SpringCloudGateway手动编写路由规则对请求进行转发
这篇文章主要是提供一种转发路由的代码实现方式，之前说的gateway都是使用配置文件来对请求进行路由，这样虽然很简单，但是不够灵活，如果后端对应很多服务实例，网关想要根据自己的规则来转发请求，比如编写不同的负载均衡策略，做一些特别的权重，以及在运行过程中动态的变更转发地址，这些用配置文件来做都不够灵活，没法自由的定义规则。

涉及的gateway版本

     <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-gateway</artifactId>
            <version>2.1.4.RELEASE</version>
        </dependency>

主要实现过程还是实现GatewayFilter接口，获取到要指定的IP地址与端口，然后组装成URI与Route，最后转发出去

import cn.hutool.core.util.ObjectUtil;
import cn.hutool.core.util.StrUtil;
import com.ecwid.consul.v1.health.model.HealthService;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.gateway.filter.GatewayFilter;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.route.Route;
import org.springframework.core.Ordered;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.util.UriComponentsBuilder;

import java.net.URI;
import java.util.List;
import java.util.Optional;

import reactor.core.publisher.Mono;

import static org.springframework.cloud.gateway.support.ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR;

/**
 * 转发路由，通过负载均衡对后端服务进行访问
 *
 */
@Slf4j
public class RouteFilter implements GatewayFilter, Ordered {

    @Autowired
    private RedisUtil redisUtil;

    @Autowired
    private LoadBalanceHandler loadBalance;

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpResponse response = exchange.getResponse();
        //获取原来的请求路径
        String requestPath = exchange.getAttribute(FilterDict.SYSTEM_REQUEST_PATH);
      //randomSelectInstance方***获取到一个"ip:port"这样结构的字符串
        String instanceInfo = loadBalance.randomSelectInstance();
        //如果没有服务，则直接返回报错
        if (StrUtil.isEmpty(instanceInfo)) {
            return response.writeWith(Mono.just(GateWayFilterUtils.writeData(exchange, RecoError.GEN_SERVER_BUSY)));
        }
        //用于测试负载均衡算法对IP分配是否均衡
//        redisUtil.zIncrementScore("test:gateway:load:ip",instanceInfo,1);
        //分割地址中IP和端口
        String[] serviceAddress = instanceInfo.split(StrUtil.COLON);
        String requestSchema = exchange.getRequest().getURI().getScheme();
        //拼接URL的数据
        assert ObjectUtil.isNotNull(requestPath);
        URI uri = UriComponentsBuilder.
                newInstance().scheme(requestSchema).
                host(serviceAddress[0].trim()).port(Integer.parseInt(serviceAddress[1].trim()))
                .path(requestPath).query(exchange.getRequest().getURI().getRawQuery()).build(true)
                .toUri();
        //将拼接好的URL装入新的exchange
        ServerWebExchange mutateExchange = exchange.mutate().request(builder -> builder.uri(uri).build()).build();
        Optional<Route> route = Optional.of(exchange.getAttribute(GATEWAY_ROUTE_ATTR));
        Route newRoute = Route.async()
                .asyncPredicate(route.get().getPredicate())
                .filters(route.get().getFilters())
                .id(route.get().getId())
                .order(route.get().getOrder())
                .uri(uri).build();
        mutateExchange.getAttributes().put(GATEWAY_ROUTE_ATTR, newRoute);
        mutateExchange.getAttributes().put(FilterDict.SYSTEM_APP_IP_ADDR, serviceAddress[0]);
        return chain.filter(mutateExchange);
    }

    @Override
    public int getOrder() {
        return FilterDict.SYSTEM_FILTER_ORDER + 4;
    }
}

单独编写路由filter以后，还需要引入才能执行，在全局配置中倒入bean，最后启动就可以执行了

import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.gateway.filter.ratelimit.RedisRateLimiter;
import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import lombok.extern.slf4j.Slf4j;

import java.time.Duration;

/**
 * 全局过滤器配置加载
 *
 * @author :wcy
 */
@Slf4j
@Configuration
public class GlobalFilterConfigure {
    //用于设置路由的
    @Bean
    public RouteFilter routeFilter(){
        return new RouteFilter();
    }

    /**
     * 将所有自定义的filter加载进来
     */
    @Bean
    public RouteLocator customerRouteLocator(RouteLocatorBuilder builder, RedisRateLimiter redisRateLimiter) {
        return builder.routes()
                .route(r -> r.path(FilterDict.GATEWAY_BASE_INTERCEPT_URL)
                        //将自定义的filter加载进来
                        .filters(f -> f.filters(routeFilter())
                                //请求大小
                                .setRequestSize(requestLimitSize)
                                //请求限流,目前使用请求IP,以后可以扩展使用其他限定组合
//                                .filter(rateLimitByIpGatewayFilter())
                        )
                        .uri("http://127.0.0.1:" + servicePort + "/actuator/health")
                        .order(FilterDict.SYSTEM_FILTER_ORDER)
                        .id(FilterDict.GATEWAY_ROUTE_NAME)
                ).build();
    }

}