Spring注解@Scope---SessionScope和RequestScope

前言

前两天分析了一波@ComponentScan注解各属性作用，通过源码看到根据类上的@Scope注解为BeanDefinition设置了ScopedProxyMode属性，并对BeanDefinition进行代理操作。大概就是如果这个BeanDefinition有@Scope，就会new一个BeanDefinition将原先的BeanDefition替换，具体看上篇文吧。注意新创建的BeanDefinition的beanClass是ScopedProxyFactoryBean，是一个FactoryBean相关代码如下

// 创建一个新的BeanDefition来作为代理的beanDefition,把原先的对象作为成员设置进去RootBeanDefinition proxyDefinition = new RootBeanDefinition(ScopedProxyFactoryBean.class);proxyDefinition.setDecoratedDefinition(new BeanDefinitionHolder(targetDefinition, targetBeanName));proxyDefinition.setOriginatingBeanDefinition(targetDefinition);

Scope常见的在Web应用中有session、request、application，还有cloud里边的@RefreshScope等。

一个一个来吧，以后碰到哪个分析完再接到这篇上。

@SessionScope和@RequestScope

每个Session或每个Request创建一个对象

先来看获取Bean对象的代码

org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean

                // 不相关代码都删了if (mbd.isSingleton()) {// 获取单例bean实例}else if (mbd.isPrototype()) {// 获取原型模式实例}else {// 获取BeanDefinition的scope，即session\requestString scopeName = mbd.getScope();// 这个集合中保存了这个字符串“session”对应的哪个Scope对象，用这个Scope对象来进行创建操作Scope scope = this.scopes.get(scopeName);if (scope == null) {throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");}try {// 获取被代理过的BeanDefition对应的FactoryBean对象// 先进去看看对应Scope对象的get操作是什么// createBean方法不用看了，就是根据bean定义创建实例，以前看过，这里不是目标就略过，知道这当作一个参数传进scope.get就可以了Object scopedInstance = scope.get(beanName, () -> {beforePrototypeCreation(beanName);try {return createBean(beanName, mbd, args);}finally {afterPrototypeCreation(beanName);}});// FactoryBean.getObject来获取真正的bean实例bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);}catch (IllegalStateException ex) {// 报异常}

beanFactory中的this.scopes集合怎么来的呢

在AbstractApplicationContext的refresh方法的postProcessBeanFactory()这一步添加的，AbstractApplicationContext这里只是模板方法，具体实现在Web容器的实现类AnnotationConfigServletWebServerApplicationContext#postProcessBeanFactory

 @Overrideprotected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {super.postProcessBeanFactory(beanFactory);if (this.basePackages != null && this.basePackages.length > 0) {this.scanner.scan(this.basePackages);}if (!this.annotatedClasses.isEmpty()) {this.reader.register(ClassUtils.toClassArray(this.annotatedClasses));}}

父类方法org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext#postProcessBeanFactory

 protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {beanFactory.addBeanPostProcessor(new WebApplicationContextServletContextAwareProcessor(this));beanFactory.ignoreDependencyInterface(ServletContextAware.class);registerWebApplicationScopes();}private void registerWebApplicationScopes() {ExistingWebApplicationScopes existingScopes = new ExistingWebApplicationScopes(getBeanFactory());WebApplicationContextUtils.registerWebApplicationScopes(getBeanFactory());existingScopes.restore();}// 直接跟到WebApplicationContextUtils.registerWebApplicationScopes(getBeanFactory());public static void registerWebApplicationScopes(ConfigurableListableBeanFactory beanFactory,@Nullable ServletContext sc) {beanFactory.registerScope(WebApplicationContext.SCOPE_REQUEST, new RequestScope());beanFactory.registerScope(WebApplicationContext.SCOPE_SESSION, new SessionScope());
}

