ajax 文件下载，实际上就是模拟表单提交，代码如下：

function download(url, data, method){

//url and data options required

if( url && data ){

//data can be string of parameters or array/object

data =typeof data =='string'? data : jQuery.param(data);

//split params into form inputs

var inputs ='';

jQuery.each(data.split('&'), function(){

var pair =this.split('=');

inputs+='<input type="hidden" name="'+ pair[0]+'" value="'+ pair[1]+'" />';

});

//send request

jQuery('<form action="'+ url +'" method="'+(method||'post')+'">'+inputs+'</form>')

.appendTo('body').submit().remove();

};

};