3.Bean的实例化以及注入过程分析
Bean的实例以及注入是在getBean时触发的,由于外部容器是与外部调用交互的桥梁,我们首先从外部容器入手,AbstractApplicationContext类实现了getBean方法,代码如下:
AbstractApplicationContext下的代码:
publicObjectgetBean(Stringname)throwsBeansException{
//Bean的获取外部容器交给了内部容器returngetBeanFactory().getBean(name);
}
内部容器由DefaultListableBeanFactory承当,但真实的getBean方法实现是由其父类AbstractBeanFactory实现的sssssssssssssssssssssss。
AbstractBeanFactory下的代码:
publicObjectgetBean(Stringname,ClassrequiredType,Object[]args)throwsBeansException{
returndoGetBean(name,requiredType,args,false);
}
3.1 doGetBean方法分析
protectedObjectdoGetBean(
finalStringname,finalClassrequiredType,finalObject[]args,booleantypeCheckOnly)throwsBeansException{
//把当前传入的beanName转化为标准beanName,例如把去除&引用(如果带&表示要获取FactoryBean)、alias转化为标准的beanName等finalStringbeanName=transformedBeanName(name);
Objectbean=null;
//Eagerlychecksingletoncacheformanuallyregisteredsingletons.
//先从singleton对象缓存中查找,如果未找到接着到早期的singleton对象缓存查找,如果还是没有找到,接下来先获得beanName的singletonFactory,然后调用getObject获得对象。ObjectsharedInstance=getSingleton(beanName);
if(sharedInstance!=null){
/**//*获得给定bean实例的对象。这里的处理过程是这样的:
(1)如果sharedInstance不是FactoryBean实例,而是个普通bean,那么直接返回;
(2)如果sharedInstance是FactoryBean实例,且name要求返回FactoryBean实例,那么直接返回;
(3)否则从本地缓存获得合并BeanDefinition,如果本地缓存不存在合并BeanDefinition,则从本地缓存取得BeanDefinition,构造合并BeanDefinition,然后通过factoryBean获得bean*/bean=getObjectForBeanInstance(sharedInstance,name,beanName,null);
}else{
//检查beanName所代表的bean是否处于正在创建阶段,主要是防止循环引用
if(isPrototypeCurrentlyInCreation(beanName)){
thrownewBeanCurrentlyInCreationException(beanName);
}
//首先检查父工厂是否存在,如果父工厂存在,且当前工厂不存在该beanName的BeanDefinition,那么当前工厂将委托父工厂完成getBean的任务.BeanFactoryparentBeanFactory=getParentBeanFactory();
if(parentBeanFactory!=null&&!containsBeanDefinition(beanName)){
//转化为标准的beanNameStringnameToLookup=originalBeanName(name);
if(args!=null){
//Delegationtoparentwithexplicitargs.returnparentBeanFactory.getBean(nameToLookup,args);
}
else{
//从父工厂获得bean,过程与本方法类似,相当于递归returnparentBeanFactory.getBean(nameToLookup,requiredType);
}}
if(!typeCheckOnly){
//是否要类型检查,如果不检查,直接把beanName标记为已创建markBeanAsCreated(beanName);
}
/**//*通过beanName,从mergedBeanDefinitions(针对mergeBeanDefinition的缓存)中取出合并的BeanDefinition,mergedBeanDefinition主要指两个BeanDefinition的合并,比如父子两个的合并*/finalRootBeanDefinitionmbd=getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd,beanName,args);
//Guaranteeinitializationofbeansthatthecurrentbeandependson.String[]dependsOn=mbd.getDependsOn();
if(dependsOn!=null){//如果bean存在依赖bean,先构建依赖bean
for(inti=0;i{
StringdependsOnBean=dependsOn[i];
getBean(dependsOnBean);
registerDependentBean(dependsOnBean,beanName);
}}
//Createbeaninstance.
if(mbd.isSingleton()){//
sharedInstance=getSingleton(beanName,newObjectFactory(){
publicObjectgetObject()throwsBeansException{
try{
/**//*所有生成Bean都有BeanWrapper封装,bean的生成采用策略模式,CglibSubclassingInstantiationStrategy实现是默认的策略
1.如果配置为工厂方法创建(配置了factory-mother的),由java反射Mehthod的invoke完成bean的创建。
2.如果采用构造子配置创建(配置了constructor-arg的),如果bean对应的类包含多个构造子,采用cglib动态字节码构造;如果只有唯一的构造子,那么采用java反射Constructor的newInstance方法
3.如果是普通bean配置,直接通过反射Class默认的Constructor,然后调用newInstance获得bean.*/returncreateBean(beanName,mbd,args);
}
catch(BeansExceptionex){
//Explicitlyremoveinstancefromsingletoncache:Itmighthavebeenputthere.
