java 验证码生成器

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;


import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class CodeCreater extends HttpServlet {


public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {


response.setContentType("text/html");
//禁止浏览器缓存
response.setDateHeader("Expires", -1);
response.setHeader("Cache-Control","no-cache");
response.setHeader("Pragma","no-cache"); 
//通知客户机，以图片的方式打开收到的数据
response.setHeader("Context-Type","image/jpeg");
//1.在内存中创建一副图片
BufferedImage image = new BufferedImage(60, 30, BufferedImage.TYPE_INT_RGB);
//2.在图片上写数据
Graphics g = image.getGraphics();
//设置背景
g.fillRect(0, 0, 60, 30);
//3.设置输入数据的颜色和字体
g.setColor(Color.red);
g.setFont(new Font(null,Font.BOLD,20));

String num = makeNum();

request.getSession().setAttribute("checkcode", num);
//向图片上写数据
g.drawString(num, 0, 20);
//把写好的数据输出给浏览器
ImageIO.write(image,"jpg",response.getOutputStream());
}

public String makeNum(){
Random r = new Random();
String num = r.nextInt(9999)+"";
StringBuffer buff = new StringBuffer();
for(int i=0;i<4-num.length();i++){
buff.append("0");
}
num = num.toString()+buff;
return num;
}


public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doGet(request, response);
}


}