文件上传下载（实例）

在编写下载文件代码时，要注意一点。若是火狐浏览器，则不需要编码，要区别对待

直接上代码

namespace 上传文件
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        public static string fileName = "";
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindDropDownList();
            }
        }

        //上传文件
        protected void Button1_Click(object sender, EventArgs e)
        {
            if (FileUpload1.HasFile)
            {
                fileName = FileUpload1.FileName;
                string result = fileUpload(fileName);
                if (!string.IsNullOrEmpty(result))
                {
                    Page.ClientScript.RegisterClientScriptBlock(Page.ClientScript.GetType(), "myscripts", "<script>alert("上传成功!");</script>");
                    BindDropDownList();
                }
                else
                {
                    Page.ClientScript.RegisterClientScriptBlock(Page.ClientScript.GetType(), "myscripts", "<script>alert("上传失败!");</script>");
                }
            }
        }


        /// <summary>
        /// 上传文件
        /// </summary>
        /// <param name="fileName">文件名称</param>
        /// <returns></returns>
        public static string fileUpload(string fileName)
        {
            string fileNewName = String.Empty;
            if (fileName.Length > 0)
            {
                string fileExtension = Path.GetExtension(fileName).ToLower();
                if (checkFileExtension(fileExtension))
                {
                    //fileNewName = DateTime.Now.ToString("yyyyMMddhhmmss") + fileExtension;
                    fileNewName = fileName;
                    HttpPostedFile file = HttpContext.Current.Request.Files[0];
                    file.SaveAs(HttpContext.Current.Server.MapPath("File/" + fileNewName));
                }
            }
            return fileNewName;
        }

        /// <summary>
        /// 检查上传文件格式是否正确
        /// </summary>
        /// <param name="fileExtension">文件扩展名</param>
        /// <returns></returns>
        public static bool checkFileExtension(string fileExtension)
        {
            string[] extensionArr = { ".doc", ".txt", ".pdf", ".rar", ".zip", ".docx", ".doc", ".ppt", ".png", ".gif", ".jpg", ".jpeg",".exe"};
            for (int i = 0; i < extensionArr.Length; i++)
            {
                if (fileExtension == extensionArr[i])
                {
                    return true;
                }
            }
            return false;
        }

        //获取所有文件文件名
        public List<string> GetFileNames()
        {
            string path = Server.MapPath("File");
            DirectoryInfo dir = new DirectoryInfo(path);
            FileInfo[] files = dir.GetFiles();
            List<string> list = new List<string>();
            foreach (FileInfo item in files)
            {
                list.Add(item.Name);
            }
            return list;
        }

        //绑定dropdownList
        private void BindDropDownList()
        {
            DropDownList1.DataSource = GetFileNames();
            DropDownList1.DataBind();
            DropDownList1.Items.Insert(0, "请选择文件");
        }

        //下载指定文件
        protected void Button2_Click(object sender, EventArgs e)
        {
            if(DropDownList1.SelectedIndex!=0)
            {
                string fileName = DropDownList1.SelectedItem.ToString();//客户端保存的文件名
                string filePath = Server.MapPath("File/") + fileName;//路径
                DownLoadFile(fileName, filePath);
            }
            else
            {
                Page.ClientScript.RegisterClientScriptBlock(Page.ClientScript.GetType(), "myscripts", "<script>alert("请选择下载文件!");</script>");
            }
        }


        /// <summary>
        /// 文件下载
        /// </summary>
        /// <param name="fileName">文件名称</param>
        /// <param name="filePath">文件绝对路径</param>
        public void DownLoadFile(string fileName, string filePath)
        {

            ////WriteFile分块下载
            string browserType = Request.Browser.Browser.ToString();//获取浏览器类型

            string fileNewName = "";
            if (browserType != "Firefox")//火狐浏览器不需要进行编码，文件名称就能显示
            {
                fileNewName = HttpUtility.UrlEncode(fileName); //如果不是火狐浏览器，加上HttpUtility.UrlEncode()方法，防止文件下载时，文件名乱码
            }
            else
            {
                fileNewName = fileName;
            }

            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=" + 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();
                
            }
        }
  

    }
}

文件的下载方式有很多，具体可以参考：http://www.cnblogs.com/zhangzt/archive/2009/12/14/1623426.html