Java / Gradle

Micronaut RequestStreamHandler to Lambda Java Runtime

Learn how to deploy a Micronaut function to AWS Lambda Java Runtime with an AWS Lambda RequestStreamHandler.

Sergio del Amo

On this guide

In this section

In this guide, we will deploy a Micronaut serverless function to AWS Lambda using a RequestStreamHandler.

Getting Started

In this guide, we will create a Micronaut application written in Java.

What you will need

To complete this guide, you will need the following:

Some time on your hands
A decent text editor or IDE (e.g. IntelliJ IDEA)
JDK 21 or greater installed with JAVA_HOME configured appropriately

Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

Download and unzip the source

Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-function-app example.micronaut.micronautguide \
    --features=aws-lambda \
    --build=gradle \
    --lang=java

Note	If you don’t specify the `--build` argument, Gradle with the Kotlin DSL is used as the build tool. If you don’t specify the `--lang` argument, Java is used as the language. If you don’t specify the `--test` argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

If you use Micronaut Launch, select "Serverless Function" as application type and add the aws-lambda feature.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

Setup IntelliJ IDEA to develop Micronaut Applications.

RequestStreamHandler

AWS Lambda RequestStreamHandler

To use your own serialization, implement the RequestStreamHandler interface. With this interface, Lambda passes your handler an input stream and output stream. The handler reads bytes from the input stream, writes to the output stream, and returns void.

The application contains a class extending MicronautRequestStreamHandler.

Replace the generated FunctionRequestHandler.java with the following:

src/main/java/example/micronaut/FunctionRequestHandler.java

package example.micronaut;

import io.micronaut.context.env.Environment;
import io.micronaut.core.annotation.Introspected;
import io.micronaut.function.aws.MicronautRequestStreamHandler;

@Introspected
public class FunctionRequestHandler extends MicronautRequestStreamHandler { // 

    @Override
    protected String resolveFunctionName(Environment env) {
        return "requestfunction"; // 
    }
}

1	The class extends MicronautRequestStreamHandler.
2	It specifies a function name.

You will use MicronautRequestStreamHandler in combination with a class annotated with @FunctionBean, which implements one of the interfaces from the java.util.function package.

src/main/java/example/micronaut/RequestFunction.java

package example.micronaut;

import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent;
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;
import io.micronaut.function.FunctionBean;
import io.micronaut.json.JsonMapper;
import jakarta.inject.Inject;

import java.io.IOException;
import java.util.Collections;
import java.util.function.Function;

@FunctionBean("requestfunction") // 
public class RequestFunction implements Function<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> { // 

    @Inject // 
    JsonMapper jsonMapper;

    @Override
    public APIGatewayProxyResponseEvent apply(APIGatewayProxyRequestEvent requestEvent) {
        APIGatewayProxyResponseEvent response = new APIGatewayProxyResponseEvent();
        try {
            String json = new String(jsonMapper.writeValueAsBytes(Collections.singletonMap("message", "Hello World")));
            response.setStatusCode(200);
            response.setBody(json);
        } catch (IOException e) {
            response.setStatusCode(500);
        }
        return response;
    }
}

1	The class is annotated with `@FunctionBean`. It specifies `requestfunction` as an annotation value, which matches what we set in `FunctionRequestHandler`.
2	It implements `java.util.function.Function`, which accepts a single argument and returns a single result. We use `APIGatewayProxyRequestEvent` and `APIGatewayProxyResponseEvent` from the AWS Lambda Java Events library.
3	Field injection

Tests

You can test that the handler behaves as expected, as shown in the following example:

src/test/java/example/micronaut/FunctionRequestHandlerTest.java

package example.micronaut;

import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent;
import io.micronaut.json.JsonMapper;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

import static org.junit.jupiter.api.Assertions.assertEquals;

class FunctionRequestHandlerTest {

    private static FunctionRequestHandler handler;

    @BeforeAll
    public static void setupServer() {
        handler = new FunctionRequestHandler(); // 
    }

    @AfterAll
    public static void stopServer() {
        if (handler != null) {
            handler.getApplicationContext().close(); // 
        }
    }

    @Test
    void testHandler() throws IOException {
        JsonMapper jsonMapper = handler.getApplicationContext().getBean(JsonMapper.class);
        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
             InputStream inputStream = createInputStreamRequest(jsonMapper)) {
            handler.execute(inputStream, baos); // 
            assertEquals("""
                    {"statusCode":200,"body":"{\\"message\\":\\"Hello World\\"}"}""", baos.toString());
        }
    }

    private InputStream createInputStreamRequest(JsonMapper jsonMapper) throws IOException {
        return new ByteArrayInputStream(jsonMapper.writeValueAsBytes(createRequest()));
    }

    private APIGatewayProxyRequestEvent createRequest() {
        APIGatewayProxyRequestEvent request = new APIGatewayProxyRequestEvent();
        request.setHttpMethod("GET");
        request.setPath("/");
        return request;
    }
}

1	When you instantiate the Handler, the application context starts.
2	Remember to close your application context when you end your test. You can use your handler to obtain it.
3	Invoke the `execute` method of the handler.

Testing the Application

To run the tests:

./gradlew test

Then open build/reports/tests/test/index.html in a browser to see the results.

Lambda

Create a Lambda function. As a runtime, select Java 21 or Java 17.

Upload Code

Create an executable jar including all dependencies:

./gradlew shadowJar

Upload it:

Handler

As Handler, set:

example.micronaut.FunctionRequestHandler

Test

You can test it easily with a JSON Event:

{
  "path": "/",
  "httpMethod": "GET",
  "headers": {
    "Accept": "application/json"
  }
}

When working with Amazon API Gateway, it’s easy to use apigateway-aws-proxy as an Event Template to get started:

You should see a 200 response:

Next Steps

Explore more features with Micronaut Guides.

Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

License

Note	All guides are released with an Apache License 2.0 for the code and a Creative Commons Attribution 4.0 license for the writing and media (images).