解决gateway跨域问题

只要与当前浏览器访问的url不同（协议，域名，端口号），就会产生跨域。

1. 配置文件解决，在gateway的配置文件中

spring:
    cloud:
        gateway:
          globalcors:
            cors-configurations:
              '[/**]':
                allowedOrigins: "*"
                allowedHeaders: "*"
                allowedMethods: "*"
          default-filters:
        		- DedupeResponseHeader=Vary Access-Control-Allow-Origin Access-Control-Allow-Credentials, RETAIN_FIRST

注：要加上最下边的配置，不然浏览器还是会报跨域问题，因为浏览器Vary 和 Access-Control-Allow-Origin 两个头重复了两次，其中浏览器对后者有唯一性限制！

2.配置类

@Component
public class CorsResponseHeaderFilter implements GlobalFilter, Ordered {
 
    private static final Logger logger = LoggerFactory.getLogger(CorsResponseHeaderFilter.class);
 
    private static final String ANY = "*";
 
    @Override
    public int getOrder() {
        // 指定此过滤器位于NettyWriteResponseFilter之后
        // 即待处理完响应体后接着处理响应头
        return NettyWriteResponseFilter.WRITE_RESPONSE_FILTER_ORDER + 1;
    }
 
    @Override
    @SuppressWarnings("serial")
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        return chain.filter(exchange).then(Mono.fromRunnable(() -> {
            exchange.getResponse().getHeaders().entrySet().stream()
                    .filter(kv -> (kv.getValue() != null && kv.getValue().size() > 1))
                    .filter(kv -> (kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)
                            || kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_CREDENTIALS)
                            || kv.getKey().equals(HttpHeaders.VARY)))
                    .forEach(kv ->
                    {
                        // Vary只需要去重即可
                        if(kv.getKey().equals(HttpHeaders.VARY))
                            kv.setValue(kv.getValue().stream().distinct().collect(Collectors.toList()));
                        else{
                            List value = new ArrayList<>();
                            if(kv.getValue().contains(ANY)){  //如果包含*，则取*
                                value.add(ANY);
                                kv.setValue(value);
                            }else{
                                value.add(kv.getValue().get(0)); // 否则默认取第一个
                                kv.setValue(value);
                            }
                        }
                    });
        }));
    }
}