<%@ page language="java" pageEncoding="utf-8" %>
<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %><%@ page session="true" %><%
	// 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(Color.white);
	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 = Math.random()*10000+"";

	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;
	}
	
	// 将认证码显示到图象中
	g.setColor(Color.black);
	g.setFont(new Font("Fixedsys",Font.BOLD,18));
	g.drawString(rand,10,16);
	
	// 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<88;i++)
	{
		int x = random.nextInt(width);
		int y = random.nextInt(height);
		g.drawLine(x,y,x,y);
	}
	
	// 图象生效
	g.dispose();
	
	// 将认证码存入SESSION
	HttpSession sessionLogin=request.getSession(true);
	sessionLogin.setAttribute("randKey",rand);
   // System.out.println("rand:"+rand);
	// 输出图象到页面
	//<IMG src="num.jsp" WIDTH=60 HEIGHT=20 > 
	ImageIO.write(image, "JPEG", response.getOutputStream());
%>