文件上传后台和前台代码（文件下载也是）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;

public partial class upload : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btupload_Click(object sender, EventArgs e)
    {
        if (FileUpload1.HasFile)
        {
            string filecontentType = FileUpload1.PostedFile.ContentType;
            if (filecontentType == "image/bmp" || filecontentType == "image/gif" || filecontentType == "image/pjpeg" || filecontentType == "image/jpeg")
            {
                string name = FileUpload1.PostedFile.FileName;
                FileInfo file = new FileInfo(name);
                string filename = file.Name;
                string webFilePath = Server.MapPath("image/" + filename);
                if (!File.Exists(webFilePath))
                {
                    try
                    {
                        FileUpload1.SaveAs(webFilePath);
                        this.lmsg.Text = "提示：文件" + filename + "上传成功！";
                        this.lpathInfo.Text = "image/" + filename;
                        this.iPic.ImageUrl = "image/" + filename;
                    }
                    catch (Exception ex)
                    {
                        this.lmsg.Text = "提示文件上传失败，失败原因" + ex.Message;

                    }
                }
                else
                {
                    this.lmsg.Text = "该文件已经存在！";
                }
            }
            else {
                this.lmsg.Text = "提示：文件类型不符";
            }
        }
    }
}

前台代码如下：

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="upload.aspx.cs" Inherits="upload" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>    
    <form id="form1" runat="server">
    <div>
    <table>
    <tr>
        <td><asp:FileUpload ID="FileUpload1" runat="server" />
       <asp:Button ID="btupload" runat="server" onclick="btupload_Click" Text="上传" /> <asp:Image 
                ID="iPic" ImageUrl="" Height="100px" runat="server" />
        </td> 
    </tr>
    <tr><td>
        <asp:Label ID="lmsg" runat="server" Text="Label"></asp:Label>        
        <asp:Label ID="lpathInfo" runat="server" Text="Label"></asp:Label>
    </td></tr>   
    </table>
    </div>
    </form>
</body>
</html>

文件下载代码