gateway如何设置优先走路由限流，如果没有设置路由限流，则走全局限流，请用代码展示

在Spring Cloud Gateway中，可以使用GatewayFilter来设置路由限流和全局限流。下面是一个示例代码，演示如何优先使用路由限流，如果没有设置路由限流，则使用全局限流。

@Configuration
public class GatewayConfig {

    @Bean
    public GatewayFilterFactory<RouteToRequestUrlFilter> routeToRequestUrlFilterFactory() {
        return new RouteToRequestUrlFilterFactory();
    }

    @Bean
    public GlobalFilter requestRateLimiterFilter() {
        return new RequestRateLimiterFilter();
    }

    private static class RouteToRequestUrlFilterFactory extends AbstractGatewayFilterFactory<RouteToRequestUrlFilter> {

        public RouteToRequestUrlFilterFactory() {
            super(RouteToRequestUrlFilter.class);
        }

        @Override
        public GatewayFilter apply(RouteToRequestUrlFilter config) {
            return (exchange, chain) -> {
                ServerWebExchangeUtils.addOriginalRequestUrl(exchange, exchange.getRequest().getURI());
                return chain.filter(exchange.mutate().request(config.apply(exchange)).build());
            };
        }
    }

    private static class RequestRateLimiterFilter implements GlobalFilter, Ordered {

        private final RateLimiter rateLimiter = RateLimiter.create(100);

        @Override
        public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
            if (exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR) != null) {
                // 使用路由限流
                String routeId = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR).toString();
                RateLimiter routeRateLimiter = getRouteRateLimiter(routeId);
                if (routeRateLimiter != null) {
                    if (routeRateLimiter.tryAcquire()) {
                        return chain.filter(exchange);
                    } else {
                        return Mono.error(new ResponseStatusException(HttpStatus.TOO_MANY_REQUESTS, "Too many requests"));
                    }
                }
            }
            // 使用全局限流
            if (rateLimiter.tryAcquire()) {
                return chain.filter(exchange);
            } else {
                return Mono.error(new ResponseStatusException(HttpStatus.TOO_MANY_REQUESTS, "Too many requests"));
            }
        }

        private RateLimiter getRouteRateLimiter(String routeId) {
            // 根据路由ID获取对应的限流器
            // ...
            return null;
        }

        @Override
        public int getOrder() {
            return Ordered.HIGHEST_PRECEDENCE;
        }
    }

}

在上述代码中，`RouteToRequestUrlFilterFactory`是一个自定义的`GatewayFilterFactory`，用于将路由转换为请求URL。`RequestRateLimiterFilter`是一个全局过滤器，用于实现限流功能。在`RequestRateLimiterFilter`中，我们首先判断当前请求是否有路由信息，如果有，则使用对应的路由限流器进行限流；如果没有，则使用全局限流器进行限流。`getRouteRateLimiter`方法是一个自定义方法，用于根据路由ID获取对应的限流器。在实际应用中，可以根据自己的需求来实现该方法。