引
接前面一章继续分析SpringAOP获取拦截器链和拦截器链的调用过程。
1.获取拦截器链
public List/**
* 获取拦截器链
*/
@Override
public List该段代码比较关键的点：
// 如果匹配，获取方法拦截器
if (match) {
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
if (mm.isRuntime()) {
// 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));
}
}
else {
interceptorList.addAll(Arrays.asList(interceptors));
}
}
通过上面的代码可以发现Spring最终还是要把增强（切面）转换为方法拦截器，来看其具体的实现：
/**
* 获取方法连接器
*/
@Override
public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
List interceptors = new ArrayList<>(3);
Advice advice = advisor.getAdvice();
// 1.如果增强是MethodInterceptor类型直接添加
if (advice instanceof MethodInterceptor) {
interceptors.add((MethodInterceptor) advice);
}
// 2.循环增强适配器,并判断是否支持
for (AdvisorAdapter adapter : this.adapters) {
if (adapter.supportsAdvice(advice)) {
interceptors.add(adapter.getInterceptor(advisor));
}
}
if (interceptors.isEmpty()) {
throw new UnknownAdviceTypeException(advisor.getAdvice());
}
// 3.返回结果
return interceptors.toArray(new MethodInterceptor[0]);
}
通过这段代码，如果增强是MethodInterceptor的实例，直接加入结果中；那么哪些增强是MethodInterceptor类型呢？先不用着急，继续看下面的处理，下面的代码里出现了一个增强适配器，我们来看一下其中都包含了哪些适配器类型：
private final List adapters = new ArrayList<>(3);
public DefaultAdvisorAdapterRegistry() {
registerAdvisorAdapter(new MethodBeforeAdviceAdapter());
registerAdvisorAdapter(new AfterReturningAdviceAdapter());
registerAdvisorAdapter(new ThrowsAdviceAdapter());
}
DefaultAdvisorAdapterRegistry通过构造函数对增强适配器进行了初始化，包含了MethodBeforeAdviceAdapter前置增强适配器、AfterReturningAdviceAdapter后置返回增强适配器、ThrowsAdviceAdapter后置异常增强适配器。那么从这里我们也可以推断出，除了这几种增强适配器对应的增强类型之外，其他的都是MethodInterceptor类型。
接下来看下这三种适配器都做了哪些工作：
- MethodBeforeAdviceAdapter
/**
* 增强适配器
* 这个方法在获取拦截器链的时候调用,从这里也可以看出,Spring中的advisor(增强/切面)
* 最终还是被转换为MethodInterceptor对象
*
* AdvisorAdapter的实现类有AfterReturningAdviceAdapter,MethodBeforeAdviceAdapter,ThrowsAdviceAdapter三个
*
* AfterReturningAdviceAdapter -> new AfterReturningAdviceInterceptor(advice) -> 后置返回增强
* MethodBeforeAdviceAdapter -> new MethodBeforeAdviceInterceptor(advice) -> 前置增强
* ThrowsAdviceAdapter -> new ThrowsAdviceInterceptor(advisor.getAdvice()) -> 该适配器有些特殊...看源码吧
*/
@Override
public MethodInterceptor getInterceptor(Advisor advisor) {
MethodBeforeAdvice advice = (MethodBeforeAdvice) advisor.getAdvice();
return new MethodBeforeAdviceInterceptor(advice);
}
- AfterReturningAdviceAdapter
public MethodInterceptor getInterceptor(Advisor advisor) {
AfterReturningAdvice advice = (AfterReturningAdvice) advisor.getAdvice();
return new AfterReturningAdviceInterceptor(advice);
}
- ThrowsAdviceAdapter
@Override
public MethodInterceptor getInterceptor(Advisor advisor) {
return new ThrowsAdviceInterceptor(advisor.getAdvice());
}
看到这里大家一定有所了解了，Spring中的增强，最终还是会转换为方法拦截器调用。
3. 拦截器链调动过程
/**
* 调用拦截器链
*
* currentInterceptorIndex维护了一个计数器，该计数器从-1开始，当计数器值等于拦截方法长度减一时，
* 表名所有的增强方法已经被调用（但是不一定被真正执行），那么此时调用连接点的方法，针对本例：即sayHello方法
*/
@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);
// 动态匹配增强
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());
// 匹配成功则执行
if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
// 匹配失败则跳过并执行下一个拦截器
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
// 静态增强
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
// System.out.println(interceptorOrInterceptionAdvice.getClass());
