ReCaptcha and Mailhide support for Grails.

8 votes
compile ":recaptcha:0.7.0"

 Documentation  Source  Issues


ReCaptcha is a CAPTCHA implementation that has a goal of better digitizing books by having users identify words that traditional OCR systems have missed. This plugin uses the ReCaptcha Java library available from

Versions 0.5 and below of this plugin will not work. ReCaptcha has changed the URL used for secure connections.


Add the following to your grails-app/conf/BuildConfig.groovy
plugins {
    compile ':recaptcha:0.6.7'
Upon installation, run grails recaptcha-quickstart to create the skeleton configuration. The quickstart has two targets: integrated or standalone , depending on where you'd like the configuration to live.

Integrated Configuration

Integrated configuration adds the following to the end of your Config.groovy file:
// Added by the Recaptcha plugin:
recaptcha {
    // These keys are generated by the ReCaptcha service
    publicKey = ""
    privateKey = ""

// Include the noscript tags in the generated captcha includeNoScript = true

// Force language change. See this for more: forceLanguageInURL = false

// Set to false to disable the display of captcha enabled = true

// Communicate using HTTPS useSecureAPI = true }

mailhide { // Generated by the Mailhide service publicKey = "" privateKey = "" }

This configuration can be modified to mimic the standalone if there is a need for different behavior depending on the current environment.

Standalone Configuration

Standalone configuration creates a file called RecaptchaConfig.groovy in grails-app/conf with the following content:
recaptcha {
   // These keys are generated by the ReCaptcha service
   publicKey = ""
   privateKey = ""

// Include the noscript tags in the generated captcha includeNoScript = true

// Force language change. See this for more: forceLanguageInURL = false }

mailhide { publicKey = "" privateKey = "" }

environments { development { recaptcha { // Set to false to disable the display of captcha enabled = false

// Communicate using HTTPS useSecureAPI = false } } production { recaptcha { // Set to false to disable the display of captcha enabled = true

// Communicate using HTTPS useSecureAPI = true } } }



This plugin is designed to make using the ReCaptcha and Mailhide services within Grails easy. In order to use this plugin, you must have a ReCaptcha account, available from

Usage - ReCaptcha

The plugin is simple to use. In order to use it, there are four basic steps:

Edit the Configuration

The values are pretty self-explanatory, and match with values used by the ReCaptcha service. You must enter your public and private ReCaptcha keys, or errors will be thrown when trying to display a captcha. Note that you can override values within the environments closure.

Use the Tag Library

The plugin includes four ReCaptcha tags: <recaptcha:ifEnabled> , <recaptcha:ifDisabled>@, @<recaptcha:recaptcha> , and <recaptcha:ifFailed> .

  • The <recaptcha:ifEnabled> tag is a simple utility tag that will render the contents of the tag if the captcha is enabled in RecaptchaConfig.groovy .
  • The <recaptcha:ifDisabled> tag is a simple utility tag that will render the contents of the tag if the captcha is disabled in RecaptchaConfig.groovy .
  • The <recaptcha:recaptcha> tag is responsible for generating the correct HTML output to display the captcha. It supports four attributes: "theme", "lang", "tabindex", and "custom_theme_widget". These attributes map directly to the values that can be set according to the ReCaptcha API. See the ReCaptcha Customization Guide for more details.
  • The <recaptcha:recaptchaAjax> tag is responsible for creating the correct HTML output to display the captcha in an AJAX manner. The tag creates a JavaScript method called showRecaptcha that takes an element name as a parameter. This element will contain the generated ReCaptcha widget. This tag supports the same attributes as the <recaptcha:recaptcha> tag.
  • The <recaptcha:ifFailed> tag will render its contents if the previous validation failed. Some ReCaptcha themes, like "clean", do not display error messages and require the developer to show an error message. Use this tag if you're using one of these themes.

Verify the Captcha

In your controller, call recaptchaService.verifyAnswer(session, request.getRemoteAddr(), params) to verify the answer provided by the user. This method will return true or false, but will set the error_message property on the captcha behind the scenes so that the error message will be properly displayed when the ReCaptcha is redisplayed. Also note that verifyAnswer will return true if the plugin has been disabled in the configuration - this means you won't have to change your controller.

