前后端分离的项目，前端是vue,后端springboot,或者maven项目，生成验证码的时候存了一份到session并存到redis里，前端调后台注册获取不到session，但当用户从session中取信息的时候发现始终取不到，每次跨域请求时ajax发送的都是新的sessionid，导致无法获取信息

解决方案：
前端在vue的main文件全局添加一下代码：

import axios from 'axios';
axios.defaults.withCredentials=true;

后台新增一个过滤器

web.xml文件

<filter>
	<filter-name>contextFilter</filter-name>
	<filter-class>com.zl.filter.ContextFilter</filter-class>
</filter>
<filter-mapping>
	<filter-name>contextFilter</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>

public class ContextFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse)servletResponse;
        HttpServletRequest request = (HttpServletRequest)servletRequest;
        String origin = request.getHeader("Origin");
        response.setHeader("Access-Control-Allow-Origin", origin);
        response.setHeader("Access-Control-Allow-Methods", "*");
        String headers = request.getHeader("Access-Control-Request-Headers");
         // 支持所有自定义头
        if (!org.springframework.util.StringUtils.isEmpty(headers)) {
            response.setHeader("Access-Control-Allow-Headers", headers);
        }
        response.setHeader("Access-Control-Allow-Credentials", "true");
        response.setHeader("Access-Control-Max-Age", "3600");
        filterChain.doFilter(request, response);
    }

    @Override
    public void destroy() {

    }
}