实现验证码也很简单，就那么几个步骤，理解就好！
下面是JSP页面：
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>登录</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form action="user?types=login" method="post">
<div>
<label>用户登陆：</label>
<input type="text" value="" maxlength="100" id="username"name="username">
</div>
<div>
<label>登陆密码：</label>
<input type="password" value="" maxlength="100" id="password" name="password">
</div>
<div>
<label>验证码</label>
<input type="text" value="" maxlength="100" id="yzm" name="veryCode" >
<!--重要的是下面这一段代码。通过JavaScript的时间函数Date().getTime()，就可以实现点击验证码图片的时候切换图片-->
<div><a href="javascript:document.getElementById('chkcode').src='imageCode.code?rnd='
+new Date().getTime();"><img src="imageCode.code" id="chkcode"/></a></div>
</div>
<div >
<input type="submit" value="提交" tabindex="4" id="send-btn">
</div>
</form>
</body>
</html>
下面是web.xml配置文件
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
<servlet>
<servlet-name>ValidateCode</servlet-name>
<servlet-class>org.Public.util.ValidateCode</servlet-class><!--Servlet类的路径-->
</servlet>
<servlet-mapping>
<servlet-name>ValidateCode</servlet-name>
<url-pattern>/imageCode.code</url-pattern>
</servlet-mapping>
</web-app>
下面是Servlet：
package org.Public.util;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* 生成验证码的工具类
* @author Administrator
*
*/
@SuppressWarnings("serial")
public class ValidateCode extends HttpServlet {
private static final int WIDTH = 120;
private static final int HEIGHT = 35;
public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 创建一个BufferedImage类的对象
BufferedImage image = new BufferedImage(WIDTH, HEIGHT,
BufferedImage.TYPE_INT_RGB);
// 创建一个Graphics类的对象
Graphics graphics = image.getGraphics();
// 设置画笔的颜色
graphics.setColor(Color.BLUE);
// 画一个矩形方框
graphics.drawRect(0, 0, WIDTH, HEIGHT);
// 设置画笔的颜色
graphics.setColor(Color.GREEN);
// 填充矩形的背景色
graphics.fillRect(1, 1, WIDTH - 2, HEIGHT - 2);
// 画干扰线
graphics.setColor(Color.RED);
Random random = new Random();
for (int i = 0; i < 5; i++) {
graphics.drawLine(random.nextInt(WIDTH), random.nextInt(HEIGHT),
random.nextInt(WIDTH), random.nextInt(HEIGHT));
}
// 画数字
// 设置字体大小
Font font = new Font("宋体", Font.ITALIC, 24);
graphics.setFont(font);
graphics.setColor(Color.BLUE);
int x = 10;
char[] ch = new char[] { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u',
'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G',
'H', 'I', 'G', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };
StringBuffer buffer = new StringBuffer();
for (int i = 0; i < 4; i++) {
int tempNum = random.nextInt(10);
if (tempNum < 5) {
// 若果随机数小于5，就画一个数字
String param1 = random.nextInt(10) + "";
graphics.drawString(param1, x, 20);
x += 30;
buffer.append(param1);
} else {
// 随机数大于5就画一个字母
String param2 = String.valueOf(ch[random.nextInt(52)]);
graphics.drawString(param2, x, 20);
x += 30;
buffer.append(param2);
}
}
// 取得当前的session对象
HttpSession session = request.getSession();
// 将这个buffer对象添加到session域中
session.setAttribute("photoCode", buffer.toString());
// 设置客户端不要缓存
response.setHeader("Expires", "1");
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
// 输出到客户端
ImageIO.write(image, "jpeg", response.getOutputStream());
}
}