Asp.Net文件下载

<%@ WebHandler Language="C#" Class="AttachmentHandler" %>

using System;
using System.Collections.Generic;
using System.Web;
using System.Data.SqlClient;
using System.Configuration;

public class AttachmentHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        string workflowID = context.Request["guid"];
        string tableName = context.Request["tb"];

        if (string.IsNullOrEmpty(workflowID) || string.IsNullOrEmpty(tableName))
            context.Response.End();

        using (SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["db"]))
        {
            conn.Open();
            var cmdText = string.Format(@"select FileName,Attachment from {0} where WorkflowID='{1}'"
                , tableName, workflowID);
            SqlCommand cmd = new SqlCommand(cmdText, conn);
            SqlDataReader dr = cmd.ExecuteReader();
            if (dr.Read())
            {
                if (!Convert.IsDBNull(dr["Attachment"]))
                {
                    context.Response.BinaryWrite((byte[])dr["Attachment"]);
                    context.Response.AppendHeader("Content-Disposition"
                        , string.Format("attachment;filename={0}"
                        , HttpUtility.UrlEncode(dr["FileName"].ToString())));
                }

                dr.Close();
                dr = null;
                context.Response.End();
            }

            conn.Close();
        }


    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

Ref:TransmitFile

    //TransmitFile实现下载
         protected void Button1_Click1(object sender, EventArgs e)
        {
            /*
             微软为Response对象提供了一个新的方法TransmitFile来解决使用Response.BinaryWrite
             下载超过400mb的文件时导致Aspnet_wp.exe进程回收而无法成功下载的问题。
             代码如下：
             */
            string strFileName = "xxx.ppt";
            Response.ContentType = "application/x-zip-compressed";
            //Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
            string filename = BLL.Config.PART_EM_UPLOAD_DOC + strFileName;

            //BLL.Config.PART_EM_UPLOAD_DOC 为路径   ("D:/EMUploadDoc/")
            Response.AddHeader("Content-Disposition", "attachment;filename=" +Server.UrlPathEncode(strFileName));

           //Server.UrlPathEncode()解决文件名的乱码问题.
           
            Response.TransmitFile(filename);
        }    
//WriteFile实现下载
    protected void Button2_Click(object sender, EventArgs e)
    {
        /*
         using System.IO;
       
         */

        string fileName = "asd.txt";//客户端保存的文件名
        string filePath = Server.MapPath("DownLoad/aaa.txt");//路径

        FileInfo fileInfo = new FileInfo(filePath);
        Response.Clear();
        Response.ClearContent();
        Response.ClearHeaders();
        Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);
        Response.AddHeader("Content-Length", fileInfo.Length.ToString());
        Response.AddHeader("Content-Transfer-Encoding", "binary");
        Response.ContentType = "application/octet-stream";
        Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
        Response.WriteFile(fileInfo.FullName);
        Response.Flush();
        Response.End();
    }

      //WriteFile分块下载
    protected void Button3_Click(object sender, EventArgs e)
    {

        string fileName = "aaa.txt";//客户端保存的文件名
        string filePath = Server.MapPath("DownLoad/aaa.txt");//路径

        System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);

        if (fileInfo.Exists == true)
        {
            const long ChunkSize = 102400;//100K 每次读取文件，只读取100Ｋ，这样可以缓解服务器的压力
            byte[] buffer = new byte[ChunkSize];

            Response.Clear();
            System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);
            long dataLengthToRead = iStream.Length;//获取下载的文件总大小
            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName));
            while (dataLengthToRead > 0 && Response.IsClientConnected)
            {
                int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//读取的大小
                Response.OutputStream.Write(buffer, 0, lengthRead);
                Response.Flush();
                dataLengthToRead = dataLengthToRead - lengthRead;
            }
            Response.Close();
        }
    }

    //流方式下载
    protected void Button4_Click(object sender, EventArgs e)
    {
        string fileName = "aaa.txt";//客户端保存的文件名
        string filePath = Server.MapPath("DownLoad/aaa.txt");//路径

        //以字符流的形式下载文件
        FileStream fs = new FileStream(filePath, FileMode.Open);
        byte[] bytes = new byte[(int)fs.Length];
        fs.Read(bytes, 0, bytes.Length);
        fs.Close();
        Response.ContentType = "application/octet-stream";
        //通知浏览器下载文件而不是打开
        Response.AddHeader("Content-Disposition", "attachment;  filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));
        Response.BinaryWrite(bytes);
        Response.Flush();
        Response.End();

    }