JSP动态生成验证码存储在session作用范围内

%@ page import="java.awt.*,java.awt.image.*,java.util.*,com.sun.image.codec.jpeg.*" %> 
%! 
//根据提供的ab产生随机的颜色变化范围 
Color getColor(int a,int b){ 
int n=b-a; 
Random rd=new Random(); 
int cr=a+rd.nextInt(n); 
int cg=a+rd.nextInt(n); 
int cb=a+rd.nextInt(n); 

return new Color(cr,cg,cb); 
} 
%> 
% //下边三行取消客户端游览器缓存验证码的功能 
response.setHeader("Pragma","No-cache"); 
response.setHeader("Cache-Control","no-cache"); 
response.setDateHeader("Expires", 0); 

int width=60, height=20; 
//在内存中生成一个图像 
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); 

Graphics g = image.getGraphics(); 

Random random = new Random(); 

g.setColor(getColor(200,250)); 
g.fillRect(0, 0, width, height); 

g.setFont(new Font("Times New Roman",Font.BOLD,18)); 

g.setColor(getColor(160,200)); 
for (int i=0;i160;i++) 
{ 
int x = random.nextInt(width); 
int y = random.nextInt(height); 
int xl = random.nextInt(12); 
int yl = random.nextInt(12); 
g.drawLine(x,y,x+xl,y+yl); 
} 

String number=String.valueOf(1000+random.nextInt(8999)); 
String name=request.getParameter("name"); 
session.setAttribute(name,number); 

g.setColor(getColor(20,130)); 
int x=(int)(width*0.2); 
int y=(int)(height*0.8); 
g.drawString(number,x,y); 
g.dispose(); 

JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(response.getOutputStream()); 
encoder.encode(image); 
out.close(); 
%>

%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %> 
!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
html xmlns="http://www.w3.org/1999/xhtml"> 
head> 
meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> 
title>无标题文档/title> 
/head> 

body> 
% //同样实现取消客户端缓存 
response.setHeader("Pragma","No-cache"); 
response.setHeader("Cache-Control","no-cache"); 
response.setDateHeader("Expires", 0); 
String name="loginCode"; 
%> 
验证码:img src="authen.jsp?name=%=name%>" /> 
/body> 
/html>