验证码
kaptcha是一个非常实用的验证码生成工具，有了它，你可以生成各种样式的验证码，因为它是可配置的。
kaptcha工作的原理是调用com.google.code.kaptcha.servlet.KaptchaServlet，生成一个图片。同时将生成的验证码字符串放到HttpSession中。
kaptcha可以配置一下信息：
验证码的字体
验证码字体的大小
验证码字体的字体颜色
验证码内容的范围(数字，字母，中文汉字！)
验证码图片的大小，边框，边框粗细，边框颜色
验证码的干扰线(可以自己继承com.google.code.kaptcha.NoiseProducer写一个自定义的干扰线)
验证码的样式(鱼眼样式、3D、普通模糊……当然也可以继承com.google.code.kaptcha.GimpyEngine自定义样式)
……
详细信息请看下面的web.xml文件
下面介绍一下用法:
1.首先去官网下载jar:http://code.google.com/p/kaptcha/
2.建立一个web项目，导入kaptcha-2.3.jar到环境变量中。
3.配置web.xml文件
其实就是配置com.google.code.kaptcha.servlet.KaptchaServlet
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 3 xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" 4 version="2.4"> 5 <servlet> 6 <servlet-name>Kaptcha</servlet-name> 7 <servlet-class>com.google.code.kaptcha.servlet.KaptchaServlet</servlet-class> 8 <init-param> 9 <description> Border around kaptcha. Legal values are yes or no. </description> 10 <param-name>kaptcha.border</param-name> 11 <param-value>no</param-value> 12 </init-param> 13 <init-param> 14 <description>Color of the border. Legal values are r,g,b (and optional alpha) or white,black,blue. </description> 15 <param-name>kaptcha.border.color</param-name> 16 <param-value>red</param-value> 17 </init-param> 18 <init-param> 19 <description>Thickness of the border around kaptcha. Legal values are > 0. </description> 20 <param-name>kaptcha.border.thickness</param-name> 21 <param-value>5</param-value> 22 </init-param> 23 <init-param> 24 <description>Width in pixels of the kaptcha image. </description> 25 <param-name>kaptcha.image.width</param-name> 26 <param-value>80</param-value> 27 </init-param> 28 <init-param> 29 <description>Height in pixels of the kaptcha image. </description> 30 <param-name>kaptcha.image.height</param-name> 31 <param-value>40</param-value> 32 </init-param> 33 <init-param> 34 <description>The image producer. </description> 35 <param-name>kaptcha.producer.impl</param-name> 36 <param-value>com.google.code.kaptcha.impl.DefaultKaptcha </param-value> 37 </init-param> 38 <init-param> 39 <description>The text producer. </description> 40 <param-name>kaptcha.textproducer.impl</param-name> 41 <param-value>com.google.code.kaptcha.text.impl.DefaultTextCreator</param-value> 42 </init-param> 43 <init-param> 44 <description>The characters that will create the kaptcha. </description> 45 <param-name>kaptcha.textproducer.char.string</param-name> 46 <param-value>abcde2345678gfynmnpwx </param-value> 47 </init-param> 48 <init-param> 49 <description>The number of characters to display. </description> 50 <param-name>kaptcha.textproducer.char.length</param-name> 51 <param-value>5</param-value> 52 </init-param> 53 <init-param> 54 <description>A list of comma separated font names.</description> 55 <param-name>kaptcha.textproducer.font.names</param-name> 56 <param-value>Arial, Courier</param-value> 57 </init-param> 58 <init-param> 59 <description>The size of the font to use. </description> 60 <param-name>kaptcha.textproducer.font.size</param-name> 61 <param-value>23</param-value> 62 </init-param> 63 <init-param> 64 <description>The color to use for the font. Legal values are r,g,b. </description> 65 <param-name>kaptcha.textproducer.font.color</param-name> 66 <param-value>black</param-value> 67 </init-param> 68 <init-param> 69 <description>The noise producer. </description> 70 <param-name>kaptcha.noise.impl</param-name> 71 <param-value>com.google.code.kaptcha.impl.NoNoise </param-value> 72 </init-param> 73 <init-param> 74 <description>The noise color. Legal