public class ValidateFilter implements GlobalFilter, Ordered {
 @Override
 public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
  ServerHttpRequest request = exchange.getRequest();
  HttpHeaders headers = request.getHeaders();
  MultiValueMap<String, HttpCookie> cookies = request.getCookies();
  MultiValueMap<String, String> queryParams = request.getQueryParams();
  Flux<DataBuffer> body = request.getBody();
  return null;
 }

 @Override
 public int getOrder() {
  return 0;
 }
}

.route("rewrite_request_upper", r -> r.host("*.rewriterequestupper.org")
 .filters(f -> f.prefixPath("/httpbin")
   .addResponseHeader("X-TestHeader", "rewrite_request_upper")
   .modifyRequestBody(String.class, String.class,
     (exchange, s) -> {
      return Mono.just(s.toUpperCase()+s.toUpperCase());
     })
 ).uri(uri)
)

/**
 * @author yibo
 */
public class ValidateFilter implements GlobalFilter, Ordered {


 @Override
 public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
  ServerRequest serverRequest = new DefaultServerRequest(exchange);
  // mediaType
  MediaType mediaType = exchange.getRequest().getHeaders().getContentType();
  // read & modify body
  Mono<String> modifiedBody = serverRequest.bodyToMono(String.class)
    .flatMap(body -> {
     if (MediaType.APPLICATION_FORM_URLENCODED.isCompatibleWith(mediaType)) {

      // origin body map
      Map<String, Object> bodyMap = decodeBody(body);

      // TODO decrypt & auth

      // new body map
      Map<String, Object> newBodyMap = new HashMap<>();

      return Mono.just(encodeBody(newBodyMap));
     }
     return Mono.empty();
    });

  BodyInserter bodyInserter = BodyInserters.fromPublisher(modifiedBody, String.class);
  HttpHeaders headers = new HttpHeaders();
  headers.putAll(exchange.getRequest().getHeaders());

  // the new content type will be computed by bodyInserter
  // and then set in the request decorator
  headers.remove(HttpHeaders.CONTENT_LENGTH);

  CachedBodyOutputMessage outputMessage = new CachedBodyOutputMessage(exchange, headers);
  return bodyInserter.insert(outputMessage, new BodyInserterContext())
    .then(Mono.defer(() -> {
     ServerHttpRequestDecorator decorator = new ServerHttpRequestDecorator(
       exchange.getRequest()) {
      @Override
      public HttpHeaders getHeaders() {
       long contentLength = headers.getContentLength();
       HttpHeaders httpHeaders = new HttpHeaders();
       httpHeaders.putAll(super.getHeaders());
       if (contentLength > 0) {
        httpHeaders.setContentLength(contentLength);
       } else {
        httpHeaders.set(HttpHeaders.TRANSFER_ENCODING, "chunked");
       }
       return httpHeaders;
      }

      @Override
      public Flux<DataBuffer> getBody() {
       return outputMessage.getBody();
      }
     };
     return chain.filter(exchange.mutate().request(decorator).build());
    }));
 }

 @Override
 public int getOrder() {
  return 0;
 }

 private Map<String, Object> decodeBody(String body) {
  return Arrays.stream(body.split("&"))
    .map(s -> s.split("="))
    .collect(Collectors.toMap(arr -> arr[0], arr -> arr[1]));
 }

 private String encodeBody(Map<String, Object> map) {
  return map.entrySet().stream().map(e -> e.getKey() + "=" + e.getValue()).collect(Collectors.joining("&"));
 }
}