Small Talks/2017/May/Use reCaptcha with ZK

Author
Hawk Chen, Engineer, Potix Corporation

Date
?

Version
ZK 8.0.4

Introduction

Google reCAPTCHA is an easy to use and free service that protects your site from spam and bot. Users usually just need one click to pass the check instead of reading twisted words like Captcha. This article will show you how to use it within ZK framework.

Get reCaptcha

Please follow Google's guide to get reCaptcha API key: https://developers.google.com/recaptcha/docs/start

How to Apply

Include recaptcha API & Configuration

<zk xmlns:c="client" xmlns:x="xhtml">
	<script type="text/javascript" src='https://www.google.com/recaptcha/api.js' defer="true" />
	...
	<x:div id="recaptcha" class="g-recaptcha" 
		data-sitekey="your-key"
		data-callback="afterValidate" />

If the key is correct, you should see the reCaptcha is rendered. If not, open developer tool / Console tab to check an error.

Verify a User Response

You also need to specify a callback function name at data-callback attribute to verify a user's response to a reCAPTCHA challenge at the server side.

<zk xmlns:c="client" xmlns:x="xhtml">
	<script type="text/javascript" src='https://www.google.com/recaptcha/api.js' defer="true" />
	<script><![CDATA[ 
		function afterValidate(response){
			zk.Widget.$('$recaptcha').fire('onUserRespond',{'response':response}, {toServer:true}); 
		} 
	]]>
	</script>
	<x:div id="recaptcha" class="g-recaptcha" 
		data-sitekey="${sitekey}"
		data-callback="afterValidate" />	
</zk>

Here we fire an event, onUserRespond, with ZK widget API to send a reCAPTCHA response to the server.

Then we can verify the response according to https://developers.google.com/recaptcha/docs/verify. The verified result is a JSON object, and you can get the success result by key success.

public class RecaptchaComposer extends SelectorComposer<Component> {

	@Wire
	Button submit;
	
	final String SECRET = "6Lcj5AYTAAAAANcaQYWvFkHVSkqR6FsBaCXXw54r"; //from reCaptcha
	
	@Listen("onUserRespond = #recaptcha")
	public void verify(Event event) throws Exception{
		JSONObject result = RecaptchaVerifier.verifyResponse(SECRET, ((JSONObject)event.getData()).get("response").toString());
		if (Boolean.parseBoolean(result.get("success").toString())){
			submit.setDisabled(false);
		}else{
			String errorCode = result.get("error-codes").toString();
			//log or show error
		}
	}
	...
}

• Line 10: RecaptchaVerifier is a helper class that I create to verify a reCAPTCHA response by sending an HTTP request. I make it independent from a composer/ViewModel, so that readers can reuse it. You can check its source code.

MVVM approach

If your controller is a ViewModel, we can send a reCAPTCHA response by client command binding.

<zk xmlns:c="client" xmlns:x="xhtml">
	<script type="text/javascript"
		src='https://www.google.com/recaptcha/api.js' defer="true" />
	<script><![CDATA[ 
		function afterValidate(response){
			var commandName = jq('#recaptcha').attr('command');
			zkbind.$('$recaptcha').command(commandName, {"response":response});
		} 
	]]>
	</script>
	<x:div id="recaptcha" class="g-recaptcha" 
		data-sitekey="@load(sitekey)"
		data-callback="afterValidate" command="@load(command)" />		
</zk>

Comments

Copyright © Potix Corporation. This article is licensed under GNU Free Documentation License.