Asp.net mvc 实时生成缩率图到硬盘

之前对于缩率图的处理是在图片上传到服务器之后，同步生成两张不同尺寸的缩率供前端调用，刚开始还能满足需求，慢慢的随着前端展示的多样化，缩率图已不能前端展示的需求，所以考虑做一个实时生成图片缩率图服务。

每次调用实时生成缩率图，不缓存着实有点浪费，所以在生成缩率的同时缓存到硬盘一份，效率提高很多。

之前从网上看了一下有人用nginx + lua实现的，效率那是没什么可说的，但是时间紧迫，自己也没时间去研究，所以暂时先用aps.net mvc4来实现 一个，以后有时间了，再慢慢修改。

用自己熟悉的.net性能可能差那么一点点，但是实现速度快，保证可以在极端的时间内上线，并且在功能上更强。

思路很简单，就是根据请求，判断需要的缩率图是否已存在于硬盘上，如果有直接返回，没有则下载原图，并生成缩率图到本地，返回给客户端。

下面直接粘贴代码片段：

/// <summary>
        /// 生成图片缩率图Action
        /// </summary>
        /// <param name="p">原图url</param>
        /// <param name="id">图片尺寸以及生成缩率图的类型</param>
        /// <returns></returns>
        [HttpGet]
        public async Task<ActionResult> Index(string p, string id)
        {
            if (string.IsNullOrEmpty(p))
            {
                return new HttpStatusCodeResult(404);
            }

            string oPath = Regex.Replace(p, @"http[s]?://(.*?)/", "/", RegexOptions.IgnoreCase);
            int? oWidth = 200, oHeight = 200;
            int cutMode = 3;
            string pPath;
            string oDir;

            if (!string.IsNullOrEmpty(id))
            {
                string[] ss = id.Split(new char[] { '_' }, StringSplitOptions.RemoveEmptyEntries);
                if (ss.Length < 2)
                {
                    return new HttpStatusCodeResult(404);
                }
                if (ss.Length > 2)
                {
                    cutMode = int.Parse(ss[2]);
                }
                oPath = oPath.Insert(oPath.LastIndexOf('/') + 1, string.Format("{0}_{1}_{2}_", ss[0], ss[1], cutMode));
                oWidth = int.Parse(ss[0]);
                oHeight = int.Parse(ss[1]);
            }

            pPath = Server.MapPath(oPath);
            oDir = Path.GetDirectoryName(pPath);

            if (!System.IO.File.Exists(pPath))
            {
                byte[] imagebytes =await FileHelper.DownLoadFileAsync(p);
                if (!Directory.Exists(oDir))
                {
                    Directory.CreateDirectory(oDir);
                }
                FileHelper.MakeThumbnail(FileHelper.BytToImg(imagebytes), oWidth.Value, oHeight.Value, (ThumbnailMode)cutMode, pPath, true);
            }

            return File(pPath, FileHelper.GetContentTypeByExtension(Path.GetExtension(pPath).ToLower()));
        }

辅助方法：

 public class FileHelper
    {
         /// <summary>
        /// 图片后缀和ContentType对应字典
        /// </summary>
        static Dictionary<string, string> extensionContentTypeDic;

        static FileHelper()
        {
            if (extensionContentTypeDic == null)
            {
                //.jpg", ".png", ".gif", ".jpeg
                extensionContentTypeDic = new Dictionary<string, string>();
                extensionContentTypeDic.Add(".jpg", "image/jpeg");
                extensionContentTypeDic.Add(".png", "image/png");
                extensionContentTypeDic.Add(".gif", "image/gif");
                extensionContentTypeDic.Add(".jpeg", "image/jpeg");
            }
        }
        /// <summary>
        /// 根据后缀名获取extension
        /// </summary>
        /// <param name="extension"></param>
        /// <returns></returns>
        public static string GetContentTypeByExtension(string extension)
        {
            if (extensionContentTypeDic.ContainsKey(extension))
            {
                return extensionContentTypeDic[extension];
            }
            return null;
        }

