spring cloud gateway跨域冲突功能的开发

gateway可以实现支持跨域功能，但如果下游也支持跨域，会出现跨域冲突。
如何解决该问题，gateway对外输出相关跨域的httpheader,只要对重复的header去掉即可。


/**
 * @author starmark
 * @date 2020/5/11  下午9:29
 */
@Slf4j
public class GatewayCorsWebFilter implements WebFilter {
    @Autowired
    private IRouteService routeService;
    private final CorsProcessor processor;

    private static List<String> configHeaderNames = new ArrayList<>();
    static{
        configHeaderNames.add(HttpHeaders.ACCESS_CONTROL_ALLOW_CREDENTIALS);
        configHeaderNames.add(HttpHeaders.ACCESS_CONTROL_ALLOW_HEADERS);
        configHeaderNames.add(HttpHeaders.ACCESS_CONTROL_ALLOW_METHODS);
        configHeaderNames.add(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN);
        configHeaderNames.add(HttpHeaders.ACCESS_CONTROL_EXPOSE_HEADERS);

    }

    public GatewayCorsWebFilter() {
        this.processor = new DefaultCorsProcessor();
    }

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        String url = request.getPath().value();
        if (url.contains("webjars") || url.contains("swagger-resources") || url.contains("/v2/api-docs") || url.contains("doc.html") || url.contains("swagger-ui.html") ||
                url.contains(".css") || url.contains(".ico") || url.contains(".js") || url.contains(".png") || url.contains(".jpg")) {
            //如果发现是css或者js文件，直接放行
            return chain.filter(exchange);
        }
        String projectCode = RequestHelper.getRequestProjectCode(request);
        Assert.hasText(projectCode, "工程编码不存在");
        CorsConfiguration corsConfiguration = routeService.getGatewayProjectCorsConfiguration(projectCode);
        boolean isValid = this.processor.process(corsConfiguration, exchange);

        if (!isValid || CorsUtils.isPreFlightRequest(request)) {
            return Mono.empty();
        }
        //解决跨域冲突的问题
        ServerHttpResponseDecorator decoratedResponse = new ServerHttpResponseDecorator(exchange.getResponse()) {

            @Override
            public HttpHeaders getHeaders() {
                HttpHeaders httpHeaders=    HttpHeaders.writableHttpHeaders(getDelegate().getHeaders());
                dedupe(httpHeaders);
                return httpHeaders;
            }
            void dedupe(HttpHeaders headers) {
                if (headers == null) {
                    return;
                }
                for (String name : configHeaderNames) {
                    dedupe(headers, name.trim());
                }
            }

            private void dedupe(HttpHeaders headers, String name) {
                List<String> values = headers.get(name);
                if (values == null || values.size() <= 1) {
                    return;
                }

                headers.set(name, values.get(values.size() - 1));

            }
        };
        return chain.filter(exchange.mutate().response(decoratedResponse).build());
    }



}

上述是我跨域功能的代码，支持跨域功能及解决跨域冲突功能的问题。
上面有一个梗， exchange.getResponse().getHeaders()的header为只读，需要通过构造响应ServerHttpResponseDecorator 来解决只读的问题。