default int filterOrder() {
        Filter f = getClass().getAnnotation(Filter.class);
        if (f != null) {
            return f.order();
        }
        throw new UnsupportedOperationException("not implemented");
    }
filterOrder() must also be defined for a filter. Filters may have the same filterOrder if precedence is not
important for a filter. filterOrders do not need to be sequential.

@return the int order of a filter
zuul-core/src/main/java/com/netflix/zuul/filters/ZuulFilter.java