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基于注解的SpringAOP源码解析（三）

技术 2022年11月10日
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注意，读完本篇文章需要很长很长时间

在之前的2篇文章：AOP源码分析（一）AOP源码分析（二）

中，我们搭建了SpringAOP源码分析的环境，介绍了@EnableAspectJAutoProxy注解和postProcessBeforeInstantiation方法是如何加载所有增强的。本篇文章则将描述一下AOP中剩余的实现逻辑

postProcessAfterInitialization

这个方法是在bean实例化之后调用的，它是适用于所有需要被代理的类的

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean != null) {
            Object cacheKey = getCacheKey(bean.getClass(), beanName);
            if (!this.earlyProxyReferences.contains(cacheKey)) {
            //往下看
                return wrapIfNecessary(bean, beanName, cacheKey);
            }
        }
        return bean;
    }    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
    //如果已经处理过
        if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
            return bean;
        }
        //如果当前类是增强类
        if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
            return bean;
        }
        //查看类是否是基础设施类，或者是否被排除
        if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
            this.advisedBeans.put(cacheKey, Boolean.FALSE);
            return bean;
        }        //校验此类是否应该被代理，获取这个类的增强
        Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
        //如果获取到了增强则需要针对增强创建代理
        if (specificInterceptors != DO_NOT_PROXY) {
            this.advisedBeans.put(cacheKey, Boolean.TRUE);
            //创建代理
            Object proxy = createProxy(
                    bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
            this.proxyTypes.put(cacheKey, proxy.getClass());
            return proxy;
        }        this.advisedBeans.put(cacheKey, Boolean.FALSE);
        return bean;
    }

上方这段代理一共有两个重点，getAdvicesAndAdvisorsForBean和createProxy这两个方法。

获取增强
    protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource) {
    //往下看
        List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
        if (advisors.isEmpty()) {
            return DO_NOT_PROXY;
        }
        return advisors.toArray();
    }    protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
        //获取容器中的所有增强
        List<Advisor> candidateAdvisors = findCandidateAdvisors();
        //验证beanClass是否该被代理，如果应该，则返回适用于这个bean的增强
        List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
        extendAdvisors(eligibleAdvisors);
        if (!eligibleAdvisors.isEmpty()) {
            eligibleAdvisors = sortAdvisors(eligibleAdvisors);
        }
        return eligibleAdvisors;
    }

上方这个获取增强又分成了2部分，获取全部和根据全部处理bean相关的

获取全部增强
protected List<Advisor> findCandidateAdvisors() {
// 调用父类的方法加载配置文件中的AOP声明（注解与XML都存在的时候）
List<Advisor> advisors = super.findCandidateAdvisors();
        //往下看
        if (this.aspectJAdvisorsBuilder != null) {
advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
}
return advisors;
}

下面的方法就是获取所有的增强的代码实现了，方法比较长，不过主要逻辑很少

  1. 获取所有beanName
  2. 找出所有标记Aspect注解的类
  3. 对标记Aspect的类提取增强器
public List<Advisor> buildAspectJAdvisors() {
List<String> aspectNames = this.aspectBeanNames;if (aspectNames == null) {
synchronized (this) {
aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
List<Advisor> advisors = new LinkedList<>();
aspectNames = new LinkedList<>();
                    //获取所有的bean
String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Object.class, true, false);
for (String beanName : beanNames) {
                      //校验不合法的类，Spring的一个扩展点，可以从子类中做排除切面的操作
if (!isEligibleBean(beanName)) {
continue;
}
//获取bean的类型
Class<?> beanType = this.beanFactory.getType(beanName);
if (beanType == null) {
continue;
}
                        //是否带有Aspect注解
if (this.advisorFactory.isAspect(beanType)) {
aspectNames.add(beanName);
AspectMetadata amd = new AspectMetadata(beanType, beanName);
if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
MetadataAwareAspectInstanceFactory factory =
new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
                                        //解析所有的增强方法，下面说
List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
if (this.beanFactory.isSingleton(beanName)) {
this.advisorsCache.put(beanName, classAdvisors);
}
else {
this.aspectFactoryCache.put(beanName, factory);
}
advisors.addAll(classAdvisors);
}
else {
if (this.beanFactory.isSingleton(beanName)) {
throw new IllegalArgumentException("Bean with name '" + beanName +
"' is a singleton, but aspect instantiation model is not singleton");
}
MetadataAwareAspectInstanceFactory factory =
new PrototypeAspectInstanceFactory(this.beanFactory, beanName);
this.aspectFactoryCache.put(beanName, factory);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
}
this.aspectBeanNames = aspectNames;
return advisors;
}
}
}if (aspectNames.isEmpty()) {
return Collections.emptyList();
}
List<Advisor> advisors = new LinkedList<>();
for (String aspectName : aspectNames) {
List<Advisor> cachedAdvisors = this.advisorsCache.get(aspectName);
if (cachedAdvisors != null) {
advisors.addAll(cachedAdvisors);
}
else {
MetadataAwareAspectInstanceFactory factory = this.aspectFactoryCache.get(aspectName);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
return advisors;
}

