前言
前两篇文章分析了Spring XML和注解的解析原理，并将其封装为BeanDefinition对象存放到IOC容器中，而这些只是refresh方法中的其中一个步骤——obtainFreshBeanFactory，接下来就将围绕着这些BeanDefinition对象进行一系列的处理，如BeanDefinitionRegistryPostProcessor对象方法的调用、BeanFactoryPostProcessor对象方法的调用以及Bean实例的创建都离不开这些BeanDefinition对象。
下面就来看看Spring是如何处理这些对象的。
正文
环境准备
首先我们先回忆下refresh方法：
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//为容器初始化做准备
prepareRefresh();
// 解析xml和注解
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 给BeanFacory设置属性值以及添加一些处理器，即准备Spring的上下文环境
prepareBeanFactory(beanFactory);
try {
// 由子类实现对BeanFacoty的一些后置处理
postProcessBeanFactory(beanFactory);
/*
* BeanDefinitionRegistryPostProcessor
* BeanFactoryPostProcessor
* 完成对这两个接口的调用
* */
invokeBeanFactoryPostProcessors(beanFactory);
/*
* 把实现了BeanPostProcessor接口的类实例化，并且加入到BeanFactory中
* */
registerBeanPostProcessors(beanFactory);
/*
* 国际化
* */
initMessageSource();
//初始化事件管理类
initApplicationEventMulticaster();
//这个方法着重理解模板设计模式，因为在springboot中，这个方法是用来做内嵌tomcat启动的
onRefresh();
/*
* 往事件管理类中注册事件类
* */
registerListeners();
/*
* 1、bean实例化过程
* 2、依赖注入
* 3、注解支持
* 4、BeanPostProcessor的执行
* 5、Aop的入口
*
* */
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
} finally {
resetCommonCaches();
}
}
}
prepareBeanFactory和postProcessBeanFactory没什么复杂的，关注一下里面设置了哪些值，添加了哪些对象就行，这些东西在后面的流程中会起到作用。
尤其是postProcessBeanFactory，这是一个模板方法，在其子类AbstractRefreshableWebApplicationContext中设置了两个重要的标识：
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// 主要看着里面
beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
}
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
// Remove from old position, if any
this.beanPostProcessors.remove(beanPostProcessor);
// Track whether it is instantiation/destruction aware
if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
this.hasInstantiatiOnAwareBeanPostProcessors= true;
}
if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
this.hasDestructiOnAwareBeanPostProcessors= true;
}
// Add to end of list
this.beanPostProcessors.add(beanPostProcessor);
}
分别将hasInstantiationAwareBeanPostProcessors、hasDestructionAwareBeanPostProcessors属性都设置成了true，可以猜一下它们有什么作用。
两个重要的Processor
在将上下文环境设置完成后，就是通过invokeBeanFactoryPostProcessors方法完成对BeanDefinitionRegistry以及BeanFactory的后置处理器的处理和调用，也就是依次调用BeanDefinitionRegistryPostProcessor接口和BeanFactoryPostProcessor接口的实现类。
我们可以通过实现这两个接口在在BeanDefinition注册完成后，对象实例化之前对容器中的BeanDefinition进行动态的增删查改，比如Spring中@Configuration注解的解析就是在这个过程中实现的。我们先来了解一下Spring内置的Processor实现有哪些：
整个体系需要有个大概的印象，其中重点关注ConfigurationClassPostProcessor类，该类就是完成对@Configuration、@Bean等注解的解析注册，这一块的源码这里暂时不分析。继续开始的流程，进入到
invokeBeanFactoryPostProcessors方法：
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// getBeanFactoryPostProcessors方法一般是获取不到值的，除非我们手动调用addBeanFactoryPostProcessor方法添加进去，
// 换言之我们可以通过注解@Component或是手动调用addBeanFactoryPostProcessor方法来注入BeanFactoryPostProcessors对象
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
省略......
