XMLHttpRequest cannot load http://www.imooc.com/data/check_f.php. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access.
解决方法：跨源问题，添加cors。
1.filter或者servlet里面添加response.setHeader("Access-Control-Allow-Origin", "");
2.response.setHeader("Access-Control-Allow-Origin", "");放到接收客户端api 的地方
3.如果是servlet的话就放到get或者post方法里面，jsp页面就扔到第一行
4.如果是filter部署就扔到dofilter()