接下来就是各个增强器的获取方法的实现

public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
        //获取所有Aspect类、类名称、并校验
Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
String aspectName = aspectInstanceFactory.getAspectMetadata().getAspectName();
validate(aspectClass);MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);List<Advisor> advisors = new LinkedList<>();
        //取出类的所有方法
for (Method method : getAdvisorMethods(aspectClass)) {
            //获取增强方法，往下看
Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);
if (advisor != null) {
advisors.add(advisor);
}
}// 如果需要增强且配置了延迟增强则在第一个位置添加同步实例化增强方法
if (!advisors.isEmpty() && lazySingletonAspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
Advisor instantiationAdvisor = new SyntheticInstantiationAdvisor(lazySingletonAspectInstanceFactory);
advisors.add(0, instantiationAdvisor);
}// 获取属性中配置DeclareParents注解的增强
for (Field field : aspectClass.getDeclaredFields()) {
Advisor advisor = getDeclareParentsAdvisor(field);
if (advisor != null) {
advisors.add(advisor);
}
}return advisors;
}

普通增强的获取

public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
int declarationOrderInAspect, String aspectName) {validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
        //获取切点
AspectJExpressionPointcut expressionPointcut = getPointcut(
candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
if (expressionPointcut == null) {
return null;
}
        //根据切点生成增强
return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}

上方代码又分为了两部分，先看一下切点信息的获取

public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {this.declaredPointcut = declaredPointcut;
this.declaringClass = aspectJAdviceMethod.getDeclaringClass();
this.methodName = aspectJAdviceMethod.getName();
this.parameterTypes = aspectJAdviceMethod.getParameterTypes();
this.aspectJAdviceMethod = aspectJAdviceMethod;
this.aspectJAdvisorFactory = aspectJAdvisorFactory;
this.aspectInstanceFactory = aspectInstanceFactory;
this.declarationOrder = declarationOrder;
this.aspectName = aspectName;if (aspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
Pointcut preInstantiationPointcut = Pointcuts.union(
aspectInstanceFactory.getAspectMetadata().getPerClausePointcut(), this.declaredPointcut);
this.pointcut = new PerTargetInstantiationModelPointcut(
this.declaredPointcut, preInstantiationPointcut, aspectInstanceFactory);
this.lazy = true;
}
else {
this.pointcut = this.declaredPointcut;
this.lazy = false;
            //初始化对应的增强器，重点
this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
}
}

