Spring源码 21 Bean生命周期
Bean 的生命周期示意图（存在循环依赖和 AOP）
执行创建 Bean
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationExceptionAbstractAutowireCapableBeanFactory
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {
// 实例化 Bean
BeanWrapper instanceWrapper = null;
// 是否为单例
if (mbd.isSingleton()) {
// 有可能在本 Bean 创建之前
// 就有其他 Bean 把当前 Bean 给创建出来了（比如依赖注入过程中）
// 所以这里先将其删除
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 创建 Bean 实例
// 根据指定 bean 使用对应的策略创建新的实例
// 如：工厂方法、构造函数自动注入、简单初始化
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
// 获得 Bean 对象
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// 后置处理合并的 BeanDefinition
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// 应用 MergedBeanDefinitionPostProcessors
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
} catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// 是否提前暴露
// 为了解决循环依赖提早缓存单例创建工厂
// 是否需要提早曝光：单例 & 允许循环依赖 & 当前 bean 正在创建中
// 用于检测循环依赖
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");
}
// 添加到三级缓存
// 为避免后期循环依赖，可以在 bean 初始化完成前将创建实例的 ObjectFactory 加入工厂
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
Object exposedObject = bean;
try {
// 属性填充
// 对 bean 进行填充，将各个属性值注入，其中，可能存在依赖于其他 bean 的属性，则会递归初始依赖 bean
populateBean(beanName, mbd, instanceWrapper);
// 初始化
// 调用初始化方法，比如 init-method
exposedObject = initializeBean(beanName, exposedObject, mbd);
} catch (Throwable ex) {
if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
throw (BeanCreationException) ex;
} else {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
if (earlySingletonExposure) {
// 获取单例对象
Object earlySingletonReference = getSingleton(beanName, false);
// 在检测到有循环依赖的情况下才会不为空
if (earlySingletonReference != null) {
// 如果 exposedObject 没有在初始化方法中被改变，也就是没有被增强
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) {
// 检测依赖
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
// 因为 bean 创建后其所依赖的 bean 一定是已经创建的
// actualDependentBeans 不为空则表示当前bean 创建后其依赖的 bean 却没有全部创建完，也就是说存在循环依赖
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
try {
// 根据 scope 注册 bean
registerDisposableBeanIfNecessary(beanName, bean, mbd);
} catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
实例化
创建 Bean 实例
根据指定 bean 使用对应的策略创建新的实例
如：工厂方法、构造函数自动注入、简单初始化
createBeanInstance(beanName, mbd, args)AbstractAutowireCapableBeanFactory
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// 解析 class
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);
}
// 如果工厂方法不为空则使用工厂方法初始化策略
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
// 一个类有多个构造函数，每个构造函数都有不同的参数， 所以调用前需要先根据参数锁定构造函数或对应的工厂方法
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
// 如果已经解析过则使用解析好的构造函数方法不需要再次锁定
if (resolved) {
// 构造函数自动注入
if (autowireNecessary) {
return autowireConstructor(beanName, mbd, null, null);
}
// 使用默认构造函数构造
else {
return instantiateBean(beanName, mbd);
}
}
// 需要根据参数解析构造函数
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
// 构造函数自动注入
return autowireConstructor(beanName, mbd, ctors, args);
}
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// 使用默认构造函数构造
return instantiateBean(beanName, mbd);
}
是否提早暴露
是否提前暴露
为了解决循环依赖提早缓存单例创建工厂
是否需要提早曝光：单例 & 允许循环依赖 & 当前 bean 正在创建中
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName))DefaultSingletonBeanRegistry
/**
* 单例是否正在创建中
*/
private final Set<String> singletonsCurrentlyInCreation = Collections.newSetFromMap(new ConcurrentHashMap<>(16));
public boolean isSingletonCurrentlyInCreation(String beanName) {
return this.singletonsCurrentlyInCreation.contains(beanName);
}
添加到三级缓存
添加到三级缓存
为避免后期循环依赖，可以在 bean 初始化完成前将创建实例的 ObjectFactory 加入工厂
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean))DefaultSingletonBeanRegistry
// 一级缓存：也叫单例池。
// 用于保存 BeanName 和创建 bean 实例之间的关系，bean name -> bean instance
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
// 二级缓存：存放提前AOP生成的代理对象，保持代理对象的单例。
private final Map<String, Object> earlySingletonObjects = new ConcurrentHashMap<>(16);
// 三级缓存：存放用于生成代理对象的Lambda，用于循环依赖中生成代理对象，以打破循环依赖。
// 用于保存 BeanName 和创建 bean 的工厂之间的关系，bean name -> ObjectFactory
