Hello World AWS Lambda Function with Gradle

This guide walks you through creating a simple Hello World AWS Lambda function using Java and Gradle, ready for deployment using our automated deployment script.

Project Setup

Create a new directory for your project:

mkdir hello-world-lambda
cd hello-world-lambda

Initialize a new Gradle project:

gradle init --type java-application

When prompted:

Choose 2 for application
Choose 3 for Java
Choose 1 for Groovy
Project name: hello-world-lambda
Source package: com.example.lambda

Configure Gradle

Replace the contents of build.gradle with:

plugins {
    id 'java'
}

repositories {
    mavenCentral()
}

dependencies {
    implementation platform('com.amazonaws:aws-java-sdk-bom:1.12.261')
    implementation 'com.amazonaws:aws-lambda-java-core:1.2.2'
    implementation 'com.amazonaws:aws-lambda-java-events:3.11.0'
    implementation 'com.google.code.gson:gson:2.10.1'
    
    testImplementation 'org.junit.jupiter:junit-jupiter:5.9.2'
}

java {
    sourceCompatibility = JavaVersion.VERSION_11
    targetCompatibility = JavaVersion.VERSION_11
}

test {
    useJUnitPlatform()
}

jar {
    manifest {
        attributes 'Main-Class': 'com.example.lambda.Handler'
    }
    
    from {
        configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) }
    }
    
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
}

Create Lambda Handler

Create the handler class in src/main/java/com/example/lambda/Handler.java:

package com.example.lambda;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import com.google.gson.Gson;
import java.util.Map;
import java.util.HashMap;

public class Handler implements RequestHandler<Map<String, Object>, Map<String, Object>> {
    private final Gson gson = new Gson();

    @Override
    public Map<String, Object> handleRequest(Map<String, Object> input, Context context) {
        context.getLogger().log("Input: " + gson.toJson(input));
        
        Map<String, Object> response = new HashMap<>();
        response.put("statusCode", 200);
        response.put("body", "Hello from AWS Lambda!");
        
        return response;
    }
}

Project Structure

Your project should now look like this:

hello-world-lambda/
├── build.gradle
├── gradlew
├── gradlew.bat
└── src/
    └── main/
        └── java/
            └── com/
                └── example/
                    └── lambda/
                        └── Handler.java

Build and Deploy

Build the project:

./gradlew clean build

Run the deployment script:

python deploy_lambda.py

When prompted, provide the following information:

Project name: hello-world-lambda
AWS region: (your preferred region)
AWS account ID: (your account ID)
IAM role name: (your Lambda execution role)
Handler path: com.example.lambda.Handler::handleRequest

Testing

After deployment, test your function using the provided curl command:

curl -X POST -H "Content-Type: application/json" -d '{"name":"test"}' https://<api-id>.execute-api.<region>.amazonaws.com/post

Expected response:

{
    "statusCode": 200,
    "body": "Hello from AWS Lambda!"
}

Troubleshooting

Common issues:

Build fails: Ensure Java 11 is installed and JAVA_HOME is set correctly
Deployment fails: Verify AWS credentials are configured properly
Runtime error: Check the handler path matches your code
Permission denied: Ensure IAM role has appropriate permissions

Required Permissions

The IAM role needs these permissions:

AWSLambdaBasicExecutionRole
CloudWatchLogsFullAccess (for logging)

Clean Up

To remove deployed resources:

Delete the Lambda function
Delete the API Gateway
Delete CloudWatch log groups

decagondev/aws_lambda_hello_world.md