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
这段代码看似简单，但是如果真的debug进去，方法栈还是比较深刻的，前面介绍过在获取到合适的增强集合之后，首先在其首位加入了ExposeInvocationInterceptor拦截器，然后对增强集合进行了排序（当然ExposeInvocationInterceptor依然会在首位），那么接下来第一个拦截器调用就是ExposeInvocationInterceptor了。
- ExposeInvocationInterceptor
public Object invoke(MethodInvocation mi) throws Throwable {
MethodInvocation oldInvocation = invocation.get();
invocation.set(mi);
try {
// 继续拦截器链调用
return mi.proceed();
}
finally {
invocation.set(oldInvocation);
}
}
- AspectJAfterThrowingAdvice
public Object invoke(MethodInvocation mi) throws Throwable {
try {
// 继续拦截器链调用
return mi.proceed();
}
catch (Throwable ex) {
if (shouldInvokeOnThrowing(ex)) {
invokeAdviceMethod(getJoinPointMatch(), null, ex);
}
throw ex;
}
}
- AspectJAfterThrowingAdvice
public Object invoke(MethodInvocation mi) throws Throwable {
try {
// 继续拦截器链调用
return mi.proceed();
}
catch (Throwable ex) {
if (shouldInvokeOnThrowing(ex)) {
invokeAdviceMethod(getJoinPointMatch(), null, ex);
}
throw ex;
}
}
- AfterReturningAdviceInterceptor
public Object invoke(MethodInvocation mi) throws Throwable {
// 继续拦截器链调用
Object retVal = mi.proceed();
this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
return retVal;
}
- AspectJAfterAdvice
public Object invoke(MethodInvocation mi) throws Throwable {
try {
// 继续拦截器链调用
return mi.proceed();
}
finally {
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
}
- AspectJAroundAdvice
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);
}
在这里终于看到了方法的调用：
protected Object invokeAdviceMethodWithGivenArgs(Object[] args) throws Throwable {
Object[] actualArgs = args;
if (this.aspectJAdviceMethod.getParameterCount() == 0) {
actualArgs = null;
}
try {
ReflectionUtils.makeAccessible(this.aspectJAdviceMethod);
// TODO AopUtils.invokeJoinpointUsingReflection
// 调用代理方法
return this.aspectJAdviceMethod.invoke(this.aspectInstanceFactory.getAspectInstance(), actualArgs);
}
catch (IllegalArgumentException ex) {
throw new AopInvocationException("Mismatch on arguments to advice method [" +
this.aspectJAdviceMethod + "]; pointcut expression [" +
this.pointcut.getPointcutExpression() + "]", ex);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
public Object invoke(Object obj, Object... args)
throws IllegalAccessException, IllegalArgumentException,
InvocationTargetException
{
if (!override) {
if (!Reflection.quickCheckMemberAccess(clazz, modifiers)) {
Class caller = Reflection.getCallerClass();
checkAccess(caller, clazz, obj, modifiers);
}
}
MethodAccessor ma = methodAccessor; // read volatile
if (ma == null) {
ma = acquireMethodAccessor();
}
return ma.invoke(obj, args);
}
代码终于执行到了Method类的invoke方法，接下来就可以调用我们的增强方法了：
- MethodBeforeAdviceInterceptor
@Around("test()")
public Object aroundTest(ProceedingJoinPoint p) throws Throwable {
System.out.println("==环绕增强开始");
// 继续拦截器链调用
Object o = p.proceed();
System.out.println("==环绕增强结束");
return o;
}
执行完之后，我们发现前置增强还没有被调用进来，继续：
public Object invoke(MethodInvocation mi) throws Throwable {
// 调用前置增强
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
return mi.proceed();
}
- 目标方法
执行完前置增强之后，再次进入到proceed方法，这时候，计数器已经满足条件了，执行目标方法调用：
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
待执行完目标方法调用后，再将之前压入方法栈的那些增强方法依次出栈并调用。这一段的代码调用用文字表述挺困难的，大家自己跟踪代码吧。。。
到这里拦截器链的调用过程分析就结束了，这里分析的不是那么明确，还是多跟踪代码吧。