第基于springbootbean的實(shí)例化過(guò)程和屬性注入過(guò)程目錄bean的實(shí)例化過(guò)程和屬性注入過(guò)程bean實(shí)例化流程說(shuō)明

bean的實(shí)例化過(guò)程和屬性注入過(guò)程

了解過(guò)springboot的加載流程的都知道springboot初始化bean都在refresh方法中。

這個(gè)方法代碼如下：

//Preparethiscontextforrefreshing.

prepareRefresh();

//Tellthesubclasstorefreshtheinternalbeanfactory.新建beanFactory

ConfigurableListableBeanFactorybeanFactory=obtainFreshBeanFactory();

//Preparethebeanfactoryforuseinthiscontext.

prepareBeanFactory(beanFactory);

try{

//Allowspost-processingofthebeanfactoryincontextsubclasses.

postProcessBeanFactory(beanFactory);

//Invokefactoryprocessorsregisteredasbeansinthecontext.

//加載實(shí)現(xiàn)beanFactoryPostProcessor的bean，bean定義的時(shí)候執(zhí)行

invokeBeanFactoryPostProcessors(beanFactory);

//Registerbeanprocessorsthatinterceptbeancreation.

//加載實(shí)現(xiàn)了beanPostProcessor，在bean實(shí)例化前、后執(zhí)行

registerBeanPostProcessors(beanFactory);

//Initializemessagesourceforthiscontext.

initMessageSource();

//Initializeeventmulticasterforthiscontext.

initApplicationEventMulticaster();

//Initializeotherspecialbeansinspecificcontextsubclasses.

onRefresh();

//Checkforlistenerbeansandregisterthem.

registerListeners();

//Instantiateallremaining(non-lazy-init)singletons.

//實(shí)例化非懶加載的bean、bean封裝、屬性注入、注解注入(主要使用BeanPostProcessor或子類實(shí)現(xiàn))等

finishBeanFactoryInitialization(beanFactory);

//Laststep:publishcorrespondingevent.

finishRefresh();

這里我們主要看下finishBeanfactoryInitialization方法。此方法實(shí)現(xiàn)了bean的實(shí)例和屬性注入等。進(jìn)入此方法的最后一行。

//Instantiateallremaining(non-lazy-init)singletons.

beanFactory.preInstantiateSingletons();

注釋寫(xiě)的很清楚，實(shí)例化剩余非懶加載的bean。此方法的實(shí)現(xiàn)是核心類DefaultLisListableBeanFactory實(shí)現(xiàn)。這個(gè)方法中有個(gè)判斷：bean是否是beanFactory的實(shí)現(xiàn)類。

如果是則獲取bean的時(shí)候會(huì)從beanFactory實(shí)現(xiàn)類的getObject中獲取，我們重點(diǎn)看看getBean這個(gè)方法。

getBean是spring中最重要、最牛逼的方法之一，具體的邏輯是通過(guò)doGetBean方法處理的。

我們看下doGetBean方法，方法很長(zhǎng)。我們分成幾個(gè)部分去看。

1、先判斷是否已經(jīng)存在緩存中，代碼如下：

if(sharedInstance!=nullargs==null){

if(logger.isDebugEnabled()){

if(isSingletonCurrentlyInCreation(beanName)){

logger.debug("Returningeagerlycachedinstanceofsingletonbean'"+beanName+

"'thatisnotfullyinitializedyet-aconsequenceofacircularreference");

else{

logger.debug("Returningcachedinstanceofsingletonbean'"+beanName+"'");

bean=getObjectForBeanInstance(sharedInstance,name,beanName,null);

2、從父beanfactory中獲取

BeanFactoryparentBeanFactory=getParentBeanFactory();

if(parentBeanFactory!=null!containsBeanDefinition(beanName)){

//Notfound-checkparent.

StringnameToLookup=originalBeanName(name);

if(parentBeanFactoryinstanceofAbstractBeanFactory){

return((AbstractBeanFactory)parentBeanFactory).doGetBean(

nameToLookup,requiredType,args,typeCheckOnly);

elseif(args!=null){

//Delegationtoparentwithexplicitargs.

return(T)parentBeanFactory.getBean(nameToLookup,args);

else{

//Noargs-delegatetostandardgetBeanmethod.

returnparentBeanFactory.getBean(nameToLookup,requiredType);

}

3、直接創(chuàng)建RootBeanDefinition

//mark給此bean馬克一下。防止重復(fù)創(chuàng)建

if(!typeCheckOnly){

markBeanAsCreated(beanName);

try{

finalRootBeanDefinitionmbd=getMergedLocalBeanDefinition(beanName);

checkMergedBeanDefinition(mbd,beanName,args);

//Guaranteeinitializationofbeansthatthecurrentbeandependson.

