IHttphandler之图片水印

IHttphandler原理已经在“IHttphandler之Url重写”一文中讲述，有不理解的同学可以参看该文章。

本文是对网站的图片进行水印处理。原理相同，关键在web.config的配置，以及GDI+操作。

首先对web.config配置如下：

<httpHandlers>
      <add verb="*" path="*.jpg" type="MyHttpHandler.WaterMarkHandler,MyHttpHandler"/>    </httpHandlers>

为什么要这么配置同样参见“IHttphandler之Url重写”一文，path为“*.jpg”,例如“logo.gif”的时候，由MyHttpHandler.WaterMarkHandler处理后返回客户端。

让我们来看下WaterMarkHandler的实现吧：

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

namespace MyHttpHandler
{
    class WaterMarkHandler : IHttpHandler
    {
        #region IHttpHandler 成员

        public bool IsReusable
        {
            get { return true; }
        }

        public void ProcessRequest(HttpContext context)
        {
            CommonDeal.DealImageRequest(context);
        }

        #endregion
    }
}

CommonDeal实现如下：

using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
using System.Web.UI;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;

namespace MyHttpHandler
{
    internal class CommonDeal
    {
        public static void DealImageRequest(HttpContext context)
        {
            Font enFont = new Font("Times New Roman", 12);

            MemoryStream ms = new MemoryStream();

            string filePath = context.Server.MapPath("Image" + context.Request.Path);
            try
            {
                Image image = Image.FromFile(filePath);
                if (IsPixelFormatIndexed(image.PixelFormat))
                {
                    Bitmap bmp = new Bitmap(image.Width, image.Height, PixelFormat.Format32bppArgb);
                    using (Graphics graphic = Graphics.FromImage(bmp))
                    {
                        graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                        graphic.DrawImage(image, 0, 0);
                        graphic.DrawString("pangxiaoliang", enFont, new SolidBrush(Color.LightGray), 2, 2);
                        graphic.DrawString("pangxiaoliang", enFont, new SolidBrush(Color.Black), 0, 0);

                    }
                    bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                    bmp.Dispose();
                }
                else
                {
                    using (Graphics graphic = Graphics.FromImage(image))
                    {
                        graphic.DrawString("pangxiaoliang", enFont, new SolidBrush(Color.LightGray), 2, 2);
                        graphic.DrawString("pangxiaoliang", enFont, new SolidBrush(Color.Black), 0, 0);

                    }

                    Bitmap theBitmap = new Bitmap(image);
                    theBitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                    theBitmap.Dispose();
                }

                context.Response.ClearContent();
                context.Response.ContentType = "image/jpg";
                context.Response.BinaryWrite(ms.ToArray());

            }
            catch
            {
                Bitmap error = new Bitmap(context.Server.MapPath("Image/error.bmp"));
                error.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                error.Dispose();
                context.Response.ClearContent();
                context.Response.ContentType = "image/jpg";
                context.Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                ms.Close();
                ms.Dispose();
                context.Response.End();
            }
        }

        public static void ReturnErrorImage(HttpContext context)
        {
            MemoryStream ms = new MemoryStream();
            try
            {
                Bitmap error = new Bitmap(context.Server.MapPath("error.bmp"));
                error.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                error.Dispose();
                context.Response.ClearContent();
                context.Response.ContentType = "image/jpg";
                context.Response.BinaryWrite(ms.ToArray());
            }
            catch
            {
            }
            finally
            {
                ms.Close();
                ms.Dispose();
                context.Response.End();
            }
        }

        /// <summary>
        /// 会产生graphics异常的PixelFormat
        /// </summary>
        private static PixelFormat[] indexedPixelFormats = { PixelFormat.Undefined, PixelFormat.DontCare,
                                            PixelFormat.Format16bppArgb1555, PixelFormat.Format1bppIndexed, PixelFormat.Format4bppIndexed,
                                            PixelFormat.Format8bppIndexed
                                            };

        /// <summary>
        /// 判断图片的PixelFormat 是否在 引发异常的 PixelFormat 之中
        /// </summary>
        /// <param name="imgPixelFormat">原图片的PixelFormat</param>
        /// <returns></returns>
        private static bool IsPixelFormatIndexed(PixelFormat imgPixelFormat)
        {
            foreach (PixelFormat pf in indexedPixelFormats)
            {
                if (pf.Equals(imgPixelFormat)) return true;
            }
            return false;
        }
    }


}

1）string filePath = context.Server.MapPath("Image" + context.Request.Path);首先得到图像在服务器上的绝对路径，使得可以对图像进行处理。

2）MemoryStream ms = new MemoryStream();内存流用来响应客户端请求，把处理后的图像返回给客户端。

3）使用GDI+对在图像上写上名字后，以流的方式将新图片返回到客户端。