关于spring bean 生命周期代码详解-产生到消亡
简述
几个重要的接口或类
AbstractBeanFactory类 ：
getBean时
AbstractAutowireCapableBeanFactory类：
创建Bean的主要类
populateBean（自动注入属性）
initializeBean：
invokeAwareMethods（BeanNameAware BeanClassLoaderAware BeanFactoryAware ）
applyBeanPostProcessorsBeforeInitialization（@PostConstruct）
invokeInitMethods（afterPropertiesSet，init-method）
applyBeanPostProcessorsAfterInitialization（）
InitializingBean接口 ：
初始化时会回调afterPropertiesSet
InitDestroyAnnotationBeanPostProcessor 初始化和消亡
主要用于根据注解反射调用
如对bean中所有的@PreDestroy、@PostConstruct方法进行调用
DisposableBeanAdapter 消亡时会回调destroy()
@PreDestroy（最终通过InitDestroyAnnotationBeanPostProcessor 调用）
disposable.destroy()；
destroy-method
产生到消亡的整体顺序：
（1）自动属性注入
（2）BeanNameAware：setBeanName(String)-》 BeanClassLoaderAware ：setBeanClassLoader(getBeanClassLoader())-》BeanFactoryAware ：setBeanFactory(AbstractAutowireCapableBeanFactory.this) 。按顺序依次回调实现的接口。
（3）applyBeanPostProcessorsBeforeInitialization （@PostConstruct），遍历所有BeanPostProcessor的实现类的applyBeanPostProcessorsAfterInitialization 方法。
（4）InitializingBean (afterPropertiesSet()) -》init-method
（5）applyBeanPostProcessorsAfterInitialization() ：遍历所有BeanPostProcessor的实现类的applyBeanPostProcessorsAfterInitialization方法。
（6）@PreDestroy
（7）DisposableBean（实现接口）：destroy()
（8）destroy-method现在开始初始化容器
这是BeanFactoryPostProcessor实现类构造器！！
BeanFactoryPostProcessor调用postProcessBeanFactory方法
这是BeanPostProcessor实现类构造器！！
这是InstantiationAwareBeanPostProcessorAdapter实现类构造器！！
InstantiationAwareBeanPostProcessor调用postProcessBeforeInstantiation方法
【构造器】调用Person的构造器实例化
InstantiationAwareBeanPostProcessor调用postProcessPropertyValues方法
【注入属性】注入属性address
【注入属性】注入属性name
【注入属性】注入属性phone
【BeanNameAware接口】调用BeanNameAware.setBeanName()
【BeanClassLoaderAware接口】调用setBeanClassLoader
【BeanFactoryAware接口】调用BeanFactoryAware.setBeanFactory()
BeanPostProcessor接口方法postProcessBeforeInitialization对属性进行更改！
【@PostConstruct注解】
【InitializingBean接口】调用InitializingBean.afterPropertiesSet()
【init-method】调用
BeanPostProcessor接口方法postProcessAfterInitialization对属性进行更改！
InstantiationAwareBeanPostProcessor调用postProcessAfterInitialization方法
容器初始化成功
Person [address=广州, name=张三, phone=110]
现在开始关闭容器！
【@PreDestroy注解】
【DiposibleBean接口】调用DiposibleBean.destory()
【destroy-method】调用
bean的产生和消亡可以回调的方法
关于在spring 容器初始化 bean 和销毁前所做的操作定义方式有三种：
第一种：通过@PostConstruct 和 @PreDestroy 方法 实现初始化和销毁bean之前进行的操作
第二种是：通过 在xml中定义init-method 和 destory-method方法
第三种是： 通过bean实现InitializingBean和 DisposableBean接口
关于bean产生简述
所有的初始化方法在bean生成时只调用一次，在BeanPostProcessor的前置后置处理方法中可以 对原实例对象 做增强代理并作为新的bean返回。
（1）bean产生的重要入口类可见AbstractAutowireCapableBeanFactory类的doCreateBean方法
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
throws BeanCreationException {
populateBean(beanName, mbd, instanceWrapper);//自动注入相关属性
if (exposedObject != null) {
//initializeBean 初始化时一些操作，
（1）回调所有实现了BeanNameAware BeanFactoryAware BeanClassLoaderAware 接口的类的相关方法
（2）回调所有实现了initializingBean接口的类 的afterPropertiesSet()方法。
（3）对所有实现了BeanPostProcessor接口的类进行方法回调，其中InitDestroyAnnotationBeanPostProcessor实现了BeanPostProcessor接口，在此类中会反射调用@PostConstruct注解的方法。
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
// Register bean as disposable.
