This method may throw any BeansException, which won't be caught
// here, if there is a critical failure such as no matching field.
// We can attempt to deal only with less serious exceptions.
//依赖属性注入--重点 先调用AbstractPropertyAccessor中的setPropertyValue
// 最终调用AbstractNestablePropertyAccessor中的setPropertyValue
setPropertyValue(pv);
}
catch (NotWritablePropertyException ex) {
if (!ignoreUnknown) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (NullValueInNestedPathException ex) {
if (!ignoreInvalid) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (PropertyAccessException ex) {
if (propertyAccessExceptions == null) {
propertyAccessExceptions = new ArrayList<>();
}
propertyAccessExceptions.add(ex);
}
}
// If we encountered individual exceptions, throw the composite exception.
if (propertyAccessExceptions != null) {
PropertyAccessException[] paeArray = propertyAccessExceptions.toArray(new PropertyAccessException[0]);
throw new PropertyBatchUpdateException(paeArray);
}
}
接着：org.springframework.beans.AbstractNestablePropertyAccessor#setPropertyValue方法
//真正调用该方法
@Override
public void setPropertyValue(PropertyValue pv) throws BeansException {
PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens;
if (tokens == null) {
String propertyName = pv.getName();
AbstractNestablePropertyAccessor nestedPa;
try {
nestedPa = getPropertyAccessorForPropertyPath(propertyName);
}
catch (NotReadablePropertyException ex) {
throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
"Nested property in path '" + propertyName + "' does not exist", ex);
}
tokens = getPropertyNameTokens(getFinalPath(nestedPa, propertyName));
if (nestedPa == this) {
pv.getOriginalPropertyValue().resolvedTokens = tokens;
}
//属性注入
nestedPa.setPropertyValue(tokens, pv);
}
else {
//属性注入
setPropertyValue(tokens, pv);
}
}
//重点
protected void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
//token.keys只要不为空，则表示要依赖的属性是集合类型的属性
if (tokens.keys != null) {
processKeyedProperty(tokens, pv);
}
else {
//重点看这个 设置非集合类型的属性
processLocalProperty(tokens, pv);
}
}
/真正调用该方法：重点--依赖的属性注入
private void processLocalProperty(PropertyTokenHolder tokens, PropertyValue pv) {
//获取属性处理器
PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);
if (ph == null || !ph.isWritable()) {
if (pv.isOptional()) {
if (logger.isDebugEnabled()) {
logger.debug("Ignoring optional value for property '" + tokens.actualName +
"' - property not found on bean class [" + getRootClass().getName() + "]");
}
return;
}
else {
throw createNotWritablePropertyException(tokens.canonicalName);
}
}
Object oldValue = null;
try {
//获得原始的值
Object originalValue = pv.getValue();
Object valueToApply = originalValue;
if (!Boolean.FALSE.equals(pv.conversionNecessary)) {
if (pv.isConverted()) {
valueToApply = pv.getConvertedValue();
}
else {
if (isExtractOldValueForEditor() && ph.isReadable()) {
try {
oldValue = ph.getValue();
}
catch (Exception ex) {
if (ex instanceof PrivilegedActionException) {
ex = ((PrivilegedActionException) ex).getException();
}
if (logger.isDebugEnabled()) {
logger.debug("Could not read previous value of property '" +
this.nestedPath + tokens.canonicalName + "'", ex);
}
}
}
valueToApply = convertForProperty(
tokens.canonicalName, oldValue, originalValue, ph.toTypeDescriptor());
}
pv.getOriginalPropertyValue().conversionNecessary = (valueToApply != originalValue);
}
//重点：通过PropertyHandler去完成依赖注入
//这里一共有两个实现类，都进去看看
ph.setValue(valueToApply);
}
catch (TypeMismatchException ex) {
throw ex;
}
catch (InvocationTargetException ex) {
PropertyChangeEvent propertyChangeEvent = new PropertyChangeEvent(
getRootInstance(), this.nestedPath + tokens.canonicalName, oldValue, pv.getValue());
if (ex.getTargetException() instanceof ClassCastException) {
throw new TypeMismatchException(propertyChangeEvent, ph.getPropertyType(), ex.getTargetException());
}
else {
Throwable cause = ex.getTargetException();
if (cause instanceof UndeclaredThrowableException) {
// May happen e.g. with Groovy-generated methods
cause = cause.getCause();
}
throw new MethodInvocationException(propertyChangeEvent, cause);
}
}
catch (Exception ex) {
PropertyChangeEvent pce = new PropertyChangeEvent(
getRootInstance(), this.nestedPath + tokens.canonicalName, oldValue, pv.getValue());
throw new MethodInvocationException(pce, ex);
}
}
接着：org.springframework.beans.DirectFieldAccessor.FieldPropertyHandler#setValue方法
//重点
@Override
public void setValue(@Nullable Object value) throws Exception {
try {
//暴力破解，针对私有属性
ReflectionUtils.makeAccessible(this.field);
//到底了，通过反射设置属性值
//Field.set(obj,value);
this.field.set(getWrappedInstance(), value);
}
catch (IllegalAccessException ex) {
throw new InvalidPropertyException(getWrappedClass(), this.field.getName(),
"Field is not accessible", ex);
}
}
总结
首先从DefaultListableBeanFactory中的beanDefinitionMap中获取到对应的BeanDefinition对象，从BeanDefinition对象中获取到PropertyValues【因为在组装BeanDefinition对象时，将类的属性放入到了PropertyValues中】，最后还是通过反射技术进行了对象属性的赋值
初始化
参照上面的bean实例化步骤可知
入口：org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean方法
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
//BeanWrapper把真实对象包装了一层，该类中的getWrappedInstance返回真实对象
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//开始创建真实对象的包装类，利用反射
//默认调用无参构造实例化bean
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//这里从包装类中拿出的是原生对象，而不是代理对象，接着下面的操作把原生对象变成代理对象
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
//重要，牛逼
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.
