SpringIOC初始化过程-完成Bean的初始化(finishBeanFactoryInitialization)

在上一篇中已经讲解完invokeBeanFactoryPostProcessors(beanFactory);方法;我们看看下面还有什么方法

@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//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.
//返回一个factory 为什么需要返回一个工厂
//因为要对工厂进行初始化
/** 这里说明一下:如果你使用是的xml配置的方式就会执行 AbstractRefreshableApplicationContext的refreshBeanFactory方法去加载xml配置信息;因为ClassPathXmlApplicationContext是它的子类;现在我们使用的是注解配置的方式所以会执行GenericApplicationContext的refreshBeanFactory方法,这个方法就是只返回了一个beanFactory**/
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

// Prepare the bean factory for use in this context.
//准备工厂
prepareBeanFactory(beanFactory);

try {
// Allows post-processing of the bean factory in context subclasses.

//这个方法在当前版本的spring是没用任何代码的
//可能spring期待在后面的版本中去扩展吧
postProcessBeanFactory(beanFactory);

// Invoke factory processors registered as beans in the context.
//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ProcessBeanFactory 和spring内部自己定义的
invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.
//注册beanPostProcessor
registerBeanPostProcessors(beanFactory);

// Initialize message source for this context.
// 初始化当前 ApplicationContext 的 MessageSource,国际化这里就不展开说了
initMessageSource();

// Initialize event multicaster for this context.
//初始化应用事件广播器
initApplicationEventMulticaster();

// Initialize other special beans in specific context subclasses.
// 从方法名就可以知道,典型的模板方法(钩子方法),
// 具体的子类可以在这里初始化一些特殊的 Bean(在初始化 singleton beans 之前)
onRefresh();

// Check for listener beans and register them.
// 注册事件监听器,监听器需要实现 ApplicationListener 接口。这也不是我们的重点,过
registerListeners();

// Instantiate all remaining (non-lazy-init) singletons.
// 重点,重点,重点
// 初始化所有的 singleton beans
//(lazy-init 的除外)
finishBeanFactoryInitialization(beanFactory);

// Last step: publish corresponding event.
// 最后,广播事件,ApplicationContext 初始化完成
finishRefresh();
}
//.......

国际化初始化应用事件广播器,注册事件监听在这里就不过多的阐述了,要不然真的是没完没了了;我们重点看下初始化所有的 singleton beans方法;

初始化所有的 singleton beans -finishBeanFactoryInitialization(beanFactory);

finishBeanFactoryInitialization(beanFactory);方法除了懒加载之外的beans,在这里都会进行初始化;

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// 首先,初始化名字为 conversionService 的 Bean。这里不是重点
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.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}

// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}

// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);

// 这里将beanDefinitionNames赋值给frozenBeanDefinitionNames
//目的就是到了这一步,Spring 已经开始预初始化 singleton beans 了,
// 不能再出现其他的 bean 定义解析、加载、注册了;
beanFactory.freezeConfiguration();

// Instantiate all remaining (non-lazy-init) singletons.
//实例化所有的单例对象
beanFactory.preInstantiateSingletons();
}

重点是preInstantiateSingletons();方法:

public void preInstantiateSingletons() throws BeansException {
if (logger.isDebugEnabled()) {
logger.debug("Pre-instantiating singletons in " + this);
}
//所有bean的名字
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

// Trigger initialization of all non-lazy singleton beans...
// 触发所有非延迟加载单例beans的初始化,主要步骤为调用getBean
for (String beanName : beanNames) {
//合并父BeanDefinition
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//是否为抽象类,是否是单例,是否是懒加载
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//是否是FactoryBean,这里肯定是不,后续文章会讲到FactoryBean和BeanFactory的区别
if (isFactoryBean(beanName)) {
//如果是FactoryBean则加上&
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 {
//不是FactoryBean直接到这个方法中
getBean(beanName);
}
}
}

// 到这里说明所有的非懒加载的 singleton beans 已经完成了初始化
// 如果我们定义的 bean 是实现了 SmartInitializingSingleton 接口的,那么在这里得到回调,忽略
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}

