Spring原始碼學習-bean的建立
阿新 • • 發佈:2021-11-19
獲取bean的流程
- org.springframework.context.support.AbstractApplicationContext#getBean(java.lang.String)
- org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
- org.springframework.beans.factory.support.AbstractBeanFactory#transformedBeanName
如果是別名,通過這個方法找到真正的bean的唯一id
- org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String)
從快取中獲取bean,獲取順序是一級快取->二級快取->三級快取。如果一級快取和二級快取都沒取到,從三級快取中取出
beanFactory
,呼叫beanFactory
的get(beanName)
方法獲取bean,並放入二級快取,然後從三級快取中刪除。/** Cache of singleton objects: bean name to bean instance. */ /** 一級快取:存放bean例項,先從這裡獲取 */ private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256); /** Cache of early singleton objects: bean name to bean instance. */ /** 二級快取:早期bean物件,半成品 */ private final Map<String, Object> earlySingletonObjects = new HashMap<>(16); /** Cache of singleton factories: bean name to ObjectFactory. */ /** 三級快取:建立bean的工廠物件 */ private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
- 如果從快取中取到了就呼叫
getObjectForBeanInstance
方法org.springframework.beans.factory.support.AbstractBeanFactory#getObjectForBeanInstance
- 如果
beanName
是&
開頭的則beanInstance
(從快取中獲取的)為beanFactory
型別的,直接返回- 如果
beanInstance
不是beanFactory
型別的,直接返回beanName
不是&
開頭且beanInstance
是beanFactory
型別的,呼叫工廠方法獲取bean物件- 呼叫
getParentBeanFactory
,優先通過父類的工廠物件建立bean- 檢測是否有迴圈依賴,先獲取依賴的bean
- 如果是單例,先從一級快取獲取一下,獲取不到就走
建立bean
的流程
如果是原型,直接走建立bean的流程org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean()
建立bean
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean()
生命週期
原始碼解析
呼叫InstantiationAwareBeanPostProcessor
介面的方法
createBean
/**
* Central method of this class: creates a bean instance,
* populates the bean instance, applies post-processors, etc.
* @see #doCreateBean
*/
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isTraceEnabled()) {
logger.trace("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.
// 解析bean的型別
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
try {
// 如果有過載的方法,進行校驗,並將標記為不過載,避免參數檢查導致效能的開銷
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
// 給了一個提供代理建立bean的機會,實現AOP的關鍵所在
// 如果是InstantiationAwareBeanPostProcessor型別的,先呼叫postProcessBeforeInstantiation()方法建立一個代理物件
// 然後再呼叫postProcessAfterInitialization方法,再給你一個改變bean的機會
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);
}
try {
// 如果你沒有把握機會,那現在去正式建立bean
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isTraceEnabled()) {
logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
resolveBeforeInstantiation
/**
* Apply before-instantiation post-processors, resolving whether there is a
* before-instantiation shortcut for the specified bean.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @return the shortcut-determined bean instance, or {@code null} if none
*/
@Nullable
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) {
// 一個手動建立bean的機會,比如代理
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
// 再給一個改變bean的機會
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}
protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
// 實現了 InstantiationAwareBeanPostProcessor 介面的bean
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
if (result != null) {
return result;
}
}
}
return null;
}
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
// 實現了BeanPostProcessor介面的bean
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
呼叫MergedBeanDefinitionPostProcessor
介面的方法
doCreateBean()
/**
* Actually create the specified bean. Pre-creation processing has already happened
* at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
* <p>Differentiates between default bean instantiation, use of a
* factory method, and autowiring a constructor.
* @param beanName the name of the bean
* @param mbd the merged bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a new instance of the bean
* @throws BeanCreationException if the bean could not be created
* @see #instantiateBean
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
*/
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 建立bean例項
// 通過factory-method、有參構造、預設無參構造建立一個BeanWrapper
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// 所有實現了MergedBeanDefinitionPostProcessor介面的bean,呼叫postProcessMergedBeanDefinition()方法
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
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");
}
// 如果允許暴露早起的bean(單例且允許迴圈引用且正在建立),新增到三級快取中。
// 當從三級快取中獲取到,呼叫getObject()方法時,呼叫getEarlyBeanReference(),
// 建立代理物件 AOP有用到
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
// 填充bean的屬性值
// 根據名稱注入,根據型別注入,
// 在賦值之前可以通過實現InstantiationAwareBeanPostProcessor介面來對值做一些操作
populateBean(beanName, mbd, instanceWrapper);
// 初始化bean例項
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<>(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 " +
"'getBeanNamesForType' 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;
}
applyMergedBeanDefinitionPostProcessors
protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof MergedBeanDefinitionPostProcessor) {
MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
}
}
}
getEarlyBeanReference()
/**
* Obtain a reference for early access to the specified bean,
* typically for the purpose of resolving a circular reference.