//eagerlybythecreationprocess,toallowforcircularreferenceresolution.
//Alsoremoveanybeansthatreceivedatemporaryreferencetothebean.destroySingleton(beanName);
throwex;
}}});
/**//*由于当前构造的bean可能是FactoryBean,所以要通过以下方法获得真实需要的bean
(1)如果sharedInstance不是FactoryBean实例,而是个普通bean,那么直接返回;
(2)如果sharedInstance是FactoryBean实例,且name要求返回FactoryBean实例,那么直接返回;
(3)否则从本地缓存获得合并BeanDefinition,如果本地缓存不存在合并BeanDefinition,则从本地缓存取得BeanDefinition,构造合并BeanDefinition,然后通过factoryBean获得bean*/bean=getObjectForBeanInstance(sharedInstance,name,beanName,mbd);
}elseif(mbd.isPrototype()){
//It'saprototype->createanewinstance.ObjectprototypeInstance=null;
try{
beforePrototypeCreation(beanName);//维护prototypesCurrentlyInCreation,主要把beanName加入到其中prototypeInstance=createBean(beanName,mbd,args);
}
finally{
afterPrototypeCreation(beanName);
}bean=getObjectForBeanInstance(prototypeInstance,name,beanName,mbd);
}else{
StringscopeName=mbd.getScope();
finalScopescope=(Scope)this.scopes.get(scopeName);
if(scope==null){
thrownewIllegalStateException("NoScoperegisteredforscope'"+scopeName+"'");
}
try{
ObjectscopedInstance=scope.get(beanName,newObjectFactory(){
publicObjectgetObject()throwsBeansException{
beforePrototypeCreation(beanName);
try{
returncreateBean(beanName,mbd,args);
}
finally{
afterPrototypeCreation(beanName);
}}});
bean=getObjectForBeanInstance(scopedInstance,name,beanName,mbd);
}
catch(IllegalStateExceptionex){
thrownewBeanCreationException(beanName,
"Scope'"+scopeName+"'isnotactiveforthecurrentthread;"+"considerdefiningascopedproxyforthisbeanifyouintendtorefertoitfromasingleton",
ex);
}}}
//Checkifrequiredtypematchesthetypeoftheactualbeaninstance.
if(requiredType!=null&&bean!=null&&!requiredType.isAssignableFrom(bean.getClass())){
thrownewBeanNotOfRequiredTypeException(name,requiredType,bean.getClass());
}returnbean;
}
3.1.1 getObjectForBeanInstance方法分析
该方法从名称上就能看出,其实现的功能是从一个给定的bean实例,获取客户端调用所真实想要的bean。由于Spring能够管理各式的bean,当bean是FactoryBean实例的时候,客户端调用可以通过&+beanName的方式获得FactoryBean实例,而如果bean实例是普通的bean,那么该方法直接返回。
protectedObjectgetObjectForBeanInstance(
ObjectbeanInstance,Stringname,StringbeanName,RootBeanDefinitionmbd){
/**//*如果bean是工厂解除参照(即name带有&),且不是FactoryBean实例,那么抛出异常。这里的意思就是说如果name带有&,而传进来的又不是FactoryBean实例*/
if(BeanFactoryUtils.isFactoryDereference(name)&&!(beanInstanceinstanceofFactoryBean)){
thrownewBeanIsNotAFactoryException(transformedBeanName(name),beanInstance.getClass());
}
/**//*现在我们拥有了bean实例,它可能是一个普通bean或者一个FactoryBean.如果是一个工厂bean,我们使用它创建一个bean实例,除非调用者确实想要工厂的引用。
如果bean实例未实现FactoryBean,或者要求返回BeanFactory自身,那么直接返回。*/
if(!(beanInstanceinstanceofFactoryBean)||BeanFactoryUtils.isFactoryDereference(name)){
returnbeanInstance;
}
/**//*以下的代码意味着处理非普通bean,而是FactoryBean之类的*/Objectobject=null;
if(mbd==null){//
/**//*这里主要是从一个FactoryBean到object映射的缓存中,取出由FactoryBean创建的object.这种映射关系是由factoryBeanObjectCache(映射关系:FactoryBeanname-->object,例如’myJndi’--->myJndiObject)字段维护,该字段位于FactoryBeanRegistrySupport中*/object=getCachedObjectForFactoryBean(beanName);
}
if(object==null){
FactoryBeanfactory=(FactoryBean)beanInstance;