}
这里面 通过委托模式调用PostProcessorRegistrationDelegate的invokeBeanFactoryPostProcessors方法，并传入了BeanFactory和Processors对象，但需要注意getBeanFactoryPostProcessors方法不是获取通过xml配置和Component注解注册到容器中的Processor对象，而是获取通过调用AbstractApplicationContext.addBeanFactoryPostProcessor方法添加的类，换言之我们实现了Processor接口后可以不在类上添加@Component，直接调用addBeanFactoryPostProcessor方法即可，但需要注意，这种方式并没有对应的BeanDefinition类，添加的对象也不存在于IOC容器中。
继续进入invokeBeanFactoryPostProcessors方法：
public static void invokeBeanFactoryPostProcessors( ConfigurableListableBeanFactory beanFactory, ListbeanFactoryPostProcessors) { // Invoke BeanDefinitionRegistryPostProcessors first, if any. Set processedBeans = new HashSet<>(); if (beanFactory instanceof BeanDefinitionRegistry) { BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; List regularPostProcessors = new ArrayList<>(); List registryProcessors = new ArrayList<>(); // 优先处理通过addBeanFactoryPostProcessor方法添加的BeanFactoryPostProcessor for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { // 优先处理BeanDefinitionRegistryPostProcessor对象 if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; registryProcessor.postProcessBeanDefinitionRegistry(registry); registryProcessors.add(registryProcessor); } else { regularPostProcessors.add(postProcessor); } } List currentRegistryProcessors = new ArrayList<>(); //获取实现了BeanDefinitionRegistryPostProcessor接口的所有类的BeanDefinition对象的beanName String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { //判断是否实现了排序接口 PriorityOrdered if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } //排序 sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); //调用过程 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered. postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { //判断是否是实现的Ordered接口 if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); //没实现排序接口的调用 boolean reiterate = true; while (reiterate) { reiterate = false; postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { if (!processedBeans.contains(ppName)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); reiterate = true; } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); // invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); } //调用postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(registryProcessors, beanFactory); invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory); } else { // Invoke factory processors registered with the context instance. invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory); } //获取实现了BeanFactoryPostProcessor接口的类，获取beanDefinition的名称 String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false); List priorityOrderedPostProcessors = new ArrayList<>(); List orderedPostProcessorNames = new ArrayList<>(); List nOnOrderedPostProcessorNames= new ArrayList<>(); for (String ppName : postProcessorNames) { if (processedBeans.contains(ppName)) { // skip - already processed in first phase above } //实现了PriorityOrdered接口的 else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class)); } //实现了Ordered接口的 else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessorNames.add(ppName); } else { //没实现接口的 nonOrderedPostProcessorNames.add(ppName); } } //排序 // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered. sortPostProcessors(priorityOrderedPostProcessors, beanFactory); //调用 invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); // Next, invoke the BeanFactoryPostProcessors that implement Ordered. List orderedPostProcessors = new ArrayList<>(); for (String postProcessorName : orderedPostProcessorNames) { orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } sortPostProcessors(orderedPostProcessors, beanFactory); invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); List nOnOrderedPostProcessors= new ArrayList<>(); for (String postProcessorName : nonOrderedPostProcessorNames) { nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory); beanFactory.clearMetadataCache(); }
这个方法很长，但逻辑并不复杂。首先判断传入的BeanFactory对象是不是BeanDefinitionRegistry对象，是的话则优先调用传入的Processor对象的postProcessBeanDefinitionRegistry方法，之后再通过beanFactory.getBeanNamesForType拿到容器中所有BeanDefinitionRegistryPostProcessor实现类的名字，然后依次实例化并调用实现了PriorityOrdered、Ordered接口（前者优先级高于后者，数字越小优先级越高）的Processor的postProcessBeanDefinitionRegistry方法，最后再实例化并调用剩余未实现排序接口的Processor的方法。当所有BeanDefinitionRegistryPostProcessor实现类调用完成后，会依次调用来自于父接口BeanFactoryPostProcessor的postProcessBeanFactory方法。
上述流程处理完成后，又会通过beanFactory.getBeanNamesForType拿到容器中所有BeanFactoryPostProcessor实现类的名字，处理流程和上面一样。
注册BeanPostProcessor对象
以上就是两个扩展点的调用流程，完成之后又会调用registerBeanPostProcessors注册所有BeanPostProcessor的子类到容器中来，这个接口也是Spring的一个重要的扩展点，它包含了两个方法：
@Nullable
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
@Nullable
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
实现了该接口的对象在实例化之前和之后分别会调用这两个方法。同样，我们先来了解下该接口的继承体系：
可以看到这个接口Spring内置的实现就比较多，可见用途之广泛。另外上面画红框的是本次需要重点记忆的类，后面Bean实例化时会出现。接着我们来看看registerBeanPostProcessors的实现逻辑：
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
//拿到工程里面所有实现了BeanPostProcessor接口的类，获取到BeanDefinition的名称
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
List priorityOrderedPostProcessors = new ArrayList<>();
List internalPostProcessors = new ArrayList<>();
List orderedPostProcessorNames = new ArrayList<>();
List nOnOrderedPostProcessorNames= new ArrayList<>();
//提前实例化BeanPostProcessor类型的bean，然后bean进行排序
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
//getBean是实例化方法，后面我们在讲bean实例化过程是会着重讲到
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
//判断类型是否是MergedBeanDefinitionPostProcessor，如果是则代码是内部使用的
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
//注册到BeanFactory中
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
List orderedPostProcessors = new ArrayList<>();
for (String ppName : orderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
orderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
sortPostProcessors(orderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// Now, register all regular BeanPostProcessors.