try {
/注册一个bean消亡时的处理的DisposableBean，其实都是DisposableBeanAdapter的实例bean，
// 会存储在DefaultSingletonBeanRegistry类中的属性disposableBeans(Map)中，key为此bean的名字,value为DisposableBeanAdapter实例例对象
registerDisposableBeanIfNecessary(beanName, bean, mbd); /
}
}
（2）所有的bean在生成时都会注册一个消亡时的处理的bean，而且都是DisposableBeanAdapter实例，具体可见AbstractAutowireCapableBeanFactory类的doCreateBean方法中调用的registerDisposableBeanIfNecessary方法。
DisposableBeanAdapter类构造方法
关于bean消亡简述
由于创建bean的时候都会注册一个 DisposableBean实例，并且都是DisposableBeanAdapter的实例bean，
此映射关系会存储在DefaultSingletonBeanRegistry类中的属性disposableBeans(Map类型)中，key为此bean的名字,value为DisposableBeanAdapter实例例对象，例如：{“UserService类的beanname”：DisposableBeanAdapter实例对象}；
所以在bean消亡时，最终会调用DisposableBeanAdapter的destroy()方法（不管bean有没有实现DisposableBean接口都会调用）。
bean的产生
一、从AbstractBeanFactory.class的getBean开始追踪
二、 继续追踪，如果单例缓存中存在bean，则直接返回bean。否则判断是单例还是多例，并进行相关操作，如果是单例，则生成bean后要存储到内存，以便下次调用。
@SuppressWarnings("unchecked")
protected T doGetBean(
final String name, final Class requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) { //如果在单例缓存中存在直接使用
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 + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
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);
}
}
if (!typeCheckOnly) {
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 dependsOnBean : dependsOn) {
if (isDependent(beanName, dependsOnBean)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
}
registerDependentBean(dependsOnBean, beanName);
getBean(dependsOnBean);
}
}
// Create bean instance. 是单例
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory
三、继续追踪到AbstractAutowireCapableBeanFactory.class
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, 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 {
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);
}
Object beanInstance = doCreateBean(beanName, mbdToUse, args); //创建bean
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}四、调用populate方法对原实例对象属性自动注入，并调用initializeBean对原实例对象的相关处理（重要）
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);//创建原对象的实例包装
}
//bean=原实例对象，此时是已经实例化过的对象。
final Object bean = (instanceWrapper != null ?
instanceWrapper.getWrappedInstance() : null);
Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isDebugEnabled()) {
logger.debug("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, new ObjectFactory
五、自动注入属性的方法 populateBean方法解析（重要）
/**
* Populate the bean instance in the given BeanWrapper with the property values
* from the bean definition.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param bw BeanWrapper with bean instance
*/
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.
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.