        ///  <summary > 
        /// 将Image对象转化成二进制流 
        ///  </summary > 
        ///  <param name="image" > </param > 
        ///  <returns > </returns > 
        public static byte[] ImageToByteArray(Image image)
        {
            MemoryStream imageStream = new MemoryStream();
            Bitmap bmp = new Bitmap(image.Width, image.Height);
            Graphics g = Graphics.FromImage(bmp);
            g.DrawImage(image, new System.Drawing.Rectangle(0, 0, image.Width, image.Height));
            try
            {
                bmp.Save(imageStream, image.RawFormat);
            }
            catch (Exception e)
            {

                bmp.Save(imageStream, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            byte[] byteImg = imageStream.GetBuffer();
            bmp.Dispose();
            g.Dispose();
            imageStream.Close();
            return byteImg;
        }

        /// <summary> 
        /// 字节流转换成图片 
        /// </summary> 
        /// <param name="byt">要转换的字节流</param> 
        /// <returns>转换得到的Image对象</returns> 
        public static Image BytToImg(byte[] byt)
        {
            MemoryStream ms = new MemoryStream(byt);
            Image img = Image.FromStream(ms);
            ms.Close();
            return img;
        }

        /// <summary>
        /// 生成缩率图
        /// </summary>
        /// <param name="originalImage">原始图片Image</param>
        /// <param name="width">缩率图宽</param>
        /// <param name="height">缩率图高</param>
        /// <param name="mode">生成缩率图的方式</param>
        /// <param name="thumbnailPath">缩率图存放的地址</param>
        public static Image MakeThumbnail(Image originalImage, int width, int height, ThumbnailMode mode, string thumbnailPath, bool isSave = true)
        {
            int towidth = width;
            int toheight = height;

            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;
            switch (mode)
            {
                case ThumbnailMode.HW://指定高宽缩放（可能变形）                  
                    break;
                case ThumbnailMode.W://指定宽，高按比例                      
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case ThumbnailMode.H://指定高，宽按比例  
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case ThumbnailMode.Cut://指定高宽裁减（不变形）                  
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;

                default:
                    break;
            }

            //新建一个bmp图片  
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
            //新建一个画板  
            Graphics g = System.Drawing.Graphics.FromImage(bitmap);
            //设置高质量插值法  
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            //设置高质量,低速度呈现平滑程度  
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //清空画布并以透明背景色填充  
            g.Clear(Color.Transparent);
            //在指定位置并且按指定大小绘制原图片的指定部分  
            g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
             new Rectangle(x, y, ow, oh),
             GraphicsUnit.Pixel);
            if (!isSave)
            {
                return bitmap;
            }
            try
            {
                //以jpg格式保存缩略图  
                //bitmap.Save(thumbnailPath, bitmap.RawFormat);
                bitmap.Save(thumbnailPath, ImageFormat.Jpeg);
                return bitmap;

            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
            return null;
        }


        /// <summary>
        /// 下载指定文件
        /// </summary>
        /// <param name="remoteUrl"></param>
        /// <param name="ss"></param>
        public static Task<byte[]> DownLoadFileAsync(string remoteUrl)
        {
            WebClient wc = new WebClient();
            try
            {
                return wc.DownloadDataTaskAsync(remoteUrl);
            }
            catch (Exception e)
            {
                throw new Exception("下载文件失败");
            }
        }

    }

    public enum ThumbnailMode
    {
        /// <summary>
        /// 指定高宽缩放（可能变形）
        /// </summary>
        HW,
        /// <summary>
        /// 指定高，宽按比例
        /// </summary>
        H,
        /// <summary>
        /// 指定宽，高按比例
        /// </summary>
        W,
        /// <summary>
        /// 指定高宽裁减（不变形）   
        /// </summary>
        Cut,

    }

访问方式：

http://www.souji8.com/Home/Index/{width}_{height}_{ThumMode}?p={imageUrl}

{imageUrl}:目标图片地址

{ThumMode}: 1:指定高宽按比例、2：指定宽，高按比例、3：指定高宽裁减（不变形） 

{Width}:期望图片宽

{Height}:期望图片高

等有时间了，再改成nginx+lua 实现。