C# 生成缩略图 并下载例子源码(asp.net)

【实例截图】

【核心代码】

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Web;

namespace GetminPic
{
    /// <summary>
    /// Getmin 的摘要说明
    /// </summary>
    public class Getmin : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            //1.获取用户上传的文件流
            HttpPostedFile file = context.Request.Files[0];
            //获取文件名
            string fileName = file.FileName;
            //获取扩展名
            string Extension = Path.GetExtension(fileName).ToUpper();
            //2.根据用户上传的文件流创建一个图片
            using (Image originalImage = Image.FromStream(file.InputStream))
            {
            //获取原始图片的宽和高
                int owidth = originalImage.Width;
                int oheight = originalImage.Height;
                //缩略图的宽
                int mwidth = Convert.ToInt32(context.Request.Form["width"]);
                //等比例的高,取整数
                int mheight = mwidth * oheight / owidth;
                //3.根据原始图片，等比例创建一个缩小后的图片
                using (Image minImage = new Bitmap(mwidth, mheight))
                {
                   //4.把大图片内容画到小图片上
                    //基于小图创建一个画面对象
                    Graphics gmin = Graphics.FromImage(minImage);
                    //把大图画到小图上
                    gmin.DrawImage(originalImage, 0, 0, mwidth, mheight);

                    //5.下载缩略图
                    MemoryStream ms = new MemoryStream();
                    //判断图片类型
                    ImageFormat imageFormat = null;
                    string ContentType = "";
                    switch (Extension)
                    {
                        case ".JPG": imageFormat = ImageFormat.Jpeg; ContentType = "image/jpeg"; break;
                        case ".PNG": imageFormat = ImageFormat.Png; ContentType = "image/png"; break;
                        case ".GIF": imageFormat = ImageFormat.Gif; ContentType = "image/gif"; break;
                        //................如需要其他图片格式继续添加
                    }
                    minImage.Save(ms,imageFormat);
                    context.Response.ClearContent();
                    context.Response.AddHeader("Content-Disposition", "attachment;  filename="   HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8)); 
                    context.Response.ContentType=ContentType;
                    context.Response.BinaryWrite(ms.ToArray());
                    context.Response.End();
                }
            }
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}