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;
}
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.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);//注意这里
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
checkDependencies(beanName, mbd, filteredPds, pvs);
}
}
applyPropertyValues(beanName, mbd, bw, pvs);
}I实现nstantiationAwareBeanPostProcessor这个接口的postProcessPropertyValues方法的类，可以获得带有带有注解的字段和方法，并注入到Bean中。
六、调用initializeBean方法对原实例对象做其他初始化操作（三个bena初始化回调顺序）
具体包括：
（1）实现了BeanNameAware 回调setBeanName(beanName)、BeanFactoryAware 回调setBeanFactory(AbstractAutowireCapableBeanFactory.this)、BeanClassLoaderAware 回调setBeanClassLoader(getBeanClassLoader())。作用是，可以在bean类中获得这些回调的参数。
（2）实现了initializingBean接口 ，回调afterPropertiesSet()。
（3）实现了BeanPostProcessor接口的类在bean初始化中 ，可以回调，此接口具体有如下两个方法
1）wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean原bean实例对象, beanName);
其中InitDestroyAnnotationBeanPostProcessor类实现了BeanPostProcessor接口，并且InitDestroyAnnotationBeanPostProcessor中的postProcessBeforeInitialization方法实现了：对@PostConstruct注解表示的方法进行反射调用。
2)wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean原bean实例对象, beanName);。
BeanPostProcessor接口重要作用：实现BeanPostProcessor接口，可以postProcessBeforeInitialization或者 applyBeanPostProcessorsAfterInitialization中做代理，并返回代理后的bean实例。
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction private void invokeAwareMethods(final String beanName, final Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
throws Throwable {
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isDebugEnabled()) {
logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged(new PrivilegedExceptionAction@Override
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;
}追踪开始applyBeanPostProcessorsBeforeInitialization，看看如何进行 被@PostConstruct注解的方法回调的
@Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessBeforeInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}继续追踪，发现有个InitDestroyAnnotationBeanPostProcessor类实现了BeanPostProcessor接口，进入查看
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
//这里获得所有的PreDestory和PostConstruct注解的方法，如何获得本文最后统一讲
LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
try {
metadata.invokeInitMethods(bean, beanName);//进行反射调用
}
catch (InvocationTargetException ex) {
throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException());
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Failed to invoke init method", ex);
}
return bean;
}继续追踪
public void invokeInitMethods(Object target, String beanName) throws Throwable {
Collection initMethodsToIterate =
(this.checkedInitMethods != null ? this.checkedInitMethods : this.initMethods);
if (!initMethodsToIterate.isEmpty()) {
boolean debug = logger.isDebugEnabled();
//遍历所有的被PostConstruct注解的方法
for (LifecycleElement element : initMethodsToIterate) {
if (debug) {
logger.debug("Invoking init method on bean '" + beanName + "': " + element.getMethod());
}
element.invoke(target);//反射调用
}
}
} 七、回到 第四步 的registerDisposableBeanIfNecessary方法，讨论实现了DisposableBean接口的bean的后续问题
protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
if (mbd.isSingleton()) {
// Register a DisposableBean implementation that performs all destruction
// work for the given bean: DestructionAwareBeanPostProcessors,
// DisposableBean interface, custom destroy method.
//注册的key=beanName,value=DisposableBeanAdapter 对象.
//所以当bean销毁时，经过DisposableBeanAdapter的destroy方法处理
registerDisposableBean(beanName,
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
}
else {
// A bean with a custom scope...
Scope scope = this.scopes.get(mbd.getScope());
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + mbd.getScope() + "'");
}
//注册的key=beanName,value=DisposableBeanAdapter 对象.
