Asp.NET 上传图片并生成缩略图

后台代码：

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
using System.IO;    //注意把这个加上
using System.Drawing;   //注意把这个加上

public partial class PhotoPage : System.Web.UI.Page
{
    SqlConnection sqlCon = new SqlConnection("");
    SqlCommand sqlCom = new SqlCommand();
    protected void Page_Load(object sender, EventArgs e)
    {

    }

　 //生成图片代码
    protected void btnOK_Click(object sender, EventArgs e)
    {
        string P_str_filePath = "";      //定义一个在客户端文件的路径的变量
        string P_str_fileExtName = "", P_str_mFileName, P_str_mPath;//文件的扩展名
        System.Text.StringBuilder strMsg = new System.Text.StringBuilder("上传图片;<hr color=red>");
        if (fileUp .PostedFile.FileName!="")   //fileUp是控件fileload控件的名称  这句是取控件的文件名称
        {
            P_str_filePath = fileUp.PostedFile.FileName;  //获取图片路径
            P_str_fileExtName = P_str_filePath.Substring(P_str_filePath.LastIndexOf(".")+1);  //获取扩展名
            try
            {
                P_str_mPath = Server.MapPath("Images/Pictures/"); //获取服务器端的文件的路径
                P_str_mFileName = P_str_filePath.Substring(P_str_filePath.LastIndexOf("\") + 1);  //获取文件的名称
                fileUp.PostedFile.SaveAs(P_str_mPath + P_str_mFileName);  //保存到制定的路径下

                //生成缩略图
                string smallFileName = Server.MapPath("Images/SmallPictures/")+P_str_mFileName;      //上传缩略图的路径
                System.Drawing . Image smallImage = System.Drawing .Image.FromStream(fileUp.PostedFile.InputStream, true);  //从文件中取出图片对象
                double width = Double.Parse(TextBox1.Text .ToString ());  //设定的高度和宽度
                double height = Double.Parse(TextBox2.Text .ToString ());
                double NewWidth, NewHeight;  //新的高度和宽度
                if (smallImage.Width > smallImage.Height)
                {
                    NewWidth = width;
                    NewHeight = smallImage.Height * (NewWidth / smallImage.Width);
                }
                else
                {
                    NewHeight = height;
                    NewWidth=smallImage.Width*(NewHeight/smallImage.Height);
                }
                if (NewHeight > height)
                {
                    NewHeight = height;
                }
                if (NewWidth > width)
                {
                    NewWidth = width;
                }
                Size size= new Size((int)NewWidth, (int)NewHeight);   //图片的大小
                System.Drawing. Image Bitmap = new System.Drawing. Bitmap(size.Width, size.Height);   //新生成一个bitmap对象
                Graphics graphics = Graphics.FromImage(Bitmap); //新生成的画板
                graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;  //设置最高的质量
                graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;        //设置高质量,低速度呈现平滑程度
                graphics.Clear(Color.White);        //清空画布

                //在指定位置画图

                graphics.DrawImage(smallImage, new System.Drawing.Rectangle(0, 0, Bitmap.Width, Bitmap.Height),

                    new System.Drawing.Rectangle(0, 0,smallImage.Width,smallImage.Height),

                    System.Drawing.GraphicsUnit.Pixel);
                //文字水印

                System.Drawing.Graphics textGraphics = System.Drawing.Graphics.FromImage(Bitmap);

                System.Drawing.Font font = new Font("宋体", 10);

                System.Drawing.Brush brush = new SolidBrush(Color.Black);

                textGraphics.DrawString(TextBox3.Text.Trim(), font, brush, 10, 10);

                textGraphics.Dispose();

                ///图片水印

                //System.Drawing.Image copyImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath("pic/1.gif"));

                //Graphics a = Graphics.FromImage(Bitmap);

                //a.DrawImage(copyImage, new Rectangle(Bitmap.Width - copyImage.Width, Bitmap.Height - copyImage.Height, copyImage.Width, copyImage.Height), 

0, 0, copyImage.Width, copyImage.Height, GraphicsUnit.Pixel);

                //保存缩略图

                try
                {

                    Bitmap.Save(smallFileName, System.Drawing.Imaging.ImageFormat.Gif);
                    

                }

                catch (Exception ex)
                {

                    Response.Write("保存缩略图失败:" + ex.Message);

                }
                string imageUrl = "";      //定义一个用来存储图片url的变量
                Image1.ImageUrl =smallFileName .Substring( smallFileName.IndexOf("));
                imageUrl=smallFileName .Substring( smallFileName.IndexOf("));
                Image1.ImageUrl ="~"+ imageUrl.Replace("\", "/");

                graphics.Dispose();

                smallImage.Dispose();

                Bitmap.Dispose();

 

                //copyImage.Dispose();

                //a.Dispose();

                //copyImage.Dispose();

            }
            catch
            { 
                
            }
        }
    }