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本文小編為大家詳細介紹“SpringBoot源碼之Bean的生命周期是什么”，內容詳細，步驟清晰，細節處理妥當，希望這篇“SpringBoot源碼之Bean的生命周期是什么”文章能幫助大家解決疑惑，下面跟著小編的思路慢慢深入，一起來學習新知識吧。
入口方法為SpringApplication#run()
1.SpringApplication#run()
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
long startTime = System.nanoTime();
DefaultBootstrapContext bootstrapContext = createBootstrapContext();
ConfigurableApplicationContext context = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(bootstrapContext, this.mainApplicationClass);
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
context.setApplicationStartup(this.applicationStartup);
prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);
}
listeners.started(context, timeTakenToStartup);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
if (ex instanceof AbandonedRunException) {
throw ex;
}
handleRunFailure(context, ex, listeners);
throw new IllegalStateException(ex);
}
try {
if (context.isRunning()) {
Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
listeners.ready(context, timeTakenToReady);
}
}
catch (Throwable ex) {
if (ex instanceof AbandonedRunException) {
throw ex;
}
handleRunFailure(context, ex, null);
throw new IllegalStateException(ex);
}
return context;
}2.SpringApplication#run()=> SpringApplication#refreshContext(context)=> SpringApplication#refresh(context)=>ConfigurableApplicationContext#refresh()=>AbstractApplicationContext#refresh()
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
beanPostProcess.end();
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
contextRefresh.end();
}
}
}3.SpringApplication#run()=> SpringApplication#refreshContext(context)=> SpringApplication#refresh(context)=>ConfigurableApplicationContext#refresh()=>AbstractApplicationContext#refresh()=>AbstractApplicationContext#finishBeanFactoryInitialization()=>ConfigurableListableBeanFactory#preInstantiateSingletons()=>DefaultListableBeanFactory#preInstantiateSingletons()
@Override
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof SmartFactoryBean<?> smartFactoryBean && smartFactoryBean.isEagerInit()) {
getBean(beanName);
}
}
else {
// 此處就是初始化bean的方法
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
// 此處就是解決循環依賴的代碼
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton smartSingleton) {
StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize")
.tag("beanName", beanName);
smartSingleton.afterSingletonsInstantiated();
smartInitialize.end();
}
}
}解決循環依賴的代碼如下：
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
// 嘗試從緩存中獲取成品的目標對象，如果存在，則直接返回
Object singletonObject = this.singletonObjects.get(beanName);
// 如果緩存中不存在目標對象，則判斷當前對象是否已經處于創建過程中，在前面的講解中，第一次嘗試獲取A對象
// 的實例之后，就會將A對象標記為正在創建中，因而最后再嘗試獲取A對象的時候，這里的if判斷就會為true
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
synchronized (this.singletonObjects) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
// 這里的singletonFactories是一個Map，其key是bean的名稱，而值是一個ObjectFactory類型的
// 對象，這里對于A和B而言，調用圖其getObject()方法返回的就是A和B對象的實例，無論是否是半成品
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
// 獲取目標對象的實例
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return singletonObject;
}一級緩存，singletonObjects 單例緩存，存儲已經實例化的單例bean。
二級緩存，earlySingletonObjects 提前暴露的單例緩存，這里存儲的bean是剛剛構造完成，但還會通過屬性注入bean。
三級緩存，singletonFactories 生產單例的工廠緩存，存儲工廠。
解決原理如下：
在第一層中，先去獲取 A 的 Bean，發現沒有就準備去創建一個，然后將 A 的代理工廠放入“三級緩存”（這個 A 其實是一個半成品，還沒有對里面的屬性進行注入），但是 A 依賴 B 的創建，就必須先去創建 B；
在第二層中，準備創建 B，發現 B 又依賴 A，需要先去創建 A，去創建 A，因為第一層已經創建了 A 的代理工廠，直接從“三級緩存”中拿到 A 的代理工廠，獲取 A 的代理對象，放入“二級緩存”，并清除“三級緩存”；
有了 A 的代理對象，對 A 的依賴完美解決（這里的 A 仍然是個半成品），B 初始化成功。在 B 初始化成功，完成 A 對象的屬性注入，然后再填充 A 的其它屬性，以及 A 的其它步驟（包括 AOP），完成對 A 完整的初始化功能（這里的 A 才是完整的 Bean）。
將 A 放入“一級緩存”。
4.SpringApplication#run()=> SpringApplication#refreshContext(context)=> SpringApplication#refresh(context)=>ConfigurableApplicationContext#refresh()=>AbstractApplicationContext#refresh()=>AbstractApplicationContext#finishBeanFactoryInitialization()=>ConfigurableListableBeanFactory#preInstantiateSingletons()=>DefaultListableBeanFactory#preInstantiateSingletons()=>AbstractBeanFactory#getBean() => AbstractBeanFactory#doGetBean()=>AbstractBeanFactory#createBean()=>AbstractAutowireCapableBeanFactory#createBean()=>AbstractAutowireCapableBeanFactory#doCreateBean()
bean的生命周期：
1.調用InstantiationAwareBeanPostProcessor# postProcessBeforeInstantiation
跟進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. 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 {
// 1.調用InstantiationAwareBeanPostProcessor# postProcessBeforeInstantiation
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 {
// 跟進doCreateBean()
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);
}
}2.創建bean實例
跟進populateBean()
跟進initializeBean()
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) {
// 2.創建bean實例
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 {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.markAsPostProcessed();
}
}
// 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");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
// 跟進populateBean()
populateBean(beanName, mbd, instanceWrapper);
// 跟進initializeBean()
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {
if (ex instanceof BeanCreationException bce && beanName.equals(bce.getBeanName())) {
throw bce;
}
else {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, ex.getMessage(), 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;
}3.調用InstantiationAwareBeanPostProcessor# postProcessAfterInstantiation
4.注入bean屬性
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
if (bw == null) {
if (mbd.hasPropertyValues()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
return;
}
}
if (bw.getWrappedClass().isRecord()) {
if (mbd.hasPropertyValues()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to a record");
}
else {
// Skip property population phase for records since they are immutable.
return;
}
}
// 3.調用InstantiationAwareBeanPostProcessor# postProcessAfterInstantiation
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
if (!bp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
return;
}
}
}
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
if (hasInstantiationAwareBeanPostProcessors()) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
PropertyValues pvsToUse = bp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
pvs = pvsToUse;
}
}
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
if (needsDepCheck) {
PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
checkDependencies(beanName, mbd, filteredPds, pvs);
}
if (pvs != null) {
// 4.注入屬性
applyPropertyValues(beanName, mbd, bw, pvs);
}
}5.設置Aware接口的屬性
6.調用BeanPostProcessor的初始化前置方法
7.先((InitializingBean) bean).afterPropertiesSet(),后調用init-method方法，進行初始化操作
8.調用BeanPostProcessor的初始化后置方法
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
// 5.設置Aware接口的屬性
invokeAwareMethods(beanName, bean);
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 5.調用BeanPostProcessor的初始化前置方法
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 6.調用init-method方法，進行初始化操作
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null), beanName, ex.getMessage(), ex);
}
if (mbd == null || !mbd.isSynthetic()) {
// 7. 調用BeanPostProcessor的初始化后置方法
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}讀到這里，這篇“SpringBoot源碼之Bean的生命周期是什么”文章已經介紹完畢，想要掌握這篇文章的知識點還需要大家自己動手實踐使用過才能領會，如果想了解更多相關內容的文章，歡迎關注億速云行業資訊頻道。
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