SpringCloud Gateway解决CROS跨域问题

[2、手动写一个 CorsResponseHeaderFilter 的 GlobalFilter 去修改Response中的头](#2、手动写一个 CorsResponseHeaderFilter 的 GlobalFilter 去修改Response中的头)

一、问题

前端代码访问后端代码时候会出现

复制代码

Access to XMLHttpRequest at 'http://localhost:8080/user/logout' from origin 'http://localhost:8800' has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header contains multiple values '*, *', but only one is allowed.

这种报错，前端会显示不允许有多个'Access-Control-Allow-Origin' CORS头

二、原因

仔细查看返回的响应头，里面包含了两份Access-Control-Allow-Origin头。

二、解决方法

1、gateway设置允许跨域

使用yml格式去设置允许跨域

java 复制代码

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

2、手动写一个 `CorsResponseHeaderFilter` 的 `GlobalFilter` 去修改Response中的头

java 复制代码

@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<String> 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);
                            }
                        }
                    });
        }));
    }
}

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