1.建立Image.jsp檔案，如下：
<%@ page contentType="image/jpeg"
import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"%>
<%!Color getRandColor(int fc, int bc) {
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);
}%>
<%
//out.clear();//這句針對resin伺服器，如果是tomacat可以不要這句
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
int width = 60, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics();
Random random = new Random();
g.setColor(getRandColor(200, 250));
g.fillRect(0, 0, width, height);
g.setFont(new Font("Times New Roman", Font.PLAIN, 18));
g.setColor(getRandColor(160, 200));
for (int i = 0; i < 155; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(10);
int yl = random.nextInt(10);
g.drawLine(x, y, x + xl, y + yl);
}
char c[] = new char[62];
for (int i = 97, j = 0; i < 123; i++, j++) {
c[j] = (char) i;
}
for (int o = 65, p = 26; o < 91; o++, p++) {
c[p] = (char) o;
}
for (int m = 48, n = 52; m < 58; m++, n++) {
c[n] = (char) m;
}
String sRand = "";
for (int i = 0; i < 4; i++) {
int x = random.nextInt(62);
String rand = String.valueOf(c[x]);
sRand += rand;
g.setColor(new Color(20 + random.nextInt(110), 20 + random
.nextInt(110), 20 + random.nextInt(110)));
g.drawString(rand, 13 * i + 6, 16);
}
// 將認證碼存入SESSION
session.setAttribute("rand", sRand);
System.out.println(sRand);
g.dispose();
ImageIO.setUseCache(true);
ImageIO.write(image, "JPEG", response.getOutputStream());
%>
2.建立驗證頁面validate.jsp，如下
<%@ page language="java" contentType="text/html; charset=GB2312"
pageEncoding="GB2312"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB2312">
<title>驗證</title>
</head>
<body>
<%!String rand = null;
String input = null;%>
<%
rand = (String) session.getAttribute("rand");
input = request.getParameter("yanzhengma");
%>
驗證碼為：
<%=rand%>
您的輸入為：
<%=input%>
<%
if (rand.equals(input)) {
%>
<font color=green>輸入相同，認證成功。</font>
<%
} else {
%>
<font color=red>輸入不同，認證失敗。</font>
<%
}
%>
</body>
</html>
3.建立登入頁面login.jsp 如下
<%@ page language="java" import="java.sql.*" errorPage=""%>
<%
request.setCharacterEncoding("GB2312");
%>
<%@page pageEncoding="GB2312"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>使用者登入</title>
<script language="javascript">
function loadimage(){
document.getElementById("randImage").src = "image.jsp?"+Math.random();
}
</script>
</head>
<body>
<table width="256" border="0" cellpadding="0" cellspacing="0">
<!--DWLayoutTable-->
<form action="validate.jsp" method="post" name="loginForm">
<tr>
<td width="118" height="22" valign="middle" align="center"><input
type="text" name="yanzhengma" size="15"></td>
<td width="138" valign="middle" align="center"><img alt="code..."
name="randImage" id="randImage" src="image.jsp" width="60"
height="20" border="1" align="absmiddle"></td>
</tr>
<tr>
<td height="36" colspan="2" align="center" valign="middle"><a
href="javascript:loadimage();"><font class=pt95>看不清點我</font></a></td>
</tr>
<tr>
<td height="36" colspan="2" align="center" valign="middle"><input
type="submit" name="login" value="提交"></td>
</tr>
</form>
</table>
</body>
</html>