重点到getBean(beanName)方法中;而初始化的过程也封装到了这个方法里。

	public Object getBean(String name) throws BeansException {
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 {

/**
* 通过 name 获取 beanName。这里不使用 name 直接作为 beanName 有两个原因
* 1、name 可能会以 & 字符开头,表明调用者想获取 FactoryBean 本身,而非 FactoryBean
* 实现类所创建的 bean。在 BeanFactory 中,FactoryBean 的实现类和其他的 bean 存储
* 方式是一致的,即 <beanName, bean>,beanName 中是没有 & 这个字符的。所以我们需要
* 将 name 的首字符 & 移除,这样才能获取到一个传统的Bean
* 2、还是别名的问题,转换需要
* &beanName
*/
final String beanName = transformedBeanName(name);
//这个是返回值
Object bean;

/**
* 这个方法在初始化的时候会调用,在getBean的时候也会调用
* 为什么需要这么做呢?
* 也就是说spring在初始化的时候先获取这个对象
* 判断这个对象是否被实例化好了
* 在初始化时候调用一般都是返回null
*/
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
//log.....
}
else {
//log.....
}
}
/**
* 如果 sharedInstance 是普通的单例 bean,下面的方法会直接返回。但如果
* sharedInstance 是 FactoryBean 类型的,则需调用 getObject 工厂方法获取真正的
* bean 实例。如果用户想获取 FactoryBean 本身,这里也不会做特别的处理,直接返回
* 即可。毕竟 FactoryBean 的实现类本身也是一种 bean,只不过具有一点特殊的功能而已。
*/
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}

else {
// 检查原型的bean是否再创建中,如果已经在创建中就抛出异常
//一般是陷入了循环依赖
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}

// 检查一下这个 Bean Definition 在工厂中是否存在
BeanFactory parentBeanFactory = getParentBeanFactory();//null
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
// 如果当前容器不存在这个 BeanDefinition,试试父容器中有没有
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
//args 是上面传过来的null
else if (args != null) {
// 返回父容器的查询结果
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> 委托给标准的getBean方法。
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
//因为上面parentBeanFactory==null,代码来到这里
if (!typeCheckOnly) {
//将beanName添加到alreadyCreated set集合当中
markBeanAsCreated(beanName);
}
/*
* 稍稍总结一下:
* 到这里的话,要准备创建 Bean 了,对于 singleton 的 Bean 来说,容器中还没创建过此 Bean;
* 对于 prototype 的 Bean 来说,本来就是要创建一个新的 Bean。
*/
try {
// 从容器中获取 beanName 相应的 GenericBeanDefinition,并将其转换为 RootBeanDefinition
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
// 检查给定的合并的 BeanDefinition
checkMergedBeanDefinition(mbd, beanName, args);
//检查dependes-on依赖
// 先初始化依赖的所有 Bean
// 注意,这里的依赖指的是 depends-on 中定义的依赖
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
//获取depends-on的属性值,如果depends-on的值存在 则添加进入dependentBeanMap缓存中
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(....);
}
// 注册一下依赖关系
registerDependentBean(dep, beanName);
try {
// 先初始化被依赖项
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(...);
}
}
}

// 创建bean实例.
if (mbd.isSingleton()) {
//jdk1.8 Lambda表达式,这里调用的是getSingleton方法中的getObject方法;
sharedInstance = getSingleton(beanName, () -> {
try {
// 执行创建 Bean
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {

destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
// 如果是 prototype scope 的,创建 prototype 的实例
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
// 执行创建 Bean
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
// 如果不是 singleton 和 prototype 的话,需要委托给相应的实现类来处理
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 {
// 执行创建 Bean
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(...)....

