asp.net 的 handler 实现 验证码

<%@ 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("黑体",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;
    }
}}