（有关跨域问题的具体原理后续有机会再补充）

<关键词>        CORS policy； No 'Access-Control-Allow-Origin'

解决方法之一：Cors

在src/java/io.renren/config/添加配置文件CorsConfig.java

package io.renren.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class CorsConfig implements WebMvcConfigurer {

    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
            .allowedOrigins("*")
            .allowCredentials(true)
            .allowedMethods("GET", "POST", "PUT", "DELETE", "OPTIONS")
            .maxAge(3600);
    }
}