Spring AOP深入理解之拦截器调用
Spring AOP代理对象生成回想
上一篇博客中：深入理解Spring AOP之二代理对象生成介绍了Spring代理对象是怎样生成的，当中重点介绍了JDK动态代理方式，简单回想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。
第一种获取比較简单，可是须要手工的进行写代码。而另外一种是通过Spring的IOC机制来控制Bean的生成。
2、不管是ProxyFactory或者ProxyFactoryBean都是要通过createAopProxy().getProxy()来获取对应的代理对象，而通过Proxyfactory比較直接，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。已经做了非常多工作，仅仅需在ProxyFactoryBean的getObject()方法中通过父类的createAopProxy()取得对应的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，在这里推断是调用JDK动态或者CGlib动态中的一种。
既然代理对象已经生成，那么拦截器是怎样被调用的呢
回想下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)。这个地方的三个參数在博客动态代理中做过具体介绍。再回想下
classloader类载入器，定义了由哪个ClassLoader对象来对生成的代理对象进行载入
proxiedInterfaces，一个Interface对象的数组，表示的是我将要给我须要代理的对象提供一组什么接口
this，表示JdkDynamicAopProxy自身，由于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
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()
@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，假设没有的话直接调用目标方法
if (chain.isEmpty()) {
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);
}
else {
//我们须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
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;
}
能够看出上面方法用到缓存的, 如果如今缓存没有对应的拦截器, 则到 AdvisorChainFactory 的对应方法中获取，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中的对应方法。比較长
/**
* 从提供的配置实例config中获取advisor列表,遍历处理这些advisor.假设是IntroductionAdvisor,
* 则推断此Advisor是否能应用到目标类targetClass上.假设是PointcutAdvisor,则推断
* 此Advisor是否能应用到目标方法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);
//查看是否包括IntroductionAdvisor
boolean hasIntroductions = hasMatchingIntroductions(config,targetClass);
//这里实际上注冊一系列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能够互换下
//将Advisor转化成Interceptor
MethodInterceptor[]interceptors = registry.getInterceptors(advisor);
//检查当前advisor的pointcut能否够匹配当前方法
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，注冊一系列AdvisorAdapter。找到GlobalAdvisorAdapterRegistry，事实上定义为 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事实上为调用了DefaultAdvisorAdapterRegistry的构造函数，然后才干在将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，正好能够匹配上面代码中的 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，事实上是通过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对应的方法。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);
}
}
拦截器方法运行
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，以下就就是推断 //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）能够看出为匹配假设不是就调用下一个
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 {
// 假设是interceptor。则调用invoke方法。这是为了兼容
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}