//所以当bean销毁时，经过DisposableBeanAdapter的destroy方法处理
scope.registerDestructionCallback(beanName,
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
}
}
}public void registerDisposableBean(String beanName, DisposableBean bean) {
synchronized (this.disposableBeans) {
this.disposableBeans.put(beanName, bean);
}
}最终（只讨论单例模式下）会被注册到 DefaultSingletonBeanRegistry类的disposableBeans属性中
/** Disposable bean instances: bean name --> disposable instance */
private final Map
什么时候被调用Disposable 中的 dispose？,在单例销毁或者容器关闭
容器关闭（bean消亡）
context.registerShutdownHook(); 是一个钩子方法，当jvm关闭退出的时候会调用这个钩子方法，在设计模式之 模板模式中 通过在抽象类中定义这样的钩子方法由实现类进行实现，这里的实现类是AbstractApplicationContext，这是spring 容器优雅关闭的方法。
容器关闭入口 AbstractApplicationContext：（重要）
public void registerShutdownHook() {
if (this.shutdownHook == null) {
this.shutdownHook = new Thread() {
@Override
public void run() {
synchronized (startupShutdownMonitor) {
doClose(); /*关闭容器*/
}
}
};
Runtime.getRuntime().addShutdownHook(this.shutdownHook);
}
}AbstractApplicationContext：
在容器注册的关闭钩子的关闭方法中都调用了doClose方法，我们来分析这个方法：
protected void doClose() {
//判断active激活标记（在初始化上下文时被设置为true用于标记激活状态）并且将closed标记设置为true
if (this.active.get() && this.closed.compareAndSet(false, true)) {
if (logger.isInfoEnabled()) {
logger.info("Closing " + this);
}
LiveBeansView.unregisterApplicationContext(this); //卸载注册的JMX的MBean
try {
publishEvent(new ContextClosedEvent(this)); //发布容器关闭事件
}
catch (Throwable ex) {
logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);
}
try {
getLifecycleProcessor().onClose(); //调用实现了Lifecycle的bean的stop方法，关于Lifecycle，我们在标签解析的文章中分析过
}
catch (Throwable ex) {
logger.warn("Exception thrown from LifecycleProcessor on context close", ex);
}
destroyBeans(); /*销毁bean*/
closeBeanFactory(); //关闭BeanFactory，将BeanFactory序列化id和本身置为null
onClose(); //子类扩展
this.active.set(false); //将激活标记置为false
}
}AbstractApplicationContext：
protected void destroyBeans() {
getBeanFactory().destroySingletons(); //销毁单例bean
}DefaultListableBeanFactory：
public void destroySingletons() {
super.destroySingletons(); /*调用父类的销毁方法销毁单例bean*/
this.manualSingletonNames.clear(); //清空手工注册的beanName的缓存
clearByTypeCache(); //清空类型-->beanName的映射缓存
}DefaultSingletonBeanRegistry：回调所有的实现DisposableBean 接口的类的destory方法
public void destroySingletons() {
if (logger.isDebugEnabled()) {
logger.debug("Destroying singletons in " + this);
}
synchronized (this.singletonObjects) {
this.singletonsCurrentlyInDestruction = true; //设置正在销毁的标记为true
}
String[] disposableBeanNames;
synchronized (this.disposableBeans) {
disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());
}
for (int i = disposableBeanNames.length - 1; i >= 0; i--) {
/*遍历销毁之前注册的所有disposableBean，所有的类在注册为bean时都会注册一个对应的disposableBean，而且都是DisposableBeanAdapter*/
destroySingleton(disposableBeanNames[i]);
}
this.containedBeanMap.clear(); //清空beanName --> 它包含的所有内部beanName集合的映射缓存
this.dependentBeanMap.clear(); //清空beanName --> 它依赖的所有beanName集合的映射缓存
this.dependenciesForBeanMap.clear(); //清空beanName --> 依赖它的所有beanName集合的映射缓存
synchronized (this.singletonObjects) {
this.singletonObjects.clear(); //清空单例bean缓存
this.singletonFactories.clear(); //清空单例工厂缓存
this.earlySingletonObjects.clear(); //清空提前暴露的beanName --> bean的映射缓存
this.registeredSingletons.clear(); //清空已经注册的单例bean缓存
this.singletonsCurrentlyInDestruction = false; //设置正在销毁的标记为false
}
}DefaultSingletonBeanRegistry：
public void destroySingleton(String beanName) {
removeSingleton(beanName); //清除bean的相应缓存
DisposableBean disposableBean;
synchronized (this.disposableBeans) {
//移除并获取disposableBean（DisposableBeanAdapter）
disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);
}
destroyBean(beanName, disposableBean); /*销毁*/
}DefaultSingletonBeanRegistry：此处会调用DisposableBeanAdapter类的destory方法。
protected void destroyBean(String beanName, DisposableBean bean) {
Set dependencies = this.dependentBeanMap.remove(beanName);
if (dependencies != null) {
if (logger.isDebugEnabled()) {
logger.debug("Retrieved dependent beans for bean '" + beanName + "': " + dependencies);
}
for (String dependentBeanName : dependencies) {
destroySingleton(dependentBeanName); //首选递归销毁所有当前bean依赖的bean
}
}
if (bean != null) {
try {
//此bean为DisposableBeanAdapter实例
//调用bean生成时注册的Disposablebean，所有bean注册的时候都是DisposableBeanAdapter实例，
//所以都会调用DisposableBeanAdapter类的destory方法!!!!!!!!!!!!!!!
