How to integrate Google reCAPTCHA in Java Web Application

Filed Under: Java EE

I never liked Captchas because the burden was always on end user to understand the letters and prove that he is a human and not a software bot. But when I recently saw new Google reCAPTCHA on a website, I instantly liked it.

Because all we need is to check a box and it will figure out if you are a human or robot. Google is calling it No CAPTCHA reCAPTCHA experience and it uses an advanced risk analysis engine and adaptive CAPTCHAs to keep automated software from engaging in abusive activities on your site.

google recaptcha

So that formed the basis of this post where I will show you how to utilize Google reCAPTCHA in your java based web application.

Before we move on with our project, first thing you need to do is go to Google reCAPTCHA and sign up. After that you will get a Site key that is used to display the reCaptcha widget on your web pages. You will also get a Secret key that should be kept secret and used in communicating with Google server to verify the captcha response.

After I registered a test site, I got below keys and I will utilize them in my project. Note that while signup you also need to provide domain name and the keys will work only on that domain name. Also keys will always work on localhost, so I can easily test it on my local server.

Google reCAPTCHA keys

Now we can head over to our example project. We will have a login page where user will enter username and password, apart from that he will also have to solve reCaptcha and submit the form.

Once the form is submitted, username and password will be validated in our application, whereas we will send the captcha response with secret key to Google reCaptcha server and get the response.

The response from Google reCaptcha is a JSON with a success boolean field, if validated success value will be true otherwise it will be false. I will use Java JSON Processing API to parse the response JSON.

Below image shows our final project in Eclipse.

Google reCAPTCHA Java Web Application

To get the project skeleton, just create a “Dynamic Web Project” in Eclipse and then convert it to Maven project. Just add below dependency in pom.xml file for JSON API.


Let’s look into each of the components one by one.

View Page with Google reCAPTCHA

Below is our login html page code.


<!DOCTYPE html>
<meta charset="US-ASCII">
<title>Login Page</title>
<script src=""></script>

	<form action="LoginServlet" method="post">

		Username: <input type="text" name="user"> <br> Password:
		<input type="password" name="pwd"> <br>
		<div class="g-recaptcha"
		<br> <input type="submit" value="Login">

We need to add Google reCaptcha JS file in the HTML head section and then add <div class="g-recaptcha" data-sitekey="Site-key"></div> in our form to get the reCaptcha widget. That’s all at the client side, it’s really this simple!

Once user is validated he will be sent to below success page.


<%@ page language="java" contentType="text/html; charset=US-ASCII"
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Login Success Page</title>
<h3>Hi Pankaj, Login successful.</h3>
<a href="login.html">Login Page</a>

Login Servlet

Below is our simple servlet code where we are validating username and password fields. For simplicity, they are embedded as WebInitParam in the servlet code itself. Note that you need to use Servlet 3 to use these annotations, so you need to use Tomcat-7 or later versions that support servlet spec 3.

package com.journaldev.servlet;


import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.journaldev.utils.VerifyRecaptcha;

 * Servlet implementation class LoginServlet
@WebServlet(description = "Login Servlet", urlPatterns = { "/LoginServlet" }, initParams = {
		@WebInitParam(name = "user", value = "Pankaj"),
		@WebInitParam(name = "password", value = "journaldev") })
public class LoginServlet extends HttpServlet {

	private static final long serialVersionUID = -6506682026701304964L;

	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {

		// get request parameters for userID and password
		String user = request.getParameter("user");
		String pwd = request.getParameter("pwd");
		// get reCAPTCHA request param
		String gRecaptchaResponse = request
		boolean verify = VerifyRecaptcha.verify(gRecaptchaResponse);

		// get servlet config init params
		String userID = getServletConfig().getInitParameter("user");
		String password = getServletConfig().getInitParameter("password");
		// logging example
		System.out.println("User=" + user + "::password=" + pwd + "::Captcha Verify"+verify);

		if (userID.equals(user) && password.equals(pwd) && verify) {
		} else {
			RequestDispatcher rd = getServletContext().getRequestDispatcher(
			PrintWriter out = response.getWriter();
			if (verify) {
				out.println("<font color=red>Either user name or password is wrong.</font>");
			} else {
				out.println("<font color=red>You missed the Captcha.</font>");
			rd.include(request, response);

Once form with captcha is submitted, we get “g-recaptcha-response” request parameter that is required to send for verification. The last part is the utility class to send POST request for verification and parse the JSON response and return accordingly.

