ASP.NET随机码生成示例

ASP.NET随机码生成示例2011-02-28现在很多网页登陆的时候都使用了随机图片的方式，是一种简单、有效的防止黑客恶意攻击的手段。今天看了一些网上的资料，明白其生成原理：从样本中，获取随机字符串，随机字符串保存进session，并以位图的方式形成随机码图片。

实现：

添加命名空间

using System.Drawing;

using System.Drawing.Imaging;

using System.Drawing.Drawing2D;

生成页代码

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
public partial class getRandImg : System.Web.UI.Page
{
   protected void Page_Load（object sender, EventArgs e）
   {
     //生成随机码图片
     SetValidateCode（）;
     //生成页面不保存到cache
     Response.Cache.SetNoStore（）;
   }
  //设置验证码
   private void SetValidateCode（）
   {
     //新建位图
     Bitmap newBitmap = new Bitmap（
                     71,
                     23,
                     PixelFormat.Format32bppArgb
                   ）;
     //从位图获得绘图画面
     Graphics g = Graphics.FromImage（newBitmap）;
     //随机数生成器
     Random r = new Random（）;
     //绘图画面清空
     g.Clear（Color.White）;
     //绘图画面划线干扰
     for （int i = 0; i < 50; i++）
     {
       int x1 = r.Next（newBitmap.Width）;
       int x2 = r.Next（newBitmap.Width）;
       int y1 = r.Next（newBitmap.Height）;
       int y2 = r.Next（newBitmap.Height）;
       g.DrawLine（new Pen（
                 Color.FromArgb（r.Next（）））,
                 x1,
                 y1,
                 x2,
                 y2
                ）;
     }
     //绘图画面点数干扰
     for （int i = 0; i < 100; i++）
     {
       int x = r.Next（newBitmap.Width）;
       int y = r.Next（newBitmap.Height）;
       newBitmap.SetPixel（
                 x,
                 y,
                 Color.FromArgb（r.Next（））
                ）;
     }
     //获得随机字符串（5位长度）
     string value = GenerateRandom（5）;
     //随机字符串赋值给Session
     Session["RandCode"] = value;
     //定义图片显示字体样式
     Font font = new Font（
                "Arial",
                14,
                FontStyle.Bold
               ）;
     Random rr = new Random（）;
     int yy = rr.Next（1, 4）;
     //定义随机字符串显示图片刷子
     LinearGradientBrush brush = new LinearGradientBrush（
                                new Rectangle（0, 0, 71, 23）,
                                Color.Red,
                                Color.Blue,
                                1.2f,
                                true
                              ）;
     g.DrawString（value, font, brush, 2, yy）;
     g.DrawRectangle（new Pen（
                  Color.Silver）,
                  0,
                  0,
                  70,
                  22
                 ）;
     System.IO.MemoryStream ms = new System.IO.MemoryStream（）;
     newBitmap.Save（ms, ImageFormat.Gif）;
     //输出图片
     Response.ClearContent（）;
     Response.ContentType = "image/gif";
     Response.BinaryWrite（ms.ToArray（））;
   }
//常量集
   private static char[] constant ={
                     "0","1","2","3","4","5","6","7","8","9",
                     "a","b","c","d","e","f","g","h","i","j",
                     "k","l","m","n","o","p","q","r","s","t",
                     "u","v","w","x","y","z"
                   };
   //生成随机字符串
   public static string GenerateRandom（int Length）
   {
     System.Text.StringBuilder newRandom = new System.Text.StringBuilder（36）;
     Random rd = new Random（）;
     for （int i = 0; i < Length; i++）
     {
       newRandom.Append（constant[rd.Next（36）]）;
     }
     return newRandom.ToString（）;
   }
}

使用随机图片的页面，IMAGE控件的写法如下：

<asp:Image ID="Image1" ImageUrl="~/getRandImg.aspx" runat="server" />

示例代码：http://www.cnblogs.com/Files/heekui/RandCode.rar