asp.net 的 handler 實現 驗證碼 、、

<%@ WebHandler Language="C#" Class="Handler" %>

using System;
using System.Web;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
using System.Web.SessionState;

public class Handler : IHttpHandler,IRequiresSessionState {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "image/jpeg";
    
        Random rand = new Random(DateTime.Now.Millisecond*1000000);
        String[] list = { "2", "3", "5", "6", "A", "f", "h", "j", "q", "v","B","P" };
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 4; i++)
        {

            sb.Append(list[rand.Next(0, list.Length)]);
            
        }
        String number=sb.ToString();
        context.Session["number"] = number.ToLower();
        Image image = new Bitmap(number.Length * 30,40);
        Font f=new Font("黑體",30);
        Brush  b=new SolidBrush(Color.White);
        Graphics g = Graphics.FromImage(image);
       
        g.Clear(Color.Black);
        g.DrawString(number, f, b, 4, 4);
        
       
        g.DrawRectangle(new Pen(Color.Yellow,1),1,1,image.Width-3,image.Height-3);
        for (int i = 0; i < 20; i++)
        {
            Pen p = new Pen(Color.FromArgb(rand.Next(50, 255),rand.Next(50,255),rand.Next(50,255)));
             
            int x1 = rand.Next(1,image.Width);
            int y1 = rand.Next(1,image.Height);
            int x2 = rand.Next(1,image.Width);
            int y2 = rand.Next(1,image.Height);
            g.DrawLine(p,x1,y1,x2,y2);
           
        }
        image.Save(context.Response.OutputStream,ImageFormat.Jpeg);
        
        image.Dispose();
        g.Dispose();
        
        
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }

}