下载文件

context.Response.ContentType = "text/plain";

string filename = context.Request.QueryString["u"];

string path = context.Request.MapPath("../images/"+filename);

//解决ie中下载时候。中文文件名称乱码的问题
filename = HttpUtility.UrlEncode(filename);

context.Response.AddHeader("Content-Disposition", "attachment;filename="+filename);

context.Response.WriteFile(path);