转自：http://ttaale.iteye.com/blog/808719

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。

使用kaptcha可以方便的配置：

• 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

  <!--Kaptcha 验证码  --><servlet>  <servlet-name>kaptcha</servlet-name>  <servlet-class>com.google.code.kaptcha.servlet.KaptchaServlet</servlet-class>  <init-param>  <param-name>kaptcha.border</param-name>  <param-value>no</param-value>  </init-param>  <init-param>  <param-name>kaptcha.border.color</param-name>  <param-value>105,179,90</param-value>  </init-param>       <init-param>  <param-name>kaptcha.textproducer.font.color</param-name>  <param-value>red</param-value>  </init-param>  <init-param>  <param-name>kaptcha.image.width</param-name>  <param-value>250</param-value>  </init-param>  <init-param>  <param-name>kaptcha.image.height</param-name>  <param-value>90</param-value>  </init-param>  <init-param>  <param-name>kaptcha.textproducer.font.size</param-name>  <param-value>70</param-value>  </init-param>  <init-param>  <param-name>kaptcha.session.key</param-name>  <param-value>code</param-value>  </init-param>  <init-param>  <param-name>kaptcha.textproducer.char.length</param-name>  <param-value>4</param-value>  </init-param>  <init-param>  <param-name>kaptcha.textproducer.font.names</param-name>  <param-value>宋体,楷体,微软雅黑</param-value>  </init-param>       </servlet> 

        <servlet-mapping><servlet-name>kaptcha</servlet-name><url-pattern>/ClinicCountManager/kaptcha.jpg</url-pattern></servlet-mapping>

  jsp页面使用：

•     <table><tr><td><img src="/ClinicCountManager/kaptcha.jpg"></td><td valign="top"><form method="POST"><br>sec code:<input type="text" name="kaptchafield"><br /><input type="submit" name="submit"></form></td></tr></table><br /><br /><br /><br /><%String c = (String)session.getAttribute(com.google.code.kaptcha.Constants.KAPTCHA_SESSION_KEY);String parm = (String) request.getParameter("kaptchafield");out.println("Parameter: " + parm + " ? Session Key: " + c + " : ");if (c != null && parm != null) {if (c.equals(parm)) {out.println("<b>true</b>");} else {out.println("<b>false</b>");}　　         }%>

  上面的配置在普通jsp环境下面是有效的，如果在spring mvc环境下，则取不到session值，对于sping mvc环境验证码配置如下：

  1.  不用在web.xml进行相关配置，在applicationContext.xml中配置

• <bean id="captchaProducer" class="com.google.code.kaptcha.impl.DefaultKaptcha"><property name="config"><bean class="com.google.code.kaptcha.util.Config"><constructor-arg><props><prop key="kaptcha.border">no</prop><prop key="kaptcha.border.color">105,179,90</prop><prop key="kaptcha.textproducer.font.color">red</prop><prop key="kaptcha.image.width">250</prop><prop key="kaptcha.textproducer.font.size">90</prop><prop key="kaptcha.image.height">90</prop><prop key="kaptcha.session.key">code</prop><prop key="kaptcha.textproducer.char.length">4</prop><prop key="kaptcha.textproducer.font.names">宋体,楷体,微软雅黑</prop></props></constructor-arg></bean></property></bean>

  新建生成图片控制类:

• import java.awt.image.BufferedImage;
  import javax.imageio.ImageIO;
  import javax.servlet.ServletOutputStream;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.stereotype.Controller;
  import org.springframework.web.bind.annotation.RequestMapping;
  import org.springframework.web.servlet.ModelAndView;
  import com.google.code.kaptcha.Constants;
  import com.google.code.kaptcha.Producer;@Controller
  @RequestMapping("/")
  public class CaptchaImageCreateController {private Producer captchaProducer = null;@Autowiredpublic void setCaptchaProducer(Producer captchaProducer) {this.captchaProducer = captchaProducer;}@RequestMapping("/captcha-image")public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {response.setDateHeader("Expires", 0);// Set standard HTTP/1.1 no-cache headers.response.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");// Set IE extended HTTP/1.1 no-cache headers (use addHeader).response.addHeader("Cache-Control", "post-check=0, pre-check=0");// Set standard HTTP/1.0 no-cache header.response.setHeader("Pragma", "no-cache");// return a jpegresponse.setContentType("image/jpeg");// create the text for the imageString capText = captchaProducer.createText();// store the text in the session
          request.getSession().setAttribute(Constants.KAPTCHA_SESSION_KEY, capText);// create the image with the textBufferedImage bi = captchaProducer.createImage(capText);ServletOutputStream out = response.getOutputStream();// write the data outImageIO.write(bi, "jpg", out);try {out.flush();} finally {out.close();}return null;}}

  前台调用方式:

•  <div class="chknumber"><label>验证码：        <input name="kaptcha" type="text" id="kaptcha" maxlength="4" class="chknumber_input" />             </label><img src="/ClinicCountManager/captcha-image.do" width="55" height="20" id="kaptchaImage"  style="margin-bottom: -3px"/> <script type="text/javascript">    $(function(){         $('#kaptchaImage').click(function () {//生成验证码$(this).hide().attr('src', '/ClinicCountManager/captcha-image.do?' + Math.floor(Math.random()*100) ).fadeIn(); })    }); </script> </div>

  取验证码的方式:

•         String code = (String)session.getAttribute(com.google.code.kaptcha.Constants.KAPTCHA_SESSION_KEY);