fix：【Gateway 网关】CorsResponseHeaderFilter 处理不正确的问题

yudao-gateway/src/main/java/cn/iocoder/yudao/gateway/filter/cors/CorsResponseHeaderFilter.java

@@ -9,7 +9,10 @@ import org.springframework.stereotype.Component;
 import org.springframework.web.server.ServerWebExchange;
 import reactor.core.publisher.Mono;
 
-import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
 
 /**
  * 解决 Spring Cloud Gateway 2.x 跨域时，出现重复 Origin 的 BUG
@@ -31,13 +34,19 @@ public class CorsResponseHeaderFilter implements GlobalFilter, Ordered {
     @Override
     public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
         return chain.filter(exchange).then(Mono.defer(() -> {
-            exchange.getResponse().getHeaders().entrySet().stream()
+            // https://gitee.com/zhijiantianya/yudao-cloud/pulls/177/
+            List<String> keysToModify = 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));
-                    }}));
+                    .map(Map.Entry::getKey)
+                    .collect(Collectors.toList());
+            keysToModify.forEach(key->{
+                List<String> values = exchange.getResponse().getHeaders().get(key);
+                if (values != null && !values.isEmpty()) {
+                    exchange.getResponse().getHeaders().put(key, Collections.singletonList(values.get(0)));
+                }
+            });
             return chain.filter(exchange);
         }));
     }