List nOnOrderedPostProcessors= new ArrayList<>();
for (String ppName : nonOrderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
nonOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
// Finally, re-register all internal BeanPostProcessors.
sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);
// Re-register post-processor for detecting inner beans as ApplicationListeners,
// moving it to the end of the processor chain (for picking up proxies etc).
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
这段代码的实现逻辑也很简单，也是先区分优先级，再获取Bean实例，最后注册到容器中，等到Bean实例化时调用。
接下来在refresh方法中调用了initMessageSource、initApplicationEventMulticaster、onRefresh、registerListeners，分别是初始化国际化资源、初始化时间广播器、容器刷新事件（子类回调）、注册监听器，这几个方法都很简单，自己看看就行，这里就不详细阐述了。
Bean对象的创建
当所有的准备工作都做好后，就该开始初始化Bean实例了，也就是finishBeanFactoryInitialization方法所做的事。不过这里可不是根据BeanDefinition new一个对象就完了，它包含了以下几个工作：
1、初始化实例
2、解析@PostConstruct，@PreDestroy，@Resource， @Autowired，@Value等注解
3、依赖注入
4、调用BeanPostProcessor方法
5、AOP入口（本篇暂不分析）
下面就来详细分析Bean实例化的整个流程：
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
......
//重点看这个方法
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("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.
// xml解析时，讲过，把所有beanName都缓存到beanDefinitionNames了
List beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
// 把父BeanDefinition里面的属性拿到子BeanDefinition中
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//如果不是抽象的，单例的，非懒加载的就实例化
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//判断bean是否实现了FactoryBean接口，这里可以不看
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)
((SmartFactoryBean) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
//主要从这里进入，看看实例化过程
getBean(beanName);
}
}
}
}
在preInstantiateSingletons方法中可以看到这里有一个判断：单例、非懒加载、非抽象，满足这三个条件才会调用getBean（Bean实例化都是通过调用该方法实现的）实例化：
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
protected T doGetBean(final String name, @Nullable final Class requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
final String beanName = transformedBeanName(name);
System.out.println("====beanName=="+beanName+"===instance begin====");
Object bean;
//从缓存中拿实例
Object sharedInstance = getSingleton(beanName);
//如果缓存里面能拿到实例
if (sharedInstance != null && args == null) {
// 该方法是FactoryBean接口的调用入口
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
//如果缓存里面没有，则走下来
//如果是scope 是Prototype的，校验是否有出现循环依赖，如果有则直接报错
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
// 父子BeanDefinition合并
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
// 检验是不是抽象类，是直接抛出异常
checkMergedBeanDefinition(mbd, beanName, args);
// 获取依赖对象属性，依赖对象要先实例化
// 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 {
//实例化
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
//大部分是单例的情况
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
});
// 该方法是FactoryBean接口的调用入口
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);
}
// 该方法是FactoryBean接口的调用入口
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);
}
});
// 该方法是FactoryBean接口的调用入口
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
}
}
}
return (T) bean;
}
这段代码首先从缓存里面拿到单例对象，如果没有，则通过scope类型去创建对应的Bean实例（直接创建或是通过getObjectForBeanInstance调用FactoryBean接口的方法创建）。在创建对象之前如果scope是prototype类型的首先会通过isPrototypeCurrentlyInCreation检验是否存在循环依赖（循环依赖这里先不讲），存在直接抛出异常，原型对象不允许有循环依赖出现；校验完成后还会通过mbd.getDependsOn拿到@DependsOn注解的值，如果有，则会优先实例化依赖的对象。
