后端也设置了允许跨域
//允许所有的域访问
httpServletResponse.setHeader("Access-Control-Allow-Origin", "*");
//允许所有方式的请求
httpServletResponse.setHeader("Access-Control-Allow-Methods", "*");
//头信息缓存有效时长(如果不设 Chromium 同时规定了一个默认值 5 秒),没有缓存将已OPTIONS进行预请求
httpServletResponse.setHeader("Access-Control-Max-Age", "3600");
//允许的头信息
httpServletResponse.setHeader("Access-Control-Allow-Headers", "x-requested-with, authorization");