/**//*containsBeanDefinition方法是由默认内部工厂DefaultListableBeanFactory实现,因为BeanDefinition是缓存在它之下的*/
if(mbd==null&&containsBeanDefinition(beanName)){
/**//*从本地获得指定beanName的合并BeanDefinition,所谓的合并BeanDefinition就是指子类的BeanDefinition与父类BeanDefinition的合并。*/mbd=getMergedLocalBeanDefinition(beanName);
}
/**//*判断beanDefinition是否是合成的,即是否与其他beanDefinition进行了合并*/booleansynthetic=(mbd!=null&&mbd.isSynthetic());
//从factoryBean获得beanobject=getObjectFromFactoryBean(factory,beanName,!synthetic);
}returnobject;
}
3.1.1.1 合并BeanDefinition获取的分析
在容器初始化阶段,对解释资源获得的BeanDefinition是由GenericBeanDefinition来定义,其只能刻画bean自身的一些特性。但bean与bean之间还存在着继承、方法覆盖、包含等一些复杂的关系。而这些关系的刻画是由RootBeanDefinition来负责的。RootBeanDefinition也就是我们下面所说的mergedBeanDefinition,mergedBeanDefinition是指对具有继承关系的bean所对应的BeanDefinition的合成,以达到完成表达一个bean的目的。
mergedBeanDefinition在获得后也将被缓存,其被缓存在mergedBeanDefinitions字段中。
protectedRootBeanDefinitiongetMergedLocalBeanDefinition(StringbeanName)throwsBeansException{
//Quickcheckontheconcurrentmapfirst,withminimallocking.RootBeanDefinitionmbd=(RootBeanDefinition)this.mergedBeanDefinitions.get(beanName);
if(mbd!=null){
returnmbd;
}returngetMergedBeanDefinition(beanName,getBeanDefinition(beanName));
}
protectedRootBeanDefinitiongetMergedBeanDefinition(StringbeanName,BeanDefinitionbd)
throwsBeanDefinitionStoreException{
returngetMergedBeanDefinition(beanName,bd,null);
}
/**//*以下是真正的合并BeanDefinition处理*/protectedRootBeanDefinitiongetMergedBeanDefinition(
StringbeanName,BeanDefinitionbd,BeanDefinitioncontainingBd)
throwsBeanDefinitionStoreException{
synchronized(this.mergedBeanDefinitions){//同步mergedBeanDefinitionsRootBeanDefinitionmbd=null;
/**//*如果containingBd为空,先从缓存中查找,containingBd代表的包含bean的beanDefinition,那么什么是包含bean呢?比如B是A的内部类,那么A的实例就是B的实例的包含bean,这里的containingBd所代表的就是那个A。*/
if(containingBd==null){
//这里说明了合并BeanDefinition的处理顺序是先里后外。mbd=(RootBeanDefinition)this.mergedBeanDefinitions.get(beanName);
}
if(mbd==null){//如果缓存中不存在
if(bd.getParentName()==null){//且无父类
//如果当前BeanDefinition不存在parentName,说明该类不存在父类,直接把该类对应的BeanDefinition拷贝到合并BeanDefinitionmbd=newRootBeanDefinition(bd);
}
else{
BeanDefinitionpbd=null;
try{
StringparentBeanName=transformedBeanName(bd.getParentName());//对beanName进行标准化
if(!beanName.equals(parentBeanName)){//如果父类的名称与当前类的名称不相等
//获得父类的合并BeanDefinition
//这里说明了合并BeanDefinition的处理顺序是先父后子pbd=getMergedBeanDefinition(parentBeanName);
}
else{
if(getParentBeanFactory()instanceofConfigurableBeanFactory){//如果相等,则从父工厂中获取pbd=((ConfigurableBeanFactory)getParentBeanFactory()).getMergedBeanDefinition(parentBeanName);
}
else{
thrownewNoSuchBeanDefinitionException(bd.getParentName(),
"Parentname'"+bd.getParentName()+"'isequaltobeanname'"+beanName+"':cannotberesolvedwithoutanAbstractBeanFactoryparent");
}}}
catch(NoSuchBeanDefinitionExceptionex){
thrownewBeanDefinitionStoreException(bd.getResourceDescription(),beanName,
"Couldnotresolveparentbeandefinition'"+bd.getParentName()+"'",ex);
}//进行深度复制mbd=newRootBeanDefinition(pbd);
//用子的BeanDefinition覆盖父亲的mbd.overrideFrom(bd);
}
if(containingBd!=null&&!containingBd.isSingleton()&&mbd.isSingleton()){
