Gateway 修改HTTP响应信息
实践Spring Cloud的过程中，使用Gateway作为路由组件，并且基于Gateway实现权限的验证、拦截、过滤，对于下游微服务的响应结果，我们总会有需要修改以统一数据格式，或者修改过滤用户没有权限看到的数据信息，这时候就需要有一个能够修改响应体的Filter。
Spring Cloud Gateway 版本为2.1.0
在当前版本，ModifyRequestBodyGatewayFilterFactory是官方提供的修改响应体的参考类，This filter is BETA and may be subject to change in a future release.，类的注释中说明这个类在以后版本中会改进，实际使用可以参考实现功能，但是性能影响较大，不过没有别的选择还是得选择这个。
实现
最终代码
先贴最终代码
public class ResponseDecryptionGlobalFilter implements GlobalFilter, Ordered {
private static Logger log = LoggerFactory.getLogger(ResponseDecryptionGlobalFilter.class);
@Override
public int getOrder() {
// 控制在NettyWriteResponseFilter后执行
return NettyWriteResponseFilter.WRITE_RESPONSE_FILTER_ORDER - 1;
}
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
return processResponse(exchange, chain);
}
private Mono<Void> processResponse(ServerWebExchange exchange, GatewayFilterChain chain) {
// 路由中如果不需要过滤则不进行过滤
if (!BooleanUtils.isTrue()) {
return chain.filter(exchange);
}
ServerHttpResponseDecorator responseDecorator = new ServerHttpResponseDecorator(exchange.getResponse()) {
@Override
public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
String originalResponseContentType = exchange.getAttribute(ORIGINAL_RESPONSE_CONTENT_TYPE_ATTR);
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.add(HttpHeaders.CONTENT_TYPE, originalResponseContentType);
ResponseAdapter responseAdapter = new ResponseAdapter(body, httpHeaders);
DefaultClientResponse clientResponse = new DefaultClientResponse(responseAdapter, ExchangeStrategies.withDefaults());
Mono<String> rawBody = clientResponse.bodyToMono(String.class).map(s -> s);
BodyInserter<Mono<String>, ReactiveHttpOutputMessage> bodyInserter = BodyInserters.fromPublisher(rawBody, String.class);
CachedBodyOutputMessage outputMessage = new CachedBodyOutputMessage(exchange, exchange.getResponse().getHeaders());
return bodyInserter.insert(outputMessage, new BodyInserterContext())
.then(Mono.defer(() -> {
Flux<DataBuffer> messageBody = outputMessage.getBody();
Flux<DataBuffer> flux = messageBody.map(buffer -> {
CharBuffer charBuffer = StandardCharsets.UTF_8.decode(buffer.asByteBuffer());
DataBufferUtils.release(buffer);
// 将响应信息转化为字符串
String responseStr = charBuffer.toString();
if (StringUtils.isNotBlank(responseStr)) {
try {
JSONObject result = JSONObject.parseObject(responseStr);
System.out.println(dataFilter(result));
if (result.containsKey("data")) {
responseStr = dataFilter(result);
} else {
log.error("响应结果序列化异常:{}", responseStr);
}
} catch (JSONException e) {
log.error("响应结果序列化异常:{}", responseStr);
}
}
return getDelegate().bufferFactory().wrap(responseStr.getBytes(StandardCharsets.UTF_8));
});
HttpHeaders headers = getDelegate().getHeaders();
// 修改响应包的大小，不修改会因为包大小不同被浏览器丢掉
flux = flux.doOnNext(data -> headers.setContentLength(data.readableByteCount()));
return getDelegate().writeWith(flux);
}));
}
};
return chain.filter(exchange.mutate().response(responseDecorator).build());
}
/**
* 权限数据过滤
*
* @param result
* @return
*/
private String dataFilter(JSONObject result) {
Object data = result.get("data");
return result.toJSONString();
}
private class ResponseAdapter implements ClientHttpResponse {
private final Flux<DataBuffer> flux;
private final HttpHeaders headers;
@SuppressWarnings("unchecked")
