后端配置了代码：

spring:application:name: spzx-server-gatewaycloud:nacos:discovery:server-addr: localhost:8848gateway:discovery:locator:enabled: trueglobalcors:cors-configurations:'[/**]':allowedOriginPatterns: "*"# 允许请求中携带的头信息allowedHeaders: "*"# 运行跨域的请求方式allowedMethods: "*"# 跨域检测的有效期,单位smaxAge: 36000

但是后端启动后，前端报错'Access-Control-Allow-Origin' CORS 多个头

是因为多重配置导致：

比如说：

package com.atguigu.spzx.product.controller;import com.atguigu.spzx.model.entity.product.Category;
import com.atguigu.spzx.model.entity.product.ProductSku;
import com.atguigu.spzx.model.vo.common.Result;
import com.atguigu.spzx.model.vo.common.ResultCodeEnum;
import com.atguigu.spzx.model.vo.h5.IndexVo;
import com.atguigu.spzx.product.service.CategoryService;
import com.atguigu.spzx.product.service.ProductSkuService;
import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.tags.Tag;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.List;@Tag(name = "首页接口管理")
@RestController
@RequestMapping(value="/api/product/index")
@CrossOrigin   重复配置跨域
public class IndexController {@Autowiredprivate CategoryService categoryService;@Autowiredprivate ProductSkuService productSkuService;//查询所有一级分类//查询畅销商品@Operation(summary = "获取首页数据")@GetMappingpublic Result<IndexVo> findData(){//查询所有一级分类List<Category> categoryList=categoryService.findOneCategory();查询畅销商品List<ProductSku> productSkuList=productSkuService.findProductSkuBySale();IndexVo indexVo=new IndexVo();indexVo.setCategoryList(categoryList);indexVo.setProductSkuList(productSkuList);return Result.build(indexVo, ResultCodeEnum.SUCCESS);}
}

如上代码：注解重复配置跨域

再比如利用java代码配置导致前端报错'Access-Control-Allow-Origin' CORS 多个头：

package com.atguigu.spzx.manager.config;import com.atguigu.spzx.manager.properties.UserAuthProperties;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@Component
@SuppressWarnings({"all","silent"})
public class WebMvcConfiguration implements WebMvcConfigurer {@Autowiredprivate UserAuthProperties userAuthProperties;@Autowiredpublic void addCorsMappings(CorsRegistry registry) {registry.addMapping("/**")       //添加路径规则.allowCredentials(true)   //是否允许在跨域情况下传递cookie.allowedOriginPatterns("*")//允许请求来源的域规则.allowedMethods("*").allowedHeaders("*");           //允许所有请求头}}