在项目中添加kaptchar的jar包，下载地址：http://code.google.com/p/kaptcha/（建议使用迅雷下载）
步骤二：
配置web.xml，详细配置如下（这里不是所有的配置，这里的参数还有很多可以酌情精简）：
<!-- 配置验证码插件servlet类 -->
<servlet>
<servlet-name>kaptcha</servlet-name>
<servlet-class>
com.google.code.kaptcha.servlet.KaptchaServlet
</servlet-class>
<!-- 给验证码插件servlet类配置参数 -->
<!-- 边框设置 yes no -->
<init-param>
<param-name>kaptcha.border</param-name>
<param-value>no</param-value>
</init-param>
<!-- 边框颜色 颜色名称 例如：red blue black等 也可以是 RGB：105,179,90 -->
<init-param>
<param-name>kaptcha.border.color</param-name>
<param-value>red</param-value>
</init-param>
<!-- 边框宽度 -->
<init-param>
<param-name>kaptcha.border.thickness</param-name>
<param-value>5</param-value>
</init-param>
<!-- 产生验证码的字符源头 兼容中文的 -->
<init-param>
<param-name>kaptcha.textproducer.char.string</param-name>
<param-value>2345共2354阿斯asdf蒂芬2345爬墙2345额问题了ewry空1254间的股fktiul份的y7u12354o私人254认可ry13254iu的身份报123告快乐</param-value>
</init-param>
<!-- 生成结果的字符个数 -->
<init-param>
<param-name>kaptcha.textproducer.char.length</param-name>
<param-value>5</param-value>
</init-param>
<!-- 生成结果的字符字体 -->
<init-param>
<param-name>kaptcha.textproducer.font.names</param-name>
<param-value>微软雅黑,宋体,楷体</param-value>
</init-param>
<!-- 生成结果的字符大小 -->
<init-param>
<param-name>kaptcha.textproducer.font.size</param-name>
<param-value>40</param-value>
</init-param>
<!-- 生成结果的字符 颜色 -->
<init-param>
<param-name>kaptcha.textproducer.font.color</param-name>
<param-value>blue</param-value>
</init-param>
<!-- 生成结果的字符 字间距 -->
<init-param>
<param-name>kaptcha.textproducer.char.space</param-name>
<param-value>2</param-value>
</init-param>
<!-- 干扰线 生成器 -->
<init-param>
<param-name>kaptcha.noise.impl</param-name>
<param-value>com.google.code.kaptcha.impl.DefaultNoise</param-value>
</init-param>
<!-- 干扰线 颜色 -->
<init-param>
<param-name>kaptcha.noise.color</param-name>
<param-value>BLACK</param-value>
</init-param>
<!-- 干扰线 背景渐变颜色 从左侧向右渐变 -->
<init-param>
<param-name>kaptcha.background.clear.from</param-name>
<param-value>green</param-value>
</init-param>
<!-- 干扰线 背景渐变颜色 从右侧向左渐变 -->
<init-param>
<param-name>kaptcha.background.clear.to</param-name>
<param-value>yellow</param-value>
</init-param>
<!-- 验证码图片宽度 -->
<init-param>
<param-name>kaptcha.image.width</param-name>
<param-value>200</param-value>
</init-param>
<!-- 验证码图片高度 -->
<init-param>
<param-name>kaptcha.image.height</param-name>
<param-value>50</param-value>
</init-param>
</servlet>
<!-- 验证码请求名 映射 -->
<servlet-mapping>
<servlet-name>kaptcha</servlet-name>
<url-pattern>/yzm</url-pattern>
</servlet-mapping>
步骤三：
在jsp页面中添加图片标签，标签的src静态资源请求地址为上面配置好的请求名 yzm，具体代码如下：
<br>
<hr>
<br>
<form action="kaptchatest" method="post">
<img title = "点我换一张" alt="" src="yzm" style="cursor:pointer;" onclick="changeVerifyCode();">
<input type="text" name="yzm">
<br>
<input type="submit" value="测试验证码">
</form>
<script type="text/javascript">
//点击切换验证码
function changeVerifyCode(){
img.src = "yzm?"+Math.floor(Math.random()*100);
}
</script>package com.kaptcha.action;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class KaptchaServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//设置request编码方式
request.setCharacterEncoding("utf-8");
//获取表单提交参数
String yzm = request.getParameter("yzm") ;
System.out.println(yzm);
//从session中获取google kaptcha 插件生成的验证码
String googlecode = request.getSession().getAttribute(com.google.code.kaptcha.Constants.KAPTCHA_SESSION_KEY).toString() ;
System.out.println(googlecode);
//比较验证码正确性
System.out.println(googlecode.equalsIgnoreCase(yzm)); //true
}
} <servlet>
<description></description>
<servlet-name>KaptchaServlet</servlet-name>
<servlet-class>com.kaptcha.action.KaptchaServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>KaptchaServlet</servlet-name>
<url-pattern>/kaptchatest</url-pattern>
</servlet-mapping>
GOOGLE kaptcha 验证码生成插件 servlet/jsp项目中使用步骤
原文地址：http://blog.csdn.net/responsecool/article/details/39295089
