Using Google reCaptcha with Spring Boot Application

Welcome, in this tutorial, we will see how to implement google captcha (reCAPTCHA v2) in a spring boot web application. reCAPTCHA is a free service that protects an application from spammers. It uses advanced risk analysis techniques to keep humans and bots apart. But before going anything I would suggest you take a look at the part1 of this tutorial.

1. Introduction

Before going further in this tutorial, we will look at the common terminology such as introduction to Spring Boot and Lombok.

1.1 Spring Boot

  • Spring boot is a module that provides rapid application development feature to the spring framework including auto-configuration, standalone-code, and production-ready code
  • It creates applications that are packaged as jar and are directly started using embedded servlet container (such as Tomcat, Jetty or, Undertow). Thus, no need to deploy the war files
  • It simplifies the maven configuration by providing the starter template and helps to resolve the dependency conflicts. It automatically identifies the required dependencies and imports them into the application
  • It helps in removing the boilerplate code, extra annotations, and XML configurations
  • It provides powerful batch processing and manages the rest endpoints
  • It provides an efficient JPA-starter library to effectively connect the application with the relational databases
  • It offers a Microservice architecture and cloud configuration that manages all the application related configuration properties in a centralized manner

1.2 Lombok

  • Lombok is nothing but a small library that reduces the amount of boilerplate Java code from the project
  • Automatically generates the getters and setters for the object by using the Lombok annotations
  • Hooks in via the Annotation processor API
  • Raw source code is passed to Lombok for code generation before the Java Compiler continues. Thus, produces properly compiled Java code in conjunction with the Java Compiler
  • Under the target/classes folder you can view the compiled class files
  • Can be used with Maven, Gradle IDE, etc.

1.2.1 Lombok features

valLocal variables are declared as final
varMutable local variables
@Slf4JCreates an SLF4J logger
@CleanupWill call close() on the resource in the finally block
@GetterCreates getter methods for all properties
@SetterCreates setter for all non-final properties
  • Generates implementations of equals(Object other) and hashCode()
  • By default will use all non-static, non-transient properties
  • Can optionally exclude specific properties
  • Generates String of class name, and each field separated by commas
  • Optional parameter to include field names
  • Optional parameter to include a call to the super toString method
  • Generates no-args constructor
  • Will cause compiler error if there are final fields
  • Can optionally force, which will initialize final fields with 0/false/null var – mutable local variables
  • Generates a constructor for all fields that are final or marked @NonNull
  • The constructor will throw a NullPointerException if any @NonNull fields are null Val – local variables are declared final
  • Generates a constructor for all properties of the class
  • Any @NotNull properties will have null checks
  • Generates typical boilerplate code for POJOs
  • Combines – @Getter, @Setter, @ToString, @EqualsAndHashCode, @RequiredArgsConstructor
  • No constructor is generated if constructors have been explicitly declared
  • Implements the Builder pattern for object creation
  • The immutable variant of @Data
  • All fields are made private and final by default

Let us go ahead with the tutorial implementation but before going any further I’m assuming that you’re aware of the Spring boot basics.

2. Using Google reCaptcha with Spring Boot Application

As this is part2 of the tutorial so we will only focus on the required changes to be made as a part of this tutorial. You can view the part1 tutorial at this link and start with the setup.

2.1 Tools Used for Spring boot application and Project Structure

We are using Eclipse Kepler SR2, JDK 8, and Maven. In case you’re confused about where you should create the corresponding files or folder, let us review the project structure of the spring boot application.

reCaptcha with Spring Boot - project structure
Fig. 1: Project structure

Let us start building the application!

3. Creating a Spring Boot application

Below are the steps involved in developing the application. Currently at the problem at hand is that if we have to include the Recaptcha validation to other endpoints, we will have to call the service method each time from the controller method. So to avoid this kind of code repetition we will make use of the Spring AOP (Aspect Oriented programming). In simpler words, we will create an AOP annotation to handle the captcha and validate it before passing the program execution to the controller method for sending out the response. Remember, the AOP annotation needs to be added to each controller method.

3.1 Maven Dependency

Add the spring-starter-aop dependency to the project’s pom.xml. Maven will automatically resolve the other dependencies.


3.2 Java Classes

Let us write the important/impacted classes as a part of this tutorial.

