java 文件下载或者预览的头部设置

谷歌浏览器需要开启pdf viewer，新版本默认开启
ie浏览器需要安装 adobe reader插件
下载
//response.setHeader("contentType", "text/html; charset=utf-8");
预览
response.setHeader("Content-Type", "image/jpg");
response.setContentType("application/octet-stream");