Spring源码追踪3——AOP机制

研究代码：

spring配置文件

<cache:annotation-driven />

Java代码

@Cacheable(value = "test", key = "#city")
public Map load(String city) {}

【cache:annotation-driven机制】

本来以为会有遍历package找类的代码（mybatis那个应该是这么干的），不过实际上只有这个。

org.springframework.cache.config.AnnotationDrivenCacheBeanDefinitionParser#parse

    public BeanDefinition parse(Element element, ParserContext parserContext) {
        String mode = element.getAttribute("mode");
        if ("aspectj".equals(mode)) {
            // mode="aspectj"
            registerCacheAspect(element, parserContext);
        }
        else {
            // mode="proxy"
            registerCacheAdvisor(element, parserContext);
        }

        return null;
    }

姑且不管aspectj，正常是走proxy模式，注册Advisor。

【拦截机制】

执行方法时通过代理执行。

org.springframework.aop.framework.JdkDynamicAopProxy#invoke

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        MethodInvocation invocation;
        Object oldProxy = null;
        boolean setProxyContext = false;

        TargetSource targetSource = this.advised.targetSource;
        Class<?> targetClass = null;
        Object target = null;

        try {
            if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
                // The target does not implement the equals(Object) method itself.
                return equals(args[0]);
            }
            if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
                // The target does not implement the hashCode() method itself.
                return hashCode();
            }
            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;

            if (this.advised.exposeProxy) {
                // Make invocation available if necessary.
                oldProxy = AopContext.setCurrentProxy(proxy);
                setProxyContext = true;
            }

            // May be null. Get as late as possible to minimize the time we "own" the target,
            // in case it comes from a pool.
            target = targetSource.getTarget();
            if (target != null) {
                targetClass = target.getClass();
            }

            // Get the interception chain for this method.
            List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

            // Check whether we have any advice. If we don't, we can fallback on direct
            // reflective invocation of the target, and avoid creating a MethodInvocation.
            if (chain.isEmpty()) {
                // We can skip creating a MethodInvocation: just invoke the target directly
                // Note that the final invoker must be an InvokerInterceptor so we know it does
                // nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
                retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);
            }
            else {
                // We need to create a method invocation...
                invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
                // Proceed to the joinpoint through the interceptor chain.
                retVal = invocation.proceed();
            }

            // Massage return value if necessary.
            Class<?> returnType = method.getReturnType();
            if (retVal != null && retVal == target && returnType.isInstance(proxy) &&
                    !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
                // Special case: it returned "this" and the return type of the method
                // is type-compatible. Note that we can't help if the target sets
                // a reference to itself in another returned object.
                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()) {
                // Must have come from TargetSource.
                targetSource.releaseTarget(target);
            }
            if (setProxyContext) {
                // Restore old proxy.
                AopContext.setCurrentProxy(oldProxy);
            }
        }
    }

通过getInterceptorsAndDynamicInterceptionAdvice获取生效的Interceptor，中间走了个缓存，此处忽略。

org.springframework.aop.framework.DefaultAdvisorChainFactory#getInterceptorsAndDynamicInterceptionAdvice

    public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
            Advised config, Method method, Class<?> targetClass) {

        // This is somewhat tricky... We have to process introductions first,
        // but we need to preserve order in the ultimate list.
        List<Object> interceptorList = new ArrayList<Object>(config.getAdvisors().length);
        Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
        boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
        AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();

        for (Advisor advisor : config.getAdvisors()) { // 遍历注册的Advisor
            if (advisor instanceof PointcutAdvisor) {
                // Add it conditionally.
                PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
                if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
                    MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
                    MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
                    if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) { // 判断方法是否适用Advisor
                        if (mm.isRuntime()) {
                            // Creating a new object instance in the getInterceptors() method
                            // isn't a problem as we normally cache created chains.
                            for (MethodInterceptor interceptor : interceptors) {
                                interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
                            }
                        }
                        else {
                            interceptorList.addAll(Arrays.asList(interceptors));
                        }
                    }
                }
            }
            else if (advisor instanceof IntroductionAdvisor) {
                IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
                if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
                    Interceptor[] interceptors = registry.getInterceptors(advisor);
                    interceptorList.addAll(Arrays.asList(interceptors));
                }
            }
            else {
                Interceptor[] interceptors = registry.getInterceptors(advisor);
                interceptorList.addAll(Arrays.asList(interceptors));
            }
        }

        return interceptorList;
    }

最终解析annotation。

spring cache：org.springframework.cache.annotation.AnnotationCacheOperationSource#determineCacheOperations

    protected Collection<CacheOperation> determineCacheOperations(AnnotatedElement ae) {
        Collection<CacheOperation> ops = null;
        for (CacheAnnotationParser annotationParser : this.annotationParsers) {
            Collection<CacheOperation> annOps = annotationParser.parseCacheAnnotations(ae);
            if (annOps != null) {
                if (ops == null) {
                    ops = new ArrayList<CacheOperation>();
                }
                ops.addAll(annOps);
            }
        }
        return ops;
    }