3.2.1 Creating a Captcha annotation

Create an annotation that will be used to handle the captcha.


import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

public @interface RequiresCaptcha {


3.2.2 Creating an Aspect class

Create an annotation that will be used to handle the captcha.


import lombok.extern.slf4j.Slf4j;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

import javax.servlet.http.HttpServletRequest;

//lombok annotation
//spring annotations
public class CaptchaAop {

    ValidateCaptcha service;

    //ensures that the below code is executed before the method(s)
    //annotated with the @RequiresCaptcha annotation
    //note - either keep the annotation class in the same package as the aspect class
    //or use the fully qualified name for the annotation class.
    public Object validateCaptchaResponse(final ProceedingJoinPoint point)
            throws Throwable {
        final HttpServletRequest request =
                ((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes()).getRequest();
        //receives the captcha header from the request
        final String captchaResponse = request.getHeader("captcha-response");
        //sends it to the service method for validation
        final boolean isValidCaptcha = service.validateCaptcha(captchaResponse);
        if (!isValidCaptcha) {
  "Throwing forbidden exception as the captcha is invalid.");
            throw new ForbiddenException("INVALID_CAPTCHA");
        //if everything is ok the response is returned
        return point.proceed();

3.2.3 Controller class

Add the following code to the controller class where each method will be annotated with the @RequiresCaptcha annotation.


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.*;

//Spring annotations
public class HelloCtrl {

    //injected to validate the captcha response coming in the request.
    ValidateCaptcha service;

    //URL - http://localhost:9001/api/welcome
    @ResponseStatus(code = HttpStatus.OK)
    //custom annotation
    public HelloResponseDto welcome(@RequestBody final HelloDto dto) {
        return new HelloResponseDto("Greetings " + dto.getName());

3.3 Client-side

Update the HTML file at the location: SpringbootandGooglecaptcha/src/main/resources/static to send the captcha response in the request header instead of the body.


<html lang="en">
    <title>Springboot and Captcha</title>
    <script src="" type="text/javascript"></script>
    <script src="" type="text/javascript"></script>

<script type="text/javascript">
    function validateAndGetCaptchaResponse() {
        const response = grecaptcha.getResponse();
        return response.length === 0 ? null : response;

    $(document).ready(function () {
        $("#button").click(function () {

            let captchaResponse = validateAndGetCaptchaResponse();
            if (captchaResponse) {
                console.log("Captcha code accepted.")
                let name = $("#name").val();
                let requestObj = {
                    'name': name.length === 0 ? 'Dummy' : name

                    type: "POST",
                    contentType: "application/json",
                    dataType: "json",
                    headers: {
                        "captcha-response": captchaResponse
                    data: JSON.stringify(requestObj),
                    url: "http://localhost:9001/api/welcome",
                    success: function (data) {
            } else {
                $("#captcha-error").html("You cannot leave the captcha code empty.");

    <h3>Springboot and Google captcha example</h3>
    <!-- User input -->
    <label for="name">Enter name:</label>
    <input id="name" placeholder="say... Daniel" type="text"/>
    <button id="button" type="submit">Submit</button>

    <div> </div>

    <!-- Google captcha (I'm not robot checkbox) -->
    <!-- SITE_KEY - Represents the site_key generated by the Google reCaptcha service -->
    <div class="g-recaptcha" data-sitekey="YOUR_SITE_KEY" id="recaptcha"></div>
    <span id="captcha-error" style="color:red"></span>

4. Run the Application

To execute the application, right-click on the class, Run As -> Java Application.

reCaptcha with Spring Boot - run the application
Fig. 2: Run the Application

5. Project Demo

When the application is started, navigate to the following URL: http://localhost:9001/ and you’ll see the index page of the application with a reCAPTCHA “I’m not a robot” checkbox as shown in Fig. 3.

reCaptcha with Spring Boot - index page
Fig. 3: Index page

The HTML code will call our backend endpoint (http://localhost:9001/api/welcome) with a name as request body and captcha-response in the request header. Enter the user details, tick the reCAPTCHA checkbox, and press the button. On successful validation by the backend code, we’ll get a greetings alert.

reCaptcha with Spring Boot - greeting response
Fig. 4: Greeting response

That is all for this tutorial and I hope the article served you whatever you were looking for. Happy Learning and do not forget to share!

6. Summary

In this section, you learned:

  • Spring boot and Google reCAPTCHA introduction
  • Steps to implement google reCAPTCHA in Spring Boot using Spring AOP

You can download the sample application as an Eclipse project in the Downloads section.

7. Download the Project

This was an example of implementing Google reCAPTCHA through Spring AOP in a Spring Boot application.

You can download the full source code of this example here: Using Google reCaptcha with Spring Boot Application


An experience full-stack engineer well versed with Core Java, Spring/Springboot, MVC, Security, AOP, Frontend (Angular & React), and cloud technologies (such as AWS, GCP, Jenkins, Docker, K8).
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