到这里之后获取所有的增强这个流程就快要完毕了

private Advice instantiateAdvice(AspectJExpressionPointcut pointcut) {
        //往下看
Advice advice = this.aspectJAdvisorFactory.getAdvice(this.aspectJAdviceMethod, pointcut,
this.aspectInstanceFactory, this.declarationOrder, this.aspectName);
return (advice != null ? advice : EMPTY_ADVICE);
}public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {Class<?> candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
validate(candidateAspectClass);AspectJAnnotation<?> aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
if (aspectJAnnotation == null) {
return null;
}if (!isAspect(candidateAspectClass)) {
throw new AopConfigException("Advice must be declared inside an aspect type: " +
"Offending method '" + candidateAdviceMethod + "' in class [" +
candidateAspectClass.getName() + "]");
}if (logger.isDebugEnabled()) {
logger.debug("Found AspectJ method: " + candidateAdviceMethod);
}AbstractAspectJAdvice springAdvice;
        //根据不同的注解类型封装不同的增强器
switch (aspectJAnnotation.getAnnotationType()) {
case AtBefore:
springAdvice = new AspectJMethodBeforeAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtAfter:
springAdvice = new AspectJAfterAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtAfterReturning:
springAdvice = new AspectJAfterReturningAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
AfterReturning afterReturningAnnotation = (AfterReturning) aspectJAnnotation.getAnnotation();
if (StringUtils.hasText(afterReturningAnnotation.returning())) {
springAdvice.setReturningName(afterReturningAnnotation.returning());
}
break;
case AtAfterThrowing:
springAdvice = new AspectJAfterThrowingAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
AfterThrowing afterThrowingAnnotation = (AfterThrowing) aspectJAnnotation.getAnnotation();
if (StringUtils.hasText(afterThrowingAnnotation.throwing())) {
springAdvice.setThrowingName(afterThrowingAnnotation.throwing());
}
break;
case AtAround:
springAdvice = new AspectJAroundAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtPointcut:
if (logger.isDebugEnabled()) {
logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
}
return null;
default:
throw new UnsupportedOperationException(
"Unsupported advice type on method: " + candidateAdviceMethod);
}springAdvice.setAspectName(aspectName);
springAdvice.setDeclarationOrder(declarationOrder);
String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
if (argNames != null) {
springAdvice.setArgumentNamesFromStringArray(argNames);
}
springAdvice.calculateArgumentBindings();
return springAdvice;
}
获取匹配增强

经过上方的长篇大论，我们终于完成了所有的增强器的解析，还记得刚才的方法走到哪了么

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
    //获取全部增强
List<Advisor> candidateAdvisors = findCandidateAdvisors();
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}

接下来看看怎么为当前的Bean匹配自己的增强吧

protected List<Advisor> findAdvisorsThatCanApply(
List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {ProxyCreationContext.setCurrentProxiedBeanName(beanName);
try {
        //往下看
return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
}
finally {
ProxyCreationContext.setCurrentProxiedBeanName(null);
}
}    public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
        if (candidateAdvisors.isEmpty()) {
            return candidateAdvisors;
        }
        List<Advisor> eligibleAdvisors = new LinkedList<Advisor>();
        for (Advisor candidate : candidateAdvisors) {
            //处理引介增强，重点，再往下看
            if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
                eligibleAdvisors.add(candidate);
            }
        }
        boolean hasIntroductions = !eligibleAdvisors.isEmpty();
        for (Advisor candidate : candidateAdvisors) {
            if (candidate instanceof IntroductionAdvisor) {
                continue;
            }
            //对普通bean的处理
            if (canApply(candidate, clazz, hasIntroductions)) {
                eligibleAdvisors.add(candidate);
            }
        }
        return eligibleAdvisors;
    }

引介增强与普通bean的处理最后都是进的同一个方法，只不过是引介增强的第三个参数默认使用的false

    public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
        //如果存在排除的配置
        if (advisor instanceof IntroductionAdvisor) {
            return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
        }
        else if (advisor instanceof PointcutAdvisor) {
            PointcutAdvisor pca = (PointcutAdvisor) advisor;
            //往下看
            return canApply(pca.getPointcut(), targetClass, hasIntroductions);
        }
        else {
            return true;
        }
    }    public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
        Assert.notNull(pc, "Pointcut must not be null");
        //切点上是否存在排除类的配置
        if (!pc.getClassFilter().matches(targetClass)) {
            return false;
        }
        //验证注解的作用域是否可以作用于方法上
        MethodMatcher methodMatcher = pc.getMethodMatcher();
        if (methodMatcher == MethodMatcher.TRUE) {
            return true;
        }        IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
        if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
            introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
        }        Set<Class<?>> classes = new LinkedHashSet<Class<?>>(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
        classes.add(targetClass);
        for (Class<?> clazz : classes) {
            Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
            for (Method method : methods) {
                //获取类所实现的所有接口和所有类层级的方法，循环验证
                if ((introductionAwareMethodMatcher != null &&
                        introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) ||
                        methodMatcher.matches(method, targetClass)) {
                    return true;
                }
            }
        }        return false;
    }