String[]dependsOn=mbd.getDependsOn();

if(dependsOn!=null){

for(Stringdep:dependsOn){

if(isDependent(beanName,dep)){

thrownewBeanCreationException(mbd.getResourceDescription(),beanName,

"Circulardepends-onrelationshipbetween'"+beanName+"'and'"+dep+"'");

registerDependentBean(dep,beanName);

getBean(dep);

4、是singleton還是prototype類型的，根據(jù)不同類型去實(shí)例化bean,代碼只貼了單例的類型：

//Createbeaninstance.

if(mbd.isSingleton()){

sharedInstance=getSingleton(beanName,()-{

try{

returncreateBean(beanName,mbd,args);

catch(BeansExceptionex){

//Explicitlyremoveinstancefromsingletoncache:Itmighthavebeenputthere

//eagerlybythecreationprocess,toallowforcircularreferenceresolution.

//Alsoremoveanybeansthatreceivedatemporaryreferencetothebean.

destroySingleton(beanName);

throwex;

bean=getObjectForBeanInstance(sharedInstance,name,beanName,mbd);

5、檢查bean的類型是否匹配

//Checkifrequiredtypematchesthetypeoftheactualbeaninstance.

if(requiredType!=null!requiredType.isInstance(bean)){

try{

TconvertedBean=getTypeConverter().convertIfNecessary(bean,requiredType);

if(convertedBean==null){

thrownewBeanNotOfRequiredTypeException(name,requiredType,bean.getClass());

returnconvertedBean;

catch(TypeMismatchExceptionex){

if(logger.isDebugEnabled()){

logger.debug("Failedtoconvertbean'"+name+"'torequiredtype'"+

ClassUtils.getQualifiedName(requiredType)+"'",ex);

thrownewBeanNotOfRequiredTypeException(name,requiredType,bean.getClass());

}

整個(gè)doGetBean方法改成這5個(gè)部分，重點(diǎn)看下第4個(gè)部分中的createBean和getObjectForBeanInstance方法。

1、createBean方法，里面主要是2個(gè)部分,bean直接是通過(guò)BeanPostProcessor的postProcessBeforeIntantiation方法獲取的。

注釋也是描述的很清楚：GiveBeanPostProcessorsachancetoreturnaproxyinsteadofthebeaninstance(英語(yǔ)渣渣不敢瞎翻譯誤導(dǎo)大家，理解就好)

代碼如下：

try{

//GiveBeanPostProcessorsachancetoreturnaproxyinsteadofthetargetbeaninstance.

Objectbean=resolveBeforeInstantiation(beanName,mbdToUse);

if(bean!=null){

returnbean;

catch(Throwableex){

thrownewBeanCreationException(mbdToUse.getResourceDescription(),beanName,

"BeanPostProcessorbeforeinstantiationofbeanfailed",ex);

第一個(gè)部分自己實(shí)現(xiàn)，那么createBean方法第2個(gè)部分毋庸置疑肯定是spring去實(shí)例化bean，代碼如下：

try{

ObjectbeanInstance=doCreateBean(beanName,mbdToUse,args);

if(logger.isDebugEnabled()){

logger.debug("Finishedcreatinginstanceofbean'"+beanName+"'");

returnbeanInstance;

}

又是do開(kāi)頭的方法，說(shuō)明這個(gè)也是一個(gè)創(chuàng)建方法，spring中一般do開(kāi)頭的都是用于創(chuàng)建某個(gè)對(duì)象。跟著代碼走，看下doCreateBean方法，在查看此方法之前，可能需要了解下BeanWarpper這個(gè)封裝類。bean的封裝、屬性注入等都是用BeanWarpper去完成的。

看下代碼：

//Instantiatethebean.

BeanWrapperinstanceWrapper=null;

if(mbd.isSingleton()){

instanceWrapper=this.factoryBeanInstanceCache.remove(beanName);

if(instanceWrapper==null){

instanceWrapper=createBeanInstance(beanName,mbd,args);

}

進(jìn)入createBeanInstance方法中，就是調(diào)用構(gòu)造器去實(shí)例化bean，返回beanWrapper。通過(guò)構(gòu)造器獲取實(shí)例代碼如下：

//Needtodeterminetheconstructor...

Constructor[]ctors=determineConstructorsFromBeanPostProcessors(beanClass,beanName);

if(ctors!=null||

mbd.getResolvedAutowireMode()==RootBeanDefinition.AUTOWIRE_CONSTRUCTOR||

mbd.hasConstructorArgumentValues()||!ObjectUtils.isEmpty(args)){

returnautowireConstructor(beanName,mbd,ctors,args);

//Nospecialhandling:simplyuseno-argconstructor.

returninstantiateBean(beanName,mbd);

這里實(shí)例化我一開(kāi)始以為就是簡(jiǎn)單的反射，后面我點(diǎn)進(jìn)去時(shí)候發(fā)現(xiàn)里面一直提策略實(shí)例化，我目前了解的是可以解決Override的問(wèn)題等。如果有興趣的可以自行查看。到這里為止。我們終于實(shí)例化bean了。下面看下第二步bean的屬性注入等。

代碼如下：

ObjectexposedObject=bean;

try{

populateBean(beanName,mbd,instanceWrapper);

exposedObject=initializeBean(beanName,exposedObject,mbd);

catch(Throwableex){

if(exinstanceofBeanCreationExceptionbeanName.equals(((BeanCreationException)ex).getBeanName())){

throw(BeanCreationException)ex;

else{

thrownewBeanCreationException(

mbd.getResourceDescription(),beanName,"Initializationofbeanfailed",ex);