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
// 用来保存当前所有已注册的 bean
private final Set<String> registeredSingletons = new LinkedHashSet<>(256);
protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(singletonFactory, "Singleton factory must not be null");
// 为了保持操作的原子性，加锁
synchronized (this.singletonObjects) {
// 单例池中是否存在
if (!this.singletonObjects.containsKey(beanName)) {
// 对应记录放人三级缓存
this.singletonFactories.put(beanName, singletonFactory);
// 二级缓存移除对应记录
this.earlySingletonObjects.remove(beanName);
// 添加到已注册的 Bean
this.registeredSingletons.add(beanName);
}
}
}
获取单例对象
获取单例对象
getSingleton(beanName, false)DefaultSingletonBeanRegistry
// 一级缓存：也叫单例池。
// 用于保存 BeanName 和创建 bean 实例之间的关系，bean name -> bean instance
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
// 二级缓存：存放提前AOP生成的代理对象，保持代理对象的单例。
private final Map<String, Object> earlySingletonObjects = new ConcurrentHashMap<>(16);
// 三级缓存：存放用于生成代理对象的Lambda，用于循环依赖中生成代理对象，以打破循环依赖。
// 用于保存 BeanName 和创建 bean 的工厂之间的关系，bean name -> ObjectFactory
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
// 检查单例池中是否存在实例
Object singletonObject = this.singletonObjects.get(beanName);
// 想要获取的 Bean 正在创建中，说明出现了循环依赖
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
// 从二级缓存中获取该 Bean 的代理对象
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
// 如果二级缓存没有，则锁定单例池并进行处理
synchronized (this.singletonObjects) {
// 检查单例池中是否存在实例
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
// 从二级缓存中获取该 Bean 的代理对象
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null) {
// 当某些方法需要提前初始化的时候则会调用 addSingletonFactory 方法将对应的 ObjectFactory 初始化策略存储在三级缓存中
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
// 从三级缓存中找到了
if (singletonFactory != null) {
// 调用预先设定的 getObject 方法
// 这里会执行 Lambda 表达式
singletonObject = singletonFactory.getObject();
// 记录在二级缓存中，删除三级缓存对应记录
// 二级缓存和三级缓存互斥
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
}
}
return singletonObject;
}
提前 AOP
提前 AOP 就是三级缓存中存放的 Lambda 表达式执行的方法
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean))AbstractAutowireCapableBeanFactory
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
Object exposedObject = bean;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (SmartInstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().smartInstantiationAware) {
// 提前 AOP
exposedObject = bp.getEarlyBeanReference(exposedObject, beanName);
}
}
return exposedObject;
}
提前 AOP
getEarlyBeanReference(exposedObject, beanName)AbstractAutoProxyCreator
public Object getEarlyBeanReference(Object bean, String beanName) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
// 早期进行 AOP，则将标识传入
// 供后面再进行 AOP 时进行判断
this.earlyProxyReferences.put(cacheKey, bean);
// 必要时填充
return wrapIfNecessary(bean, beanName, cacheKey);
}
正常 AOP
初始化
initializeBean(beanName, exposedObject, mbd)AbstractAutowireCapableBeanFactory
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
} else {
// 对特殊的 bean 处理：Aware、BeanClassLoaderAware、BeanFactoryAware
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 初始化前
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 激活用户自定义的 init 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()) {
// 初始化后
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
初始化后
applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName)AbstractAutowireCapableBeanFactory
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
// 初始化后的后处理
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
初始化后的后处理
postProcessAfterInitialization(result, beanName)AbstractAutoProxyCreator
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
// 如果前面没有进行过 AOP，这里进行 AOP
// 如果前面进行过 AOP，删除对应记录，这里不进行 AOP
if (this.earlyProxyReferences.remove(cacheKey) != bean) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
参考
https://www.bilibili.com/video/BV1tR4y1F75R?spm_id_from=333.337.search-card.all.click
https://www.bilibili.com/video/BV12Z4y197MU?spm_id_from=333.999.0.0
《Spring源码深度解析（第2版）》
版本
Spring 5.3.15
天河有尽身作涯，星海无边前是岸。
