Asp.net验证码

刚做一网站，需要验证码。网上看了好多，自己又改了改，写成下面这个，基于C#

先看下效果：





网站->添加新项->一般处理程序，添加一个名为VerificationCode.ashx的文件。

代码如下：

<%@ WebHandler Language="C#" Class="VerificationCode" %>
using System;
using System.Web;
using System.Drawing;
using System.Drawing.Imaging;
using System.Text;
using System.Web.SessionState;
public class VerificationCode : IHttpHandler, IRequiresSessionState /*加上这个接口，否则不能读写Session*/
{
#region 私有成员

string code;     //验证码
int codeLength = 4;    //验证码长度
int width = 70;   //图片宽度
int height = 25;   //图片高度
int fontSize = 14;    //验证码字体大小
static char[] Chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();     //字符集

//画刷
static Brush[] BrushItems = new Brush[]{
Brushes.OliveDrab,
Brushes.ForestGreen,
Brushes.DarkCyan,
Brushes.LightSlateGray,
Brushes.RoyalBlue,
Brushes.SlateBlue,
Brushes.DarkViolet,
Brushes.MediumVioletRed,
Brushes.IndianRed,
Brushes.Firebrick,
Brushes.Chocolate,
Brushes.Peru,
Brushes.Goldenrod
};

//字体
static string[] FontItems = new string[]{
"Arial",
"Helvetica",
"Geneva",
"sans-serif",
"Verdana"
};

#endregion

public void ProcessRequest (HttpContext context) {
context.Response.ContentType = "image/jpeg";
context.Response.Cache.SetCacheability(HttpCacheability.NoCache);    //不缓存图片
code = MakeCode(codeLength);     //生成验证码
context.Session["VerificationCode"] = code;    //将验证码存入Session
Bitmap bmp = new Bitmap(width, height);
Graphics g = Graphics.FromImage(bmp);
DrawBackground(g);   //绘制背景
Font font = MakeFont();
Brush brush = MakeBrush();
g.DrawString(code, font, brush, 3, 3); //绘制验证码字符串
DrawStain(bmp,0.08);     //绘制噪声点
bmp.Save(context.Response.OutputStream, ImageFormat.Jpeg);
}

public bool IsReusable {
get {
return false;
}
}
/// <summary>
/// 生成指定位数的随机验证码字符串
/// </summary>
/// <param name="length">验证码长度</param>
/// <returns>验证码字符串</returns>
private string MakeCode(int length)
{
StringBuilder s = new StringBuilder();
Random r = new Random();
//生成随机字符串
for (int i = 0; i < length; ++i)
{
int index = r.Next(Chars.Length);
s.Append(Chars[index]);
}
return s.ToString();
}
/// <summary>
/// 绘制图片背景
/// </summary>
/// <param name="g"></param>
private void DrawBackground(Graphics g)
{
g.Clear(Color.White);
}
/// <summary>
/// 在位图中绘制指定比例的噪声点
/// </summary>
/// <param name="bmp"></param>
/// <param name="percentage">噪声点所占百分比</param>
private void DrawStain(Bitmap bmp, double percentage)
{
int width = bmp.Width;
int height = bmp.Height;
int n =  Convert.ToInt32(width * height * percentage);
Random r = new Random();
//随机颜色
int red = r.Next(255);
int green = r.Next(255);
int blue = r.Next(255);
Color color = Color.FromArgb(red,green,blue);
for(int i=0;i<n;++i)
{
//随机坐标
int x = r.Next(1,width);
int y = r.Next(1,height);
bmp.SetPixel(x, y, color);
}
}

/// <summary>
/// 生成随机字体格式（字体、字号、字形）
/// </summary>
/// <returns></returns>
private Font MakeFont()
{
Random r = new Random();
int i = r.Next(FontItems.Length);
string familyName =FontItems[i];    //字体
FontStyle fontStyle = GetFontStyle(r.Next(0,2));   //字形
return new Font(familyName, fontSize, fontStyle);
}

/// <summary>
/// 取得字体样式
/// </summary>
/// <param name="index">索引，取值0-2</param>
/// <returns></returns>
private FontStyle GetFontStyle(int index)
{
switch (index)
{
case 0:
return FontStyle.Bold;
case 1:
return FontStyle.Italic;
default:
return FontStyle.Regular;
}
}
/// <summary>
/// 生成随机画刷
/// </summary>
/// <returns></returns>
private Brush MakeBrush()
{
Random r = new Random();
int i = r.Next(BrushItems.Length);
return BrushItems[i];
}
}

生成的验证码存入Session，验证时判断一下即可。

使用时可以用img:

<img alt="验证码" id="imgCode"  src="VerificationCode.ashx"
onclick="this.src='VerificationCode.ashx?tmp='+new Date().getTime().toString(36);" title="看不清楚，换一张"  />

这样可以实现点击图片，刷新验证码的功能。