学习spring源码主框架，从源码角度开发学习Spring bean的生命周期。spring创建bean方法org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String, java.lang.Class )
public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
//doGetBean是获取bean的真实方法
return doGetBean(name, requiredType, null, false);
}真正执行spring创建bean方法doGetBeanorg.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
//获取的beanname可能是重命名后的，这个获取原始的beanname，这里做别名解析
final String beanName = transformedBeanName(name);
Object bean;
//先从spring缓存池中获取bean，这里是解决循环依赖的根本
Object sharedInstance = getSingleton(beanName);
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 "'");
}
}
//如果从缓存中获取到bean，进行后续处理。
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
//判断当前创建的bean是不是原型的，如果存在循环依赖，则抛异常
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
//获取父工厂
BeanFactory parentBeanFactory = getParentBeanFactory();
//判断父工厂是否为空，以及当前容器中是否包含bean定义
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
//根据构造函数是否有参数，来创建不同的bean
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 {
//合并bean定义，存在抽象父bean定义，专门给子bean做继承的
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
//检查bean定义的是否为抽象的，如果是则抛出异常
checkMergedBeanDefinition(mbd, beanName, args);
//获取bean初始化的前置依赖beanname
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 "'");
}
//解析以来的bean，并注册依赖的bean
registerDependentBean(dep, beanName);
try {
//递归调用获取依赖bean
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" beanName "' depends on missing bean '" dep "'", ex);
}
}
}
// 创建bean的实例
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
try {
//构建bean的实例
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
}
});
//如果获取的bean是factroybean，那么要处理工厂bean。
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
//创建原型bean
Object prototypeInstance = null;
try {
//在原型bena创建之前回调底层spring函数，开放性方法
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
//开放性方法
afterPrototypeCreation(beanName);
}
//如果获取的bean是factroybean，那么要处理工厂bean。
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 {
//根据bean定义的scope来创建bean
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;
}
}
// 判断获取的类型是否匹配实际的bean实例
if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
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;
}org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, boolean)这个方法是解决spring循环依赖问题
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
//从一级缓存中获取实例bean，如果有直接返回对象
Object singletonObject = this.singletonObjects.get(beanName);
//singletonObject为空并且 beanname是否正在创建中的标识
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
//防止并发获取bean
synchronized (this.singletonObjects) {
//从earlySingletonObjects早期缓冲池中获取bean
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
//从singletonFactories中获取bean的objectfactory
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
//调用objectfactory的getObject方法获取singletonObject
singletonObject = singletonFactory.getObject();
//同时放到earlySingletonObjects提前暴露出来
this.earlySingletonObjects.put(beanName, singletonObject);
//并从singletonFactories移除
this.singletonFactories.remove(beanName);
}
}
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}获取实例beanorg.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory )
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
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 "'");
}
//标识当前正在创建的对象，放到singletonsCurrentlyInCreation缓存中
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<Exception>();
}
try {
//调用接口objectfacotry的getObject方法， 这个方法被重写
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
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;
}
//当前bean已经创建好了，到singletonsCurrentlyInCreation中bean移除掉
afterSingletonCreation(beanName);
}
if (newSingleton) {
//把创建好的bean加载到缓存池中，并移除二三级缓存
addSingleton(beanName, singletonObject);
}
}
//对bean判空
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
}创建bean实例org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean(java.lang.String, org.springframework.beans.factory.support.RootBeanDefinition, java.lang.Object[])
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 {
// 这里给后置处理器一个机会去创建代理对象，第一次创建bean到这里还没有创建好bean， 仅仅把切面信息解析出来放入缓存中
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);
}
//真正执行创建bean实例的方法doCreateBean
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" beanName "'");
}
return beanInstance;
}真正执行创建bean实例的方法doCreateBeanorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//根据@bean， @autowire来创建有参构造函数， 或者无参数构造函数
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
mbd.resolvedTargetType = beanType;
//允许后置处理器去修改merge后的bean定义
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;
}
}
// 判断earlySingletonObjects是否提前暴露bean对象
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");
}
//将已经创建好但是属性还没有赋值的bean对象，通过objectfacotry的形式来加载到缓存中用来解决循环依赖的问题
addSingletonFactory(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
return getEarlyBeanReference(beanName, mbd, bean);
}
});
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//为刚刚创建的bean对象进行赋值
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
//初始化bean，并且通过开放性方法为bean赋值
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<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
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 "
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
try {
//注册自定义销毁bean的方法
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}初始化已经创建好的bean实例org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
//权限校验是否判断是否可以回调底层组件方法
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
invokeAwareMethods(beanName, bean);
return null;
}
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//实现自定义的bean的后置处理器的前置方法
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//调用自定义的init方法或InitializingBean
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()) {
//实现自定义的bean的后置处理器的后置方法
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}以上，就是spring ioc模块bean生命周期的源代码解析。
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