SpringFramework之ReflectiveMethodInvocation

克虏伯

发布于 2019-07-15 14:38:24

1.4K0

发布于 2019-07-15 14:38:24

文章被收录于专栏：软件开发-青出于蓝软件开发-青出于蓝

Spring版本是5.0.4.release.

ReflectiveMethodInvocation是AOP中一个重要的类，这个类在JdkDynamicAopProxy的invoke方法中使用到它，如下的List-1

List-1

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        ...
        
            // We need to create a method invocation...
            invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
            // Proceed to the joinpoint through the interceptor chain.
            retVal = invocation.proceed();
        ...
}

如下图1所示

图1

ReflectiveMethodInvocation实现了aop联盟的MethodInvocation，间接实现了Invocation和Joinpoint。如下List-2所示，target是目标类，targetClass是目标类的class，method是目标方法，arguments是对应的方法参数，而interceptorsAndDynamicMethodMatchers则是对应的拦截器。

List-2

protected ReflectiveMethodInvocation(
    Object proxy, @Nullable Object target, Method method, @Nullable Object[] arguments,
    @Nullable Class<?> targetClass, List<Object> interceptorsAndDynamicMethodMatchers) {

    this.proxy = proxy;
    this.target = target;
    this.targetClass = targetClass;
    this.method = BridgeMethodResolver.findBridgedMethod(method);
    this.arguments = AopProxyUtils.adaptArgumentsIfNecessary(method, arguments);
    this.interceptorsAndDynamicMethodMatchers = interceptorsAndDynamicMethodMatchers;
}

ReflectiveMethodInvocation一个重要的方法是proceed()，如下List-3，currentInterceptorIndex表示访问到第几个拦截器，如果是最后一个，那么调用invokeJoinpoint()，如List-4所示，利用反射方式调用目标方法。

List-3

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);
    }
}

List-3中，如果拦截器还没有执行完，则用递归的方式，调用下一个拦截器，

如果是InterceptorAndDynamicMethodMatcher，则获取其MethodMatcher判断是否match，如果match则调用其MethodInterceptor.
如果不是则直接调用MethodInterceptor的invoke方法，invoke方法中传入this，会递归的调用下一个，这个和Spring security中的FilterProxy很相似。可以看一个MethodInterceptor的实现类AspectJAfterAdvice的实现，如下List-5.

List-4

protected Object invokeJoinpoint() throws Throwable {
    return AopUtils.invokeJoinpointUsingReflection(this.target, this.method, this.arguments);
}

public static Object invokeJoinpointUsingReflection(@Nullable Object target, Method method, Object[] args)
    throws Throwable {
    ...
    ReflectionUtils.makeAccessible(method);
    return method.invoke(target, args);
    ...
}

如下的List-5中，首先调用proceed()，之后才会执行invokeAdviceMethod方法。

List-5

public class AspectJAfterAdvice extends AbstractAspectJAdvice
		implements MethodInterceptor, AfterAdvice, Serializable {
    ...

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		try {
			return mi.proceed();
		}
		finally {
			invokeAdviceMethod(getJoinPointMatch(), null, null);
		}
	}
    ...

整体来说，就是Spring aop构造一个拦截器链，在动态代理时调用，根据我们定义的aop，会在目标方法前后执行。