import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;
import reactor.core.publisher.Mono;
import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
import static org.springframework.web.reactive.function.server.RequestPredicates.accept;
import static org.springframework.web.reactive.function.server.RouterFunctions.route;
/**
 * 某業(yè)務 Handler
 */
@Component
public class SplashHandler {
  private Mono<ServerResponse> execute(ServerRequest serverRequest) {
    ... 業(yè)務代碼
    // serverRequest 獲得 IP ？
    ... 業(yè)務代碼
  }
  @Configuration
  public static class RoutingConfiguration {
    @Bean
    public RouterFunction<ServerResponse> execute(SplashHandler handler) {
      return route(
          GET("/api/ad").and(accept(MediaType.TEXT_HTML)),
          handler::execute
      );
    }
  }
}

org.springframework.web.server.ServerWebExchange#getRequest
org.springframework.http.server.reactive.ServerHttpRequest#getRemoteAddress

import org.springframework.context.annotation.Configuration;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.config.CorsRegistry;
import org.springframework.web.reactive.config.WebFluxConfigurer;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import reactor.core.publisher.Mono;
import java.net.InetSocketAddress;
import java.util.Objects;
/*
If you want to keep Spring Boot WebFlux features and you want to add additional WebFlux configuration, you can add your own @Configuration class of type WebFluxConfigurer but without @EnableWebFlux.
If you want to take complete control of Spring WebFlux, you can add your own @Configuration annotated with @EnableWebFlux.
 */
@Configuration
public class WebConfiguration implements WebFluxConfigurer {
  @Override
  public void addCorsMappings(CorsRegistry registry) {
    registry
        .addMapping("/**")
        .allowedOrigins("*")
        .allowedMethods("GET", "POST", "PUT", "PATCH", "DELETE", "OPTION")
        .allowedHeaders("header1", "header2", "header3")
        .exposedHeaders("header1", "header2")
        .allowCredentials(true)
        .maxAge(3600);
  }
  /**
   * https://stackoverflow.com/questions/51192630/how-do-you-get-clients-ip-address-spring-webflux-websocket?rq=1
   * https://stackoverflow.com/questions/50981136/how-to-get-client-ip-in-webflux
   * https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#webflux-filters
   * 由于在低版本的 spring-webflux 中不支持直接獲得請求 IP（https://jira.spring.io/browse/SPR-16681），因此寫了一個補丁曲線救國，
   * 從 org.springframework.web.server.ServerWebExchange 中獲得 IP 后，在放到 header 里
   */
  @Component
  public static class RetrieveClientIpWebFilter implements WebFilter {
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
      InetSocketAddress remoteAddress = exchange.getRequest().getRemoteAddress();
      String clientIp = Objects.requireNonNull(remoteAddress).getAddress().getHostAddress();
      ServerHttpRequest mutatedServerHttpRequest = exchange.getRequest().mutate().header("X-CLIENT-IP", clientIp).build();
      ServerWebExchange mutatedServerWebExchange = exchange.mutate().request(mutatedServerHttpRequest).build();
      return chain.filter(mutatedServerWebExchange);
    }
  }
}

private Mono<ServerResponse> execute(ServerRequest serverRequest) {
  String clientIp = serverRequest.headers().asHttpHeaders().getFirst("X-CLIENT-IP")
  ... 業(yè)務代碼
}