SpringCloud-Gateway自定义过滤器，解决body流不能重复读的问题

        网上的代码千奇百怪，这个是我测试后整理的。

        当前端请求不含body时，也能兼容。

1.读取body流进行缓存

/**
 * 获取body请求数据（解决流不能重复读取问题）
 * 这个过滤器的order设置的是Ordered.HIGHEST_PRECEDENCE，即最高优先级的过滤器。
 * 优先级设置这么高的原因是某些系统内置的过滤器可能也会去读body，
 * 这样就会导致我们自定义过滤器中获取body的时候报body只能读取一次这样的错误
 * @author yuchen
 */
@Slf4j
@Component
public class CacheRequestFilter implements GlobalFilter, Ordered {
 
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        if (request.getHeaders().getContentType() == null) {
            return chain.filter(exchange);
        }
        HttpMethod method = request.getMethod();
        if (method == null || method.matches("GET") || method.matches("DELETE")) {
            return chain.filter(exchange);
        }
        //当body中没有缓存时，只会执行这一个拦截器， 原因是fileMap中的代码没有执行，所以需要在波多野为空时构建一个空的缓存
        DefaultDataBufferFactory defaultDataBufferFactory = new DefaultDataBufferFactory();
        DefaultDataBuffer defaultDataBuffer = defaultDataBufferFactory.allocateBuffer(0);
        //构建新数据流， 当body为空时，构建空流
        Flux<DataBuffer> bodyDataBuffer = exchange.getRequest().getBody().defaultIfEmpty(defaultDataBuffer);
        return DataBufferUtils.join(bodyDataBuffer)
                .flatMap(dataBuffer -> {
                    DataBufferUtils.retain(dataBuffer);
                    Flux<DataBuffer> cachedFlux = Flux
                            .defer(() -> Flux.just(dataBuffer.slice(0, dataBuffer.readableByteCount())));
                    ServerHttpRequest mutatedRequest = new ServerHttpRequestDecorator(exchange.getRequest()) {
                        @Override
                        public Flux<DataBuffer> getBody() {
                            return cachedFlux;
                        }
                    };
                    //exchange.getAttributes().put(CACHE_REQUEST_BODY_OBJECT_KEY, cachedFlux);
                    return chain.filter(exchange.mutate().request(mutatedRequest).build());
                });
    }
 
    @Override
    public int getOrder() {
        return Ordered.HIGHEST_PRECEDENCE;
    }
 
}

2.从缓存读取body，就可以重复读：

    private static String resolveBodyFromRequest(ServerHttpRequest serverHttpRequest) {
        // 获取请求体
        Flux<DataBuffer> body = serverHttpRequest.getBody();
        AtomicReference<String> bodyRef = new AtomicReference<>();
        body.subscribe(buffer -> {
            CharBuffer charBuffer = StandardCharsets.UTF_8.decode(buffer.asByteBuffer());
            DataBufferUtils.release(buffer);
            bodyRef.set(charBuffer.toString());
        });
        return bodyRef.get();
    }