Spring AOP深入理解之拦截器调用

Spring AOP代理对象生成回顾

上一篇博客中：深入理解Spring AOP之二代理对象生成介绍了Spring代理对象是如何生成的，其中重点介绍了JDK动态代理方式，简单回顾下代理对象生成过程：

1、上面讲到了两种生成代理对象的方法，一种是通过ProxyFactory，一种是通过ProxyFactoryBean。第一种获取比较简单，但是需要手工的进行写代码，而第二种是通过Spring的IOC机制来控制Bean的生成。

2、无论是ProxyFactory或者ProxyFactoryBean都是要通过createAopProxy().getProxy()来获取相应的代理对象，而通过Proxyfactory比较直接，上面重点介绍的是通过ProxyFactoryBean获得proxy。

3、首先，找到ProxyFactoryBean的getObject方法，为什么？（主要是跟Bean容器中getObject能返回代理对象）

4、其次调用getSingletonInstance（），在getSingletonInstance方法中引入了super中的方法，super是指ProxyCreatorSupport，这里ProxyCreatorSupport是ProxyFactoryBean和ProxyFactory的父类，已经做了很多工作，只需在ProxyFactoryBean的getObject()方法中通过父类的createAopProxy()取得相应的AopProxy。

5、跟踪createAopProxy方法，追踪到了ProxyCreatorSupport中，然后，借助了AopProxyFactory，此时得到的aopProxyFactory，在构造函数中已经定义为DefaultAopProxyFactory

6、进入DefaultAopProxyFactory中，找到createAopProxy方法，在这里判断是调用JDK动态或者CGlib动态中的一种。

既然代理对象已经生成，那么拦截器是如何被调用的呢

回顾下JdkDynamicAopProxy中生成proxy方法

@Override    public Object getProxy(ClassLoader classLoader) {        if (logger.isDebugEnabled()) {            logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());        }        Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);        findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);        return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);    }

看最后一句return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this)。这个地方的三个参数在博客动态代理中做过详细介绍，再回顾下

• classloader类加载器，定义了由哪个ClassLoader对象来对生成的代理对象进行加载

• proxiedInterfaces，一个Interface对象的数组，表示的是我将要给我需要代理的对象提供一组什么接口

• this，表示JdkDynamicAopProxy自身，因为JdkDynamicAopProxy实现了InvocationHandler接口

在动态代理这篇博客中我们分析过，生成的proxy代理类被调用时，会调用super.h.method()方法，这里的super一般指的是Proxy，而Proxy中有一个InvocationHandler，即h。所以InvocationHandler的invoke方法会被作为回调函数调用

@Override    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)) {                //目标对象未实现equals方法                return equals(args[0]);            }            if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {                //目标对象未实现hashcode方法                return hashCode();            }            if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&                    method.getDeclaringClass().isAssignableFrom(Advised.class)) {            //这里就是目标对象方法的调用                return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);            }            Object retVal;            if (this.advised.exposeProxy) {                // 获得当前的对象                oldProxy = AopContext.setCurrentProxy(proxy);                setProxyContext = true;            }            //目标对象可能源自一个池或者一个简单的方法            target = targetSource.getTarget();            if (target != null) {                targetClass = target.getClass();            }            // 得到拦截器链            List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);            // 检查是否定义了拦截器方法，如果没有的话直接调用目标方法            if (chain.isEmpty()) {                retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);            }            else {                //我们需要创建一个调用方法                invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);                // proceed内部实现了递归调用遍历拦截器链                retVal = invocation.proceed();            }            Class<?> returnType = method.getReturnType();            if (retVal != null && retVal == target && 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()) {                // 释放target对象                targetSource.releaseTarget(target);            }            if (setProxyContext) {                // 替换回原来的proxy                AopContext.setCurrentProxy(oldProxy);            }        }    }

上面的invoke（）主要分为三部分

拦截器链的获取， this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass)

目标对象方法的调用，即invokeJoinpointUsingReflection（）方法

拦截器对象方法的调用，即ReflectiveMethodInvocation中proceed()

首先看拦截器链是如获得的。

进入AdvisedSupport（advised为AdvisedSupport实例）的getInterceptorsAndDynamicInterceptionAdvice()方法

public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, Class<?> targetClass) {        MethodCacheKey cacheKey = new MethodCacheKey(method);        List<Object> cached = this.methodCache.get(cacheKey);        if (cached == null) {            cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(                    this, method, targetClass);            this.methodCache.put(cacheKey, cached);        }        return cached;    }

可以看出上面方法用到缓存的, 假设现在缓存没有相应的拦截器, 则到 AdvisorChainFactory 的相应方法中获取，继续跟踪AdvisorChainFactory，发现定义为new DefaultAdvisorChainFactory()，这里是不是有一点眼熟，对的，在上一篇中讲到动态代理是也有一个DefaultAopProxy，进入DefaultAdvisorChainFactory中的相应方法，比较长

