Java中的Constants类
1、遇到代码中的问题
String userName = (String) request.getParameter("userName");
String passWord = (String) request.getParameter("passWord");
String inputKaptcha = (String) request.getParameter("kaptcha");
//下面这句代码是什么意思？？？
String sessionKaptcha = (String) request.getSession().getAttribute(Constants.KAPTCHA_SESSION_KEY);
2、查询解决
a、Constants
com.google.code.kaptcha.Constants，这是该类所属的jar包，经过查询后，发现这是谷歌开发的一个验证码生产工具，
3、kaptcha 工具介绍
a、生成验证码的原理
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。
b、可以实现的功能
- 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)
c、下载相关的jar包
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。
d、web.xml配置
代码如下：
<!--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> lt;/servlet-mapping>
e、jsp页面中使用
<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：
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>
f、新建生成代码的类
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;
@Autowired
public 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 jpeg
response.setContentType("image/jpeg");
// create the text for the image
String capText = captchaProducer.createText();
// store the text in the session
request.getSession().setAttribute(Constants.KAPTCHA_SESSION_KEY, capText);
// create the image with the text
BufferedImage bi = captchaProducer.createImage(capText);
ServletOutputStream out = response.getOutputStream();
// write the data out
ImageIO.write(bi, "jpg", out);
try {
out.flush();
} finally {
out.close();
}
return null;
}
}
g、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>
h、取验证码的方式
String code = (String)session.getAttribute(com.google.code.kaptcha.Constants.KAPTCHA_SESSION_KEY);
i、验证码全部是数字
<init-param>
<param-name>kaptcha.textproducer.char.string</param-name>
<param-value>0123456789</param-value>
</init-param>
j、去掉干扰线
<init-param>
<param-name>kaptcha.noise.impl</param-name>
<param-value>com.google.code.kaptcha.impl.NoNoise </param-value>
</init-param>
文章来自：http://www.cnblogs.com/huiyuantang/p/5407195.html