引用上一篇的分析spring循环依赖图片的图片
分析一下spring加载bean的过程
1 getBean方法里就调用一个AbstractBeanFactory.doGetBean方法
1.1 doGetBean 这个方法就是加载spring加载bean的骨架
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
//提取对应的beanName,因为传入的可能是别名,又或者是FactoryBean,所以需要另行解析
final String beanName = transformedBeanName(name);
Object bean;
// 直接尝试从缓存中获取或者singletonFactories中的ObjectFactory中获取
Object sharedInstance = getSingleton(beanName);//2 下面有详细介绍
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
//有时候BeanFactory并不是直接返回实例本身而是需要返回指定方法返回的实例
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);//3 下面有详细介绍
}
else {
//原型模式的情况下，存在循环依赖直接抛出异常
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
//尝试从parentBeanFactroy中检测
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);
}
}
//如果不是只做类型检查的，那么就是要打算创建bean了,alreadyCreated在记录下要创建的beanName
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
//如存在依赖实例化依赖的bean
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.
//单例模式下bean的创建
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {//4 下面有详细介绍
@Override
public Object getObject() throws BeansException {
try {
//这个方法是一个回掉方法，将在调用实例工厂的getObject()时候调用
//这个才是真正创建bean的方法
//5 下面有详细介绍 return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
}
});
//这个方法使用的频率很高，对返回可能是factoryBean/factoryBean.getObject()返回的bean进行后处理器处理/bean的情况进行处理
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
//原型模式下bean的创建
else if (mbd.isPrototype()) {
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
//其他模式下bean的创建
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, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
catch (TypeMismatchException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type [" +
ClassUtils.getQualifiedName(requiredType) + "]", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
2 getSingleton方法
//这个方法里有三个缓存singletonObjects,earlySingletonObjects,singletonFactories
//如果能在singletonFactories中获取该bean的工厂实例,用工厂实例的getObject()方法创建实例,并缓存到earlySingletonObjects；
//singletonObjects保存的是beanName和beanInstance的关系
//singletonFactories保存的是beanName和bean工厂的关系
//earlySingletonObjects保存的是beanName和beanInstance的关系,它和singletonObjects不同点在于earlySingletonObjects保存的beanInstance还在创建中,
//可以通过getBean方法获取，但是获取的bean实例属性还未赋值，是个空对象
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
synchronized (this.singletonObjects) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
3 getObjectForBeanInstance方法
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
//如果指定的name是工厂相关(&为前缀)且beanInstance又不是FactoryBean类型,直接抛出异常
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}
//如果beanInstance不是FactoryBean (那就是返回的正常的beanInstance) 或者就是想返回factoyBeanInstance(name需要以&作为前缀)
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
//下面就是通过FactoryBean的getObject()返回bean
Object object = null;
if (mbd == null) {
//尝试从缓存中加载bean
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
//这个方法就是从FactoryBean的getObject()获取bean实例以及调用ObjectFactory的后处理
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
4.getSingleton
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
//检查bean是否已经加载过,单例模式下的bean就是复用以前的创建的bean,同一个容器唯一
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while the 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 + "'");
}
//将当前创建的bean记录下来，用来在循环依赖中检测
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
//调用createBean创建实例
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
throw ex;
}
}
catch (BeanCreationException ex) {
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
//和beforeSingletonCreation方法对应，bean加载完毕后移除该bean的正在加载状态的记录
afterSingletonCreation(beanName);
}
if (newSingleton) {
//在singletonObjects中增加beanName和beanInstance的关系，并且将辅助状态删除
addSingleton(beanName, singletonObject);
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
}
5.createBean 方法
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
if (logger.isDebugEnabled()) {
logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
//锁定class，根据设置的class属性或者根据className来解析Class
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
//验证以及准备覆盖的方法
try {
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
//给BeanPostProcessors一个机会返回代理来替代真在的代理
//bean应用初始化前的后处理，解析指定bean是否存在初始化前的短路操作
//这里是为AOP功能作为判断的，如果要创建的beanName被aop返回一个代理对象，那么就直接返回,不需要进入doCreateBean
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);//5.1 下面有详细介绍
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);//5.2下面有详细介绍
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
5.1resolveBeforeInstantiation 方法
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
//如果返回bean的不为空（即被post-processors处理后返回的代理对象），那么他就不会经历普通bean的创建，所以只能在这里应用后处理器的postProcessAfterInitialization方法
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}
5.2 doCreateBean
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) {
//根据指定的bean 使用对应的策略创建新的实例，如工厂方法,构造方法自动注入，简单初始化
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
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;
}
}
//是否需要提早曝光:单例&允许循环依赖&当前正在创建,检测循环依赖
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");
}
//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, new ObjectFactory<Object>() {// 5.2.1 下面有详细介绍
@Override
public Object getObject() throws BeansException {
//对bean再一次依赖引用,主要应用SmartInstantiationAwareBeanPostProcessor
//aop就是在这里将advice动态织入bean中，如没有SmartInstantiationAwareBeanPostProcessor直接返回bean 不做任何处理
return getEarlyBeanReference(beanName, mbd, bean);
}
});
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//对bean进行填充,将各个属性织入，可能存在依赖其他bean,则会递归初始化依赖bean
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
//调用init-method方法
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);//earlySingletonReference只有在检测到有循环依赖的情况下才不会为空
if (earlySingletonReference != null) {
if (exposedObject == bean) {// 如果exposedObject没有在初始化方法中被改变，就是没哦与被增强
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);
}
}
if (!actualDependentBeans.isEmpty()) {//因为bean创建后其所依赖的bean一定是已经创建 actualDependentBeans不为空表示当前bean创建后其依赖的bean却没有完全被创建，也就是存在循环依赖
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
5.2.1 addSingletonFactory
// 这方法和doGetBean方法中getSingleton()呼应起来
protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(singletonFactory, "Singleton factory must not be null");
synchronized (this.singletonObjects) {
if (!this.singletonObjects.containsKey(beanName)) {
this.singletonFactories.put(beanName, singletonFactory);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
}
还有createBeanInstance 和populateBean 内容没有贴出来
未完待续
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