[原创]C# Web应用程序文件下载帮助类

using System;
using System.Text;
using System.IO;

namespace Utility
{
    /// <summary>
    /// 文件下载帮助类
    /// </summary>
    public class DownloadFileHelper
    {
        /// <summary>
        /// TransmitFile方式下载
        /// 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。
        /// </summary>
        /// <param name="filepath">被下载文件的web服务器相对路径</param>
        /// <returns></returns>
        public static void DownloadByTransmitFile(string filepath)
        {
            try
            {
                string filename = GetFilenameByFilepath(filepath);
                filename = Encoding.UTF8.GetString(Encoding.Default.GetBytes(filename));

                if (filename.Length > 0)
                {
                    string extension = filename.Split(',')[1].ToLower();
                    if (extension == "zip")
                    {
                        System.Web.HttpContext.Current.Response.ContentType = "application/x-zip-compressed";
                    }
                    else
                    {
                        System.Web.HttpContext.Current.Response.ContentType = "application/octet-stream";
                    }

                    System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", filename));

                    filepath = System.Web.HttpContext.Current.Server.MapPath(filepath);
                    System.Web.HttpContext.Current.Response.TransmitFile(filepath);
                }
            }
            catch (Exception)
            { }
        }

        /// <summary>
        /// WriteFile方式下载
        /// </summary>
        /// <param name="filepath">被下载文件的web服务器相对路径</param>
        public static void DownloadByWriteFile(string filepath)
        {
            try
            {
                string fileName = GetFilenameByFilepath(filepath);//客户端保存的文件名
                fileName = Encoding.GetEncoding("gb2312").GetString(Encoding.Default.GetBytes(fileName));

                string filePath = System.Web.HttpContext.Current.Server.MapPath(filepath);//路径

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

        /// <summary>
        /// WriteFile下载分块
        /// </summary>
        /// <param name="filepath">被下载文件的web服务器相对路径</param>
        public static void ChunkDownloadByWriteFile(string filepath)
        {
            try
            {
                string fileName = GetFilenameByFilepath(filepath);//客户端保存的文件名
                fileName = Encoding.UTF8.GetString(Encoding.Default.GetBytes(fileName));

                string filePath = System.Web.HttpContext.Current.Server.MapPath(filepath);//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];

                    System.Web.HttpContext.Current.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
                    System.Web.HttpContext.Current.Response.ContentType = "application/octet-stream";
                    System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" + fileName);
                    while (dataLengthToRead > 0 && System.Web.HttpContext.Current.Response.IsClientConnected)
                    {
                        int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//读取的大小
                        System.Web.HttpContext.Current.Response.OutputStream.Write(buffer, 0, lengthRead);
                        System.Web.HttpContext.Current.Response.Flush();
                        dataLengthToRead = dataLengthToRead - lengthRead;
                    }
                    System.Web.HttpContext.Current.Response.Close();
                }
            }
            catch (Exception)
            { }
        }

        /// <summary>
        /// 流方式下载
        /// </summary>
        /// <param name="filepath">被下载文件的web服务器相对路径</param>
        public static void DownloadByFileStream(string filepath)
        {
            try
            {
                string fileName = GetFilenameByFilepath(filepath);//客户端保存的文件名
                fileName=Encoding.UTF8.GetString(Encoding.Default.GetBytes(fileName));

                string filePath = System.Web.HttpContext.Current.Server.MapPath(filepath);//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();
                System.Web.HttpContext.Current.Response.ContentType = "application/octet-stream";
                //通知浏览器下载文件而不是打开
                System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;  filename=" + fileName);
                System.Web.HttpContext.Current.Response.BinaryWrite(bytes);
                System.Web.HttpContext.Current.Response.Flush();
                System.Web.HttpContext.Current.Response.End();
            }
            catch (Exception)
            { }
        }

        /// <summary>
        /// 获取文件名称
        /// </summary>
        /// <param name="filepath">文件的web服务器的相对路径</param>
        /// <returns></returns>
        public static string GetFilenameByFilepath(string filepath)
        {
            string filename = "";
            string[] array1 = filepath.Split('/');
            try
            {
                string[] array2 = array1[array1.Length - 1].Split('?');
                filename = array2[0];
            }
            catch (Exception)
            { }
            return filename;
        }
    }
}