AOP通知方法如何执行
先看下整体的AOP基本通知方法的内部执行顺序结构：
我们拿JDK动态代理为例，CGLIB也是类似，当调用某个方法的时候，会进行JdkDynamicAopProxy代理的invoke执行：
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
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.
return equals(args[0]);
}
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
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;
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
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.
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
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.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// We need to create a method invocation...
MethodInvocation 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 != Object.class && 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);
}
}
}
一堆，其实重要的就这么几句，首先获取所有通知List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);然后封装成ReflectiveMethodInvocation调用proceed方法。我把AOP的一般方法都用上了，可以看到这里他已经是排序完的，具体怎么排序的，可以去研究下，比较复杂，其实就是为了形成一个调用栈顺序，后面我会画出来，我们先看这些用到的，第一个其实没什么具体用，他会直接执行第二个，然后顺序执行下去：
ReflectiveMethodInvocation的proceed循环执行
主要是递归获取通知，然后执行。
@Override
@Nullable
public Object proceed() throws Throwable {
// 循环执行，直到执行完
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
//获得通知方法
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;
Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
if (dm.methodMatcher.matches(this.method, 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 {//执行
// 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);
}
}
ExposeInvocationInterceptor的invoke
没做什么，主要是mi.proceed()，也就是继续调用ReflectiveMethodInvocation的proceed来进行递归调用。
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
MethodInvocation oldInvocation = invocation.get();
invocation.set(mi);
try {
return mi.proceed();
}
finally {
invocation.set(oldInvocation);
}
}
AspectJAfterThrowingAdvice的invoke异常通知
其实就是在外面包了一层捕获异常，然后继续调用mi.proceed();，如果出异常了可以捕获到执行invokeAdviceMethod。
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
try {
return mi.proceed();
}
catch (Throwable ex) {
if (shouldInvokeOnThrowing(ex)) {
invokeAdviceMethod(getJoinPointMatch(), null, ex);
}
throw ex;
}
}
AbstractAspectJAdvice的invokeAdviceMethod通知方法
其实这个是通用的通知方法，只要有要调用的通知方法，都会去调用这个内部最终调用了这个：
AfterReturningAdviceInterceptor的invoke成功返回后通知
只是在返回后加了方法，内部就是调用invokeAdviceMethod。
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
Object retVal = mi.proceed();
this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
return retVal;
}
AspectJAfterAdvice的invoke方法后通知
就是在执行完后执行invokeAdviceMethod。
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
try {
return mi.proceed();
}
finally {
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
}
AspectJAroundAdvice的invoke环绕通知
这个会先把MethodInvocation封装成ProceedingJoinPoint，然后在调用的时候当做参数传进去。
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
if (!(mi instanceof ProxyMethodInvocation)) {
throw new IllegalStateException("MethodInvocation is not a Spring ProxyMethodInvocation: " + mi);
}
ProxyMethodInvocation pmi = (ProxyMethodInvocation) mi;
ProceedingJoinPoint pjp = lazyGetProceedingJoinPoint(pmi);
JoinPointMatch jpm = getJoinPointMatch(pmi);
return invokeAdviceMethod(pjp, jpm, null, null);
}
先封装：
后使用：
然后里面会进行克隆，或许是代理为了保护源数据信息吧，然后再调用proceed：
MethodBeforeAdviceInterceptor的invoke方法前通知
先调用方法前通知方法，在调用方法。
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
return mi.proceed();
}
基本的流程就是这样下来的，所以为什么环绕是在最前面，因为环绕代理了后面要执行的方法，提前进行了环绕前处理：
如果有异常的话：
再看下整个结构是这样的：
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正常情况可以对照，就是没有异常的，没啥问题。
如果出现异常，就是出现在System.out.println("方法调用");因此直接执行System.out.println("logAfter");，不会去执行logReturning，直接进到catch里面了，跟异常时候的信息也对的起来。
好了，基本的AOP调用分析完了，其实就是通知方法排序好之后，递归调用。其实还有其他的功能，比如DeclareParents，target，args等注解功能，这个基础的有了，应该不难，自己研究下好了。
好了，今天就到这里了，希望对学习理解有帮助，大神看见勿喷，仅为自己的学习理解，能力有限，请多包涵。
