使用jcaptcha插件生成验证码

1.从官网http://jcaptcha.sourceforge.net/下载插件。将对应jar包导入到lib文件夹下



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默认把这些受訪问限制的API设成了ERROR。

仅仅要把Windows-Preferences-Java-Complicer-Errors/Warnings里面的Deprecated
and restricted API中的Forbidden references(access rules)选为Warning就能够编译通过。
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>