//如果包含bean存在,且包含Bean不是单例的(也就是意味着是原型的),而当前bean却是单例的,那么当前bean的scope应与包含bean的一致。mbd.setScope(containingBd.getScope());
}
if(containingBd==null&&isCacheBeanMetadata()&&isBeanEligibleForMetadataCaching(beanName)){
this.mergedBeanDefinitions.put(beanName,mbd);//置入缓存}}
returnmbd;
}}
3.1.1.2 getObjectFromFactoryBean方法分析
//主要是从FactoryBean获得object
protectedObjectgetObjectFromFactoryBean(FactoryBeanfactory,StringbeanName,booleanshouldPostProcess){
if(factory.isSingleton()&&containsSingleton(beanName)){
//如果facoryBean是单例的话,需要维护factoryBean与object的关系。我们在这里整理一下几个缓存的关系
//<1>factoryBeanObjectCache里存在的一定是由FactoryBean所创建的bean,其对应关系为beanName-->bean实例;
synchronized(getSingletonMutex()){
Objectobject=this.factoryBeanObjectCache.get(beanName);
if(object==null){
//这里通过调用factory.getObject()获取对象object=doGetObjectFromFactoryBean(factory,beanName,shouldPostProcess);
this.factoryBeanObjectCache.put(beanName,(object!=null?object:NULL_OBJECT));
}return(object!=NULL_OBJECT?object:null);
}}
else{
returndoGetObjectFromFactoryBean(factory,beanName,shouldPostProcess);
}}
3.1.2 getSingleton方法分析
publicObjectgetSingleton(StringbeanName,ObjectFactorysingletonFactory){
synchronized(this.singletonObjects){
ObjectsingletonObject=this.singletonObjects.get(beanName);
if(singletonObject==null){
if(this.singletonsCurrentlyInDestruction){
//如果当前工厂的单例缓存处于销毁状态,抛出异常thrownewBeanCreationNotAllowedException(beanName,
"Singletonbeancreationnotallowedwhilethesingletonsofthisfactoryareindestruction"+"(DonotrequestabeanfromaBeanFactoryinadestroymethodimplementation!)");
}//把beanName加入到正在创建状态队列中,用以标识beanName正在创建中beforeSingletonCreation(beanName);
booleanrecordSuppressedExceptions=(this.suppressedExceptions==null);
if(recordSuppressedExceptions){
this.suppressedExceptions=newLinkedHashSet();
}
try{
//这里将要调用creatBean方法singletonObject=singletonFactory.getObject();
}
catch(BeanCreationExceptionex){
if(recordSuppressedExceptions){
for(Iteratorit=this.suppressedExceptions.iterator();it.hasNext();){
ex.addRelatedCause((Exception)it.next());
}}throwex;
}
finally{
if(recordSuppressedExceptions){
this.suppressedExceptions=null;
}//把beanName从正在创建队列中删除afterSingletonCreation(beanName);}addSingleton(beanName,singletonObject);
}return(singletonObject!=NULL_OBJECT?singletonObject:null);
}}
3.1.3 createBean方法分析
protectedObjectcreateBean(finalStringbeanName,finalRootBeanDefinitionmbd,finalObject[]args)
throwsBeanCreationException{
AccessControlContextacc=AccessController.getContext();
returnAccessController.doPrivileged(newPrivilegedAction(){
publicObjectrun(){
//检查BeanDefinition中的beanClass是否存在,如果不存在则通过工具类对className处理获得resolveBeanClass(mbd,beanName);
//Preparemethodoverrides.
//预处理方法的overload情况(对应lookup-method、replaced-method元素),如果方法在当前beanClass上实现的数量、在beanClass实现的接口声明的数量、在beanClass超类上声明或实现的数量相加的和等于1,那么将overload设为false。如果对lookup-method不熟悉请参看后面的lookup-method使用示例。
//
try{
mbd.prepareMethodOverrides();
}
catch(BeanDefinitionValidationExceptionex){
……
}
try{
//GiveBeanPostProcessorsachancetoreturnaproxyinsteadofthetargetbeaninstance.
