生成有4個隨機(jī)數(shù)字和雜亂背景的圖片，數(shù)字和背景顏色會改變，服務(wù)器端刷新（用history.go(-1)也會變）
原型參考ALIBABA  http://china.alibaba.com/member/showimage

產(chǎn)生驗(yàn)證碼圖片的文件-----image.jsp

%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
%!
Color getRandColor(int fc,int bc){//給定范圍獲得隨機(jī)顏色
        Random random = new Random();
        if(fc>255) fc=255;
        if(bc>255) bc=255;
        int r=fc+random.nextInt(bc-fc);
        int g=fc+random.nextInt(bc-fc);
        int b=fc+random.nextInt(bc-fc);
        return new Color(r,g,b);
        }
%>
%
//設(shè)置頁面不緩存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);

// 在內(nèi)存中創(chuàng)建圖象
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

// 獲取圖形上下文
Graphics g = image.getGraphics();

//生成隨機(jī)類
Random random = new Random();

// 設(shè)定背景色
g.setColor(getRandColor(200,250));
g.fillRect(0, 0, width, height);

//設(shè)定字體
g.setFont(new Font("Times New Roman",Font.PLAIN,18));

//畫邊框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);

// 隨機(jī)產(chǎn)生155條干擾線，使圖象中的認(rèn)證碼不易被其它程序探測到
g.setColor(getRandColor(160,200));
for (int i=0;i155;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);
}

// 取隨機(jī)產(chǎn)生的認(rèn)證碼(4位數(shù)字)
String sRand="";
for (int i=0;i4;i++){
    String rand=String.valueOf(random.nextInt(10));
    sRand+=rand;
    // 將認(rèn)證碼顯示到圖象中
    g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//調(diào)用函數(shù)出來的顏色相同，可能是因?yàn)榉N子太接近，所以只能直接生成
    g.drawString(rand,13*i+6,16);
}

// 將認(rèn)證碼存入SESSION
session.setAttribute("rand",sRand);

// 圖象生效
g.dispose();

// 輸出圖象到頁面
ImageIO.write(image, "JPEG", response.getOutputStream());

%>

---------------使用驗(yàn)證碼圖片的文件---------a.jsp------------------------------------

%@ page contentType="text/html;charset=gb2312" %>
!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
html>
head>
title>認(rèn)證碼輸入頁面/title>
meta http-equiv="Content-Type" content="text/html; charset=gb2312">
META HTTP-EQUIV="Pragma" CONTENT="no-cache">
META HTTP-EQUIV="Cache-Control" CONTENT="no-cache">
META HTTP-EQUIV="Expires" CONTENT="0">
/head>
body>
form method=post action="check.jsp">
table>
tr>
td align=left>系統(tǒng)產(chǎn)生的認(rèn)證碼：/td>
td>img border=0 src="image.jsp">/td>
/tr>
tr>
td align=left>輸入上面的認(rèn)證碼：/td>
td>input type=text name=rand maxlength=4 value="">/td>
/tr>
tr>
td colspan=2 align=center>input type=submit value="提交檢測">/td>
/tr>
/form>
/body>
/html>

-----------------驗(yàn)證的頁面----------check.jsp

%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
html>
head>
title>認(rèn)證碼驗(yàn)證頁面/title>
meta http-equiv="Content-Type" content="text/html; charset=gb2312">
META HTTP-EQUIV="Pragma" CONTENT="no-cache">
META HTTP-EQUIV="Cache-Control" CONTENT="no-cache">
META HTTP-EQUIV="Expires" CONTENT="0">
/head>

body>
%
 String rand = (String)session.getAttribute("rand");
 String input = request.getParameter("rand");
%>
系統(tǒng)產(chǎn)生的認(rèn)證碼為： %= rand %>br>
您輸入的認(rèn)證碼為： %= input %>br>
br>
%
  if (rand.equals(input)) {
%>
font color=green>輸入相同，認(rèn)證成功！/font>
%
  } else {
%>
font color=red>輸入不同，認(rèn)證失敗！/font>
%
  }
%>
/body>
/html>