C# ASP.NET 文件上传下载 下载时图片不自动打开

 using System;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Web;
using System.Web.UI.HtmlControls;
using Care365.Model;

namespace Care365.Tools
{
    public abstract class FileHelper
    {
        static Hashtable _allExtension;

        public static Hashtable AllExtension
        {
            get
            {
                if (_allExtension != null)
                {
                    return _allExtension;
                }
                else
                {
                   
                        _allExtension = FillExtension();
                   
                    return _allExtension;
                }
            }
        }
        /// <summary>
        /// 配置允许用户上传的文件集合
        /// </summary>
        /// <returns></returns>
        private static Hashtable FillExtension()
        {
            Hashtable table = new Hashtable();
            table.Add(".gif", ".gif");
            table.Add(".jpg", ".jpg");
            table.Add(".jpeg", ".jpeg");
            table.Add(".bmp", ".bmp");
            table.Add(".png", ".png");

            return table;
        }
        /// <summary>
        /// 上传文件
        /// </summary>
        /// <param name="relativePath"></param>
        /// <returns></returns>
        public static List<UploadFile> UploadFile(string relativePath)
        {
            if (relativePath.LastIndexOf('//') == relativePath.Length)
            {
                relativePath += "//";
            }

            //确认目录存在
            if (!Directory.Exists(HttpContext.Current.Server.MapPath(relativePath))) Directory.CreateDirectory(HttpContext.Current.Server.MapPath(relativePath));

            HttpFileCollection collection = HttpContext.Current.Request.Files;
            List<UploadFile> list = new List<UploadFile>();
            string fileName;
            string clientName;
            string servername;
            int length = collection.Count;
            for (int i = 0; i < length; i++)
            {
                HttpPostedFile item = collection[i];
                fileName = item.FileName;
                if (fileName != null && fileName.Trim().Length > 0)
                {
                    string strExtension = fileName.Substring(fileName.LastIndexOf('.'));
                    //校验上传文件的格式
                    if (!ExistUploadType(strExtension))
                    {
                        UploadFile uf = new UploadFile();
                        uf.Upload = false;
                        uf.Remark = "此格式的文件不允许上传!";
                        list.Add(uf);
                        continue;
                    }
                    //校验文件大小
                    if (!IsAllowedLength(item.ContentLength))
                    {
                        UploadFile uf = new UploadFile();
                        uf.Upload = false;
                        uf.Remark = "文件长度过大!";
                        list.Add(uf);
                        continue;
                    }

                    clientName = fileName.Substring(fileName.LastIndexOf('//') + 1);

                    servername = string.Format("{0}{1}{2}", relativePath, Code.GetMd5HashCode(Code.GetGUID()), strExtension);

                    try
                    {
                        item.SaveAs(HttpContext.Current.Server.MapPath(servername));
                    }
                    catch (Exception e)
                    {
                        UploadFile uf = new UploadFile();
                        uf.Upload = false;
                        uf.Remark = e.Message;
                        list.Add(uf);
                        continue;
                    }

                    UploadFile upf = new UploadFile();
                    upf.Upload = true;
                    upf.ServerName = servername;
                    upf.ClientName = clientName;
                    upf.Remark = "上传成功!";

                    list.Add(upf);
                }
            }

            return list;
        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="file"></param>
        /// <param name="relativePath">相对路径</param>
        /// <returns></returns>
        public static UploadFile UploadFile(HttpPostedFile file, string relativePath)
        {
            if (relativePath.LastIndexOf('//') == relativePath.Length)
            {
                relativePath += "//";
            }

            if (!Directory.Exists(relativePath)) Directory.CreateDirectory(relativePath);

            string fileName;
            string clientName;
            string servername;

            fileName = file.FileName;
            if (fileName != null && fileName.Trim().Length > 0)
            {
                string strExtension = fileName.Substring(fileName.LastIndexOf('.'));
                //校验上传文件的格式
                if (!ExistUploadType(strExtension))
                {
                    UploadFile uf = new UploadFile();
                    uf.Upload = false;
                    uf.Remark = "此格式的文件不允许上传!";
                    return uf;
                }
                //校验文件大小
                if (!IsAllowedLength(file.ContentLength))
                {
                    UploadFile uf = new UploadFile();
                    uf.Upload = false;
                    uf.Remark = "文件长度过大!";
                    return uf;
                }

                clientName = fileName.Substring(fileName.LastIndexOf('//') + 1);

                servername = string.Format("{0}{1}{2}", relativePath, Code.GetMd5HashCode(Code.GetGUID()), strExtension);
                try
                {
                    file.SaveAs(HttpContext.Current.Server.MapPath(servername));
                }
                catch (Exception e)
                {
                    UploadFile uf = new UploadFile();
                    uf.Upload = false;
                    uf.Remark = e.Message;
                    return uf;
                }

                UploadFile upf = new UploadFile();
                upf.Upload = true;
                upf.ServerName = servername;
                upf.ClientName = clientName;
                upf.Remark = "上传成功!";

                return upf;
            }

            return null;
        }
        /// <summary>
        /// 文件下载
        /// </summary>
        /// <param name="Response"></param>
        /// <param name="filePath"></param>
        public static void DownloadFile(System.Web.HttpResponse Response, string filePath)
        {
            filePath = filePath.Replace("/", "//");
            string fileName = filePath.Substring(filePath.LastIndexOf('//') + 1);

