说明：

SpringCloud-Gateway是基于webflux框架的(响应式编程WEB框架)，就导致不能用正常的springMVC获取httpServletResponse返回值方法来统一获取返回值，所以本文就针对解决此问题
注意:
1.如果返回不是json的话（一般项目都是JSON），就不要转为json，是什么格式就用什么格式解析
2.代码中"//TODO" 标记的地方，即可对返回值进行统一处理，也可以拿到gatewayContext（gatewayContext可以看我这篇博文）
3.代码形式如此，不要纠结代码写法。reactor的思想和API使然
4.废话不多说，看代码吧

Filter代码：

import cn.hutool.http.ContentType;
import cn.hutool.http.Header;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.google.common.base.Charsets;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.reactivestreams.Publisher;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.core.io.buffer.DefaultDataBufferFactory;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.http.server.reactive.ServerHttpResponseDecorator;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.util.Objects;

/**
 * @author kam
 *
 *         <p>
 *         返回内容覆盖过滤器 处理返回内容
 *         </p>
 */
@Component
@Slf4j
public class ResponseCoverFilter implements WebFilter, Ordered {

    /**
     * 返回值处理
     *
     * @param exchange
     * @param chain
     * @return
     */
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        ServerHttpResponse originalResponse = exchange.getResponse();
        DataBufferFactory bufferFactory = originalResponse.bufferFactory();
        ServerHttpResponseDecorator decoratedResponse = new ServerHttpResponseDecorator(originalResponse) {
            @Override
            public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
                if (body instanceof Flux) {
                    if (ContentType.JSON.toString()
                        .equals(originalResponse.getHeaders().getFirst(Header.CONTENT_TYPE.toString()))) {
                        Flux<? extends DataBuffer> fluxBody = (Flux<? extends DataBuffer>)body;
                        return super.writeWith(fluxBody.buffer().map(dataBuffers -> {
                            DataBufferFactory dataBufferFactory = new DefaultDataBufferFactory();
                            DataBuffer join = dataBufferFactory.join(dataBuffers);
                            byte[] content = new byte[join.readableByteCount()];
                            join.read(content);
                            // 释放掉内存
                            DataBufferUtils.release(join);
                            String responseData = new String(content, Charsets.UTF_8);
                            GatewayContext gatewayContext = exchange.getAttribute(GatewayContext.CACHE_GATEWAY_CONTEXT);
                            if (Objects.nonNull(gatewayContext) && StringUtils.isNotBlank(responseData)) {
                                //此处拿到参数转为JSONObject 处理参数内容
                                JSONObject jsonObject = JSON.parseObject(responseData);
                                //TODO 对返回值JSONObject进行put remove get等操作

                                responseData = JSONObject.toJSONString(jsonObject, SerializerFeature.MapSortField);
                            }
                            byte[] uppedContent = responseData.getBytes(Charsets.UTF_8);
                            return bufferFactory.wrap(uppedContent);
                        }));
                    }
                }
                return super.writeWith(body);
            }

        };
        // replace response with decorator
        return chain.filter(exchange.mutate().response(decoratedResponse).build());
    }

    @Override
    public int getOrder() {
        return 101;
    }
}

希望能帮到你，有问题在留言区讨论~~