那此时beanFactory有了session和request的Scope对象，来看SessionScope的get方法

org.springframework.web.context.request.SessionScope#get

@Overridepublic Object get(String name, ObjectFactory<?> objectFactory) {Object mutex = RequestContextHolder.currentRequestAttributes().getSessionMutex();synchronized (mutex) {return super.get(name, objectFactory);}}// 进父类@Overridepublic Object get(String name, ObjectFactory<?> objectFactory) {// 从ThreadLocal变量中获取当前request的属性对象RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();// 从属性中根据bean名获取bean对象Object scopedObject = attributes.getAttribute(name, getScope());if (scopedObject == null) {// 如果没有会调用CreateBean方法新建一个，并设置到当前请求上下文属性中scopedObject = objectFactory.getObject();attributes.setAttribute(name, scopedObject, getScope());// Retrieve object again, registering it for implicit session attribute updates.// As a bonus, we also allow for potential decoration at the getAttribute level.Object retrievedObject = attributes.getAttribute(name, getScope());if (retrievedObject != null) {// Only proceed with retrieved object if still present (the expected case).// If it disappeared concurrently, we return our locally created instance.scopedObject = retrievedObject;}}return scopedObject;}

跟进去再看看RequestAttributes这个请求属性对象哪来的

public abstract class RequestContextHolder  {private static final ThreadLocal<RequestAttributes> requestAttributesHolder =new NamedThreadLocal<>("Request attributes");private static final ThreadLocal<RequestAttributes> inheritableRequestAttributesHolder =new NamedInheritableThreadLocal<>("Request context");public static RequestAttributes getRequestAttributes() {RequestAttributes attributes = requestAttributesHolder.get();if (attributes == null) {attributes = inheritableRequestAttributesHolder.get();}return attributes;}
}

从请求对象RequestAttribute中根据beanName获取实例代码

 @Overridepublic Object getAttribute(String name, int scope) {// scope是requestif (scope == SCOPE_REQUEST) {// 如果请求已经处理完毕，判断了一个boolean值，下边有介绍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) {this.sessionAttributesToUpdate.put(name, value);}return value;}catch (IllegalStateException ex) {// Session invalidated - shouldn't usually happen.}}return null;}}

好家伙，又来新知识了，这个RequestAttribute对象很关键，从线程ThreadLocal变量获取的，这可以理解，一个请求一个线程来处理嘛，那这个对象啥时候被设置进去的呢。思考了下，估计是DispatchServlet接受请求分发的时候处理，我们继续跟代码

DispatchServlet那肯定先看service()，先走爷爷类HttpServlet#service，这里没有，再看父类FrameworkServlet#service，有了

org.springframework.web.servlet.FrameworkServlet#service

 @Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());if (httpMethod == HttpMethod.PATCH || httpMethod == null) {// 这里processRequest(request, response);}else {super.service(request, response);}}protected final void processRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// 忽略了无关代码// 获取原先的RequestAttributeRequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();// new一个新的ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);// 设置到RequestContextHolder的ThreadLocal中initContextHolders(request, localeContext, requestAttributes);// diService()执行try {doService(request, response);}catch (ServletException | IOException ex) {failureCause = ex;throw ex;}catch (Throwable ex) {failureCause = ex;throw new NestedServletException("Request processing failed", ex);}finally {// 重新设置回原来的resetContextHolders(request, previousLocaleContext, previousAttributes);if (requestAttributes != null) {// 请求处理完毕，把刚才new的那个requestAttributes请求标志置为完成// 上边判断请求是否存活isRequestActive()，就是跟这个有关requestAttributes.requestCompleted();}logResult(request, response, failureCause, asyncManager);publishRequestHandledEvent(request, response, startTime, failureCause);}}protected ServletRequestAttributes buildRequestAttributes(HttpServletRequest request,@Nullable HttpServletResponse response, @Nullable RequestAttributes previousAttributes) {if (previousAttributes == null || previousAttributes instanceof ServletRequestAttributes) {// 实际上RequestAttributes对象是一个ServletRequestAttributes对象// 绑定了request和responsereturn new ServletRequestAttributes(request, response);}else {return null;  // preserve the pre-bound RequestAttributes instance}}// 把ServletRequestAttributes 设置到当前的ThreadLocal变量中private void initContextHolders(HttpServletRequest request,@Nullable LocaleContext localeContext, @Nullable RequestAttributes requestAttributes) {if (localeContext != null) {LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);}if (requestAttributes != null) {RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);}}

