ASP.NET上传下载文件，使用TransmitFile方法实现下载。

 using System;
using System.Text;
using System.Collections.Generic;

namespace RongPan.TuDou.Common
{
    public class FileHelp
    {
        public static void DownloadFile(System.Web.HttpResponse response,string filePath)
        {
            response.Clear();
            response.ContentType = "application/x-zip-compressed";
            response.TransmitFile(filePath);
            response.End();
        }
        /// <summary>
        /// 上传文件并获得服务器上的文件名
        /// </summary>
        /// <param name="inputFile"></param>
        /// <param name="strAbsolutePath"></param>
        /// <returns></returns>
        public static string UpLoadFile(System.Web.UI.HtmlControls.HtmlInputFile inputFile, string strAbsolutePath)
        {
            string strOldFilePath = inputFile.PostedFile.FileName;
            string strExtension = string.Empty;
            string strNewFilePath = string.Empty;
            if (strOldFilePath != null)
            {
                strNewFilePath = GetNewFileName(strOldFilePath);
                try
                {
                    inputFile.PostedFile.SaveAs(GetSavePath(strNewFilePath, strAbsolutePath));
                }
                catch
                {
                    throw new Exception(string.Format("{0}文件上传失败", strOldFilePath));
                }
            }
            else
            {
                throw new Exception("文件不存在，无法上传！");
            }
            return strNewFilePath;
        }
        /// <summary>
        /// 多文件上传
        /// </summary>
        /// <param name="files"></param>
        /// <param name="strAbsolutePath"></param>
        /// <returns></returns>
        public static List<Filer> UpLoadFile(System.Web.HttpFileCollection files, string strAbsolutePath)
        {
            if (files.Count > 0)
            {
                List<Filer> list = new List<Filer>();
                foreach (System.Web.UI.HtmlControls.HtmlInputFile item in files)
                {
                    string oldFileName = item.PostedFile.FileName;
                    oldFileName = oldFileName.Substring(oldFileName.LastIndexOf('//'));
                    string fileName = string.Empty;
                    try
                    {
                        fileName = UpLoadFile(item, strAbsolutePath);
                    }
                    catch (Exception e)
                    {
                        throw e;
                    }
                    finally
                    {
                        if (list.Count>0)
                        {
                            foreach (Filer temp in list)
                            {
                                DeleteFile(temp.AbsolutePath);
                            }
                        }
                    }
                    string absolutePath = GetSavePath(fileName, strAbsolutePath);

                    list.Add(new Filer(fileName, absolutePath, oldFileName));
                }
                return list;
            }
            else
            {
                throw new Exception("没有找到将要上传的文件！");
            }
        }
        public static List<Filer> UpLoadFile(System.Web.HttpRequest request, string strAbsolutePath)
        {
            return UpLoadFile(request.Files, strAbsolutePath);
        }
        public static List<Filer> UpLoadFile(System.Web.HttpContext context, string strAbsolutePath)
        {
            return UpLoadFile(context.Request.Files, strAbsolutePath);
        }
        /// <summary>
        /// 删除指定的文件
        /// </summary>
        /// <param name="absolutePath">文件不存在不会引发异常</param>
        public static void DeleteFile(string absolutePath)
        {
            System.IO.File.Delete(absolutePath);
        }
        /// <summary>
        /// 删除指定的文件
        /// </summary>
        /// <param name="fileName">文件不存在不会引发异常</param>
        /// <param name="absolutepath">文件不存在不会引发异常</param>
        public static void DeleteFile(string fileName, string absolutepath)
        {
            DeleteFile(GetSavePath(fileName,absolutepath));
        }
        /// <summary>
        /// 获得文件名的扩展名
        /// </summary>
        /// <param name="pathString"></param>
        /// <returns></returns>
        public static string GetPathStringExtension(string pathString)
        {
            if (pathString.Length > 0)
            {
                return pathString.Substring(pathString.LastIndexOf('.'));
            }
            else
            {
                throw new Exception("文件名为空，无法获取其扩展名！");
            }
        }
        /// <summary>
        /// 拼接文件绝对路径
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="absolutePath"></param>
        /// <returns></returns>
        public static string GetSavePath(string fileName, string absolutePath)
        {
            string savePath = string.Empty;
            if (absolutePath.LastIndexOf('//') == absolutePath.Length)
            {
                savePath = absolutePath + fileName;
            }
            else
            {
                savePath = absolutePath + "//" + fileName;
            }
            return savePath;
        }
        /// <summary>
        /// 获得一个唯一的文件名
        /// </summary>
        /// <param name="fileName"></param>
        /// <returns></returns>
        public static string GetNewFileName(string fileName)
        {
            string newFileName = string.Empty;
            string extension = GetPathStringExtension(fileName);
            return Code.GetGUID() + extension;