现在所有的bean对应的增强都已经获取到了，那么就可以根据类的所有增强数组创建代理

创建代理

回到最上方开始获取增强的地方，当增强获取到之后就可以执行下面这个操作了

protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
@Nullable Object[] specificInterceptors, TargetSource targetSource) {if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}ProxyFactory proxyFactory = new ProxyFactory();
        使用proxyFactory对象copy当前类中的相关属性
proxyFactory.copyFrom(this);
        //判断是否使用Cglib动态代理
if (!proxyFactory.isProxyTargetClass()) {
          //如果配置开启使用则直接设置开启
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
            //如果没有配置开启则判断bean是否有合适的接口使用JDK的动态代理（JDK动态代理必须是带有接口的类，如果类没有实现任何接口则只能使用Cglib动态代理）
            //关于代理的基础知识可以参考我的另一篇文章：https://mp.weixin.qq.com/s/1DRmvuky5_NMRcH-toTLqQ
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
        //添加所有增强
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
proxyFactory.addAdvisors(advisors);
        //设置要代理的类
proxyFactory.setTargetSource(targetSource);
        //Spring的一个扩展点，默认实现为空。留给我们在需要对代理进行特殊操作的时候实现
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
        //使用代理工厂获取代理对象
return proxyFactory.getProxy(getProxyClassLoader());
}
获取代理对象
public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
return getAopProxyFactory().createAopProxy(this);
}
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
Class<?> targetClass = config.getTargetClass();
if (targetClass == null) {
throw new AopConfigException("TargetSource cannot determine target class: " +
"Either an interface or a target is required for proxy creation.");
}
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}
增强何时调用？

代理创建出来了，那么我们的前置增强、后置增强、环绕增强等是如何在代理中体现的呢，对代理模式还不熟悉的同学一定要先看一下这篇文章呦：https://mp.weixin.qq.com/s/1DRmvuky5_NMRcH-toTLqQ

这里就简单看一下JDK动态代理的实现吧

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
MethodInvocation invocation;
Object oldProxy = null;
boolean setProxyContext = false;TargetSource targetSource = this.advised.targetSource;
Object target = null;try {
            //equals方法处理
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
return equals(args[0]);
}
            //hash代码处理
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
return AopProxyUtils.ultimateTargetClass(this.advised);
}
else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
method.getDeclaringClass().isAssignableFrom(Advised.class)) {
// Service invocations on ProxyConfig with the proxy config...
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}Object retVal;
            //如果配置内部方法调用的增强
if (this.advised.exposeProxy) {
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);// 获取当前方法的拦截器链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);if (chain.isEmpty()) {
                //如果没有拦截器直接调用切点方法
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
                //执行拦截器链，重点，往下看
retVal = invocation.proceed();
}Class<?> returnType = method.getReturnType();
            //返回结果
if (retVal != null && retVal == target &&
returnType != Object.class && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
retVal = proxy;
}
else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
throw new AopInvocationException(
"Null return value from advice does not match primitive return type for: " + method);
}
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
targetSource.releaseTarget(target);
}
if (setProxyContext) {
AopContext.setCurrentProxy(oldProxy);
}
}
}

看完上方的代码，可以猜到，所有的增强都在这个拦截器里面了，那么这个拦截器又是如何实现的呢

public Object proceed() throws Throwable {
//执行完所有的增强后执行切点方法
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
        //获取下一个要执行的拦截器
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}

至此SpringAOP的源码解析已经完成

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