教你制作简单的验证码

每次登录优快云博客都需要输入验证码，有时候明明看着写对了，却是经常显示验证码输入错误。想着前一时间段刚学了如何生成和使用验证码，加之最近正在学习JS，所以在此总结一下验证码的生成和使用，增加常用代码的积累，借鉴了牛腩的新闻发布系统。

生成验证码代码：

<%@ WebHandler Language="C#" Class="WaterMark" %>
using System;
using System.Web;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Web.SessionState;  
public class WaterMark : IHttpHandler, IRequiresSessionState  // 要使用session必须实现该接口,记得要导入System.Web.SessionState命名空间
{

    public void ProcessRequest(HttpContext context)
    {
        string checkCode = GenCode(5);  // 产生5位随机字符，可更改
        context.Session["Code"] = checkCode; //将字符串保存到Session中，以便需要时进行验证
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(120, 22);//定义验证码图片的宽度和高度
        Graphics g = Graphics.FromImage(image);
        try
        {
            //生成随机生成器
            Random random = new Random();
           //清空图片背景色
            g.Clear(Color.White);
            // 画图片的背景噪音线
            int i;
            for (i = 0; i < 25; 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.Silver), x1, y1, x2, y2);
            }
             Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold));
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2F, true);
            g.DrawString(checkCode, font, brush, 2, 2);
             //画图片的前景噪音点
            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);
            context.Response.ClearContent();
            context.Response.ContentType = "image/Gif";
            context.Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }

    /// <summary>
    /// 产生随机字符串
    /// </summary>
    /// <param name="num">随机出几个字符</param>
    /// <returns>随机出的字符串</returns>
    private string GenCode(int num)
    {
        string str = "廊坊师范学院提高班第八期李达";//图片上出现的文字为这些之一，可重复
        char[] chastr = str.ToCharArray(); 
        // string[] source ={ "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", "#", "$", "%", "&", "@" };
        string code = "";  
        Random rd = new Random();
        int i;
        for (i = 0; i < num; i++)
        {
            //code += source[rd.Next(0, source.Length)];
            code += str.Substring(rd.Next(0, str.Length), 1);
        }
        return code;
 }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

登录界面：

<p >验证码：<img src="../handler/WaterMark.ashx" id="vimg" alt="" onclick="changeCode()"/>

使用JS避免浏览器缓存问题：

     <script language="javascript" type="text/javascript">
         function changeCode() {
             var imgNode = document.getElementById("vimg");
             imgNode.src = "../handler/WaterMark.ashx?t=" + (new Date()).valueOf();  // 这里加个时间的参数是为了防止浏览器缓存的问题   
         }  
    </script>

登录界面后台代码：

        // 判断验证码是否输入正确
        string code = txtCode.Text.Trim().ToUpper();
        string rightCode = Session["Code"].ToString();
        if (code != rightCode)
        {
            Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('验证码输入错误！');</script>");
            return;
        }

运行界面：


简单介绍一下原理。首先是生成验证图片，在图片上添加线和点等视觉噪音，在图片上添加生成的字符，生成的验证码保存在session["code"]；为了避免缓存问题，给验证码添加时间标记；使用时判断输入的字符与验证码字符是否相同即可。