private ResponseAdapter(Publisher<? extends DataBuffer> body, HttpHeaders headers) {
this.headers = headers;
if (body instanceof Flux) {
flux = (Flux) body;
} else {
flux = ((Mono) body).flux();
}
}
@Override
public Flux<DataBuffer> getBody() {
return flux;
}
@Override
public HttpHeaders getHeaders() {
return headers;
}
@Override
public HttpStatus getStatusCode() {
return null;
}
@Override
public int getRawStatusCode() {
return 0;
}
@Override
public MultiValueMap<String, ResponseCookie> getCookies() {
return null;
}
}
}
踩过的坑
响应体报文过大: 起初直接读取buffer的响应信息，包小的情况没有问题，但是包大了会抛出json无法转换异常，因为没能读取完整的响应内容，参考ModifyRequestBodyGatewayFilter，等待buffer全部读完再转为数组，然后执行处理。本质原因是底层的Reactor-Netty的数据块读取大小限制导致获取到的DataBuffer实例里面的数据是不完整的。 修改响应信息后，响应的ContentLength会发生变化，忘记修改response中的Content-Length长度，导致前端请求无法获取修改后的响应结果。flux = flux.doOnNext(data -> headers.setContentLength(data.readableByteCount()));order值必须小于-1，因为覆盖返回响应体，自定义的GlobalFilter必须比NettyWriteResponseFilter处理完后执行。order越小越早进行处理，越晚处理响应结果。
理解ServerWebExchange
先看ServerWebExchange的注释：
Contract for an HTTP request-response interaction. Provides access to the HTTP request and response and also exposes additional server-side processing related properties and features such as request attributes.
翻译一下大概是：
ServerWebExchange是一个**HTTP请求-响应交互的契约。**提供对HTTP请求和响应的访问，并公开额外的服务器端处理相关属性和特性，如请求属性。
ServerWebExchange有点像Context的角色，我把它理解为http请求信息在Filter透传的容器，之所以称之为容器，因为它可以存储我们像放进去的数据。
注意：
ServerHttpRequest是一个只读类，因此需要通过下面例子的方法来进行修改，对于读多写少的场景，这种设计模式是值得借鉴的
ServerHttpRequest newRequest = request.mutate().headers("key","value").path("/myPath").build();
ServerWebExchange newExchange = exchange.mutate().response(responseDecorator).build();
Gateway 修改返回的响应体
问题描述：
在gateway中修改返回的响应体，在全局Filter中添加如下代码：
import org.springframework.core.Ordered;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;
@Component
public class RequestGlobalFilter implements GlobalFilter, Ordered {
//...
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
//...
ResponseDecorator decorator = new ResponseDecorator(exchange.getResponse());
return chain.filter(exchange.mutate().response(decorator).build());
}
@Override
public int getOrder() {
return -1000;
}
}
通过.response(decorator)设置一个响应装饰器（自定义），以下是装饰器具体实现：
import cn.hutool.json.JSONObject;
import org.reactivestreams.Publisher;
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 reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import java.nio.charset.Charset;
/**
* @author visy.wang
* @desc 响应装饰器（重构响应体）
*/
public class ResponseDecorator extends ServerHttpResponseDecorator{
public ResponseDecorator(ServerHttpResponse delegate){
super(delegate);
}
@Override
@SuppressWarnings(value = "unchecked")
public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
if(body instanceof Flux) {
Flux<DataBuffer> fluxBody = (Flux<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);
DataBufferUtils.release(join);// 释放掉内存
String bodyStr = new String(content, Charset.forName("UTF-8"));
//修改响应体
bodyStr = modifyBody(bodyStr);
getDelegate().getHeaders().setContentLength(bodyStr.getBytes().length);
return bufferFactory().wrap(bodyStr.getBytes());
}));
}
return super.writeWith(body);
}
//重写这个函数即可
private String modifyBody(String jsonStr){
JSONObject json = new JSONObject(jsonStr);
//TODO...修改响应体
return json.toString();
}
}
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。
