自己在前后端联调的过程中，有时候会出现跨域问题
例如:

Access to XMLHttpRequest at 'http://localhost:9090/article/categories' from origin 'http://localhost:9091' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

什么意思呢？简单点说就是请求成功发出去了，但是被拦截了，后端没收到这个请求。而且只要是端口不一致都有可能发生。

我的 springboot 项目的解决方案：

package com.feixin.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
import org.springframework.web.filter.CorsFilter;

@Configuration
public class CorsConfig {
    @Bean
    public CorsFilter corsFilter() {
        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        CorsConfiguration config = new CorsConfiguration();

        // 允许哪些源访问
        config.addAllowedOrigin("http://localhost:9091");

        // 允许哪些 HTTP 方法<el-menu-item>关于本站</el-menu-item>
        config.addAllowedMethod("*");
        config.addAllowedHeader("*");
        config.setAllowCredentials(true);
        source.registerCorsConfiguration("/**", config);


        return new CorsFilter(source);
    }
}

在config包下新建了一个配置类，允许该端口的所有请求访问