Spring Cloud Gateway 2.x 跨域出现The 'Access-Control-Allow-Origin' header contains multiple values,....but only one is allowed 的问题解决

问题描述：vue前端调用后端登陆接口报错如下

Access to XMLHttpRequest at 'http://localhost:88/api/sys/login' from origin 'http://localhost:8002' has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header contains multiple values 'http://localhost:8002, http://localhost:8002', but only one is allowed.

 原因：spring NettyRoutingFilter 添加了两次Access-Control-Allow-Origin

解决方案：

1.新增CorsResponseHeaderFilter.java

import java.util.ArrayList;

import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.filter.NettyWriteResponseFilter;
import org.springframework.core.Ordered;
import org.springframework.http.HttpHeaders;
import org.springframework.web.server.ServerWebExchange;/**
 * 跨域请求头处理过滤器扩展
 */
public class CorsResponseHeaderFilter implements GlobalFilter, Ordered {
    @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.defer(() -> {
            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)))
                    .forEach(kv -> 
            {
                kv.setValue(new ArrayList<String>() {{add(kv.getValue().get(0));}});
            });
            
            return chain.filter(exchange);
        }));
    }
}

2.跨域全局配置：CorsConfiguration.java

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpMethod;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.reactive.CorsWebFilter;
import org.springframework.web.cors.reactive.DefaultCorsProcessor;
import org.springframework.web.cors.reactive.UrlBasedCorsConfigurationSource;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.util.pattern.PathPatternParser;

/**
 * 网关跨域配置
 */
@Configuration
public class CorsConfiguration {
    @Bean
    public CorsResponseHeaderFilter corsResponseHeaderFilter() {
        return new CorsResponseHeaderFilter();
    }
    
    @Bean
    public CorsWebFilter corsFilter() {
        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource(new PathPatternParser());
        source.registerCorsConfiguration("/**", buildCorsConfiguration());
        
        CorsWebFilter corsWebFilter = new CorsWebFilter(source, new DefaultCorsProcessor() {
            @Override
            protected boolean handleInternal(ServerWebExchange exchange, CorsConfiguration config, 
                boolean preFlightRequest) 
            {
                // 预留扩展点
                // if (exchange.getRequest().getMethod() == HttpMethod.OPTIONS) {
                    return super.handleInternal(exchange, config, preFlightRequest);
                // }

                // return true;
            }
        });
        
        return corsWebFilter;
    }
    
    private CorsConfiguration buildCorsConfiguration() {
        CorsConfiguration corsConfiguration = new CorsConfiguration();
        corsConfiguration.addAllowedOrigin("*");
        
        corsConfiguration.addAllowedMethod(HttpMethod.OPTIONS);
        corsConfiguration.addAllowedMethod(HttpMethod.POST);
        corsConfiguration.addAllowedMethod(HttpMethod.GET);
        corsConfiguration.addAllowedMethod(HttpMethod.PUT);
        corsConfiguration.addAllowedMethod(HttpMethod.DELETE);
        corsConfiguration.addAllowedMethod(HttpMethod.PATCH);
        // corsConfiguration.addAllowedMethod("*");
corsConfiguration.addAllowedHeader("*");
        
        corsConfiguration.setMaxAge(7200L);
        corsConfiguration.setAllowCredentials(true);
        return corsConfiguration;
    }
}