}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}

// 最后,检查一下类型对不对,不对的话就抛异常,对的话就返回了.
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()) {
//log....
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}

在上面这个方法中源码大概实在315行左右,涉及到jdk1.8新特新Lambda表达式getSingleton();在这个方法中调用了getObject()方法;进入getSingleton()方法中简单看下:

public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
//当前beanName IndexDaoImpl还没有放入singletonObjects中,所以这里是null
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
//检查是否在销毁,如果在销毁就抛出异常
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(.....);
}
//log.....
/**
* 将beanName添加到singletonsCurrentlyInCreation这样一个set集合中
* 表示beanName对应的bean正在创建中
*/
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
//调用getObject()方法,这个方法其实就是调用上面Lambda表达式中那个createBean()
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
//.......
throw ex;
}
catch (BeanCreationException ex) {
//.......
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
//把标识为正在创建的标识去掉
afterSingletonCreation(beanName);
}
if (newSingleton) {
//向集合中添加数据
/**
* protected void addSingleton(String beanName, Object singletonObject) {
* synchronized (this.singletonObjects) {
* this.singletonObjects.put(beanName, singletonObject);
* this.singletonFactories.remove(beanName);
* this.earlySingletonObjects.remove(beanName);
* this.registeredSingletons.add(beanName);
* }
*/
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}

我们接下来看看getObject()方法,上面注释也说到了getObject()方法中其实就在调用createBean()

接下来我们重点分析一下 createBean() 方法;

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean(java.lang.String, org.springframework.beans.factory.support.RootBeanDefinition, java.lang.Object[])

第三个参数 args 数组代表创建实例需要的参数,不就是给构造方法用的参数,或者是工厂 Bean 的参数嘛,不过要注意,在我们的初始化阶段,args 是 null。

看类名我们到了一个新的类 AbstractAutowireCapableBeanFactory,主要是为了 @Autowired 注解注入属性值

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;

// 确保 BeanDefinition 中的 Class 被加载
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 method
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(...);
}

try {
// 在 bean 初始化前应用后置处理,如果后置处理返回的 bean 不为空,则直接返回
//这个类需要通过代码演示
//这里执行了bean=applyBeanPostProcessorsBeforeInstantiation(targetType, beanName); 在AOP中使用到可以返回一个代理对象
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(.....);
}

try {
// 重头戏
// 调用doCreateBean 创建bean
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
//log.....
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {

throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(......);
}
}

我们继续向doCreateBean()方法中看:

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 bean 实例,并将实例包裹在 BeanWrapper 实现类对象中返回。
* createBeanInstance中包含三种创建 bean 实例的方式:
* 1. 通过工厂方法创建 bean 实例
* 2. 通过构造方法自动注入(autowire by constructor)的方式创建 bean 实例
* 3. 通过无参构造方法方法创建 bean 实例
*
* 若 bean 的配置信息中配置了 lookup-method 和 replace-method,则会使用 CGLIB
* 增强 bean 实例。关于lookup-method和replace-method后面再说。
*/
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}

// 建议跳过吧,涉及接口:MergedBeanDefinitionPostProcessor
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}

// 下面这块代码是为了解决循环依赖的问题;后续文章会讲解到
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isDebugEnabled()) {
//log....
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}

// Initialize the bean instance.
Object exposedObject = bean;
try {
//设置属性,非常重要
// 这一步负责属性装配,因为前面的实例只是实例化了,并没有设值,这里就是设值
populateBean(beanName, mbd, instanceWrapper);
//执行后置处理器,aop就是在这里完成的处理
exposedObject = initializeBean(beanName, exposedObject, mbd);
}

//......省略了一些不重要的代码

// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(.....);
}

return exposedObject;
}

上面这段代码重点方法是createBeanInstance();

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// 确保已经加载了此 class
Class<?> beanClass = resolveBeanClass(mbd, beanName);

/**
* 检测一个类的访问权限spring默认情况下对于非public的类是允许访问的。
*/
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,则通过工厂方法构建 bean 对象
* 这种构建 bean 的方式可以自己写个demo去试试
* 源码就不做深入分析了,有兴趣的同学可以和我私下讨论
*/
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}