因为大部分都是创建单例对象，所以下面我以getSingleton方法来分析，需要注意该方法传入了一个Lambda表达式，在该表达式中调用了createBean方法，观察其它scope创建bean会发现都调用了该方法，所以实际创建bean对象就是该方法，不过我们还是先进入getSingleton方法看看做了些什么：
public Object getSingleton(String beanName, ObjectFactory singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
// 如果缓存中有，则直接返回
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 + "'");
}
// 把beanName添加到singletonsCurrentlyInCreation Set容器中，在这个集合里面的bean都是正在实例化的bean
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptiOns= (this.suppressedExceptiOns== null);
if (recordSuppressedExceptions) {
this.suppressedExceptiOns= new LinkedHashSet<>();
}
try {
// 如果这里有返回值，就代表这个bean已经结束创建了，已经完全创建成功
singletOnObject= singletonFactory.getObject();
newSingleton = true;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptiOns= null;
}
//bean创建完成后singletonsCurrentlyInCreation要删除该bean
afterSingletonCreation(beanName);
}
if (newSingleton) {
System.out.println("====beanName==" + beanName + "===instance end====");
// 创建对象成功时，把对象缓存到singletonObjects缓存中,bean创建完成时放入一级缓存
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
这个方法里面首先是从缓存中获取对象，如果有直接返回，如果没有则将该对象的beanName加入到singletonsCurrentlyInCreation缓存中，如果添加不成功，说明已经有其它地方正在创建该对象，当前创建直接抛出异常，如果添加成功，则调用singletonFactory.getObject去创建对象，这个方法就是传入的Lambda表达式，创建完成后删除掉singletonsCurrentlyInCreation缓存中的值并将对象添加到一级缓存，后续需要该对象时，都是从一级缓存中获取的。
在getObject中通过createBean去创建对象，而该方法又调用了doCreateBean，我们直接来看这个方法：
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//创建实例,,重点看
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = instanceWrapper.getWrappedInstance();
Class beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// Bean实例化完成后收集类中的注解（@PostConstruct，@PreDestroy，@Resource， @Autowired，@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;
}
}
// 单例bean提前暴露
boolean earlySingletOnExposure= (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
// 这里着重理解，对理解循环依赖帮助非常大，添加三级缓存
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
// ioc di，依赖注入的核心方法
populateBean(beanName, mbd, instanceWrapper);
// bean 实例化+ioc依赖注入完以后的调用
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 actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
}
}
}
// Register bean as disposable.
try {
//注册bean销毁时的类DisposableBeanAdapter
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
return exposedObject;
}
这个方法里面首先去通过createBeanInstance创建对象的实例，创建完成后又通过applyMergedBeanDefinitionPostProcessors收集类中的注解@Autowired、@Value、@PostConstruct，@PreDestroy，@Resource准备依赖注入或是方法调用，紧接着调用addSingletonFactory添加三级缓存处理循环依赖，之后通过populateBean依赖注入真正完成一个完整对象的创建，最后在initializeBean中触发事件和一些方法的调用。
下面逐个分析这些方法。
createBeanInstance
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
//反射拿到Class对象
Class beanClass = resolveBeanClass(mbd, beanName);
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
}
Supplier instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
// 在xml配置bean时指定factory-bean属性和factory-method以及@Bean注解
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Candidate constructors for autowiring?
//寻找当前正在实例化的bean中有@Autowired注解的构造函数
Constructor[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
//如果ctors不为空，就说明构造函数上有@Autowired注解
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
//无参构造函数的实例化,大部分的实例是采用的无参构造函数的方式实例化
// No special handling: simply use no-arg constructor.
