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。