DownHandler.ashx后台代码public class DownHandler : IHttpHandler
    {
        public void ProcessRequest(HttpContext context)
        {
            //获取要下载的的文件名
            string file = context.Request["downfile"];
            if (System.IO.File.Exists(file))
            {
                FileStream fs = new FileStream(file, FileMode.Open);
                byte[] fileBytes = new byte[(int)fs.Length];
                fs.Read(fileBytes, 0, fileBytes.Length);
                fs.Close();                context.Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(file, System.Text.Encoding.UTF8));
                context.Response.AppendHeader("Content-Length", fileBytes.Length.ToString());
                context.Response.ContentType = "application/octet-stream";
                context.Response.OutputStream.Write(fileBytes, 0, fileBytes.Length);
                context.Response.End();
            }
        }
    }
JS代码function DownAtt(file){
//JS调用后台DownHandler下载文件,怎样将文件存储在本地?
$.get("DownHandler.ashx?id=3",{ downfile: file }, function (data) {        return true;
    });
}