/**     * 从提供的配置实例config中获取advisor列表,遍历处理这些advisor.如果是IntroductionAdvisor,     * 则判断此Advisor能否应用到目标类targetClass上.如果是PointcutAdvisor,则判断     * 此Advisor能否应用到目标方法method上.将满足条件的Advisor通过AdvisorAdaptor转化成Interceptor列表返回.     */  

    public List getInterceptorsAndDynamicInterceptionAdvice(Advised config, Methodmethod, Class targetClass) {       List interceptorList = new ArrayList(config.getAdvisors().length);       //查看是否包含IntroductionAdvisor       boolean hasIntroductions = hasMatchingIntroductions(config,targetClass);       //这里实际上注册一系列AdvisorAdapter,用于将Advisor转化成MethodInterceptor       AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();       Advisor[] advisors = config.getAdvisors();        for (int i = 0; i <advisors.length; i++) {           Advisor advisor = advisors[i];           if (advisor instanceof PointcutAdvisor) {                // Add it conditionally.                PointcutAdvisor pointcutAdvisor= (PointcutAdvisor) advisor;                if(config.isPreFiltered() ||pointcutAdvisor.getPointcut().getClassFilter().matches(targetClass)) {                    //TODO: 这个地方这两个方法的位置可以互换下                    //将Advisor转化成Interceptor                    MethodInterceptor[]interceptors = registry.getInterceptors(advisor);                    //检查当前advisor的pointcut是否可以匹配当前方法                    MethodMatcher mm =pointcutAdvisor.getPointcut().getMethodMatcher();                    if (MethodMatchers.matches(mm,method, targetClass, hasIntroductions)) {                        if(mm.isRuntime()) {                            // Creating a newobject instance in the getInterceptors() method                            // isn't a problemas we normally cache created chains.                            for (intj = 0; j < interceptors.length; j++) {                               interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptors[j],mm));                            }                        } else {                            interceptorList.addAll(Arrays.asList(interceptors));                        }                    }                }           } else if (advisor instanceof IntroductionAdvisor){                IntroductionAdvisor ia =(IntroductionAdvisor) advisor;                if(config.isPreFiltered() || ia.getClassFilter().matches(targetClass)) {                    Interceptor[] interceptors= registry.getInterceptors(advisor);                    interceptorList.addAll(Arrays.asList(interceptors));                }           } else {                Interceptor[] interceptors =registry.getInterceptors(advisor);                interceptorList.addAll(Arrays.asList(interceptors));           }       }       return interceptorList;}

注意上面代码中的一行，注册一系列AdvisorAdapter，找到GlobalAdvisorAdapterRegistry，其实定义为 new DefaultAdvisorAdapterRegistry()，又是default~~~

AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();instance = new DefaultAdvisorAdapterRegistry();public DefaultAdvisorAdapterRegistry() {        registerAdvisorAdapter(new MethodBeforeAdviceAdapter());        registerAdvisorAdapter(new AfterReturningAdviceAdapter());        registerAdvisorAdapter(new ThrowsAdviceAdapter());    }

所以registry其实为调用了DefaultAdvisorAdapterRegistry的构造函数，然后才能在将Advisor转化成Interceptor时，调用DefaultAdvisorAdapterRegistry的getInterceptors（）方法。

    @Override    public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {        List<MethodInterceptor> interceptors = new ArrayList<MethodInterceptor>(3);        Advice advice = advisor.getAdvice();        if (advice instanceof MethodInterceptor) {            interceptors.add((MethodInterceptor) advice);        }        for (AdvisorAdapter adapter : this.adapters) {            if (adapter.supportsAdvice(advice)) {                interceptors.add(adapter.getInterceptor(advisor));            }        }        if (interceptors.isEmpty()) {            throw new UnknownAdviceTypeException(advisor.getAdvice());        }        return interceptors.toArray(new MethodInterceptor[interceptors.size()]);    }

这里的MethodInterceptor[]返回值，正好可以匹配上面代码中的 MethodInterceptor[]interceptors = registry.getInterceptors(advisor);

目标对象方法的调用

来看看invokeJoinpointUsingReflection（），即上面所说的目标对象方法的调用，其实是通过AopUtils的方法调用，使用反射机制来对目标对象的方法进行的：

    public static Object invokeJoinpointUsingReflection(Object target, Method method, Object[] args)            throws Throwable {        // 通过反射机制来获得相应的方法，并调用invoke        try {            ReflectionUtils.makeAccessible(method);            return method.invoke(target, args);        }        catch (InvocationTargetException ex) {            throw ex.getTargetException();        }        catch (IllegalArgumentException ex) {            throw new AopInvocationException("AOP configuration seems to be invalid: tried calling method [" +                    method + "] on target [" + target + "]", ex);        }        catch (IllegalAccessException ex) {            throw new AopInvocationException("Could not access method [" + method + "]", ex);        }    }

拦截器方法执行

看看拦截器对象，即ReflectiveMethodInvocation中proceed()方法的调用

invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);retVal = invocation.proceed();

invocation是一个new ReflectiveMethodInvocation（）实例，找到ReflectiveMethodInvocation的proceed()方法

private int currentInterceptorIndex = -1;    @Override    public Object proceed() throws Throwable {        //  currentInterceptorIndex初始化的长度为-1，下面就就是判断          //interceptorsAndDynamicMethodMatchers长度是否为0        if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {            return invokeJoinpoint();        }        Object interceptorOrInterceptionAdvice =                this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);        if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {            //匹配是否为正确的方法逻辑，（MethodMatcher）可以看出为匹配如果不是就调用下一个            InterceptorAndDynamicMethodMatcher dm =                    (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;            if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {                return dm.interceptor.invoke(this);            }            else {                //匹配失败，跳过这个拦截器，继续下一个                return proceed();            }        }        else {            // 如果是interceptor，则调用invoke方法，这是为了兼容            return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);        }    }