使用jcaptcha插件生成验证码

1.从官网http://jcaptcha.sourceforge.net/下载插件，将相应jar包导入到lib目录下

2.创建一个CaptchaServiceSingleton类用来获取jcaptcha自己实现的默认验证码生成器对象DefaultManageableImageCaptchaService（使用单例模式）。

package com.xhc.jcaptcha;import com.octo.captcha.service.image.DefaultManageableImageCaptchaService;import com.octo.captcha.service.image.ImageCaptchaService;public class CaptchaServiceSingleton {  private static ImageCaptchaService instance = new DefaultManageableImageCaptchaService();      public static ImageCaptchaService getInstance(){         return instance;     }}

3.创建处理验证码生成的servlet

package com.xhc.jcaptcha;import java.awt.image.BufferedImage;import java.awt.image.Raster;import java.io.ByteArrayOutputStream;import java.io.IOException;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 com.octo.captcha.service.CaptchaServiceException;import com.sun.image.codec.jpeg.JPEGCodec;import com.sun.image.codec.jpeg.JPEGImageEncoder;public class ImageCaptchaServlet extends HttpServlet { public void destroy() {  super.destroy(); } public void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)   throws ServletException, IOException {    byte[] captchaChallengeAsJpeg = null;        // the output stream to render the captcha image as jpeg into         ByteArrayOutputStream jpegOutputStream = new ByteArrayOutputStream();         try {         // get the session id that will identify the generated captcha.         //the same id must be used to validate the response, the session id is a good candidate!         String captchaId = httpServletRequest.getSession().getId();         // call the ImageCaptchaService getChallenge method             BufferedImage challenge = new BufferedImage(68, 22, BufferedImage.TYPE_INT_RGB);                     challenge=CaptchaServiceSingleton.getInstance().getImageChallengeForID(captchaId,                             httpServletRequest.getLocale());             // a jpeg encoder             JPEGImageEncoder jpegEncoder =                     JPEGCodec.createJPEGEncoder(jpegOutputStream);             jpegEncoder.encode(challenge);         } catch (IllegalArgumentException e) {             httpServletResponse.sendError(HttpServletResponse.SC_NOT_FOUND);             return;         } catch (CaptchaServiceException e) {             httpServletResponse.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);             return;         }          captchaChallengeAsJpeg = jpegOutputStream.toByteArray();          // flush it in the response         httpServletResponse.setHeader("Cache-Control", "no-store");         httpServletResponse.setHeader("Pragma", "no-cache");         httpServletResponse.setDateHeader("Expires", 0);         httpServletResponse.setContentType("image/jpeg");         ServletOutputStream responseOutputStream =                 httpServletResponse.getOutputStream();         responseOutputStream.write(captchaChallengeAsJpeg);         responseOutputStream.flush();         responseOutputStream.close(); } public void init(ServletConfig servletConfig) throws ServletException {  super.init(servletConfig); }}

若导入这两个类时报错

import com.sun.image.codec.jpeg.JPEGCodec;

import com.sun.image.codec.jpeg.JPEGImageEncoder;

原因：Eclipse默认把这些受访问限制的API设成了ERROR。只要把Windows-Preferences-Java-Complicer-Errors/Warnings里面的Deprecated  and restricted API中的Forbidden references(access rules)选为Warning就可以编译通过。

4.创建用来做验证的servlet

package com.xhc.jcaptcha;import java.io.IOException;import java.io.PrintWriter;import java.net.HttpRetryException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.octo.captcha.service.CaptchaServiceException;public class ValidationServlet extends HttpServlet { public void destroy() {  super.destroy(); // Just puts "destroy" string in log  // Put your code here } public void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)   throws ServletException, IOException {  Boolean isResponseCorrect =Boolean.FALSE;        //remenber that we need an id to validate!        String captchaId = httpServletRequest.getSession().getId();        //retrieve the response        String response = httpServletRequest.getParameter("j_captcha_response");        // Call the Service method        httpServletResponse.setContentType("text/html;charset=utf-8");       PrintWriter wt=httpServletResponse.getWriter();               try {             isResponseCorrect = CaptchaServiceSingleton.getInstance().validateResponseForID(captchaId,                     response);             if(isResponseCorrect){              wt.write("<a>验证码输入成功</a>");             }else{              wt.write("<a>验证码输入失败</a>");             }         } catch (CaptchaServiceException e) {              //should not happen, may be thrown if the id is not valid         } }  public void init() throws ServletException { }}

5.配置web.xml

 

<servlet>    <servlet-name>ImageCaptchaServlet</servlet-name>    <servlet-class>com.xhc.jcaptcha.ImageCaptchaServlet</servlet-class>    <load-on-startup>0</load-on-startup>  </servlet>  <servlet>    <servlet-name>ValidationServlet</servlet-name>    <servlet-class>com.xhc.jcaptcha.ValidationServlet</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>ImageCaptchaServlet</servlet-name>    <url-pattern>/servlet/ImageCaptchaServlet</url-pattern>  </servlet-mapping>  <servlet-mapping>    <servlet-name>ValidationServlet</servlet-name>    <url-pattern>/servlet/ValidationServlet</url-pattern>  </servlet-mapping>

6.jsp页面

<body> <form action="servlet/ValidationServlet" method="GET">  <input type="text" name="j_captcha_response">  <img src="servlet/ImageCaptchaServlet" height="50" width="100">   <input type="submit" value="提交" /> </form></body>