package com.journaldev.utils;


import javax.json.Json;
import javax.json.JsonObject;
import javax.json.JsonReader;

public class VerifyRecaptcha {

	public static final String url = "";
	public static final String secret = "6LdMAgMTAAAAAJOAqKgjWe9DUujd2iyTmzjXilM7";
	private final static String USER_AGENT = "Mozilla/5.0";

	public static boolean verify(String gRecaptchaResponse) throws IOException {
		if (gRecaptchaResponse == null || "".equals(gRecaptchaResponse)) {
			return false;
		URL obj = new URL(url);
		HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();

		// add reuqest header
		con.setRequestProperty("User-Agent", USER_AGENT);
		con.setRequestProperty("Accept-Language", "en-US,en;q=0.5");

		String postParams = "secret=" + secret + "&response="
				+ gRecaptchaResponse;

		// Send post request
		DataOutputStream wr = new DataOutputStream(con.getOutputStream());

		int responseCode = con.getResponseCode();
		System.out.println("\nSending 'POST' request to URL : " + url);
		System.out.println("Post parameters : " + postParams);
		System.out.println("Response Code : " + responseCode);

		BufferedReader in = new BufferedReader(new InputStreamReader(
		String inputLine;
		StringBuffer response = new StringBuffer();

		while ((inputLine = in.readLine()) != null) {

		// print result
		//parse JSON response and return 'success' value
		JsonReader jsonReader = Json.createReader(new StringReader(response.toString()));
		JsonObject jsonObject = jsonReader.readObject();
		return jsonObject.getBoolean("success");
		}catch(Exception e){
			return false;

That’s all. Our application is ready, below are the response pages we get based on user inputs.

Login Page with Google Recaptcha Widget

Google Recaptcha Widget

Google Recaptcha Validated at client side

Google Recaptcha Validated

Response page after server side Google Recaptcha Validation

Google Recaptcha Server Validated

Response where Recaptcha was not solved

Google Recaptcha Java Not Solved

Recaptcha Solved but user/password didn’t match

java captcha Other validation error

You can download the project from below link and play around with it to learn more.


  1. Manisha says:

    I’m getting below error on JSF page:
    Uncaught (in promise) SyntaxError: Unexpected token � in JSON at position 0
    at JSON.parse ()
    at recaptcha__en.js:59
    at recaptcha__en.js:81
    at Array. (recaptcha__en.js:93)
    at Array. (recaptcha__en.js:80)
    at KA.B (recaptcha__en.js:59)
    at Array. (recaptcha__en.js:53)
    at (recaptcha__en.js:259)
    at h (recaptcha__en.js:325)
    Can you please help with this?

  2. André Hiroshi Tanaka says:

    Very good!
    I made a version with JSF / ManagedBean / Controller based in you example and works!

    1. Marcos Yonamine says:

      Hello Tanaka, I am trying to implement this recaptcha in an ADF application (JSF), would you have any guidance that I can offer?

  3. Vu Nguyen says:

    Thank you for sharing!

  4. Hema says:

    Getting NULL value of reCaptcha response.

  5. jojo says:

    “Localhost is not in the list of supported domains for this site key” i keep seeing this in the captcha, i have given the label and the domain name as localhost.Please help me resolve this.

  6. shajo says:

    i ran the codein the eclipse and i gave the corresponding keys the site key and the security key,but it shows that error with the captcha site owner.Please help

  7. Prakash says:

    Hi Pankaj,

    I am receiving below exception while implementing google captcha on localhost PKIX path building failed: unable to find valid certification path to requested target.

    Please help

  8. Prakash says:

    Hi Pankaj,

    I ma receiving below exception at localhost.

    19/04/15 07:18:58 Connection refused: connect
    19/04/15 07:18:58 at Method)

  9. Tejas Dahake says:

    Hello Pankaj sir,

    i got an error : Localhost is not in the list of supported domains for this site key.

    please help me.

    1. SRL says:

      Go to this link and put localhost as a domain releven to your key

    2. shajo says:

      you found the solution to that?

    3. Gopal Mohankuda says:

      please give the domain name instead of will work

  10. Ali Bahadar says:

    This code is not working on IE11

  11. lok says:

    Nice article…….worked for me

  12. Anupam says:

    This is not going to work when proxy server in place

    Do you have steps how to make it work when application is hidden behind proxy.

    At the time of captcha verification, application could not able to connect to google verification url and throws unknownHostException

  13. Leo Wu says:

    Nice writting. Very helpful.

    Do you know how to integrate reCaptcha with Spring security?

  14. Serge says:

    Works perfectly well on localhost. Haven’t tested on live server, but I haven’t had such a need, just needed to quickly test the recaptcha. For a live scenario I’d use a different JSON and HTTP client libraries.

