Creating Captcha Application

Posted on 01/11/2013 by Admin

We can generate Captcha application in 2 modes
1.Online mode
2.Offline mode

Online Mode:
Needs internet,we are going to use re-captcha api,which internally
uses db to store images and voices,it is widely used capcha in the
internet,like facebook etc.
re-captcha api is given by Google.

Offline mode:
We are going to use some other offline apis like
It generates captcha but it is one per session,
so if you refresh the page,it wont give you new captcha

In this article we will see both procedures i.e Online Mode & Offline Mode.

1. Online Captcha

MyOnlineCapcha
     |
     |—->WEB-INF
     |         |——>web.xml
     |         |——>lib
     |                    |—–>recaptcha4j-0.0.7.jar
     |——>index.jsp
     |——>process.jsp
Creating Capcha in your Application using google Re-Captcha

1.Open the below link and Click get re-CAPTCHA Link

   http://www.google.com/recaptcha

2. Click on “Sign up Now!” button and signup  to Your gmail Account inorder to use Re-Captcha.

3. Create a reCAPTCHA Key.Enter a domain(can be anything,non-existing as well),Select
Enable this key on all domains.Otherwise the capcha will work only on your domain,if
you want to use them in all other domains you must select them as well.

    Click on create Key.

4. The above step will generate private and public key for captcha.

5. We are now going to use those private and pubic key in our java application inorder to
generate captcha.Download the re-Captcha library from the below link

    http://code.google.com/p/recaptcha/downloads/list?q=label:java-Latest

6. Create a New web Project.Include the jars into the project

    To show the image Include the following code in index.jsp

index.jsp

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<%@ page import="net.tanesha.recaptcha.ReCaptcha"%>   <%@ page import="net.tanesha.recaptcha.ReCaptchaFactory"%>   <html> <body>     <form action="process.jsp" method="post">         <%           //ReCaptcha c = ReCaptchaFactory.newReCaptcha("your_public_key", "your_private_key", false);           ReCaptcha captcha = ReCaptchaFactory.newReCaptcha("6LfwU-kSAAAAANon6jhYZbfeeH-vgCKncnzs9WOr", "6LfwU-kSAAAAAGiis8gP7kS42ty9Wt_1euOGzj3J", false);           out.print(captcha.createRecaptchaHtml(null, null));         %>         <input type="submit" value="submit" />     </form> </body> </html>

7. To Process the answer create process.jsp

process.jsp

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<%@ page import="net.tanesha.recaptcha.ReCaptchaImpl"%> <%@ page import="net.tanesha.recaptcha.ReCaptchaResponse"%>   <html> <body>     <%         String remoteAddr = request.getRemoteAddr();         ReCaptchaImpl reCaptcha = new ReCaptchaImpl();         reCaptcha.setPrivateKey("6LfwU-kSAAAAAGiis8gP7kS42ty9Wt_1euOGzj3J");           String challenge = request.getParameter("recaptcha_challenge_field");         String uresponse = request.getParameter("recaptcha_response_field");         ReCaptchaResponse reCaptchaResponse = reCaptcha.checkAnswer(remoteAddr, challenge, uresponse);           if (reCaptchaResponse.isValid())         {             out.print("Answer was entered correctly!");         } else         {             out.print("Answer is wrong");         }     %> </body> </html>

2. Offline Captcha

Directory Structure

SimpleCaptchaDemo
       |
       |——–>WEB-INF
       |           |——>web.xml
       |           |——>lib
       |                    |—–>simplecaptcha-1.2-jdk1.5.jar
       |–>index.jsp
       |–>process.jsp

1. Create web.xml

web.xml

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<web-app>     <servlet>         <servlet-name>demo</servlet-name>         <servlet-class> nl.captcha.servlet.StickyCaptchaServlet         </servlet-class>     </servlet>       <servlet-mapping>         <servlet-name>demo</servlet-name>         <url-pattern>/stickyImage</url-pattern>     </servlet-mapping> </web-app>

2. Create index.jsp to show image.

index.jsp

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<img src="stickyImage" /> <form action="process.jsp"> Your Answer<input type="text" name="answer"> <input type="submit" name="submit"/> </form>

3. To process the answer create process.jsp

process.jsp

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<%@page import="nl.captcha.Captcha"%> <%     Captcha captcha=(Captcha)session.getAttribute(Captcha.NAME);     request.setCharacterEncoding("UTF-8");       String answer=request.getParameter("answer");       if(captcha.isCorrect(answer))        out.println("Correct");       else         out.println("Incorrect"); %>