安裝

Add jcaptcha-all.jar (provided in bin-distribution) and ehcache.jar (not provided see ehcache site) to your application class path, ie in you WEB-INF/lib folder.

實例一個jcaptcha服務，注意，必須是單例模式的
import com.octo.captcha.service.image.ImageCaptchaService;
import com.octo.captcha.service.image.DefaultManageableImageCaptchaService;

public class CaptchaServiceSingleton {
???
??? private static ImageCaptchaService instance = new DefaultManageableImageCaptchaService();
???
??? public static ImageCaptchaService getInstance(){
??????? return instance;
??? }
}
注:以上是默認的一個實現，下面是其他更多的實現

SimpleListSoundCaptchaEngine?? //還可以用聲音，真爽哦
SpellerSoundCaptchaEngine
SpellerSoundCaptchaEngine
DefaultGimpyEngineCaptcha???????????
BaffleListGimpyEngineCaptcha???????????
BasicListGimpyEngineCaptcha???????????
DeformedBaffleListGimpyEngineCaptcha???????????
DoubleRandomListGimpyEngineCaptcha???????????
SimpleListImageCaptchaEngineCaptcha???????????
SimpleFishEyeEngineCaptcha
具體請參考官方說明

編寫一個產生圖片的servlet

import com.octo.captcha.service.CaptchaServiceException;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

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 java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

public class ImageCaptchaServlet extends HttpServlet {

??? public void init(ServletConfig servletConfig) throws ServletException {

??????? super.init(servletConfig);

??? }

??? protected 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 =
??????????????????? 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();
??? }
}

為servlet修改web.xml配置文件
<servlet>
??????? <servlet-name>jcaptcha</servlet-name>
??????? <servlet-class>ImageCaptchaServlet</servlet-class>
??????? <load-on-startup>0</load-on-startup>
??? </servlet>

<servlet-mapping>
??????? <servlet-name>jcaptcha</servlet-name>
??????? <url-pattern>/jcaptcha</url-pattern>
</servlet-mapping>

編寫你的客戶端的展示
<img src="jcaptcha">
<input type='text' name='j_captcha_response' value=''>
上面的src="jcaptcha"? 就是調用了上面的servlet,text里是用戶填寫的確認驗證碼

后臺邏輯驗證
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
??????????? try {
??????????????? isResponseCorrect = CaptchaServiceSingleton.getInstance().validateResponseForID(captchaId,
??????????????????????? response);
??????????? } catch (CaptchaServiceException e) {
???????????????? //should not happen, may be thrown if the id is not valid
??????????? }