GatewayApplication.java

package com.example.demogatewaypathtoparam;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.gateway.filter.GatewayFilter;
import org.springframework.cloud.gateway.filter.factory.AbstractGatewayFilterFactory;
import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.web.util.UriComponentsBuilder;
import org.springframework.web.util.pattern.PathPattern;

import java.net.URI;
import java.util.Collections;
import java.util.Map;

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

@SpringBootApplication
public class GatewayApplication {

	@Bean
	public RouteLocator routes(RouteLocatorBuilder builder) {
		return builder.routes()
				.route("path_to_query", r -> r.path("/{ticker}")
						.filters(f -> f.setPath("/get")
								.filter(pathToParamGatewayFilterFactory().apply("")))
						.uri("http://httpbin.org"))
				.build();
	}

	@Bean
	public PathToParamGatewayFilterFactory pathToParamGatewayFilterFactory() {
		return new PathToParamGatewayFilterFactory();
	}

	static class PathToParamGatewayFilterFactory extends AbstractGatewayFilterFactory<Object> {

		@Override
		public GatewayFilter apply(Object config) {
			return (exchange, chain) -> {
				PathPattern.PathMatchInfo variables = exchange.getAttribute(URI_TEMPLATE_VARIABLES_ATTRIBUTE);

				Map<String, String> uriVariables;
				if (variables != null) {
					uriVariables = variables.getUriVariables();
				} else {
					uriVariables = Collections.emptyMap();
				}

				if (uriVariables.containsKey("ticker")) {
					String ticker = uriVariables.get("ticker");
					URI uri = exchange.getRequest().getURI();
					URI newUri = UriComponentsBuilder.fromUri(uri)
							.replaceQuery("ticker="+ticker)
							.build(true)
							.toUri();

					ServerHttpRequest request = exchange.getRequest().mutate().uri(newUri).build();
					return chain.filter(exchange.mutate().request(request).build());
				}

				return chain.filter(exchange);
			};
		}
	}

	public static void main(String[] args) {
		SpringApplication.run(DemogatewaypathtoparamApplication.class, args);
	}
}

log.txt

$ http :8080/PVTL
HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Access-Control-Allow-Origin: *
Content-Length: 427
Content-Type: application/json
Date: Tue, 11 Dec 2018 02:05:15 GMT
Server: gunicorn/19.9.0
Via: 1.1 vegur

{
    "args": {
        "ticker": "PVTL"
    },
    "headers": {
        "Accept": "*/*",
        "Accept-Encoding": "gzip, deflate",
        "Connection": "close",
        "Forwarded": "proto=http;host=\"localhost:8080\";for=\"127.0.0.1:33410\"",
        "Host": "httpbin.org",
        "User-Agent": "HTTPie/0.9.8",
        "X-Forwarded-Host": "localhost:8080"
    },
    "origin": "127.0.0.1, 107.5.46.99",
    "url": "http://localhost:8080/get?ticker=PVTL"
}