* @param beanName the name of the bean (for error handling purposes)
* @param mbd the merged bean definition for the bean
* @param bean the raw bean instance
* @return the object to expose as bean reference
*/
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
Object exposedObject = bean;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
}
}
}
return exposedObject;
}
呼叫BeanNameAware
介面的方法
呼叫BeanClassLoaderAware
介面的方法
呼叫BeanFactoryAware
介面的方法
呼叫BeanPostProcessor
介面的postProcessBeforeInitialization
方法
呼叫ApplicationContextAware、EnvironmentAware
等介面的方法
如果bean實現了
ApplicationContextAware、EnvironmentAware
等介面
參見:org.springframework.context.support.ApplicationContextAwareProcessor#invokeAwareInterfaces
呼叫InitializingBean
介面的方法
呼叫BeanPostProcessor
介面的postProcessAfterInitialization
方法
initializeBean()
呼叫
BeanNameAware、BeanClassLoaderAware、BeanFactoryAware、InitializingBean
等介面的方法
通過org.springframework.context.support.ApplicationContextAwareProcessor#invokeAwareInterfaces
方法呼叫ApplicationContextAware
等xxxAware介面的方法。
/**
* Initialize the given bean instance, applying factory callbacks
* as well as init methods and bean post processors.
* <p>Called from {@link #createBean} for traditionally defined beans,
* and from {@link #initializeBean} for existing bean instances.
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @return the initialized bean instance (potentially wrapped)
* @see BeanNameAware
* @see BeanClassLoaderAware
* @see BeanFactoryAware
* @see #applyBeanPostProcessorsBeforeInitialization
* @see #invokeInitMethods
* @see #applyBeanPostProcessorsAfterInitialization
*/
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 {
// 呼叫實現了BeanNameAware、BeanClassLoaderAware、BeanFactoryAware的bean的介面方法
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 初始化之前,實現了 BeanPostProcessor的bean,呼叫postProcessBeforeInitialization() 方法
// ApplicationContextAware等xxxAware介面方法呼叫的入口,參考org.springframework.context.support.ApplicationContextAwareProcessor#invokeAwareInterfaces
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 給bean一個機會,如果bean實現了InitializingBean介面,在賦值之後呼叫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()) {
// 初始化之後,實現了 BeanPostProcessor的bean,呼叫postProcessAfterInitialization() 方法
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
invokeAwareMethods
private void invokeAwareMethods(final String beanName, final Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
applyBeanPostProcessorsBeforeInitialization
@Override
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;
}
@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware ||
bean instanceof ApplicationStartupAware)) {
return bean;
}
AccessControlContext acc = null;
if (System.getSecurityManager() != null) {
acc = this.applicationContext.getBeanFactory().getAccessControlContext();
}
if (acc != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareInterfaces(bean);
return null;
}, acc);
}
else {
invokeAwareInterfaces(bean);
}
return bean;
}
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof EnvironmentAware) {
((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
}
if (bean instanceof EmbeddedValueResolverAware) {
((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
}
if (bean instanceof ResourceLoaderAware) {
((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
}
if (bean instanceof ApplicationEventPublisherAware) {
((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
}
if (bean instanceof MessageSourceAware) {
((MessageSourceAware) bean).setMessageSource(this.applicationContext);
}
if (bean instanceof ApplicationStartupAware) {
((ApplicationStartupAware) bean).setApplicationStartup(this.applicationContext.getApplicationStartup());
}
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}
invokeInitMethods
protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
throws Throwable {
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isTraceEnabled()) {
logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
((InitializingBean) bean).afterPropertiesSet();
return null;
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null && bean.getClass() != NullBean.class) {
String initMethodName = mbd.getInitMethodName();
if (StringUtils.hasLength(initMethodName) &&
!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
呼叫DestructionAwareBeanPostProcessor
的方法
protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
if (mbd.isSingleton()) {
// Register a DisposableBean implementation that performs all destruction
// work for the given bean: DestructionAwareBeanPostProcessors,
// DisposableBean interface, custom destroy method.
registerDisposableBean(beanName,
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
}
else {
// A bean with a custom scope...
Scope scope = this.scopes.get(mbd.getScope());
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + mbd.getScope() + "'");
}
scope.registerDestructionCallback(beanName,
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
}
}
}