springcloud gateway 添加post请求参数

在 Spring Cloud Gateway 中，可以通过修改请求的属性来添加 POST 请求参数。下面是一个示例代码：

@Component
public class AddParameterFilter implements GatewayFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();

        // 获取请求方法
        HttpMethod method = request.getMethod();
        if (method == HttpMethod.POST) {
            // 获取请求参数
            MultiValueMap<String, String> queryParams = request.getQueryParams();
            // 将请求参数添加到请求体中
            Flux<DataBuffer> body = DataBufferUtils.join(exchange.getRequest().getBody())
                    .map(dataBuffer -> {
                        byte[] bytes = new byte[dataBuffer.readableByteCount()];
                        dataBuffer.read(bytes);
                        DataBufferUtils.release(dataBuffer);
                        return bytes;
                    });
            String bodyStr = new String(ByteUtils.revert(body.block().asByteBuffer().array()));
            for (String key : queryParams.keySet()) {
                String value = queryParams.getFirst(key);
                bodyStr = bodyStr + "&" + key + "=" + value;
            }
            byte[] bytes = bodyStr.getBytes(StandardCharsets.UTF_8);
            DataBuffer buffer = exchange.getResponse().bufferFactory().wrap(bytes);
            HttpHeaders headers = new HttpHeaders();
            headers.putAll(exchange.getRequest().getHeaders());
            headers.remove(HttpHeaders.CONTENT_LENGTH);
            headers.add(HttpHeaders.CONTENT_LENGTH, Integer.toString(bytes.length));
            headers.set(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_FORM_URLENCODED_VALUE);
            CachedBodyOutputMessage outputMessage = new CachedBodyOutputMessage(exchange, headers);
            return DataBufferUtils.write(buffer, outputMessage.getBody())
                    .then(Mono.defer(() -> {
                        ServerHttpRequest decorator = decorate(exchange, headers, outputMessage);
                        return chain.filter(exchange.mutate().request(decorator).build());
                    }));
        }
        return chain.filter(exchange);
    }

    private ServerHttpRequestDecorator decorate(ServerWebExchange exchange, HttpHeaders headers,
                                                CachedBodyOutputMessage outputMessage) {
        return new ServerHttpRequestDecorator(exchange.getRequest()) {
            @Override
            public HttpHeaders getHeaders() {
                long contentLength = headers.getContentLength();
                HttpHeaders httpHeaders = new HttpHeaders();
                httpHeaders.putAll(super.getHeaders());
                if (contentLength > 0) {
                    httpHeaders.setContentLength(contentLength);
                } else {
                    httpHeaders.set(HttpHeaders.TRANSFER_ENCODING, "chunked");
                }
                return httpHeaders;
            }

            @Override
            public Flux<DataBuffer> getBody() {
                return outputMessage.getBody();
            }
        };
    }
}

这个过滤器会将请求的参数添加到请求体中，然后将请求体设置到请求中。需要注意的是，这个过滤器只会在 POST 请求中生效。