        }
        /// <summary>
        /// 修改上传的文件
        /// </summary>
        /// <param name="ffFile"></param>
        /// <param name="strAbsolutePath"></param>
        /// <param name="strOldFileName"></param>
        /// <returns></returns>
        public static string CoverFile(System.Web.UI.HtmlControls.HtmlInputFile ffFile,string strAbsolutePath,string strOldFileName)
        {
            if (ffFile.PostedFile.FileName != string.Empty)
            {
                if (strOldFileName != string.Empty)
                {
                    DeleteFile(strOldFileName, strAbsolutePath);
                }
                return UpLoadFile(ffFile, strAbsolutePath);
            }
            else
            {
                throw new Exception("文件不存在，无法上传！");
            }
        }
        /// <summary>
        /// 批量修改
        /// </summary>
        /// <param name="files"></param>
        /// <param name="strAbsolutePath"></param>
        /// <param name="oldFilers"></param>
        /// <returns></returns>
        public static List<Filer> CoverFile(System.Web.HttpFileCollection files, string strAbsolutePath, List<Filer> oldFilers)
        {
            if (files.Count > 0)
            {
                List<Filer> list = UpLoadFile(files, strAbsolutePath);
                foreach (Filer item in oldFilers)
                {
                    DeleteFile(item.AbsolutePath);
                }
                return list;
            }
            else
            {
                throw new Exception("没有找到将要上传的文件！");
            }
        }
        public static List<Filer> CoverFile(System.Web.HttpRequest request, string absolutePath, List<Filer> oldFilers)
        {
            return CoverFile(request.Files,absolutePath,oldFilers);
        }
        public static List<Filer> CoverFile(System.Web.HttpContext context, string ablsolutePath, List<Filer> oldFilers)
        {
            return CoverFile(context.Request.Files,ablsolutePath,oldFilers);
        }
    }
}
 

Code类，用来实现加密、获取全局唯一键等功能。

在上面的例子中可能用到。

 using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography;

namespace RongPan.TuDou.Common
{
    public class Code
    {
        /// <summary>
        /// 获得字符串的MD5编码,速度快
        /// </summary>
        /// <param name="input">需要加密的字符串</param>
        /// <returns>MD5 Code</returns>
        public static string GetMd5HashCode(string input)
        {
            //
            // Create a new instance of the MD5CryptoServiceProvider object.
            MD5 md5Hasher = MD5.Create();

            // Convert the input string to a byte array and compute the hash.
            byte[] data = md5Hasher.ComputeHash(Encoding.Default.GetBytes(input));

            // Create a new Stringbuilder to collect the bytes
            // and create a string.
            StringBuilder sBuilder = new StringBuilder();

            // Loop through each byte of the hashed data
            // and format each one as a hexadecimal string.
            foreach (byte b in data)
            {
                sBuilder.Append(b.ToString("x2"));
            }

            // Return the hexadecimal string.
            return sBuilder.ToString();
        }
        /// <summary>
        /// 获得字符串的SHA1编码,更安全
        /// </summary>
        /// <param name="input">需要加密的字符串</param>
        /// <returns>SHA1 Code</returns>
        public static string GetSHA1HashCode(string input)
        {
            //
            byte[] data = Encoding.Default.GetBytes(input);
            byte[] result;

            SHA1 sha = new SHA1CryptoServiceProvider();
            // This is one implementation of the abstract class SHA1.
            result = sha.ComputeHash(data);

            StringBuilder sBuilder = new StringBuilder();
            foreach(byte b in result)
            {
                sBuilder.Append(b.ToString("x2"));
            }

            return sBuilder.ToString();
        }
        /// <summary>
        /// 获得全局唯一标识
        /// </summary>
        /// <returns></returns>
        public static string GetGUID()
        {
            return Guid.NewGuid().ToString().Replace('-', '/0');
        }
        /// <summary>
        /// 编码
        /// </summary>
        /// <param name="var"></param>
        /// <returns></returns>
        public static string DoCode(string var)
        {
            string code = string.Empty;
            //进行编码
            return code;
        }
        /// <summary>
        /// 反编码
        /// </summary>
        /// <param name="code"></param>
        /// <returns></returns>
        public static string DeCode(string code)
        {
            string var = string.Empty;
            //进行反编码
            return var;
        }
        /// <summary>
        /// 生成指定长度英文字母
        /// </summary>
        /// <param name="codeCount"></param>
        /// <returns></returns>
        public static string NextCheckCode(int codeCount)
        {
            string[] allChar = new string[] { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", " K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "W", " X", "Y", "Z " };
            Random rnd = new Random((int)DateTime.Now.Ticks);
            StringBuilder code = new StringBuilder();
            for (int i = 0; i < codeCount; i++)
            {
                code.Append(allChar[rnd.Next(0, 25)]);
            }
            return code.ToString().Replace(" ","");
        }
        /// <summary>
        /// 生成5位随机英文字母
        /// </summary>
        /// <returns></returns>
        public static string NextCheckCode()
        {
            return NextCheckCode(5);
        }
    }
}