return instantiateBean(beanName, mbd);
}
在这个方法里面又做了很多判断，首先是拿到factoryMethodName，当我们在xml配置bean时指定了factory-bean属性和factory-method属性或者是使用了@Bean注解时这里就会拿到值，然后就会通过FactoryMethod去创建一个实例对象；如果不存在factoryMethodName，那么就需要通过构造函数来实例化对象，但构造函数上可能存在注解@Autowired，因此需要通过determineConstructorsFromBeanPostProcessors获取到所有带@Autowired注解的构造函数：
protected Constructor[] determineConstructorsFromBeanPostProcessors(@Nullable Class beanClass, String beanName)
throws BeansException {
/**
* 通过AutowiredAnnotationBeanPostProcessor（在component-scan解析时
* 通过registerComponents方法注册的，然后又在refresh中调用registerBeanPostProcessors方法
* 实例化的）类找到标记了@Autowired注解的构造函数
*/
if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
Constructor[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
if (ctors != null) {
return ctors;
}
}
}
}
return null;
}
拿到所有带@Autowired注解的构造函数后就是通过调用autowireConstructor来进行实例化，具体则是通过委托给ConstructorResolver类进行处理，包括上面通过factoryMethod创建对象也是委托给这个类。如果没有带@Autowired的构造函数才会调用instantiateBean方法，利用反射通过无参构造函数去创建对象并返回，也是大部分对象实例化所走的流程。
至此，简单对象的实例化完成。
addSingletonFactory
这个方法就是添加三级缓存解决循环依赖问题，暂时不分析。
populateBean
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
boolean cOntinueWithPropertyPopulation= true;
// 这里可以写接口可以让所有类都不能依赖注入，没有什么实际作用
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
//是否需要DI，依赖注入
cOntinueWithPropertyPopulation= false;
break;
}
}
}
}
if (!continueWithPropertyPopulation) {
return;
}
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_NAME || mbd.getResolvedAutowireMode() == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
//重点看这个if代码块
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
//依赖注入过程，@Autowired的支持
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
//老版本用这个完成依赖注入过程，@Autowired的支持
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
if (needsDepCheck) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
// xml中标签的依赖注入
if (pvs != null) {
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
这里面主要有三个方法是完成依赖注入的：postProcessProperties（当前主要使用）、postProcessPropertyValues（老版本废弃API）、applyPropertyValues（xml中property标签）。
所以主要看看postProcessProperties方法，而这个方法又是来自于InstantiationAwareBeanPostProcessor接口（希望你还记得这个接口的继承体系），主要看看AutowiredAnnotationBeanPostProcessor，这个就是解决@Autowired依赖注入的。
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
try {
metadata.inject(bean, beanName, pvs);
}
return pvs;
}
见名知意，findAutowiringMetadata方法就是拿到@Autowired注解的属性并封装为InjectionMetadata对象，再调用inject进行依赖注入，注意这里是包含了属性和方法的（方法也不一定是setter方法才可以，只要是标记了@Autowired且参数类型正确都能依赖成功）。
这就是@Autowired的注入过程，另外还有@Resource的注入，在CommonAnnotationBeanPostProcessor类中，流程和这个基本一样，这里就不阐述了。
initializeBean
以上过程都是对Bean的实例化，以及对象中属性的注入，都完成过后这个Bean对象才是我们真正可以直接使用的对象，所以接着就是处理一些方法的调用了（包含一些事件通知）。
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
// 调用Aware方法
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//对类中某些特殊方法的调用，比如@PostConstruct，Aware接口
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//InitializingBean接口，afterPropertiesSet，init-method属性调用,非常重要
invokeInitMethods(beanName, wrappedBean, mbd);
}
if (mbd == null || !mbd.isSynthetic()) {
// 这个地方可能生出代理实例，是aop的入口
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
private void invokeAwareMethods(final String beanName, final Object bean) {
if (bean instanceof Aware) {
// 实现该接口可以在bean实例化完成后获取到bean的名称
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
// 实现该接口可以在bean实例化完成后获取到当前的类加载器
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
// 实现该接口可以在bean实例化完成后获取到当前的AbstractAutowireCapableBeanFactory对象
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
首先是Aware接口的方法调用，这个很简单不多说。接着就是applyBeanPostProcessorsBeforeInitialization方法调用，这个就是BeanPostProcessor接口的postProcessBeforeInitialization方法调用（看到这里你是否会发现自己之前理解错了呢，以为该方法是在对象实例化之前调用，实际上也是实例化完成之后）：
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
这里面着重看几个实现类的调用：ApplicationContextAwareProcessor（ApplicationEventPublisherAware、ApplicationContextAware等Aware接口的调用）、InitDestroyAnnotationBeanPostProcessor（@PostConstruct注解方法的调用）、ImportAwareBeanPostProcessor（ImportAware类型实例setImportMetadata调用，对理解SpringBoot帮助很大，这里可以暂时不看）。
紧着着又通过invokeInitMethods方法调用InitializingBean接口的afterPropertiesSet方法以及init-method属性配置的自定义初始化方法。
最后则是通过applyBeanPostProcessorsAfterInitialization方法调用BeanPostProcessor的postProcessAfterInitialization方法，因为涉及到AOP知识，这里不详细分析。
至此，Bean的整个实例化过程分析完成，看到这里，你应该对于Bean的生命周期函数有个基本的认识了，最后放上我画的Bean实例化流程时序图：
总结
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