用ServletJSP动态生成英文、数字图像验证码

1：首先实现一个servlet用来生成图片（当然也可以用
jsp实现）：

/*

* ClassName: ValidateCode.java

* Author: qiujy

*
Version: v1.0

* CreateDate: 2005-12-30

*

* Copyright
2005-2006 www.mobstar.cn


All rights reserved.

*/

package com.mob.common;
import java.awt.Color;

import java.awt.Font;

import
java.awt.Graphics;

import java.awt.image.BufferedImage;

import
java.io.IOException;

import java.util.Date;

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;
public class ValidateCode extends HttpServlet {
// Process the HTTP Get request
public void doGet(HttpServletRequest request,
HttpServletResponse response)

throws ServletException, IOException
{

// 设置页面不缓存

response.setHeader("Pragma", "No-cache");

response.setHeader("Cache-Control",
"no-cache");

response.setDateHeader("Expires", 0);
// 设置图片的长宽

int width = 62, height = 22;
// ////// 创建内存图像

BufferedImage image = new
BufferedImage(width, height,

BufferedImage.TYPE_INT_RGB);

//
获取图形上下文

Graphics g = image.createGraphics();
// 设定图像背景色(因为是做背景，所以偏淡)

g.setColor(getRandColor(180,
250));

g.fillRect(0, 0, width, height);

// 设置字体

g.setFont(new
Font("Times New Roman", Font.PLAIN, 17));
// /////设置默认生成4个验证码

int length = 4;

java.util.Random
rand = new Random(); // 设置随机种子
/*

* if (request.getParameter("length") !=
null) { try { length =

*
Integer.parseInt(request.getParameter("length")); }catch

*
(NumberFormatException e) {} }

*/

// 设置备选验证码:包括"a-z"和数字"0-9"

String
base = "abcdefghijklmnopqrstuvwxyz0123456789";

int size =
base.length();

StringBuffer str = new StringBuffer();

for (int
i = 0; i < length; i++) {

int start = rand.nextInt(size);

String
tmpStr = base.substring(start, start + 1);
str.append(tmpStr);

// 生成随机颜色(因为是做前景，所以偏深)

g.setColor(getRandColor(10,
150));
// 将此字画到图片上

// g.drawString(str.toString(),
4, 17);

g.drawString(tmpStr, 13 * i + 6 + rand.nextInt(5), 14 +
rand

.nextInt(6));
}
// 将认证码存入session

request.getSession().setAttribute("valiCode",
str.toString());
// 图象生效

g.dispose();
// 输出图象到页面

ImageIO.write(image, "JPEG",
response.getOutputStream());
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)

throws ServletException, IOException
{

this.doGet(request, response);

}
// 给定范围获得一个随机颜色

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);

}
}
2：在web.xml中做如下配置

<!-- validate code maker
begin -->

<servlet>

<servlet-name>CodeMakerServlet</servlet-name>

<servlet-class>com.mob.common.ValidateCode</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>CodeMakerServlet</servlet-name>

<url-pattern>/codeMaker</url-pattern>

</servlet-mapping>

<!--
　validate code maker end -->
3：然后在需要显示验证码的地方加入以下代码就可以了
<img alt="" src="/codeMaker" width="60"
height="22"/>
4：若要验证是否填写正确：可如下做法
　在输入页面加入如下代码
<tr>

<td
align="right">输入验证码:  </td>

<td><input type="text" name="check_num" id="check_num"
size="10" maxlength="10"> 

<img
src="codeMaker"/>

<!--<img alt=""
src="com/mob/common/ValidateCode" width="40" height="16"/>-->

</td>

</tr>
在处理请求的java类（如struts中的action中）中只需要这样做这要可以了：
String valiCode = null;

Object obj =
request.getSession().getAttribute("valiCode");

if (obj != null
&& !obj.equals("")) {

valiCode = obj.toString();

}
String check_num = loginForm.getCheck_num();

if
(check_num != null && !check_num.equals("") &&
!check_num.trim().equals(valiCode)) {

request

.setAttribute("errorMessage",

"
请注意正确输入登录验证码!");

return mapping.getInputForward();

}