Spring AOP 拦截器调用流程
1、代理对象调用invoke方法
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
/**
* 【1】获取代理工厂
*/
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.
/**
* 【2】 获取真实对象
*/
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
// Get the interception chain for this method.
/**
* 【3】 获取方法链
*
* (1) 根据代理工厂获取有效的advisors
* (2) 遍历advisors，匹配类、匹配方法为true的advisor,获取advice，封装成MethodInterceptor对象。
* (3) 将构建出来的MethodInterceptor对象,添加到拦截链中。
*
*/
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.
/**
* 【4】 如果没有调用链，直接反射调用方法
*/
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.
/**
* 【5】 链式调取
*/
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);
}
}
}
2、获取执行链
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, Class<?> targetClass) {
MethodCacheKey cacheKey = new MethodCacheKey(method);
// 从缓存中获取
List<Object> cached = this.methodCache.get(cacheKey);
// 缓存未命中，则进行下一步处理
if (cached == null) {
// 获取所有的拦截器
cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
this, method, targetClass);
// 存入缓存
this.methodCache.put(cacheKey, cached);
}
return cached;
}
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
Advised config, Method method, Class<?> targetClass) {
List<Object> interceptorList = new ArrayList<Object>(config.getAdvisors().length);
Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
// registry 为 DefaultAdvisorAdapterRegistry 类型
AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
// 遍历通知器列表
for (Advisor advisor : config.getAdvisors()) {
if (advisor instanceof PointcutAdvisor) {
PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
/*
* 调用 ClassFilter 对 bean 类型进行匹配，无法匹配则说明当前通知器
* 不适合应用在当前 bean 上
*/
if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
// 将 advisor 中的 advice 转成相应的拦截器
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
// 通过方法匹配器对目标方法进行匹配
if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) {
// 若 isRuntime 返回 true，则表明 MethodMatcher 要在运行时做一些检测
if (mm.isRuntime()) {
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;
// IntroductionAdvisor 类型的通知器，仅需进行类级别的匹配即可
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;
}
public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
List<MethodInterceptor> interceptors = new ArrayList<MethodInterceptor>(3);
Advice advice = advisor.getAdvice();
/*
* 若 advice 是 MethodInterceptor 类型的，直接添加到 interceptors 中即可。
* 比如 AspectJAfterAdvice 就实现了 MethodInterceptor 接口
*/
if (advice instanceof MethodInterceptor) {
interceptors.add((MethodInterceptor) advice);
}
/*
* 对于 AspectJMethodBeforeAdvice 等类型的通知，由于没有实现 MethodInterceptor
* 接口，所以这里需要通过适配器进行转换
*/
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()]);
}3、 执行拦截器链
ReflectiveMethodInvocation 贯穿于拦截器链执行的始终，可以说是核心。该类的 proceed 方法用于启动启动拦截器链
public class ReflectiveMethodInvocation implements ProxyMethodInvocation {
private int currentInterceptorIndex = -1;
public Object proceed() throws Throwable {
// 拦截器链中的最后一个拦截器执行完后，即可执行目标方法
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
// 执行目标方法
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
/*
* 调用具有三个参数（3-args）的 matches 方法动态匹配目标方法，
* 两个参数（2-args）的 matches 方法用于静态匹配
*/
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
// 调用拦截器逻辑
return dm.interceptor.invoke(this);
}
else {
// 如果匹配失败，则忽略当前的拦截器
return proceed();
}
}
else {
// 调用拦截器逻辑，并传递 ReflectiveMethodInvocation 对象
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
}如上，proceed 根据 currentInterceptorIndex 来确定当前应执行哪个拦截器，并在调用拦截器的 invoke 方法时，将自己作为参数传给该方法。前面的章节中，我们看过了前置拦截器的源码，这里来看一下后置拦截器源码。如下：
public class AspectJAfterAdvice extends AbstractAspectJAdvice
implements MethodInterceptor, AfterAdvice, Serializable {
public AspectJAfterAdvice(
Method aspectJBeforeAdviceMethod, AspectJExpressionPointcut pointcut, AspectInstanceFactory aif) {
super(aspectJBeforeAdviceMethod, pointcut, aif);
}
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
try {
// 调用 proceed
return mi.proceed();
}
finally {
// 调用后置通知逻辑
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
}
//...
}如上，由于后置通知需要在目标方法返回后执行，所以 AspectJAfterAdvice 先调用 mi.proceed() 执行下一个拦截器逻辑，等下一个拦截器返回后，再执行后置通知逻辑。