bean.destroy();
}
catch (Throwable ex) {
logger.error("Destroy method on bean with name '" + beanName + "' threw an exception", ex);
}
}
Set containedBeans = this.containedBeanMap.remove(beanName);
if (containedBeans != null) {
for (String containedBeanName : containedBeans) {
destroySingleton(containedBeanName); //递归销毁当前bean包含的所有内部bean
}
}
synchronized (this.dependentBeanMap) {
//遍历找出所有依赖当前bean的列表，将当前bean从被依赖的列表中移除
for (Iterator>> it = this.dependentBeanMap.entrySet().iterator(); it.hasNext();) {
Map.Entry> entry = it.next();
Set dependenciesToClean = entry.getValue();
dependenciesToClean.remove(beanName);
if (dependenciesToClean.isEmpty()) {
it.remove();
}
}
}
this.dependenciesForBeanMap.remove(beanName); //从所有依赖当前bean的映射中移除依赖关系
} 关于DisposableBeanAdapter类三个bean销毁时自定义的回调方法的顺序（重要）
由于创建所有bean的时候注册消亡的disposablebean都是DisposableBeanAdapter（具体可看doCreateBean方法中调用的registerDisposableBeanIfNecessary方法），所以所有的bean的消亡都会经过DisposableBeanAdapter的destroy方法。
DisposableBeanAdapter实现了DisposableBean接口类，当bean销毁时也会调用此类的destory（）方法，此类中有关于三个bean销毁时的回调方法。
@Override
public void destroy() {
if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {
for (DestructionAwareBeanPostProcessor processor : this.beanPostProcessors) {
//此处会反射调用 @PreDestory注解的方法
processor.postProcessBeforeDestruction(this.bean, this.beanName);
}
}
if (this.invokeDisposableBean) {//判断是否是实现DisposableBean接口的类
if (logger.isDebugEnabled()) {
logger.debug("Invoking destroy() on bean with name '" + this.beanName + "'");
}
try {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedExceptionAction追踪DisposableBean的destory()方法。
进入到DefaultSingletonBeanRegistry
public void destroySingleton(String beanName) {
// Remove a registered singleton of the given name, if any.
removeSingleton(beanName);
// Destroy the corresponding DisposableBean instance.