【advisor的注册】

在spring完成bean创建时经过AbstractAutoProxyCreator类：

org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#wrapIfNecessary

    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
            return bean;
        }
        if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
            return bean;
        }
        if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
            this.advisedBeans.put(cacheKey, Boolean.FALSE);
            return bean;
        }

        // Create proxy if we have advice.
        Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
        if (specificInterceptors != DO_NOT_PROXY) {
            this.advisedBeans.put(cacheKey, Boolean.TRUE);
            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;
    }

获取specificInterceptors：

org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator#findEligibleAdvisors

    protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
        List<Advisor> candidateAdvisors = findCandidateAdvisors(); // 获取候选advisors
        List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName); // 过滤出可用的advisors
        extendAdvisors(eligibleAdvisors);
        if (!eligibleAdvisors.isEmpty()) {
            eligibleAdvisors = sortAdvisors(eligibleAdvisors);
        }
        return eligibleAdvisors;
    }

org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator#findAdvisorsThatCanApply

    protected List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {

        ProxyCreationContext.setCurrentProxiedBeanName(beanName);

        try {
            return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
        }
        finally {
            ProxyCreationContext.setCurrentProxiedBeanName(null);
        }
    }

org.springframework.aop.framework.autoproxy.ProxyCreationContext#setCurrentProxiedBeanName

    static void setCurrentProxiedBeanName(String beanName) {
        if (beanName != null) {
            currentProxiedBeanName.set(beanName); // ThreadLocal
        } else {
            currentProxiedBeanName.remove();
        }
    }

org.springframework.aop.support.AopUtils#canApply(org.springframework.aop.Advisor, java.lang.Class<?>, boolean)

    public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
        if (advisor instanceof IntroductionAdvisor) {
            return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
        }
        else if (advisor instanceof PointcutAdvisor) {
            PointcutAdvisor pca = (PointcutAdvisor) advisor;
            return canApply(pca.getPointcut(), targetClass, hasIntroductions);
        }
        else {
            // It doesn't have a pointcut so we assume it applies.
            return true;
        }
    }

org.springframework.aop.support.AopUtils#canApply(org.springframework.aop.Pointcut, java.lang.Class<?>, boolean)

    public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
        Assert.notNull(pc, "Pointcut must not be null");
        if (!pc.getClassFilter().matches(targetClass)) {
            return false;
        }

        MethodMatcher methodMatcher = pc.getMethodMatcher();
        IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
        if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
            introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
        }

        Set<Class<?>> classes = new HashSet<Class<?>>(ClassUtils.getAllInterfacesForClassAsSet(targetClass)); // 获取目标类和所有父类
        classes.add(targetClass);
        for (Class<?> clazz : classes) {
            Method[] methods = clazz.getMethods();
            for (Method method : methods) { // 遍历方法如果有满足的则返回true
                if ((introductionAwareMethodMatcher != null &&
                        introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) ||
                        methodMatcher.matches(method, targetClass)) {
                    return true;
                }
            }
        }

        return false;
    }

常用methodMatcher：

1. org.springframework.transaction.interceptor.TransactionAttributeSourcePointcut 事务

2. org.springframework.aop.aspectj.AspectJExpressionPointcut aspectj表达式

创建代理：

org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#createProxy

    protected Object createProxy(Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {

        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.copyFrom(this);

        if (!proxyFactory.isProxyTargetClass()) {
            if (shouldProxyTargetClass(beanClass, beanName)) {
                proxyFactory.setProxyTargetClass(true);
            }
            else {
                evaluateProxyInterfaces(beanClass, proxyFactory);
            }
        }

        Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
        for (Advisor advisor : advisors) {
            proxyFactory.addAdvisor(advisor);
        }

        proxyFactory.setTargetSource(targetSource);
        customizeProxyFactory(proxyFactory);

        proxyFactory.setFrozen(this.freezeProxy);
        if (advisorsPreFiltered()) {
            proxyFactory.setPreFiltered(true);
        }

        return proxyFactory.getProxy(getProxyClassLoader());
    }