SpringCloud GateWay通过过滤器GatewayFilter修改请求或响应内容

Spring Cloud Gateway在有些场景中需要获取request body内容进行参数校验或参数修改，我们通过在GatewayFilter中获取请求内容来获取和修改请求体，下面我们就基于ServerWebExchange来实现：

ServerWebExchange命名为服务网络交换器，存放着重要的请求-响应属性、请求实例和响应实例等等，有点像Context的角色，其中有两个重要的接口方法：

   // 获取ServerHttpRequest对象
    ServerHttpRequest getRequest();

    // 获取ServerHttpResponse对象
    ServerHttpResponse getResponse();

创建一个GatewayFilter，必须实现Ordered接口，返回一个小于-1的order值，这是因为NettyWriteResponseFilter的order值为-1，我们需要覆盖返回响应体的逻辑，自定义的GlobalFilter必须比NettyWriteResponseFilter优先执行。

public class RequestGatewayFilter implements GatewayFilter, Ordered {
   
   
@Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
   
   
        ServerHttpRequest request = exchange.getRequest();
        HttpHeaders headers = request.getHeaders();

        // 处理参数
        MediaType contentType = headers.getContentType();

        if (exchange.getRequest().getMethod().equals(HttpMethod.POST)) {
   
   
        //Content-type为“application/json”
            if (MediaType.APPLICATION_JSON.isCompatibleWith(contentType)) {
   
   
                return readBody(exchange, chain);
            }
            //Content-type为“application/x-www-form-urlencoded”
            else if(MediaType.APPLICATION_FORM_URLENCODED.isCompatibleWith(contentType)){
   
   
                GatewayContext gatewayContext = new GatewayContext();
                gatewayContext.setRequestHeaders(headers);
                gatewayContext.getAllRequestData().addAll(request.getQueryParams());
                exchange.getAttributes().put(GatewayContext.CACHE_GATEWAY_CONTEXT,gatewayContext);

                return readFormData(exchange, chain, gatewayContext);

            }
//Content-type为“multipart/form-data”
else if (MediaType.MULTIPART_FORM_DATA.isCompatibleWith(contentType)) {
   
   
                GatewayContext gatewayContext = new GatewayContext();
                gatewayContext.setRequestHeaders(headers);
                gatewayContext.getAllRequestData().addAll(request.getQueryParams());
                exchange.getAttributes().put(GatewayContext.CACHE_GATEWAY_CONTEXT,gatewayContext);

                return readMultipartData(exchange, chain, gatewayContext);
            }
        } else {
   
   
            return readGetData(exchange, chain);
        }
        return chain.filter(exchange);
    }
    @Override
    public int getOrder() {
   
   
        return -2;
    }
}

处理content-type为application/json的方法：

/**
     * ReadJsonBody
     *
     * @param exchange
     * @param chain
     * @return
     */
    private Mono<Void> readBody(ServerWebExchange exchange, GatewayFilterChain chain) {
   
   
        /**
         * join the body
         */
        return DataBufferUtils.join(exchange.getRequest().getBody(