1、前言

在网关应用中，如果我想要记录所有请求的参数，然后将请求流转到下游，就会遇到读取RequestBody的问题。无论在Spring5的webflux编程或者普通web编程中，只能从request中获取body一次，后面无法再获取，这个问题怎么解决呢？
网上博客有多种处理办法，对不同的spring cloud gateway版本不一定有用。本文着重说明下版本环境：
spring cloud gateway 2.2.1.RELEASE版，并且在spring cloud gateway 2.2.2.RELEASE也验证通过。spring cloud版本为Hoxton.SR1。

2、普通读取requestbody的示例

controller类代码如下：

package cn.iocoder.springcloud.labx08.gatewaydemo.controller;

import cn.hutool.json.JSONUtil;
import cn.iocoder.springcloud.labx08.gatewaydemo.domain.Blog;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.*;

import javax.servlet.http.HttpServletRequest;
import java.util.HashMap;
import java.util.Map;

@RestController
@RequestMapping("blog")
public class DemoController {

    private Logger logger = LoggerFactory.getLogger(getClass());

    /**
     * 测试 @Value 注解的属性
     */
    @PostMapping("/blog01")
    public Map<String, Object> blog01(@RequestBody Blog blog,HttpServletRequest request) {
        Map<String, Object> result = new HashMap<>();
        result.put("params" , request.getParameter("token"));
        result.put("bodydata" , JSONUtil.toJsonStr(blog));
        return result;
    }
}

Blog代码如下：

@Data
public class Blog{
    private String title;

    private String content;

    @JsonFormat(pattern = "yyyy-MM-dd")
    private Date publishDate;
}

请求示例

3、使用spring cloud gateway代理

yaml配置

server:
  port: 8888

spring:
  application:
    name: gateway-application
  cloud:
    # Spring Cloud Gateway 配置项，对应 GatewayProperties 类
    gateway:
      # 路由配置项，对应 RouteDefinition 数组
      routes:
        - id: csdn1 # 路由的编号
          uri: http://localhost:9090
          predicates: # 断言，作为路由的匹配条件，对应 RouteDefinition 数组
            - Path=/csdnblog/**
          filters:
            - StripPrefix=1

gateway代码，该代码提供了两种读取body参数的方法，分别为APPLICATION_JSON，APPLICATION_FORM_URLENCODED。处理办法是在向下游请求时，构造新的ServerWebExchange，并将参数传递进去。如果依然使用原ServerWebExchange向下游传递，下游由于请求参数不匹配，直接报404错误。

package cn.iocoder.springcloud.labx08.gatewaydemo.filter;

import cn.iocoder.springcloud.labx08.gatewaydemo.context.GatewayContext;
import lombok.extern.slf4j.Slf4j;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.filter.factory.rewrite.CachedBodyOutputMessage;
import org.springframework.cloud.gateway.route.Route;
import org.springframework.cloud.gateway.support.BodyInserterContext;
import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ReactiveHttpOutputMessage;
import org.springframework.http.codec.HttpMessageReader;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpRequestDecorator;
import org.springframework.stereotype.Component;
import org.springframework.util.CollectionUtils;
import org.springframework.util.MultiValueMap;
import org.springframework.web.reactive.function.BodyInserter;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.server.HandlerStrategies;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.io.UnsupportedEncodingException;
import java.net.URI;
import java.net.URLEncoder;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.Map;

/**
 * Gateway Context Filter
 * @author chenggang
 * @date 2019/01/29
 */

@Slf4j
@Component
public class GatewayContextFilter implements GlobalFilter, Ordered {
    /**
     * default HttpMessageReader
     */
    private static final List<HttpMessageReader<?>> MESSAGE_READERS = HandlerStrategies.withDefaults().messageReaders();

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        GatewayContext gatewayContext = new GatewayContext();
        HttpHeaders headers = request.getHeaders();
        gatewayContext.setRequestHeaders(headers);
        gatewayContext.getAllRequestData().addAll(request.getQueryParams());
        /*
         * save gateway context into exchange
         */
        exchange.getAttributes().put(GatewayContext.CACHE_GATEWAY_CONTEXT,gatewayContext);
        MediaType contentType = headers.getContentType();
        if(headers.getContentLength()>0){
            if(MediaType.APPLICATION_JSON.equals(contentType) || MediaType.APPLICATION_JSON_UTF8.equals(contentType)){
                return readBody(exchange, chain,gatewayContext);
            }
            if(MediaType.APPLICATION_FORM_URLENCODED.equals(contentType)){
                return readFormData(exchange, chain,gatewayContext);
            }
        }
        log.debug("[GatewayContext]ContentType:{},Gateway context is set with {}",contentType, gatewayContext);
        return chain.filter(exchange);

