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。
1：前期工作：准备kaptcha的jar包
<!--kaptcha--><dependency><groupId>com.github.axet</groupId><artifactId>kaptcha</artifactId><version>0.0.9</version></dependency>
2：在spring配置文件中配置图片生成器的bean
<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">80</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>
里面配置了很多图片生成器的属性，比如字体颜色，字体大小等，根据英文意思就能理解大概配置的是什么内容了
3：生成图片的控制器
@Controllerpublic class CaptchaImageCreateController {@Autowiredprivate Producer captchaProducer;//验证码生成器@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 sessionrequest.getSession().setAttribute(Constants.KAPTCHA_SESSION_KEY, capText);//将生成的验证码保存在session中// 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;}}
4.验证码验证控制器
@Controllerpublic class VerifyController {@RequestMapping(value = "/checkVerificationCode")@ResponseBodypublic boolean checkVerificationCode(@RequestParam("verifyCode")String verifyCode,HttpServletRequest request){//验证码的值String kaptchaExpected = (String)request.getSession().getAttribute(com.google.code.kaptcha.Constants.KAPTCHA_SESSION_KEY);//用户输入的验证码的值String kaptchaReceived = verifyCode;System.out.println("实际的验证码为："+kaptchaExpected);System.out.println("输入的验证码为："+kaptchaReceived);if(kaptchaReceived == null || !kaptchaReceived.equalsIgnoreCase(kaptchaExpected)) {return false;}return true;}}
期待输入的验证码从session中取出，和实际输入的验证码进行比较，如果相同，则返回true,否则返回false
5:前端页面
<div class="title"> 用户登录 </div><div class="loginbox"><form id="loginForm" action="/checkVerificationCode" method="post"><div style="height:40px;"><label class="tip">登录名: </label><input name="name" type="text" id="name" class="user-text" value="" /></div><div style="height:40px;"><label class="tip">密 码：</label><input type="password" id="password" name="password" class="user-text" value="" /></div><div style="height:60px;"><label class="tip">验证码: </label><input type="text" name="verifyCode" id="verifyCode" class="usertext" value="" />οnchange="changeVerifyCode();"/><img src="captcha-image.jpg" width="110" height="30" id="kaptchaImage"style="margin-bottom: -13px"/></div><div style="margin-left:15px"><input type="submit" class="login-btn" value="登录" /><input type="reset" class="login-btn" style="margin-left:10px;" value="重置" /></div></form></div>
src="captcha-image.jpg",将触发生成图片的控制器，返回一张图片,action="/checkVerificationCode",将调用验证验证码的控制器，返回相应的结果。
