获取并修改springcloud gateway响应体的问题_spring cloud gateway 在nettywriteresponsefilter之前获取

问题说明

网关用springcloud gateway路由调用接口，现在需要获取到接口响应数据并做修改。遇到如下几个问题：
1.用postman调用接口没有响应，后端也没报错信息；
2.有响应数据但数据不完整，解析出错；
3.数据响应类型丢失。
头一回用springcloud gateway就遇到这几个问题，困扰好久不过也是长知识了。下面则是我的解决办法，亲测可用，如有不完善的地方请多指教。

使用全局过滤器GlobalFilter获取响应数据

import lombok.extern.slf4j.Slf4j;
import org.reactivestreams.Publisher;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.filter.NettyWriteResponseFilter;
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.HttpHeaders;
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 reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.nio.charset.StandardCharsets;

@Slf4j
@Component
public class TestFilter implements GlobalFilter, Ordered {
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpResponse originalResponse = exchange.getResponse();
        DataBufferFactory bufferFactory = originalResponse.bufferFactory();
        // 定义新的消息头
        HttpHeaders headers = new HttpHeaders();
        headers.putAll(exchange.getResponse().getHeaders());
        
    //在ServerHttpResponseDecorator 这个类里面实现对响应数据的处理，复写writeWith()和 getHeaders()两个方法
        ServerHttpResponseDecorator decoratedResponse = new ServerHttpResponseDecorator(originalResponse) {
            @Override
            public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
                if (body instanceof Flux) {
                    Flux<? extends DataBuffer> fluxBody = (Flux<? extends DataBuffer>) body;
                    return super.writeWith(fluxBody.buffer().map(dataBuffer -> {
                    
                        //过滤器后置逻辑
                        //上面第2个问题是因为响应体数据量太大，分段截取时造成的数据错误问题
                        //使用dataBufferFactory.join解决该问题
                        
                        DataBufferFactory dataBufferFactory = new DefaultDataBufferFactory();
                        DataBuffer join = dataBufferFactory.join(dataBuffer);
                        byte[] content = new byte[join.readableByteCount()];
                        join.read(content);
                        //释放掉内存
                        DataBufferUtils.release(join);
                        //实际获取到的响应数据
                        String responseStr = new String(content, StandardCharsets.UTF_8);

                        //这里 自定义一个新的响应数据，作为返回数据，相当于修改响应体
                        String newResponseStr = "{\"hhhh\":666}";
                        byte[] newResponseBytes = newResponseStr.getBytes(StandardCharsets.UTF_8);
                        
                        // 给header设置长度 解决上面第1个无响应数据的问题
                        headers.setContentLength(newResponseBytes.length);
                        HttpHeaders httpHeaders = originalResponse.getHeaders();
                        
                        //设置响应体类型 Content-Type 解决第3个问题
                        httpHeaders.add("Content-Type", "application/json; charset=UTF-8");
                        //newResponseBytes是修改之后要返回的响应体数据
                        return bufferFactory.wrap(newResponseBytes);
                    }));
                }
                return super.writeWith(body);
            }

            @Override
            public HttpHeaders getHeaders() {
                HttpHeaders httpHeaders = new HttpHeaders();
                httpHeaders.putAll(super.getHeaders());
                //由于修改了请求体的body，导致content-length长度不确定，因此使用分块编码
                httpHeaders.remove(HttpHeaders.CONTENT_LENGTH);
                httpHeaders.set(HttpHeaders.TRANSFER_ENCODING, "chunked");
                return httpHeaders;
            }

        };
        return chain.filter(exchange.mutate().response(decoratedResponse).build());
    }

    @Override
    public int getOrder() {
        //order越小越先执行 当前Filter要在NettyWriteResponseFilter 之前运行
        return NettyWriteResponseFilter.WRITE_RESPONSE_FILTER_ORDER - 1;
    }
}
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