ashx生成验证码

using System.Web.SessionState; //用到session

public class Validate : IHttpHandler,IRequiresSessionState //为要使用session实现的接口

{
   
    public void ProcessRequest (HttpContext context)
    {
        string checkCode = GetValidation(5);  // 产生5位随机验证码字符
        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(70, 22);
        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>
    /// 随即获取验证码

    /// </summary>
    /// <param name="num">位数</param>
    /// <returns>返回验证码</returns>
    public string GetValidation(int num)
    {
        string str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; //"或者写汉字也行"
        string validatecode = "";
        Random rd = new Random();
        for (int i = 0; i < num; i++)
        {
            validatecode += str.Substring(rd.Next(0, str.Length), 1);
        }
        return validatecode;
    }
   
    public bool IsReusable {
        get {
            return false;
        }
    }

}

//前台页面

<script language="javascript" type="text/javascript">
    function changeCode() {  
        var imgNode = document.getElementById("vimg");  
        imgNode.src = "Validate.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>

<img src="Validate.ashx" id="vimg" alt="不区分大小写,点击切换" onclick="changeCode()" />