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

            if (file.Exists)
            {
                long dataLengthToRead = file.Length; // 获取下载的文件总大小

                Response.AddHeader("Content-Length", dataLengthToRead.ToString());
                Response.AddHeader("Content-Disposition", "attachment;filename=" + System.Web.HttpUtility.UrlEncode(fileName));

                switch (file.Extension)
                {
                    case "gif":
                        Response.ContentType = "image/gif";
                        break;
                    case "jpg":
                        Response.ContentType = "image/jpeg";
                        break;
                    case "bmp":
                        Response.ContentType = "image/bmp";
                        break;
                    case "zip":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "rar":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "txt":
                        Response.ContentType = "text/plain";
                        break;
                    case "wps":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "doc":
                        Response.ContentType = "application/ms-word";
                        break;
                    case "xls":
                        Response.ContentType = "application/ms-excel";
                        break;
                    case "swf":
                        Response.ContentType = "application/x-shockwave-flash";
                        break;
                    case "ppt":
                        Response.ContentType = "application/ms-powerpoint";
                        break;
                    case "fla":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "mp3":
                        Response.ContentType = "audio/mp3";
                        break;
                }
                Response.TransmitFile(filePath);
                Response.End();
            }
        }
        /// <summary>
        /// 文件下载
        /// </summary>
        /// <param name="Response">发送对象</param>
        /// <param name="filePath">客户端下载文件地址</param>
        /// <param name="clientName">指定客户端下载文件名</param>
        public static void DownloadFile(System.Web.HttpResponse Response, string filePath, string clientName)
        {
            filePath = filePath.Replace("/", "//");
            string fileName = filePath.Substring(filePath.LastIndexOf('//') + 1);

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

            if (file.Exists)
            {
                long dataLengthToRead = file.Length; // 获取下载的文件总大小
                //文件名超过16个字符就会自动截取,防止出现乱码
                string temp = clientName.Substring(0, clientName.LastIndexOf('.'));
                string ex = clientName.Substring(clientName.LastIndexOf('.'));
                if (temp.Length > 16)
                {
                    temp = temp.Substring(0, 16) + ex;
                }
                else
                {
                    temp = clientName;
                }
                Response.AddHeader("Content-Length", dataLengthToRead.ToString());
                Response.AddHeader("Content-Disposition", "attachment;filename=/"" + System.Web.HttpUtility.UrlEncode(temp, Encoding.UTF8) + "/"");
                switch (file.Extension)
                {
                    case "gif":
                        Response.ContentType = "image/gif";
                        break;
                    case "jpg":
                        Response.ContentType = "image/jpeg";
                        break;
                    case "bmp":
                        Response.ContentType = "image/bmp";
                        break;
                    case "zip":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "rar":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "txt":
                        Response.ContentType = "text/plain";
                        break;
                    case "wps":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "doc":
                        Response.ContentType = "application/ms-word";
                        break;
                    case "xls":
                        Response.ContentType = "application/ms-excel";
                        break;
                    case "swf":
                        Response.ContentType = "application/x-shockwave-flash";
                        break;
                    case "ppt":
                        Response.ContentType = "application/ms-powerpoint";
                        break;
                    case "fla":
                        Response.ContentType = "application/octet-stream";
                        break;
                    case "mp3":
                        Response.ContentType = "audio/mp3";
                        break;
                }
                Response.TransmitFile(filePath);
                Response.End();
            }
        }
        /// <summary>
        /// 校验上传文件是否被允许上传
        /// </summary>
        /// <param name="extension"></param>
        /// <returns></returns>
        private static bool ExistUploadType(string extension)
        {
            if (extension.IndexOf('.') < 0) extension.Insert(0, ".");

            return AllExtension.Contains(extension);
        }
        /// <summary>
        /// 如果上传文件的大小超过最大值,返回flase,否则返回true.
        /// </summary>
        /// <param name="length"></param>
        /// <returns></returns>
        public static bool IsAllowedLength(int length)
        {
            //允许上传文件大小的最大值,可以保存在xml文件中,单位为MB
            int i = 4;
            //如果上传文件的大小超过最大值,返回flase,否则返回true.
            if (length > i * 1048576)
            {
                return false;
            }
            return true;
        }
        /// <summary>
        /// 删除文件,当文件不存在的时候不会产生错误
        /// </summary>
        /// <param name="path">相对路径</param>
        public static void DeleteFile(string path)
        {
            File.Delete(HttpContext.Current.Server.MapPath(path));
        }
    }
}

//实体类

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

namespace Care365.Model
{
    public class UploadFile
    {
        string _serverName;

        public string ServerName
        {
            get { return _serverName; }
            set { _serverName = value; }
        }
        string _clientName;

        public string ClientName
        {
            get { return _clientName; }
            set { _clientName = value; }
        }
        bool _upload;

        public bool Upload
        {
            get { return _upload; }
            set { _upload = value; }
        }

        string _remark;

        public string Remark
        {
            get { return _remark; }
            set { _remark = value; }
        }
    }
}