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();
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