實踐Spring Cloud的過程中，使用Gateway作爲路由組件，並且基於Gateway實現權限的驗證、攔截、過濾，對於下游微服務的響應結果，我們總會有需要修改以統一數據格式，或者修改過濾用戶沒有權限看到的數據信息，這時候就需要有一個能夠修改響應體的Filter。
Spring Cloud Gateway 版本爲2.1.0
在當前版本，ModifyRequestBodyGatewayFilterFactory是官方提供的修改響應體的參考類，This filter is BETA and may be subject to change in a future release.，類的註釋中說明這個類在以後版本中會改進，實際使用可以參考實現功能，但是性能影響較大，不過沒有別的選擇還是得選擇這個。
實現
最終代碼
先貼最終代碼
public class ResponseDecryptionGlobalFilter implements GlobalFilter, Ordered {
private static Logger log = LoggerFactory.getLogger(ResponseDecryptionGlobalFilter.class);
@Override
public int getOrder() {
// 控制在NettyWriteResponseFilter後執行
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) {
// 路由中如果不需要過濾則不進行過濾
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);
// 將響應信息轉化爲字符串
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("響應結果序列化異常:{}", responseStr);
}
} catch (JSONException e) {
log.error("響應結果序列化異常:{}", responseStr);
}
}
return getDelegate().bufferFactory().wrap(responseStr.getBytes(StandardCharsets.UTF_8));
});
HttpHeaders headers = getDelegate().getHeaders();
// 修改響應包的大小，不修改會因爲包大小不同被瀏覽器丟掉
flux = flux.doOnNext(data -> headers.setContentLength(data.readableByteCount()));
return getDelegate().writeWith(flux);
}));
}
};
return chain.filter(exchange.mutate().response(responseDecorator).build());
}
/**
* 權限數據過濾
*
* @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;
}
}
}
踩過的坑
- 響應體報文過大: 起初直接讀取buffer的響應信息，包小的情況沒有問題，但是包大了會拋出json無法轉換異常，因爲沒能讀取完整的響應內容，參考ModifyRequestBodyGatewayFilter，等待buffer全部讀完再轉爲數組，然後執行處理。本質原因是底層的Reactor-Netty的數據塊讀取大小限制導致獲取到的DataBuffer實例裏面的數據是不完整的。
- 修改響應信息後，響應的ContentLength會發生變化，忘記修改response中的Content-Length長度，導致前端請求無法獲取修改後的響應結果。
flux = flux.doOnNext(data -> headers.setContentLength(data.readableByteCount()));
- order值必須小於-1，因爲覆蓋返回響應體，自定義的GlobalFilter必須比NettyWriteResponseFilter處理完後執行。order越小越早進行處理，越晚處理響應結果。
理解ServerWebExchange
先看ServerWebExchange的註釋：
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.
翻譯一下大概是：
ServerWebExchange是一個**HTTP請求-響應交互的契約。**提供對HTTP請求和響應的訪問，並公開額外的服務器端處理相關屬性和特性，如請求屬性。
ServerWebExchange有點像Context的角色，我把它理解爲http請求信息在Filter透傳的容器，之所以稱之爲容器，因爲它可以存儲我們像放進去的數據。
注意：
ServerHttpRequest是一個只讀類，因此需要通過下面例子的方法來進行修改，對於讀多寫少的場景，這種設計模式是值得借鑑的
ServerHttpRequest newRequest = request.mutate().headers("key","value").path("/myPath").build();
ServerWebExchange newExchange = exchange.mutate().response(responseDecorator).build();
參考：https://juejin.im/post/5cdfb8fe6fb9a07f04201838#heading-10