// Shortcut when re-creating the same bean...
/**
* 从spring的原始注释可以知道这个是一个Shortcut,什么意思呢?
* 当多次构建同一个 bean 时,可以使用这个Shortcut,
* 也就是说不在需要每次推断应该使用哪种方式构造bean
* 比如在多次构建同一个prototype类型的 bean 时,就可以走此处的Shortcut
* 这里的 resolved 和 mbd.constructorArgumentsResolved 将会在 bean 第一次实例
* 化的过程中被设置;
*/
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
//如果已经解析了构造方法的参数,则必须要通过一个带参构造方法来实例
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
// 通过构造方法自动装配的方式构造 bean 对象
return autowireConstructor(beanName, mbd, null, null);
}
else {
//通过默认的无参构造方法进行
return instantiateBean(beanName, mbd);
}
}

// Candidate constructors for autowiring?
//由后置处理器决定返回哪些构造方法
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进行初始化
return instantiateBean(beanName, mbd);
}

我们看看无参构造是怎么实例化对象的

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
//默认情况下是得到一个反射的实例化策略
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
//包装一下进行返回
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}

关键代码在:

beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);

得到反射的实例化策略之后进入instantiate方法:

public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
//检测 bean 配置中是否配置了 lookup-method 或 replace-method
//如果配置了就需使用 CGLIB 构建 bean 对象
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 {
//得到无参构造
constructorToUse = clazz.getDeclaredConstructor();
}
//在这里给resolvedConstructorOrFactoryMethod赋了值
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
//实例化
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// Must generate CGLIB subclass.
return instantiateWithMethodInjection(bd, beanName, owner);
}
}

进入instantiateClass方法进行实例化:

public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
// 设置构造方法为可访问
ReflectionUtils.makeAccessible(ctor);
//反射创建对象
return (KotlinDetector.isKotlinType(ctor.getDeclaringClass()) ?
KotlinDelegate.instantiateClass(ctor, args) : ctor.newInstance(args));
}

这里就比较简单了就是使用反射ctor.newInstance(args)进行实例化;这里拿到实例化之后的Bean返回到:

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean

中设置属性,处理依赖

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
// bean 实例的所有属性都在这里了
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;
}
}

// 到这步的时候,bean 实例化完成(通过工厂方法或构造方法),但是还没开始属性设值,
// InstantiationAwareBeanPostProcessor 的实现类可以在这里对 bean 进行状态修改,
// 我也没找到有实际的使用,所以我们暂且忽略这块吧
boolean continueWithPropertyPopulation = true;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
// 如果返回 false,代表不需要进行后续的属性设值,也不需要再经过其他的 BeanPostProcessor 的处理
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);

// 通过名字找到所有属性值,如果是 bean 依赖,先初始化依赖的 bean。记录依赖关系
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}

// 通过类型装配。复杂一些
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;
// 这里有个非常有用的 BeanPostProcessor 进到这里: AutowiredAnnotationBeanPostProcessor
// 对采用 @Autowired、@Value 注解的依赖进行设值,这里的内容也是非常丰富的,不过本文不会展开说了,感兴趣的读者请自行研究
pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
checkDependencies(beanName, mbd, filteredPds, pvs);
}
}
// 设置 bean 实例的属性值
applyPropertyValues(beanName, mbd, bw, pvs);
}

属性注入完成后,紧接着就是处理各种回调:

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 {
// 如果 bean 实现了 BeanNameAware、BeanClassLoaderAware 或 BeanFactoryAware 接口,回调
invokeAwareMethods(beanName, bean);
}

Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//执行后置处理的befor
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}

try {
//执行bean的声明周期回调中的init方法
// 或者如果 bean 实现了 InitializingBean 接口,调用 afterPropertiesSet() 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()) {
//执行后置处理器的after方法
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}

return wrappedBean;
}

BeanPostProcessor 的两个回调都发生在这边,只不过中间处理了 init-method

到这里整个初始化过程就讲解完了;下面画个图讲解一下finishBeanFactoryInitialization方法的整个过程:

因为图片有点大,我把大缩小了,如果觉得图片看不清,可以把地址抠出来,在浏览器中看;

image.png