.net一般处理程序（httphandler）实现文件下载功能

Handler文件代码如下：

public class MDMExporterWeb : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            string url = context.Request.Form["fileName"];
            //判断服务端是否生成Excel文件
            if (File.Exists(context.Server.MapPath(url)))
            {
                //获取文件路径和文件名           
                string filePath = context.Server.MapPath(url);
                string fileName = Path.GetFileName(filePath);

                //将文件转换为字节流
                //byte[] file = ImpExpWebPublic.ConvertToBinary(filePath);
                FileStream fs = new FileStream(filePath, FileMode.Open);
                byte[] bytes = new byte[(int)fs.Length];
                fs.Read(bytes, 0, bytes.Length);
                fs.Close();

                using (MemoryStream stream = new MemoryStream(bytes))
                {
                    //文件导出到客户端(Web)
                    ResponseFile(context.Request, context.Response, fileName, stream, 10240);
                }
            }
            else
            {
                context.Response.Write("<script> alert('错误信息:未导出Excel文件');window.close();</script>");
            }                
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }

        /// <summary>
        /// 文件下载
        /// </summary>
        /// <param name="_Request">Request对象</param>
        /// <param name="_Response">Response对象</param>
        /// <param name="_fileName">文件名</param>
        /// <param name="stream">发送的流</param>
        /// <param name="block">每次读取的字节数</param>
        /// <returns></returns>
        public static bool ResponseFile(HttpRequest _Request, HttpResponse _Response, string _fileName, Stream stream, int block)
        {
            try
            {
                _Response.Clear();
                using (var br = new BinaryReader(stream))
                {

                    _Response.AddHeader("Accept-Ranges", "bytes");
                    _Response.Buffer = false;
                    long fileLength = stream.Length;
                    long startBytes = 0;

                    int pack = block; //每次读取的字节数
                    if (_Request.Headers["Range"] != null)
                    {
                        _Response.StatusCode = 206;
                        string[] range = _Request.Headers["Range"].Split(new char[] { '=', '-' });
                        startBytes = Convert.ToInt64(range[1]);
                    }
                    _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
                    if (startBytes != 0)
                    {
                        _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
                    }
                    _Response.AddHeader("Connection", "Keep-Alive");
                    _Response.ContentType = "application/octet-stream";

                    _Response.AddHeader("Content-Disposition", "attachment;filename=" + Uri.EscapeUriString(_fileName));

                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
                    int maxCount = (int)Math.Floor((fileLength - startBytes) / (double)pack) + 1;

                    for (int i = 0; i < maxCount; i++)
                    {
                        if (_Response.IsClientConnected)
                        {
                            _Response.BinaryWrite(br.ReadBytes(pack));
                        }
                        else
                        {
                            i = maxCount;
                        }
                    }
                    br.Close();
                    stream.Close();
                }
            }
            catch (Exception e)
            {
                _Response.Write(e.Message + e.StackTrace);
                _Response.Flush();
            }
            return true;
        }
    }

javascript代码如下：

var fileName = '/cwbase/test1.xls';//相对路径
var postUrlE = '/cwbase/MDMWeb/MDMExporterWeb.ashx';
var form = $('<form  action="' + postUrlE + '" method="POST" name="fileDownload" id="fileDownload" target="_blank"></form>');
$('<input type="text" name="fileName" value="' + fileName + '">').appendTo(form);
$(form).appendTo('body');
form.submit();//表单提交
$(form).remove();

document.characterSet = 'UTF-8';
document.charset = 'UTF-8';