//如果bean配置了PostProcessor,那么这里返回的是一个proxyObjectbean=resolveBeforeInstantiation(beanName,mbd);
if(bean!=null){
returnbean;
}}
catch(Throwableex){
thrownewBeanCreationException(mbd.getResourceDescription(),beanName,
"BeanPostProcessorbeforeinstantiationofbeanfailed",ex);
}//所有生成Bean都有BeanWrapper封装,bean的生成采用策略模式,CglibSubclassingInstantiationStrategy实现是默认的策略
//1.如果配置为工厂方法创建(配置了factory-mother的),由java反射Mehthod的invoke完成bean的创建。
//2.如果采用构造子配置创建(配置了constructor-arg的),如果bean对应的类包含多个构造子,采用cglib动态字节码构造;如果只有唯一的构造子,那么采用java反射Constructor的newInstance方法
//3.如果是普通bean配置,直接通过反射Class默认的Constructor,然后调用newInstance获得bean.ObjectbeanInstance=doCreateBean(beanName,mbd,args);
if(logger.isDebugEnabled()){
logger.debug("Finishedcreatinginstanceofbean'"+beanName+"'");
}returnbeanInstance;
}},acc);
}
3.1.3.1 doCreateBean方法分析
protectedObjectdoCreateBean(finalStringbeanName,finalRootBeanDefinitionmbd,finalObject[]args){
//Instantiatethebean.BeanWrapperinstanceWrapper=null;
if(mbd.isSingleton()){//如果是singleton类型的,先删除factoryBeaninstanceWrapper=(BeanWrapper)this.factoryBeanInstanceCache.remove(beanName);
}
if(instanceWrapper==null){
//所有生成Bean都有BeanWrapper封装,bean的生成采用策略模式,CglibSubclassingInstantiationStrategy实现是默认的策略
//1.如果配置为工厂方法创建(配置了factory-mother的),由java反射Mehthod的invoke完成bean的创建。
//2.如果采用构造子配置创建(配置了constructor-arg的),如果bean对应的类包含多个构造子,采用cglib动态字节码构造;如果只有唯一的构造子,那么采用java反射Constructor的newInstance方法
//3.如果是普通bean配置,直接通过反射Class默认的Constructor,然后调用newInstance获得bean.instanceWrapper=createBeanInstance(beanName,mbd,args);
}finalObjectbean=(instanceWrapper!=null?instanceWrapper.getWrappedInstance():null);
ClassbeanType=(instanceWrapper!=null?instanceWrapper.getWrappedClass():null);
//Allowpost-processorstomodifythemergedbeandefinition.
synchronized(mbd.postProcessingLock){
if(!mbd.postProcessed){
applyMergedBeanDefinitionPostProcessors(mbd,beanType,beanName);
mbd.postProcessed=true;
}}
booleanearlySingletonExposure=(mbd.isSingleton()&&this.allowCircularReferences&&isSingletonCurrentlyInCreation(beanName));
if(earlySingletonExposure){
if(logger.isDebugEnabled()){
logger.debug("Eagerlycachingbean'"+beanName+"'toallowforresolvingpotentialcircularreferences");
}
addSingletonFactory(beanName,newObjectFactory(){
publicObjectgetObject()throwsBeansException{
returngetEarlyBeanReference(beanName,mbd,bean);
}});
}
//Initializethebeaninstance.ObjectexposedObject=bean;
try{
populateBean(beanName,mbd,instanceWrapper);
exposedObject=initializeBean(beanName,exposedObject,mbd);
}
catch(Throwableex){
if(exinstanceofBeanCreationException&&beanName.equals(((BeanCreationException)ex).getBeanName())){
throw(BeanCreationException)ex;
}
else{
thrownewBeanCreationException(mbd.getResourceDescription(),beanName,"Initializationofbeanfailed",ex);
}}
if(earlySingletonExposure){
ObjectearlySingletonReference=getSingleton(beanName,false);
if(earlySingletonReference!=null){
if(exposedObject==bean){
exposedObject=earlySingletonReference;
}
elseif(!this.allowRawInjectionDespiteWrapping&&hasDependentBean(beanName)){
String[]dependentBeans=getDependentBeans(beanName);
SetactualDependentBeans=newLinkedHashSet(dependentBeans.length);
for(inti=0;i{
StringdependentBean=dependentBeans[i];
if(!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)){
actualDependentBeans.add(dependentBean);
}}
if(!actualDependentBeans.isEmpty()){
thrownewBeanCurrentlyInCreationException(beanName,
"Beanwithname'"+beanName+"'hasbeeninjectedintootherbeans["+StringUtils.collectionToCommaDelimitedString(actualDependentBeans)+"]initsrawversionaspartofacircularreference,buthaseventuallybeen"+"wrapped.Thismeansthatsaidotherbeansdonotusethefinalversionofthe"+"bean.Thisisoftentheresultofover-eagertypematching-considerusing"+"'getBeanNamesOfType'withthe'allowEagerInit'flagturnedoff,forexample.");
}}}}
//Registerbeanasdisposable.registerDisposableBeanIfNecessary(beanName,bean,mbd);
returnexposedObject;
}
posted on -01-30 16:04 zhangxl 阅读(3197) 评论(0) 编辑 收藏 所属分类: Spring