values are r,g,b. </description> 75 <param-name>kaptcha.noise.color</param-name> 76 <param-value>black</param-value> 77 </init-param> 78 <init-param> 79 <description>The obscurificator implementation. </description> 80 <param-name>kaptcha.obscurificator.impl</param-name> 81 <param-value>com.google.code.kaptcha.impl.ShadowGimpy</param-value> 82 </init-param> 83 <init-param> 84 <description>The background implementation. </description> 85 <param-name>kaptcha.background.impl</param-name> 86 <param-value>com.google.code.kaptcha.impl.DefaultBackground</param-value> 87 </init-param> 88 <init-param> 89 <description>Ending background color. Legal values are r,g,b. </description> 90 <param-name>kaptcha.background.clear.to</param-name> 91 <param-value>white</param-value> 92 </init-param> 93 <init-param> 94 <description>The word renderer implementation. </description> 95 <param-name>kaptcha.word.impl</param-name> 96 <param-value>com.google.code.kaptcha.text.impl.DefaultWordRenderer</param-value> 97 </init-param> 98 <init-param> 99 <description>The value for the kaptcha is generated and is put into the HttpSession. This is the key value for that item in the session. </description> 100 <param-name>kaptcha.session.key</param-name> 101 <param-value>KAPTCHA_SESSION_KEY</param-value> 102 </init-param> 103 <init-param> 104 <description>The date the kaptcha is generated is put into the HttpSession. This is the key value for that item in the session. </description> 105 <param-name>kaptcha.session.date</param-name> 106 <param-value>KAPTCHA_SESSION_DATE</param-value> 107 </init-param> 108 </servlet> 109 <servlet-mapping> 110 <servlet-name>Kaptcha</servlet-name> 111 <url-pattern>/Kaptcha.jpg</url-pattern> 112 </servlet-mapping> 113 <welcome-file-list> 114 <welcome-file>KaptchaExample.jsp</welcome-file> 115 </welcome-file-list> 116 </web-app>
4.编写KaptchaExample.jsp
这里用到了jQuery，所以添加了jQuery的库
1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2 <html> 3 <head> 4 <%@ page language="java" contentType="text/html; charset=UTF-8"%> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 6 <title>Kaptcha Example</title> 7 <mce:script type="text/javascript" src="js/jquery-1.3.2.js" mce_src="js/jquery-1.3.2.js"></mce:script> 8 </head> 9 <body> 10 Enter in the 11 <a href="http://code.google.com/p/kaptcha/" mce_href="http://code.google.com/p/kaptcha/">Kaptcha</a> to see if it 12 matches what is stored in the session attributes. 13 <table> 14 <tr> 15 <td> 16 <img src="Kaptcha.jpg" mce_src="Kaptcha.jpg" id="kaptchaImage" /> 17 <mce:script type="text/javascript"><!-- 18 $('#kaptchaImage').click( 19 function() { 20 $(this).hide().attr('src', 21 'Kaptcha.jpg?' + Math.floor(Math.random() * 100)).fadeIn(); 22 }) 23 // --></mce:script> 24 <br /> 25 单击换图片 26 </td> 27 <td valign="top"> 28 <form method="POST"> 29 <br> 30 验证码:: 31 <input type="text" name="kaptchafield"> 32 <br /> 33 <input type="submit" name="submit"> 34 </form> 35 </td> 36 </tr> 37 </table> 38 <br /> 39 <br /> 40 <br /> 41 <br /> 42 <% 43 String c = (String) session 44 .getAttribute(com.google.code.kaptcha.Constants.KAPTCHA_SESSION_KEY); 45 String parm = (String) request.getParameter("kaptchafield"); 46 47 System.out.println(c); 48 out.println("Parameter: " + parm + " ? Session Key: " + c + " : "); 49 if (c != null && parm != null) 50 { 51 if (c.equals(parm)) 52 { 53 out.println("<b>true</b>"); 54 } else 55 { 56 out.println("<b>false</b>"); 57 } 58 } 59 %> 60 </body> 61 </html>
参考文献：
http://blog.csdn.net/ol_beta/article/details/5877630