  15. Hi pankaj,

    Tried of searching many tutos but found this is very useful, while implementing your exercise I’m getting this error: ” ERROR for site owner: Invalid site key “.

    I have given proper site and secret key, googled it with google suggestion recreated my site keys but on my local site I’m not getting can you please help in this regard.

    Thanks a lot,

    1. rahul chauhan says:

      Even i am getting same issue. Have u found the solution?

  16. Ravi Sah says:

    very nice i tried to implement is and its working good thank you!!

  17. Ali Faradjpour says:

    Occasionally I see posts like this one, that works as a charm, without any effort,
    Great thank you guy

  18. Paulo Silveira says:

    You help us. Thank you so much. This tutorial is perfect man.

  19. Singh says:

    Hi Pankaj,

    Do you have any mock test for reCaptcha?

  20. Prasad says:

    recaptcha requires google certificate on application server, and validity on certificate is is just couple of months, how to maintain ever changing certificate on production servers.

  21. leb says:

    very good simple sample~~
    thank you.


    getting recaptcha verified without i click on any images that we get after clicking on check-box, instead it is directly getting verified without any user input. How to resolve this issue

  23. Parkash Kumar says:

    Really nice article, I found it quite helpful while integrating Google captcha in my application.

  24. Elmar Christen says:

    Great sample page, right-to-the-pont explanation what to do, truly working examples and helpful code snippets. You just saved me a few hours of time. Thank you!

  25. Manjunath says:

    Connection Timeout Exception is thrown from:
    DataOutputStream wr = new DataOutputStream(con.getOutputStream());

    If I open URL from browser along with secretkey and response value, JSON object returning true.

    For example:

    “success”: true

  26. Manjunath says:

    When I try to use your example I am getting connection timeout errors.
    I have registered localhost and got the sitekey and secret key. and it all works fine when I directly hit the verify URL in the browser. JSON obj is returning true, but its not wokring in the code. Connection timed out: connect

    1. Sunny Roy says:

      I am getting the same issue. Did you find out the solution ?

  27. zoom says:


    It’s possible to make a unit test with Mockito framework ? If not, what Is the Best Way to test the recaptcha.

  28. wahid says:

    I am trying to do this in JSF 2. I am able to show the script, but fail to get the parameter. truied following way

    HttpServletRequest req = (HttpServletRequest)context.getExternalContext().getRequest();
    String val = req.getParameter(“g-recaptcha-response”);

    Should it be straight forward like in jsp?

  29. iridiumcao says:

    Thank you, Pankaj, this demo helps me a lot!

  30. Renan Campos says:

    This tip helped me too much, I was giving up already to make recaptcha, then I saw here I have to do the server-side validation, not the angularJS. Thank You !!!

  31. Gaspar says:

    Congrats on this post, very helpfull!

  32. Venkatesa Kumar says:

    Post is useful. Thanks.

    As per above post, we do the captcha verification from servlet code. Servlet code mostly deployed in application server in production site. It is not practice to allow internet access from production application server. Since we have to hit google url “”, what is the alternative to verify the “g-recaptcha-response” before reach to servlet(server), that is get the verification done at browser code itself.

  33. vasu says:

    It is working fine when I integrate this in our web application. But how can I remove Privacy Terms in the widget, because our business doesn’t want to display google terms and conditions on our web application.

    1. Pankaj says:

      I don’t think there is a way to remove it, since you are using Google service you will have to respect their privacy terms.

  34. BlueMan says:

    I get error: “Require String parameter ‘g-recaptcha-response’ is not present”.
    I’m a newbie, please help me.
    Below are the images:
    error :

  35. FlyingCat says:

    Thank you sir

  36. saranya says:

    i am not able to connect to —verify url . The problem is in making a https connection .Please reply how did you trust the certificates to make the https connection

  37. Sagar Rout says:

    Connection.getoutputstream and getInputstream() showing connection timeout exception. What is the issue behind this ? Please respond asap

  38. zahamed says:

    This recaptcha is working in with localhost tomcat.How when I put on live server in a Linux machine does not work. Could I plz help. I am really struggling.

    1. Pankaj says:

      What is not working, are you not getting the widget in UI, or you are not getting the response tag to server in the form or you are not able to validate it by submitting request to server. If you are putting on a live server with domain name, make sure your keys are registered with that domain name.

      1. Sadiq says:

        Hi Pankaj,

        I am using above example for our website. It is working in local host but it is not working in linux live server. I am getting connection timed out error. Could I plz help. I am really struggling.

        Sadiq Ali

        1. surendra says:

          use recaptcha v2

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