Extjs 4通过ajax调用下载文件

The problem is very simple: i have to download a file when i submit a form, it's an ajax call when the form is submitted which lets me build a file with the data taken from the form, server side, and then send it as a link to an alert. The fact is that my boss want the file to be downloaded directly and not through a link in an alert. So i had to make sure that the file is available server side through tornado(web):The problem is very simple: i have to download