看到这，这个BeanDefinition对应的bean实例化出来了，那开篇说过，有@Scope注解的beanDefinition是被狸猫换太子的，是一个FactoryBean（ScopedProxyFactoryBean），还得继续看ScopedProxyFactoryBean.getObject()

ScopedProxyFactoryBean实现了BeanFactoryAware，setBeanFactory方法执行的时候创建的代理对象，getObject返回代理对象。

怎么代理的就先不管了，单写一篇学习代理。代理对象的方法拦截器DynamicAdvisedInterceptor中会再getBean()从beanFactory获取最初的beanDefinition的对象进行invoke，最初的beanDefinition也是个scope类型，跟上边的ScopedProxyFactoryBean实例化走一个路子。

public class ScopedProxyFactoryBean extends ProxyConfigimplements FactoryBean<Object>, BeanFactoryAware, AopInfrastructureBean {@Overridepublic void setBeanFactory(BeanFactory beanFactory) {if (!(beanFactory instanceof ConfigurableBeanFactory)) {throw new IllegalStateException("Not running in a ConfigurableBeanFactory: " + beanFactory);}ConfigurableBeanFactory cbf = (ConfigurableBeanFactory) beanFactory;this.scopedTargetSource.setBeanFactory(beanFactory);ProxyFactory pf = new ProxyFactory();pf.copyFrom(this);pf.setTargetSource(this.scopedTargetSource);Assert.notNull(this.targetBeanName, "Property 'targetBeanName' is required");Class<?> beanType = beanFactory.getType(this.targetBeanName);if (beanType == null) {throw new IllegalStateException("Cannot create scoped proxy for bean '" + this.targetBeanName +"': Target type could not be determined at the time of proxy creation.");}if (!isProxyTargetClass() || beanType.isInterface() || Modifier.isPrivate(beanType.getModifiers())) {pf.setInterfaces(ClassUtils.getAllInterfacesForClass(beanType, cbf.getBeanClassLoader()));}// Add an introduction that implements only the methods on ScopedObject.ScopedObject scopedObject = new DefaultScopedObject(cbf, this.scopedTargetSource.getTargetBeanName());pf.addAdvice(new DelegatingIntroductionInterceptor(scopedObject));// Add the AopInfrastructureBean marker to indicate that the scoped proxy// itself is not subject to auto-proxying! Only its target bean is.pf.addInterface(AopInfrastructureBean.class);this.proxy = pf.getProxy(cbf.getBeanClassLoader());}@Overridepublic Object getObject() {if (this.proxy == null) {throw new FactoryBeanNotInitializedException();}return this.proxy;}}

到这基本就完事了，总结：

1、每次请求上来将新建一个ServletRequestAttribute对象绑定request和response，并注册到RequestContextHolder类中的ThreadLocal变量上

2、在Web容器refresh方法，ServletWebServerApplicationContext#postProcessBeanFactory中注册工具类SessionScope和RequestScope用来实例化bean时调用

3、解析beanDefinition时，@SessionScope或@RequestScope注解的beanDefinition的Scope属性设置为request或session，并且原先的beanDefinition已经被替换（ScopedProxyFactoryBean）

4、doGetBean获取Scope属性为request或session类型的bean类实例时使用SessionScope.get(beanName, ObjectFactory)或RequestScope.get(beanName, ObjectFactory)来获取，先获取这个ServletRequestAttribute对象，如果这对象中对应的HttpServletRequest或request对应的Session没有这个bean实例，再调用ObjectFactory.getObject()方法创建，getObject()具体工作是由AbstractBeanFactory#createBean来创建

5、上一步创建的东西只是ScopedProxyFactoryBean，FactoryBean.getObject() 获取代理对象，代理对象拦截器方法中再getBean()获取真正的bean对象执行操作

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Spring注解@Scope---SessionScope和RequestScope

前言

@SessionScope和@RequestScope

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