<%@ page contentType="image/jpeg" import="java.awt.*,    
java.awt.image.*,java.util.*,javax.imageio.*" %>    
<%    
// 在内存中创建图象    
int width=60, height=20;    
BufferedImage image = new BufferedImage(width, height,    
BufferedImage.TYPE_INT_RGB);    

// 获取图形上下文    
Graphics g = image.getGraphics();    

// 设定背景色    
g.setColor(new Color(0xDCDCDC));    
g.fillRect(0, 0, width, height);    

//画边框    
g.setColor(Color.black);    
g.drawRect(0,0,width-1,height-1);    

// 取随机产生的认证码(4位数字)    
String rand = request.getParameter("rand");    
rand = rand.substring(0,rand.indexOf("."));    
switch(rand.length())    
{    
case 1: rand = "000"+rand; break;    
case 2: rand = "00"+rand; break;    
case 3: rand = "0"+rand; break;    
default: rand = rand.substring(0,4); break;    
}    

// 将认证码存入SESSION    
session.setAttribute("rand",rand);    

// 将认证码显示到图象中    
g.setColor(Color.black);    
Integer tempNumber = new Integer(rand);    
String numberStr = tempNumber.toString();    

g.setFont(new Font("Atlantic Inline",Font.PLAIN,18));    
String Str = numberStr.substring(0,1);    
g.drawString(Str,8,17);    

Str = numberStr.substring(1,2);    
g.drawString(Str,20,15);    
Str = numberStr.substring(2,3);    
g.drawString(Str,35,18);    

Str = numberStr.substring(3,4);    
g.drawString(Str,45,15);    

// 随机产生88个干扰点，使图象中的认证码不易被其它程序探测到    
Random random = new Random();    
for (int i=0;i<20;i++)    
{    
int x = random.nextInt(width);    
int y = random.nextInt(height);    
g.drawOval(x,y,0,0);    
}    

// 图象生效    
g.dispose();    

// 输出图象到页面    
ImageIO.write(image, "JPEG", response.getOutputStream());    
%>

[url]http://localhost:8080/test/codetest.jsp?rand=1080.[/url]