java及前端请求跨域问题

   主要代码：<meta http-equiv="Access-Control-Allow-Origin" content="*">

   说明一下什么情况下我们用到这个标签：如果chrome浏览器报

XMLHttpRequest cannot load http://google.com/. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://run.jsbin.io' is therefore not allowed access.
在html页面加入：

<meta http-equiv="Access-Control-Allow-Origin" content="*">

在java代码中加入跨域：
controller类中加入

response.setHeader("Access-Control-Allow-Origin", "*");