驗證碼是用來進行登錄驗證的一個有效方式，下面就為大家講解如何在jsp中使用。下面僅介紹最簡單的實現方法，稍後我們還會加入Ajax等來使驗證更為正式。
本文直接使用jsp頁面作為載體，也就是說直接把生成驗證碼的圖片放在了jsp中來實現，感興趣的朋友可以放在servlet中，這樣更方便管理。
1.image.jsp---生成隨機驗證碼圖片的Jsp頁面
<%@ 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服務器，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(12);
int yl = random.nextInt(12);
g.drawLine(x,y,x+xl,y+yl);
}
String sRand="";
for (int i=0;i<4;i++){
String rand=String.valueOf(random.nextInt(10));
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);
g.dispose();
ImageIO.write(image, "JPEG", response.getOutputStream());
%>
效果如下：
2.logic.jsp----登陸頁面，在這裡提供輸入驗證碼然後提交並驗證 ，這個頁面裡加載image.jsp實現驗證
<%@ page contentType="text/html;charset=gbk" %>
<%@ page language="java" import="java.sql.*" errorPage="" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>用戶登錄</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="rand" 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>
效果如下：
3.validate.jsp----用來驗證輸入的驗證碼是否正確
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<%
String rand = (String)session.getAttribute("rand");
String input = request.getParameter("rand");
if(rand.equals(input)){
out.print("<script>alert('驗證通過！');</script>");
} else{
out.print("<script>alert('請輸入正確的驗證碼！');location.href='login.jsp';</script>");
}
%>
效果如下;
因為我之前輸入的驗證碼不正確，所以如上顯示。
作者：wangjinyu501