DisposableBean disposableBean;
synchronized (this.disposableBeans) {
disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);
}
destroyBean(beanName, disposableBean);
}继续追踪postProcessBeforeDestruction方法。
发现有个InitDestroyAnnotationBeanPostProcessor类实现了DestructionAwareBeanPostProcessor接口
@Override
public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());//获得此bean中所有的PreDestory注解的方法 （1）
try {
metadata.invokeDestroyMethods(bean, beanName); //执行PreDestory （2）
}
catch (InvocationTargetException ex) {
String msg = "Invocation of destroy method failed on bean with name '" + beanName + "'";
if (logger.isDebugEnabled()) {
logger.warn(msg, ex.getTargetException());
}
else {
logger.warn(msg + ": " + ex.getTargetException());
}
}
catch (Throwable ex) {
logger.error("Failed to invoke destroy method on bean with name '" + beanName + "'", ex);
}
}上述代码（1）中findLifecycleMetadata方法是为了获当前Bean所有注解了PreDestory和PostConstruct的方法，最后我们会统一讲。
继续追踪上述代码（2）
public void invokeDestroyMethods(Object target, String beanName) throws Throwable {
Collection destroyMethodsToUse =
(this.checkedDestroyMethods != null ? this.checkedDestroyMethods : this.destroyMethods);
if (!destroyMethodsToUse.isEmpty()) {
boolean debug = logger.isDebugEnabled();
for (LifecycleElement element : destroyMethodsToUse) { //循环遍历所有被PreDestory注解的方法
if (debug) {
logger.debug("Invoking destroy method on bean '" + beanName + "': " + element.getMethod());
}
element.invoke(target);//反射执行，tagret是bean实例对象
}
}
}
到此bean销毁过程全部结束
PreDestory和PostConstruct的问题之findLifecycleMetadata方法
关于InitDestroyAnnotationBeanPostProcessor类中findLifecycleMetadata方法。
如何获得前Bean所有注解了PreDestory和PostConstruct的方法的问题。
private LifecycleMetadata findLifecycleMetadata(Class clazz) {
if (this.lifecycleMetadataCache == null) {
// Happens after deserialization, during destruction...
return buildLifecycleMetadata(clazz);
}
// Quick check on the concurrent map first, with minimal locking.
LifecycleMetadata metadata = this.lifecycleMetadataCache.get(clazz);
if (metadata == null) {
synchronized (this.lifecycleMetadataCache) {
metadata = this.lifecycleMetadataCache.get(clazz);
if (metadata == null) {
metadata = buildLifecycleMetadata(clazz);
this.lifecycleMetadataCache.put(clazz, metadata);
}
return metadata;
}
}
return metadata;
}private LifecycleMetadata buildLifecycleMetadata(final Class clazz) {
final boolean debug = logger.isDebugEnabled();
LinkedList initMethods = new LinkedList();
LinkedList destroyMethods = new LinkedList();
Class targetClass = clazz;
do {
final LinkedList currInitMethods = new LinkedList();
final LinkedList currDestroyMethods = new LinkedList();
ReflectionUtils.doWithLocalMethods(targetClass, new ReflectionUtils.MethodCallback() {
@Override
public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
if (initAnnotationType != null) {
//获得此Bean所有带有initAnnotationType注解的方法（其实就是PostConstruct注解）
if (method.getAnnotation(initAnnotationType) != null) {
LifecycleElement element = new LifecycleElement(method);
currInitMethods.add(element);
if (debug) {
logger.debug("Found init method on class [" + clazz.getName() + "]: " + method);
}
}
}
if (destroyAnnotationType != null) {
////获得此Bean所有带有destroyAnnotationType注解的方法（其实就是PreDestory注解）
if (method.getAnnotation(destroyAnnotationType) != null) {
currDestroyMethods.add(new LifecycleElement(method));
if (debug) {
logger.debug("Found destroy method on class [" + clazz.getName() + "]: " + method);
}
}
}
}
});
initMethods.addAll(0, currInitMethods);
destroyMethods.addAll(currDestroyMethods);
targetClass = targetClass.getSuperclass();
}
while (targetClass != null && targetClass != Object.class);
return new LifecycleMetadata(clazz, initMethods, destroyMethods);
}
关于initAnnotationType和destroyAnnotationType到底是什么，在InitDestroyAnnotationBeanPostProcessor类中有两个方法
上述这两个方法在CommonAnnotationBeanPostProcessor初始化构造函数的时候会被调用，代码如下。
public CommonAnnotationBeanPostProcessor() {
setOrder(Ordered.LOWEST_PRECEDENCE - 3);
setInitAnnotationType(PostConstruct.class);
setDestroyAnnotationType(PreDestroy.class);
ignoreResourceType("javax.xml.ws.WebServiceContext");
}而CommonAnnotationBeanPostProcessor继承InitDestroyAnnotationBeanPostProcessor，在容器启动或者刷新时 会实例化 CommonAnnotationBeanPostProcessor，就会触发构造方法。
