java验证码学习一

package com.sys.web.sesoion;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.http.HttpSession;

public class CheckCodeServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        BufferedImage image = new BufferedImage(50,25,BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        g.drawString(Token.getNum(),15,15);
        ImageIO.write(image,"JPG",response.getOutputStream());
        response.setHeader("expires","-1");
        response.setHeader("cache-control","no-cache");  //没有缓成
        response.setHeader("pragma","no-cache");

    }

}
//用于产生随机数
class Token{
    public static String getNum(){
        Random r = new Random();
        int num = r.nextInt(10000);
        return num + "";
    }
}