spring aop 源码解读之我见
spring aop 都是动态代理，分为jdk代理和cglib代理。默认的情况下，如果类有实现了接口，使用jdk代理。如果没有实现接口，则使用cglib代理。在下面的代码中，我会标明对应的这段代码。
和以前一样，关键代码我会标红色。
首先，分析jdk代理。之前一直找不到jdk代理的源码入口。后来网上看大神的源码分析，在结合自己写的例子，终于是发现了入口，入口的关键点，是InvocationHandler。由于jdk代理也实现了这个接口，所以也实现了自己的invoke方法。代码如下：
/** * Implementation of {@code InvocationHandler.invoke}. * <p>Callers will see exactly the exception thrown by the target, * unless a hook method throws an exception. */ @Override @Nullable
//实现invoke方法。 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 { if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) { // The target does not implement the equals(Object) method itself.
//不实现equals方法
return equals(args[0]); } else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) { // The target does not implement the hashCode() method itself.
//不实现hasCode方法
return hashCode();
} else if (method.getDeclaringClass() == DecoratingProxy.class) { // There is only getDecoratedClass() declared -> dispatch to proxy config.
// 循环调用，最终返回单例的目标类 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...
//使用代理配置对ProxyConfig的服务调用
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args); } Object retVal; if (this.advised.exposeProxy) { // Make invocation available if necessary.
// 提供调用
oldProxy = AopContext.setCurrentProxy(proxy); setProxyContext = true; } // Get as late as possible to minimize the time we "own" the target, // in case it comes from a pool. target = targetSource.getTarget(); Class<?> targetClass = (target != null ? target.getClass() : null); // Get the interception chain for this method.
// 获得方法的拦截器链
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.
// 检查是否有通知。如果没有，则直接反射调用目标类，不会创建方法调用(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.
// 允许直接执行目标类，而不创建方法调用invocation。注意，最终的调用者依然是InvokerInterceptor，尽管只是直接反射操作，没有任何的拦截。
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args); //适配器模式 retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse); //直接使用反射调用 } else { // We need to create a method invocation...
// 创建一个方法调用 invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain); // Proceed to the joinpoint through the interceptor chain.
// 执行拦截器连的切入点 retVal = invocation.proceed(); } // Massage return value if necessary. Class<?> returnType = method.getReturnType(); if (retVal != null && retVal == target && returnType != Object.class && returnType.isInstance(proxy) && !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) { //返回类型一样&&非子类 // 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); } } }
先跟进 getInterceptorsAndDynamicInterceptionAdvice(method, targetClass)
/** * Determine a list of {@link org.aopalliance.intercept.MethodInterceptor} objects * for the given method, based on this configuration. * @param method the proxied method * @param targetClass the target class * @return a List of MethodInterceptors (may also include InterceptorAndDynamicMethodMatchers) */
//基于方法的配置，获取它的拦截器 集合。这里可以看出，拦截器 集合是一个list，放在map中,map的key则是方法名称和hascode组成
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, @Nullable 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; }
@Override public List<Object> getInterceptorsAndDynamicInterceptionAdvice( Advised config, Method method, @Nullable 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); //检查是否有匹配配置的类 AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance(); for (Advisor advisor : config.getAdvisors()) { //遍历advisor if (advisor instanceof PointcutAdvisor) { //如果是切入点的的advisor（方法级别） // Add it conditionally. PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor; if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) { //检查经过过滤的类是否还匹配advisor MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher(); if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) { //检查匹配的方法 MethodInterceptor[] interceptors = registry.getInterceptors(advisor); //获取方法拦截器 if (mm.isRuntime()) { //如果是运行时起作用的拦截器 // 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)); //添加到拦截器链中 } } else { interceptorList.addAll(Arrays.asList(interceptors)); //如果不是运行时起作业给作用的拦截器，则直接添加到拦截器链中 } } } } else if (advisor instanceof IntroductionAdvisor) { //类级别的拦截器 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; }
下面看下：invocation.proceed() 。这个方法真正地使拦截器起作用。代码如下：
@Override @Nullable public Object proceed() throws Throwable { // We start with an index of -1 and increment early. if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) { return invokeJoinpoint(); } Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex); if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) { // Evaluate dynamic method matcher here: static part will already have // been evaluated and found to match. 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); } }
//org\springframework\aop\framework\ReflectiveMethodInvocation.class
public Object proceed() throws Throwable { if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) { //如果是自后一个匹配的拦截器，则直接调用 return this.invokeJoinpoint(); //可以看出，这里有反射和cglig两种实现方法，也就是，对应jdk和cglib } else { Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex); if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) { //如果是匹配的拦截器&方法 InterceptorAndDynamicMethodMatcher dm = (InterceptorAndDynamicMethodMatcher)interceptorOrInterceptionAdvice; return dm.methodMatcher.matches(this.method, this.targetClass, this.arguments) ? dm.interceptor.invoke(this) : this.proceed(); //如果类的方法完全匹配，则直接执行，否则执行回调 } else { return ((MethodInterceptor)interceptorOrInterceptionAdvice).invoke(this); } } }
jdk和cglib其实都是一样的意思，简单看下cglib的invokeJoinPoint()
protected Object invokeJoinpoint() throws Throwable { return this.publicMethod ? this.methodProxy.invoke(this.target, this.arguments) : super.invokeJoinpoint(); }
public Object invoke(Object obj, Object[] args) throws Throwable { try { this.init(); MethodProxy.FastClassInfo fci = this.fastClassInfo; return fci.f1.invoke(fci.i1, obj, args); } catch (InvocationTargetException var4) { throw var4.getTargetException(); } catch (IllegalArgumentException var5) { if (this.fastClassInfo.i1 < 0) { throw new IllegalArgumentException("Protected method: " + this.sig1); } else { throw var5; } } }
在这里看到 fci.f1.invoke(fci.i1, obj, args)。也就是我们的拦截器织入的方法执行。这里又个有意义的现象，就是使用fci.f1.invoke ，这中fastclass的方式来执行，之所以使用这种方式，是因为cglib生成动态代理的子类的时候，已经为每一个方法增加了一个独一无二的索引，有了索引之后，这样执行会比直接调用快，具体的可以去百度下。
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总结：spring aop的执行流程，分为两步：1、生成拦截器链 2、切入点（方法）织入代码，进行拦截
