Struts2的灵魂——Interceptor

楼主对struts2拦截器讲解的非常精妙，抛开什么设计模式和递归，想问问lz一个低级的问题。
问题：struts2 DefaultActionInvocation的部分源码
public String invoke() throws Exception {
   // 。。。。
       if (interceptors.hasNext()) {
                final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
                String interceptorMsg = "interceptor: " + interceptor.getName();
                UtilTimerStack.push(interceptorMsg);
                try {
                                resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
                            }
                finally {
                    UtilTimerStack.pop(interceptorMsg);
                }
            } else {
                resultCode = invokeActionOnly();
            }
}
//interceptors红色字体实例变量为   public  Iterator<InterceptorMapping>  interceptors 如何保证每次都按照顺序依次迭代 InterceptorMapping对象呢？