使用开源组件生成随机验证码

首先在项目中导入lsimplecaptcha-20050925.jar
1.在jsp文件中加入如下脚本：

1.   <script language ="javascript" type ="text/javascript">
2.      function reloadcode()
3.      { 
4.        document.getElementById('safecode').src = 'Captcha.jpg?' +   Math.random();
5.      } 
6.   </script>

2.加入如下图片链接:

1. <a href="javascript:reloadcode();"><img id="safecode" border="0" src="Captcha.jpg">再换一张</a>

3.在web.xml文件中加入如下配置：

1. <servlet>
2.         <servlet-name>SimpleCaptcha</servlet-name>      
3.         <servlet-class>nl.captcha.servlet.SimpleCaptcha</servlet-class>
4.  </servlet>
5.   <servlet>
6.         <servlet-name>Captcha</servlet-name>        
7.         <servlet-class>nl.captcha.servlet.CaptchaServlet</servlet-class>
8.           <init-param>
9.             <param-name>cap.border</param-name>
10.             <param-value>no</param-value>
11.           </init-param>
13.           <init-param>
14.             <param-name>cap.char.arr.l</param-name>
15.             <param-value>4</param-value>
16.           </init-param>
17. <init-param>
18.             <param-name>cap.font.arr</param-name>
19.             <param-value>"Times New Roman", Times, serif</param-value>
20.           </init-param>
21.           <init-param>
22.           <param-name>cap.background.c.to</param-name>
23.           <param-value>white</param-value>
24.           </init-param>
26. <init-param>
27.           <param-name>cap.background.c.from</param-name>
28.           <param-value>white</param-value>
29.           </init-param>
30.        </servlet>
31. <servlet-mapping>
32.         <servlet-name>SimpleCaptcha</servlet-name>
33.         <url-pattern>/SimpleCaptcha.jpg</url-pattern>
34.     </servlet-mapping>
35.     <servlet-mapping>
36.         <servlet-name>Captcha</servlet-name>
37.         <url-pattern>/Captcha.jpg</url-pattern>
38.     </servlet-mapping>

4.可以使用如下方法得到随机码上的文字：

1. String rc=(String)request.getSession().getAttribute(nl.captcha.servlet.Constants.SIMPLE_CAPCHA_SESSION_KEY);