/**
* 解决循环依赖的关键步骤
*/
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
//如果要提前暴露单理bean，则将该bean加入到三级缓存中
if (earlySingletonExposure) {
if (logger.isDebugEnabled()) {
logger.debug("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
//重要，一定要进去看看
//把创建出来的对象放入相应的map中
//将刚创建的bean放入到三级缓存中 singleFactories(key是besnName,value是FactoryBean)
//singletonFactory是通过lamda表达式获取得到的
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//赋值属性的，重要
//主要借助Common和Autowired两个后置处理器来填充属性
//bean初始化第二步：填充属性（DI依赖注入发生在此步骤）
populateBean(beanName, mbd, instanceWrapper);
/**
* 重点，这里就是把原生对象变成代理对象的地方
* bean初始化第三步：调用初始化方法，完成bean的初始化，aop发生在此步骤
* 例如<besn init-method=""></besn>中的init-method方法就是在这里调用的
*/
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);
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 " +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
/**
* 重点，该方法就是把原生对象变成代理对象的
*/
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 {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//重点
/**
* 前置处理器
* 执行BeanPostProcessor的Beforexxx方法，执行完before方法后还是原生对象
* 还没完成代理，执行完Afterxxx方法，就完成代理
* 执行BeanPostProcessor的postProcessBeforeInitialization方法
* 即该部分在初始化方法执行之前调用
*/
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//重点：执行初始化方法（先调用InitializingBean的afterPropertiesSet,再调用init-method属性指定的初始化方法）
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()) {
//后置处理器
//该部分在初始化方法执行之后调用
//重点
//aop在这里完成
//执行完后置处理器的Afterxxx方法，把原生对象变成代理对象
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
throws Throwable {
boolean isInitializingBean = (bean instanceof InitializingBean);
//如果是InitializingBean的实现类，则先初始化InitializingBean的实现类
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 {
//调用InitializingBean接口的afterPropertiesSet方法
((InitializingBean) bean).afterPropertiesSet();
}
}
//重点
//然后再初始化<bean>标签中的init-method属性中对应的方法
if (mbd != null && bean.getClass() != NullBean.class) {
String initMethodName = mbd.getInitMethodName();
if (StringUtils.hasLength(initMethodName) &&
!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
//调用自定义的初始化方法
//还是通过反射调用init-method属性中对应的方法
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
/**
* 自定义的初始化方法，底层还是通过反射
*/
protected void invokeCustomInitMethod(String beanName, final Object bean, RootBeanDefinition mbd)
throws Throwable {
//从BeanDefinition对象中获取到init-method属性值，即初始化方法的名称
String initMethodName = mbd.getInitMethodName();
Assert.state(initMethodName != null, "No init method set");
//通过初始化方法名称以及bean对象获取到真正的Method
final Method initMethod = (mbd.isNonPublicAccessAllowed() ?
BeanUtils.findMethod(bean.getClass(), initMethodName) :
ClassUtils.getMethodIfAvailable(bean.getClass(), initMethodName));
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.isDebugEnabled()) {
logger.debug("No default init method named '" + initMethodName +
"' found on bean with name '" + beanName + "'");
}
// Ignore non-existent default lifecycle methods.
return;
}
}
if (logger.isDebugEnabled()) {
logger.debug("Invoking init method '" + initMethodName + "' on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
ReflectionUtils.makeAccessible(initMethod);
return null;
});
try {
AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () ->
initMethod.invoke(bean), getAccessControlContext());
}
catch (PrivilegedActionException pae) {
InvocationTargetException ex = (InvocationTargetException) pae.getException();
throw ex.getTargetException();
}
}
else {
try {
ReflectionUtils.makeAccessible(initMethod);
//通过反射调用方法
initMethod.invoke(bean);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
}
总结
从DefaultListableBeanFactory中的beanDefinitionMap中获取到对应的BeanDefinition对象，接着从BeanDefintion对象中获取到init-method对应的初始化方法名称，接着通过bean实例，以及方法名称获取到Method，最后通过Method.invoke(bean对象)调用初始化方法，底层本质还是通过反射技术。
