C#实现文件下载的几种方法

//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();
            //如果是中文名称可能会出现乱码的现象可以使用Server.UrlEncode(fileName)进行编码
            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();
        }