使用kaptcha插件生成加法计算验证码

1.从官网https://code.google.com/p/kaptcha/下载kaptcha压缩文件，解压文件后里面有一个war文件，打开Eclipse/MyEclipse将其import进去，然后部署到服务器，在浏览器输入url即可看到kaptcha官方提供的基本demo的运行情况，现在将其改为加法计算验证。

2.首先查看web.xml文件发现用来生成验证码的servlet为KaptchaServlet

3.找到KaptchaServlet.class文件，然后进行反编译。

4.新建一个自己的验证码MyKaptchaServlet，将反编译得到的源码拷贝进来。

5.对MyKaptchaServlet做如下修改。

修改后MyKaptchaServlet.java代码如下：

package com.xhc.kaptchaServlet;import com.google.code.kaptcha.Producer;import com.google.code.kaptcha.util.Config;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Date;import java.util.Enumeration;import java.util.Properties;import javax.imageio.ImageIO;import javax.servlet.Servlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class MyKaptchaServlet extends HttpServlet implements Servlet { private Properties props; private Producer kaptchaProducer; private String sessionKeyValue; private String sessionKeyDateValue; public MyKaptchaServlet() {  this.props = new Properties();  this.kaptchaProducer = null;  this.sessionKeyValue = null;  this.sessionKeyDateValue = null; } public void init(ServletConfig conf) throws ServletException {  super.init(conf);  ImageIO.setUseCache(false);  Enumeration initParams = conf.getInitParameterNames();  while (initParams.hasMoreElements()) {   String key = (String) initParams.nextElement();   String value = conf.getInitParameter(key);   this.props.put(key, value);  }  Config config = new Config(this.props);  this.kaptchaProducer = config.getProducerImpl();  this.sessionKeyValue = config.getSessionKey();  this.sessionKeyDateValue = config.getSessionDate(); } public void doGet(HttpServletRequest req, HttpServletResponse resp)   throws ServletException, IOException {  resp.setDateHeader("Expires", 0L);  resp.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");  resp.addHeader("Cache-Control", "post-check=0, pre-check=0");  resp.setHeader("Pragma", "no-cache");  resp.setContentType("image/jpeg");  String capText = this.kaptchaProducer.createText();  String str1 = capText.substring(0, 2);  String str2 = capText.substring(2, 4);  int result = Integer.valueOf(str1) + Integer.valueOf(str2);  req.getSession().setAttribute(this.sessionKeyValue, result+"");  req.getSession().setAttribute(this.sessionKeyDateValue, new Date());  BufferedImage bi = this.kaptchaProducer.createImage(str1 + "+" + str2    + "=?");  ServletOutputStream out = resp.getOutputStream();  ImageIO.write(bi, "jpg", out); }}

6.修改web.xml配置文件，将servlet-class指定到MyKaptchaServlet

参考官方文档https://code.google.com/p/kaptcha/wiki/ConfigParameters将其他属性也配置进去，修改后web.xml文件如下：

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"version="2.4"><servlet><servlet-name>Kaptcha</servlet-name><!-- <servlet-class>com.google.code.kaptcha.servlet.KaptchaServlet</servlet-class> --><servlet-class>com.xhc.kaptchaServlet.MyKaptchaServlet</servlet-class><!-- For a complete list of Init Parameters, please see: http://code.google.com/p/kaptcha/wiki/ConfigParameters --><!-- 验证码边界，合法值yes or no --><init-param><param-name>kaptcha.border</param-name><param-value>yes</param-value></init-param><!-- 边界颜色，合法值 r,g,b (and optional alpha) or white,black,blue --><init-param><param-name>kaptcha.border.color</param-name><param-value>black</param-value></init-param><!-- 边界厚度,合法值 大于0 --><init-param><param-name>kaptcha.border.thickness</param-name><param-value>1</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><!-- 验证码图片生成类，默认由DefaultKaptcha类生成，可以自己写一个图片生成类，需要实现Producer接口并继承Configurable 类 --><init-param><param-name>kaptcha.producer.impl</param-name><param-value>com.google.code.kaptcha.impl.DefaultKaptcha</param-value></init-param><!-- 验证码生成类，默认由DefaultTextCreator类生成，可以自己写一个验证码生成类，需要实现TextProducer接口并继承Configurable 类 --><init-param><param-name>kaptcha.textproducer.impl</param-name><param-value>com.google.code.kaptcha.text.impl.DefaultTextCreator</param-value></init-param><!-- 用来生成验证码的字符集 --><init-param><param-name>kaptcha.textproducer.char.string</param-name><param-value>01234565789</param-value></init-param><!-- 生成验证码的长度 --><init-param><param-name>kaptcha.textproducer.char.length</param-name><param-value>4</param-value></init-param><!-- 验证码字体，多个值用逗号隔开 --><init-param><param-name>kaptcha.textproducer.font.names</param-name><param-value>Arial,Courier</param-value></init-param><!-- 字体大小 --><init-param><param-name>kaptcha.textproducer.font.size</param-name><param-value>40</param-value></init-param><!-- 字体颜色 --><init-param><param-name>kaptcha.textproducer.font.color</param-name><param-value>blue</param-value></init-param><!-- 验证码字符间隔 --><init-param><param-name>kaptcha.textproducer.char.space</param-name><param-value>5</param-value></init-param><!-- 图片干扰生成类，默认由DefaultNoise类生成，可以自己写一个图片干扰类，需要实现NoiseProducer接口并继承Configurable 类 --><init-param><param-name>kaptcha.noise.impl</param-name><param-value>com.google.code.kaptcha.impl.DefaultNoise</param-value></init-param><!-- 干扰颜色 --><init-param><param-name>kaptcha.noise.color</param-name><param-value>yellow</param-value></init-param><!--获取扭曲的不同风格的验证码，官方实现的有ShadowGimpy,FishEyeGimpy,WaterRipple,其中用来FishEyeGimpy之后上面设定的干扰线不起作用--><init-param><param-name>kaptcha.obscurificator.impl</param-name><param-value>com.google.code.kaptcha.impl.FishEyeGimpy</param-value></init-param><!--渐变背景色，初始颜色 --><init-param><param-name>kaptcha.background.clear.from</param-name><param-value>gray</param-value></init-param><!-- 渐变北京市，最终颜色 --><init-param><param-name>kaptcha.background.clear.to</param-name><param-value>white</param-value></init-param><!-- 文字渲染器 --><init-param><param-name>kaptcha.word.impl</param-name><param-value>com.google.code.kaptcha.text.impl.DefaultWordRenderer</param-value></init-param><init-param><param-name>kaptcha.session.key</param-name><param-value>KAPTCHA_SESSION_KEY</param-value></init-param><init-param><param-name>kaptcha.session.date</param-name><param-value>KAPTCHA_SESSION_DATE</param-value></init-param></servlet><servlet-mapping><servlet-name>Kaptcha</servlet-name><url-pattern>/Kaptcha.jpg</url-pattern></servlet-mapping><welcome-file-list><welcome-file>KaptchaExample.jsp</welcome-file></welcome-file-list></web-app>

7.效果图