<%@ 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());
%>