使用Httphandle 实现水印效果

先看效果

下面有2张图片一个有水印的，一个无水印的.

代码:

首先我们定义处理图片的类

public class ImageHandler:IHttpHandler
{
	public ImageHandler()
	{
		//
		// TODO: Add constructor logic here
		//
	}
    public bool IsReusable
    {
        get { return true; }
    }

    public void ProcessRequest(HttpContext context)
    {
        string imagePath = context.Request.PhysicalPath;
        Bitmap image = null;
        //如果挡墙缓存中不存在当前图片则为该图片添加水印并缓存
        if (context.Cache[imagePath] == null)
        {
            image = new Bitmap(imagePath);
            image = AddColorImage(image);
            context.Cache[imagePath] = image;
        }
        else
        {
            //从缓存中获取当前图片
            image = context.Cache[imagePath] as Bitmap;
        }
        image.Save(context.Response.OutputStream, ImageFormat.Jpeg);
    }
    //添加水印
    public static Bitmap AddColorImage(Bitmap image)
    {
        string text = ConfigurationManager.AppSettings["waterMark"].ToString();
        int fontSize = int.Parse(ConfigurationManager.AppSettings["fontSize"].ToString());

        Font f = new Font("宋体", fontSize);
        //定义刷子的颜色
        Brush b = Brushes.Purple;
        //从指定的Image 获取一个新的 Graphics
        Graphics g = Graphics.FromImage(image);
        //用指定的Font 绘制指定的字符串返回一个SizeF结构,该结构表示由指定的text,使用 font 绘制的字符串大小
        SizeF sf = g.MeasureString(text, f);
        g.DrawString(text, f, b, image.Width - sf.Width, image.Height - sf.Height);
        g.Dispose();
        return image;
    }
}

然后定义一个html 页面

    <table class="style1">
        <tr>
            <td colspan="2" style="text-align: center">
                <h1>
                    水印图片</h1>
            </td>
        </tr>
        <tr>
            <td style="text-align: right">
                图片(无水印):</td>
            <td>
                <img src="hangzhou.PNG" /></td>
        </tr>
                <tr>
            <td style="text-align: right">
                图片:</td>
            <td>
                <img src="UploadImage/GuoHu.PNG" /></td>
        </tr>
    </table>

Webconfig:

<configuration>
  <appSettings>
    <!--添加到图片上的水印文字-->
    <add key="waterMark" value="http://blog.csdn.net/ws_hgo"/>
    <!--字体大小-->
    <add key="fontSize" value="24"/>
  </appSettings>
	<connectionStrings>
		<add name="ApplicationServices" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\aspnetdb.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
	</connectionStrings>
	<system.web>
    <httpHandlers>
      <!--只对文件夹UploadImage下面请求的文件映射到类ImageHandler-->
      <add path="UploadImage/*.*" verb="*" type="ImageHandler" />
    </httpHandlers>
		<compilation debug="true" targetFramework="4.0"/>
		<authentication mode="Forms">
			<forms loginUrl="~/Account/Login.aspx" timeout="2880"/>
		</authentication>
		<membership>
			<providers>
				<clear/>
				<add name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServices" enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false" maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10" applicationName="/"/>
			</providers>
		</membership>
		<profile>
			<providers>
				<clear/>
				<add name="AspNetSqlProfileProvider" type="System.Web.Profile.SqlProfileProvider" connectionStringName="ApplicationServices" applicationName="/"/>
			</providers>
		</profile>
		<roleManager enabled="false">
			<providers>
				<clear/>
				<add name="AspNetSqlRoleProvider" type="System.Web.Security.SqlRoleProvider" connectionStringName="ApplicationServices" applicationName="/"/>
				<add name="AspNetWindowsTokenRoleProvider" type="System.Web.Security.WindowsTokenRoleProvider" applicationName="/"/>
			</providers>
		</roleManager>
	</system.web>
	<system.webServer>
		<modules runAllManagedModulesForAllRequests="true"/>
	</system.webServer>
</configuration>