    }


    @Override
    public int getOrder() {
        return -2;
    }


    /**
     * ReadFormData
     * @param exchange
     * @param chain
     * @return
     */
    private Mono<Void> readFormData(ServerWebExchange exchange, GatewayFilterChain chain, GatewayContext gatewayContext){
        HttpHeaders headers = exchange.getRequest().getHeaders();
        return exchange.getFormData()
                .doOnNext(multiValueMap -> {
                    gatewayContext.setFormData(multiValueMap);
                    gatewayContext.getAllRequestData().addAll(multiValueMap);
                    log.debug("[GatewayContext]Read FormData Success");
                })
                .then(Mono.defer(() -> {
                    Charset charset = headers.getContentType().getCharset();
                    charset = charset == null? StandardCharsets.UTF_8:charset;
                    String charsetName = charset.name();
                    MultiValueMap<String, String> formData = gatewayContext.getFormData();
                    /*
                     * formData is empty just return
                     */
                    if(null == formData || formData.isEmpty()){
                        return chain.filter(exchange);
                    }
                    StringBuilder formDataBodyBuilder = new StringBuilder();
                    String entryKey;
                    List<String> entryValue;
                    try {
                        /*
                         * repackage form data
                         */
                        for (Map.Entry<String, List<String>> entry : formData.entrySet()) {
                            entryKey = entry.getKey();
                            entryValue = entry.getValue();
                            if (entryValue.size() > 1) {
                                for(String value : entryValue){
                                    formDataBodyBuilder.append(entryKey).append("=").append(URLEncoder.encode(value, charsetName)).append("&");
                                }
                            } else {
                                formDataBodyBuilder.append(entryKey).append("=").append(URLEncoder.encode(entryValue.get(0), charsetName)).append("&");
                            }
                        }
                    }catch (UnsupportedEncodingException e){}
                    /*
                     * substring with the last char '&'
                     */
                    String formDataBodyString = "";
                    if(formDataBodyBuilder.length()>0){
                        formDataBodyString = formDataBodyBuilder.substring(0, formDataBodyBuilder.length() - 1);
                    }
                    /*
                     * get data bytes
                     */
                    byte[] bodyBytes =  formDataBodyString.getBytes(charset);
                    int contentLength = bodyBytes.length;
                    HttpHeaders httpHeaders = new HttpHeaders();
                    httpHeaders.putAll(exchange.getRequest().getHeaders());
                    httpHeaders.remove(HttpHeaders.CONTENT_LENGTH);
                    /*
                     * in case of content-length not matched
                     */
                    httpHeaders.setContentLength(contentLength);
                    /*
                     * use BodyInserter to InsertFormData Body
                     */
                    BodyInserter<String, ReactiveHttpOutputMessage> bodyInserter = BodyInserters.fromObject(formDataBodyString);
                    CachedBodyOutputMessage cachedBodyOutputMessage = new CachedBodyOutputMessage(exchange, httpHeaders);
                    log.debug("[GatewayContext]Rewrite Form Data :{}",formDataBodyString);
                    return bodyInserter.insert(cachedBodyOutputMessage,  new BodyInserterContext())
                            .then(Mono.defer(() -> {
                                ServerHttpRequestDecorator decorator = new ServerHttpRequestDecorator(
                                        exchange.getRequest()) {
                                    @Override
                                    public HttpHeaders getHeaders() {
                                        return httpHeaders;
                                    }
                                    @Override
                                    public Flux<DataBuffer> getBody() {
                                        return cachedBodyOutputMessage.getBody();
                                    }
                                };
                                return chain.filter(exchange.mutate().request(decorator).build());
                            }));
                }));
    }

    /**
     * ReadJsonBody
     * @param exchange
     * @param chain
     * @return
     */
    private Mono<Void> readBody(ServerWebExchange exchange, GatewayFilterChain chain, GatewayContext gatewayContext){
        return DataBufferUtils.join(exchange.getRequest().getBody())
                .flatMap(dataBuffer -> {
                    /*
                     * read the body Flux<DataBuffer>, and release the buffer
                     * //TODO when SpringCloudGateway Version Release To G.SR2,this can be update with the new version's feature
                     * see PR https://github.com/spring-cloud/spring-cloud-gateway/pull/1095
                     */
                    byte[] bytes = new byte[dataBuffer.readableByteCount()];
                    dataBuffer.read(bytes);
                    DataBufferUtils.release(dataBuffer);
                    Flux<DataBuffer> cachedFlux = Flux.defer(() -> {
                        DataBuffer buffer = exchange.getResponse().bufferFactory().wrap(bytes);
                        DataBufferUtils.retain(buffer);
                        return Mono.just(buffer);
                    });
                    log.debug("[GatewayContext]Read JsonBody Success");
                    /*
                     * repackage ServerHttpRequest
                     */
                    ServerHttpRequest mutatedRequest = new ServerHttpRequestDecorator(exchange.getRequest()) {
                        @Override
                        public Flux<DataBuffer> getBody() {
                            return cachedFlux;
                        }
                    };
                    ServerWebExchange mutatedExchange = exchange.mutate().request(mutatedRequest).build();
                    return ServerRequest.create(mutatedExchange, MESSAGE_READERS)
                            .bodyToMono(String.class)
                            .doOnNext(objectValue -> {
                                gatewayContext.setRequestBody(objectValue);
                            }).then(chain.filter(mutatedExchange/*exchange*/));
                });
    }

}

源码：https://github.com/muziye2013/SpringBoot-Labs 请参考labx-08/labx-08-ex-gateway-demo02，labx-08/labx-08-ex-gateway-demo02-controller两个模块的代码。

主要参考的文章及代码：
关于Spring-webflux编程中body只能获取一次的问题解决方案：
SpringCloud Gateway 记录缓存请求Body和Form表单
Spring Cloud Gateway-ServerWebExchange核心方法与请求或者响应内容的修改 注意该文的处理方法只适用于其对应版本
Spring Cloud Gateway 之 Filter，对于filter的讲解很详细。
除此之外，还要学会从spring cloud gateway的issue中寻找问题以及对应的处理办法。