网页验证码的产生和判断

        目前，很多网站都有验证码的功能，比如说中国知网吧，在登录的时候就需要验证。。。那他是怎么实现的呢？咱们就看看吧。。。

        首先建立一个一般处理程序，如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;
using System.Web.SessionState;
namespace WebApplication1
{
/// <summary>
/// Handler1 的摘要说明
/// </summary>
public class Handler1 : IHttpHandler, IRequiresSessionState
{
public void ProcessRequest(HttpContext context)
{
string checkCode = CreateCode(4);
context.Session["CheckCode"] = checkCode;
CreateImage(checkCode,context );
}
//产生验证码
public string CreateCode(int codeLength)
{

string so = "1,2,3,4,5,6,7,8,9,0,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,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";
string[] strArr = so.Split(',');
string code = "";
Random rand = new Random();
for (int i = 0; i < codeLength; i++)
{
code += strArr[rand.Next(0, strArr.Length)];
}
return code;
}

/*产生验证图片*/
public void CreateImage(string code, HttpContext context)
{
Bitmap image = new Bitmap(80, 20);
Graphics g = Graphics.FromImage(image);

//清空图片背景色
g.Clear(Color.White);
Random random = new Random();
//画图片的背景噪音线
for (int i = 0; i < 12; i++)
{
int x1 = random.Next(image.Width);
int x2 = random.Next(image.Width);
int y1 = random.Next(image.Height);
int y2 = random.Next(image.Height);

g.DrawLine(new Pen(Color.LightGray), x1, y1, x2, y2);
}
Font font = new Font("Arial", 15, FontStyle.Bold | FontStyle.Italic);
System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(
new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.Gray, 1.2f, true);
g.DrawString(code, font, brush, 0, 0);

//画图片的前景噪音点
for (int i = 0; i < 10; i++)
{
int x = random.Next(image.Width);
int y = random.Next(image.Height);
image.SetPixel(x, y, Color.White);
}

//画图片的边框线
g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

System.IO.MemoryStream ms = new System.IO.MemoryStream();
image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
//Response.ClearContent();
//Response.ContentType = "image/Gif";
//Response.BinaryWrite(ms.ToArray());
context.Response.ClearContent();
context.Response.ContentType = "image/Gif";
context.Response.BinaryWrite(ms.ToArray());
g.Dispose();
image.Dispose();
}
public bool IsReusable
{
get
{
return false;
}
}
}
}
        然后新建aspx页面，在牛腩中用到javascript来获取验证码，这里采用的是 onclick="this.src=this.src+'?'"，前台html：

<%@ Page Title="主页" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
CodeBehind="Default.aspx.cs" Inherits="WebApplication1._Default" %>

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<p>
验证码：
<asp:TextBox ID="txtCode" ValidationGroup ="pinglun" runat="server" ></asp:TextBox>
<a name="com"> </a> <img src="Handler1.ashx" id="vimg" alt ="" onclick="this.src=this.src+'?'"/>
<asp:RequiredFieldValidator ValidationGroup ="pinglun" ID="RequiredFieldValidator1" runat="server" ControlToValidate ="txtCode" ErrorMessage="请输入验证码！" Text ="*" ForeColor ="red"></asp:RequiredFieldValidator>
<asp:Button ID="btnSub" ValidationGroup ="pinglun" runat="server" Text="提交" onclick="btnSub_Click" /></asp:Button>
<asp:ValidationSummary ValidationGroup ="pinglun" ID="ValidationSummary1" runat="server" ShowMessageBox ="true" ShowSummary ="false" />
</p>
</asp:Content>前台代码：
public partial class _Default : System.Web.UI.Page
{
protected void btnSub_Click(object sender, EventArgs e)
{
string code = txtCode.Text.Trim().ToUpper();//当前输入的验证码
string rightcode = Session["CheckCode"].ToString();//验证码本身
if (code != rightcode)
{
Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('验证码输入错误！');</script>");
return;
}
else
{
Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('验证码输入正确！');</script>");
}
}
}

效果展示：点击验证码时会自动更换验证码