}

populateBean方法名稱就暴露他是干啥的：填充bean。我放一段比較重要的部分：

if(hasInstAwareBpps||needsDepCheck){

if(pvs==null){

pvs=mbd.getPropertyValues();

PropertyDescriptor[]filteredPds=filterPropertyDescriptorsForDependencyCheck(bw,mbd.allowCaching);

if(hasInstAwareBpps){

for(BeanPostProcessorbp:getBeanPostProcessors()){

if(bpinstanceofInstantiationAwareBeanPostProcessor){

InstantiationAwareBeanPostProcessoribp=(InstantiationAwareBeanPostProcessor)bp;

pvs=ibp.postProcessPropertyValues(pvs,filteredPds,bw.getWrappedInstance(),beanName);

if(pvs==null){

return;

if(needsDepCheck){

checkDependencies(beanName,mbd,filteredPds,pvs);

}

這段代碼貌似沒(méi)有什么注入、填充什么的，我們看下InstantiationAwareBeanPostProcessor這個(gè)接口，發(fā)現(xiàn)這個(gè)接口有個(gè)很熟悉的實(shí)現(xiàn)類是：AutowiredAnnotationBeanPostProcessor。這個(gè)類的方法中我們看到終于看到了jnject方法。但是在inject之前需要調(diào)用下findAutowiringMatedata方法獲取一下元數(shù)據(jù)：

//Fallbacktoclassnameascachekey,forbackwardscompatibilitywithcustomcallers.

StringcacheKey=(StringUtils.hasLength(beanName)beanName:clazz.getName());

//Quickcheckontheconcurrentmapfirst,withminimallocking.

InjectionMetadatametadata=this.injectionMetadataCache.get(cacheKey);

if(InjectionMetadata.needsRefresh(metadata,clazz)){

synchronized(this.injectionMetadataCache){

metadata=this.injectionMetadataCache.get(cacheKey);

if(InjectionMetadata.needsRefresh(metadata,clazz)){

if(metadata!=null){

metadata.clear(pvs);

metadata=buildAutowiringMetadata(clazz);

this.injectionMetadataCache.put(cacheKey,metadata);

returnmetadata;

那么問(wèn)題又來(lái)了，這個(gè)injectionMetadataCache集合值是從那里來(lái)的呢？AutowiredAnnotationBeanPostProcessor實(shí)現(xiàn)了MergeBeandefinitionPostProcessor,那么就好了，肯定是在bean實(shí)例的時(shí)候調(diào)用了postProcessMergedBeanDefintion這個(gè)方法。

果然在doCreateBean方法中有這么一段：

//Allowpost-processorstomodifythemergedbeandefinition.

synchronized(mbd.postProcessingLock){

if(!mbd.postProcessed){

try{

//通過(guò)BeanPostProcessor將需要注解的元數(shù)據(jù)放到Map中

applyMergedBeanDefinitionPostProcessors(mbd,beanType,beanName);

catch(Throwableex){

thrownewBeanCreationException(mbd.getResourceDescription(),beanName,

"Post-processingofmergedbeandefinitionfailed",ex);

mbd.postProcessed=true;

}

哎，spring縝密啊。元數(shù)據(jù)有了，下面我們看下element.inject()方法是如何操作的：

if(this.isField){

Fieldfield=(Field)this.member;

ReflectionUtils.makeAccessible(field);

field.set(target,getResourceToInject(target,requestingBeanName));

else{

if(checkPropertySkipping(pvs)){

return;

try{

Methodmethod=(Method)this.member;

ReflectionUtils.makeAccessible(method);

method.invoke(target,getResourceToInject(target,requestingBeanName));

catch(InvocationTargetExceptionex){

throwex.getTargetException();

}

方法簡(jiǎn)單明了，直接使用反射將值set到屬性中，至此bean的實(shí)例、屬性注入基本完成，下面我們回頭來(lái)看doGetBean的另一個(gè)方法getObjectForBeanInstance。

2、getObjectForBeanInstance方法。對(duì)于是FactoryBean類型的bean通過(guò)getObject獲取到bean的代理實(shí)例，跟著方法一直走下去會(huì)到getObejct()方法中。

if(System.getSecurityManager()!=null){

AccessControlContextacc=getAccessControlContext();

try{

object=AccessController.doPrivileged((PrivilegedExceptionActionObject)factory::getObject,acc);

catch(PrivilegedActionExceptionpae){

throwpae.getException();

else{

//從FactoryBean實(shí)現(xiàn)bean中g(shù)etObejct獲取到bean

object=factory.getObject();

}

到此finishBeanfactoryInitialization方法執(zhí)行結(jié)束！

bean實(shí)例化流程說(shuō)明

bean實(shí)例化流程流程是在onRefresh方法的finishBeanFactoryInitialization中。進(jìn)入該方法

protectedvoidfinishBeanFactoryInitialization(ConfigurableListableBeanFactorybeanFactory){

//Initializeconversionserviceforthiscontext.

if(beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME)

beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME,ConversionService.class)){

beanFactory.setConversionServi