获取SpringCloud gateway 响应的response的值，可以查看、修改

gateway获取、修改客户端请求Request的参数，我们在上一篇已经讲过了。那么网关发起请求后，微服务返回回来的response的值，还是要经过网关才发给客户端的。很多时候，我们希望能看到响应的值，或者修改它。那么怎么做呢？

    import org.reactivestreams.Publisher;
    import org.springframework.cloud.gateway.filter.GatewayFilterChain;
    import org.springframework.cloud.gateway.filter.GlobalFilter;
    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.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.Charset;
     
    /**
     * @author wuweifeng wrote on 2018/10/31.
     */
    @Component
    public class WrapperResponseGlobalFilter implements GlobalFilter, Ordered {
        @Override
        public int getOrder() {
            // -1 is response write filter, must be called before that
            return -2;
        }
     
        @Override
        public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain 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) {
                        Flux<? extends DataBuffer> fluxBody = (Flux<? extends DataBuffer>) body;
                        return super.writeWith(fluxBody.map(dataBuffer -> {
                            // probably should reuse buffers
                            byte[] content = new byte[dataBuffer.readableByteCount()];
                            dataBuffer.read(content);
                            //释放掉内存
                            DataBufferUtils.release(dataBuffer);
                            String s = new String(content, Charset.forName("UTF-8"));
                            //TODO，s就是response的值，想修改、查看就随意而为了
                            byte[] uppedContent = new String(content, Charset.forName("UTF-8")).getBytes();
                            return bufferFactory.wrap(uppedContent);
                        }));
                    }
                    // if body is not a flux. never got there.
                    return super.writeWith(body);
                }
            };
            // replace response with decorator
            return chain.filter(exchange.mutate().response(decoratedResponse).build());
        }
    }

就是定义这样一个GlobalFilter，注意order要小于-1.通过上面的类，就能查看服务端响应的值了。

参考：https://github.com/spring-cloud/spring-cloud-gateway/issues/47