spring源码分析之——spring scope的实现原理
大家都知道spring中的bean是有生命周期的，比如:singleton,prototype,session,request,globalsession.
那么这些生命周期是如何实现的呢？
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继续前面章节的分析，回到AbstractBeanFactory中对bean的获取代码上面来：
private <T> T doGetBean(final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)throws BeansException {final String beanName = transformedBeanName(name);Object bean;// Eagerly check singleton cache for manually registered singletons.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 + "'");}}bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);}else {// Fail if we're already creating this bean instance:// We're assumably within a circular reference.if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);}// Check if bean definition exists in this factory.BeanFactory parentBeanFactory = getParentBeanFactory();if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {// Not found -> check parent.String nameToLookup = originalBeanName(name);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);}final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);checkMergedBeanDefinition(mbd, beanName, args);// Guarantee initialization of beans that the current bean depends on.String[] dependsOn = mbd.getDependsOn();if (dependsOn != null) {for (String dependsOnBean : dependsOn) {getBean(dependsOnBean);registerDependentBean(dependsOnBean, beanName);}}// Create bean instance.if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, new ObjectFactory() {public Object getObject() throws BeansException {try {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;}}});bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);}else if (mbd.isPrototype()) {// It's a prototype -> create a new instance.Object prototypeInstance = null;try {beforePrototypeCreation(beanName);prototypeInstance = createBean(beanName, mbd, args);}finally {afterPrototypeCreation(beanName);}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 '" + scopeName + "'");}try {Object scopedInstance = scope.get(beanName, new ObjectFactory() {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);}}}// Check if required type matches the type of the actual bean instance.if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());}return (T) bean;}?? 可见，当bean的scope是prototype的时候，直接创建一个新object.这个object用完自然也就回收了，没啥好说的。
??????????? 当bean的scope是singleton的时候，在DefaultSingletonBeanRegistry下面有一个map负责维护singleton?? bean的缓存。生命周期就是容器的生命周期。
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? 最后到了非prototype，非singleton的情况。
? 这种情况下需要从scope里面获取。
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?? 在当前线程下面有一个绑定的RequestAttributes，scope就是通过这个RequestAttributes来获取维护的bean的信息。查看一下这个接口的实现类：ServletRequestAttributes，里面的getAttribute方法实现了对bean的获取：
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public Object getAttribute(String name, int scope) {if (scope == SCOPE_REQUEST) {if (!isRequestActive()) {throw new IllegalStateException("Cannot ask for request attribute - request is not active anymore!");}return this.request.getAttribute(name);}else {HttpSession session = getSession(false);if (session != null) {try {Object value = session.getAttribute(name);if (value != null) {synchronized (this.sessionAttributesToUpdate) {this.sessionAttributesToUpdate.put(name, value);}}return value;}catch (IllegalStateException ex) {// Session invalidated - shouldn't usually happen.}}return null;}}??? 可见，当scope是requestscope的时候，bean建立之后放在request里面，需要时取出。
???????????? 当scopde是sessionscope/globalsessionscope的时候，bean建立之后放在session/globalsession里面，需要时取出。
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