Clean up After Yourself

Once the captcha has been verified, call recaptchaService.cleanUp(session) . This is not strictly needed, but it will clean the errors from the session.


Here's a simple example pulled from an account creation application.

Tag Usage

In create.gsp , we add the code to show the captcha:

    <recaptcha:recaptcha theme="blackglass"/>
In this example, we're using ReCaptcha's "blackglass" theme. Leaving out the "theme" attribute will default the captcha to the "red" theme.

If you are using a theme that does not supply error messages, your code might look like this:

    <recaptcha:recaptcha theme="clean"/>
    <recaptcha:ifFailed>CAPTCHA Failed</recaptcha:ifFailed>

AJAX Tag Usage

<g:form action="someAction">
      <recaptcha:recaptchaAjax theme="blackglass"/>
  <g:submitButton name="show" onclick="showRecaptcha(mydiv); return false;"/>
  <g:submitButton value="Submit" name="submit"/><br/>
  <div id="mydiv"></div>
  <recaptcha:ifFailed>CAPTCHA Failed</recaptcha:ifFailed>

When the show button is clicked, the ReCaptcha widget will be created and displayed in the mydiv element. The div used to display the widget must be enclosed in the <g:form> or the parameters will not be captured correctly.

It is recommended to use the <recaptcha:ifFailed> tag in conjunction with the AJAX tag.

Customizing the Language

If you want to change the language your captcha uses, there are two routes you can follow.

  • Set lang = "someLang" in the <recaptcha/> tag. This will show the desired language if the user has their browser set to display that language.
  • Set forceLanguageInURL = true in ReCaptchaConfig.groovy in addition to the above step. This will add another parameter to the generated URL, forcing the captcha to be shown in the desired language.
See this discussion for more information about changing the language. See ReCaptcha Customization Guide for available languages.

Verify User Input

Here's an abbreviated controller class that verifies the captcha value when a new user is saved:

import com.megatome.grails.RecaptchaService
class UserController {
    RecaptchaService recaptchaService

def save = { def user = new User(params) ...other validation… def recaptchaOK = true if (!recaptchaService.verifyAnswer(session, request.getRemoteAddr(), params)) { recaptchaOK = false } if(!user.hasErrors() && recaptchaOK && { recaptchaService.cleanUp(session) ...other account creation acivities… render(view:'showConfirmation',model:[user:user]) } else { render(view:'create',model:[user:user]) } } }

Sample Using a Custom Theme

<g:form action="validateCustom" method="post" >
    <div id="recaptcha_widget" style="display:none">
        <div id="recaptcha_image" style="width:300px;height:57px;"></div>
        <div class="recaptcha_only_if_incorrect_sol" style="color:red;">
            Incorrect Answer
        Enter the words above:
        <input id="recaptcha_response_field" name="recaptcha_response_field" type="text" autocomplete="off"/>
            <a href="javascript:Recaptcha.reload()">Get another CAPTCHA</a>
        <div class="recaptcha_only_if_image">
            <a href="javascript:Recaptcha.switch_type('audio')">Get an audio CAPTCHA</a>
            <a href="javascript:Recaptcha.showhelp()">Help</a>
       <recaptcha:recaptcha theme="custom" lang="en" custom_theme_widget="recaptcha_widget"/>
   <g:submitButton name="submit"/>


With version 0.4.5, the plugin should be easier to integrate into test scenarios. You can look at the test cases in the plugin itself, or you can implement something similar to:

private void buildAndCheckAnswer(def postText, def expectedValid, def expectedErrorMessage) {
    def mocker = new MockFor(Post.class)
    mocker.demand.getQueryString(4..4) { new QueryString() }
    mocker.demand.getText { postText }
    mocker.use {
      def response = recaptchaService.checkAnswer("", "abcdefghijklmnop", "response")

assertTrue response.valid == expectedValid assertEquals expectedErrorMessage, response.errorMessage } }

The postText parameter represents the response from the ReCaptcha server. Here are examples of simulating success and failure results:

public void testCheckAnswerSuccess() {
    // ReCaptcha server will return true to indicate success
    buildAndCheckAnswer("true", true, null)

public void testCheckAnswerFailure() { // ReCaptcha server will return false, followed by the error message on a new line for failure buildAndCheckAnswer("false\\nError Message", false, "Error Message") }

Usage - Mailhide

Edit the Configuration

The recaptcha-quickstart plugin creates basic configuration. You must enter your public and private Mailhide keys, or errors will be thrown when trying to display a Mailhide link.

