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);
     }
 }