Session应用之验证码

package com.aeolia.view;

import java.awt.Color;
import java.awt.Font;
import java.awt.image.BufferedImage;
import java.io.IOException;
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 CheckCode extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //禁止浏览器缓存随即图片
        response.setDateHeader("Expires", -1);
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cahce");
        //通知客户机以图片方式打开发送过去的数据
        response.setHeader("Content-Type","image/jpeg");
        //在内存中创建一幅图片
        java.awt.image.BufferedImage image=new BufferedImage(80,30,BufferedImage.TYPE_INT_RGB);
        //向图片上写数据
        java.awt.Graphics g=image.getGraphics();
        //设置背景色
        g.setColor(Color.white);
        //设置矩形框
        g.fillRect(0,0,80,30);
        //设置背景色写入数据的字体和颜色
        g.setColor(Color.red);
        g.setFont(new Font(null,Font.BOLD,20));
        //向图片上写数据
        String nums=makeNums();
        request.getSession().setAttribute("checkcode", nums);
        g.drawString(nums, 0,20);
        //把写好的数据的图片输出给浏览器
        ImageIO.write(image, "jpg", response.getOutputStream());
    }
    private String makeNums() {
        java.util.Random r=new java.util.Random();
        String nums=r.nextInt(9999)+"";
        StringBuffer sb=new StringBuffer(nums);
        for(int i=0;i<4-nums.length();i++){
            sb.append("0");
        }
        return sb.toString();
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        this.doGet(request, response);
    }
}