Use the Tag Library

The plugin includes two Mailhide tags: <recaptcha:mailhide> and <recaptcha:mailhideURL> .

  • The <recaptcha:mailhide> tag creates a Mailhide URL that opens in a new, pop-up window per the Mailhide specification. It supports one attribute: "emailAddress", to specify the email to be hidden. The link will be created around whatever content is in the body of the tag.
  • The <recaptcha:mailhideURL> tag creates a "raw" URL that can be used however desired. This is useful if the pop-up behavior of the other tag is not wanted. It supports two attributes: "emailAddress" and "var". The "emailAddress" attribute specifies the email to be hidden, while the "var" attribute specifies the name of the variable that the created URL should be available under in the page. The URL variable is only available in the context of the tag body.


mailhide tag

<recaptcha:mailhide emailAddress="">Some text to wrap in a link</recaptcha:mailhide>

will create:

<a href=""
     onclick="'', '', 
     'toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=0,width=500,height=300'); return false;" 
     title="Reveal this e-mail address">Some text to wrap in a link</a>

mailhideURL tag

<recaptcha:mailhideURL emailAddress="" var="mu">
Created Mailhide URL: ${mu}

will create:

Created Mailhide URL:



  • 0.6.7 Fix a stupid bug that would cause a crash when determining if it's enabled. (GitHub Issue #14)
  • 0.6.6 Behave correctly when config options are "false" or missing. (GitHub Issue #13)
  • 0.6.5 Don't crash when boolean configuration options are missing. (GitHub Issue #10) Establish defaults for boolean options in case they go missing. (GitHub Issue #11) Don't crash when creating an AJAX captcha. (GitHub Issue #12)
  • 0.6.4 Ensure that true/false seetings are loaded correctly from a .properties file. (GitHub Issue #9)
  • 0.6.3 Ensure that AJAX tags properly use HTTPS when specified. (GitHub Issue #7)
  • 0.6.2 Remove spurious println left over. Change install behavior to not create RecaptchaConfig.groovy in _Install.groovy . Add new script recaptcha-quickstart to handle creation of required configuration.
  • 0.6.0 Add the ability to display the widget using AJAX. Change plugin to require Grails 2.0 at a minimum.
  • 0.5.3 Add the ability to force a different language to be displayed.
  • 0.5.1 &amp; 0.5.2 Update to use the new ReCaptcha URLs.
  • 0.5.0 Add Mailhide support. Add support for specifying configuration options elsewhere than RecaptchaConfig.groovy via the grails.config.locations method.
  • 0.4.5 Add code to perform the ReCaptcha functionality - removed recaptcha4j library. Don't add captcha instance to session to avoid serialization issues. Hopefully make it easier to test against.
  • 0.4 New version number for Grails 1.1. Same functionality as 0.3.2
  • 0.3.2 Moved code into packages. Tried to make licensing easier to discern. Updated to Grails 1.0.4
  • 0.3 Added support for environments and new <recaptcha:ifFailed> tag. Updated to Grails 1.0.3
  • 0.2 initial release, developed and tested against Grails 1.0.2


  • If you are testing locally on a Mac, you may need to change recaptchaService.verifyAnswer(session, request.getRemoteAddr(), params) to recaptchaService.verifyAnswer(session, "", params) . This seems to be an issue with the ReCaptcha service not being able to handle the IPV6 localhost identifier.


  • Automate session cleanup


Suggestions or Comments

Feel free to submit questions or comments to the Grails users mailing list.

Alternatively you can contact me directly - cjohnston at megatome dot com