App development

Write an AWS Lambda Perform with Kotlin and Micronaut [FREE]

Serverless options comparable to AWS Lambda enable builders to run code with out fascinated with servers. Furthermore, they give you the power to pay just for the compute time you devour as a substitute of a set month-to-month fee. They’re changing into particularly suited to situations comparable to cell phone utility back-ends.

On this tutorial, you’ll take the next steps to create an AWS Lambda operate utilizing Kotlin:

Create a Kotlin mission utilizing Gradle.
Add a “Discuss like a pirate” translator to the mission.
Construct an AWS Lambda RequestHandler.
Deploy your operate to AWS.
Add an API-Gateway Set off.
Re-do the mission utilizing the Micronaut framework, and re-deploy.


With a view to observe together with this tutorial step-by-step, you’ll want the next:

You’ll be creating the tutorial mission from scratch, and you’ll obtain the ultimate mission utilizing the Obtain Supplies button on the prime or backside of the tutorial.

Writing the Perform

Time to get began creating your AWS Lambda operate with Kotlin!

Create a Kotlin App with Gradle

Open a Terminal, make a brand new listing named pirate-translator, cd into the brand new empty listing, and kind gradle init. You’ll see the next output:

$ gradle init
Choose kind of mission to generate:
1: primary
2: utility
three: library
four: Gradle plugin
Enter choice (default: primary) [1..4]

Choose utility, kind 2, and press return.

Then, gradle will immediate you to decide on an implementation language:

Choose implementation language:
1: C++
2: Groovy
three: Java
four: Kotlin
5: Swift

Choose Kotlin, kind four, and press return.

Then, you’ll be prompted to decide on a Construct script DSL:

Choose construct script DSL:
1: Groovy
2: Kotlin
Enter choice (default: Kotlin) [1..2] 2

Choose Kotlin DSL, kind 2, and press return.

As mission identify enter pirate-translator

As supply bundle enter com.raywenderlich.

Congratulations! You may have created a Kotlin app which builds utilizing Gradle.

Code a Pirate Translator

On this part, you’ll create Kotlin lessons. You need to use any textual content editor, however I like to recommend you employ IntelliJ IDEA 2019.2 or later (Group or Final) by JetBrains – the corporate behind Kotlin.

In case you’re utilizing IntelliJ IDEA, click on File ➤ Open and open the pirate-translator listing you made earlier than.

Create a brand new Kotlin file named PirateTranslator.kt and place within the listing src/principal/kotlin/com/raywenderlich. Add an interface as contract for the Discuss like a pirate translator.

// src/principal/kotlin/com/raywenderlich/PirateTranslator.kt
bundle com.raywenderlich

interface PirateTranslator
// 1
enjoyable translate(message: String): String

Within the interface, you specify a translate() technique which takes a String and returns a String.

Subsequent you’ll write a Pirate translator mind :]

It ought to have the next habits:

For enter Sure, it returns Aye.
For enter Hey, it returns Ahoy.
For enter Sure, Captain!, it returns Aye Aye!.

For instance, for enter,

“Hey, I’m Captain Jack Sparrow”

the pirate translator returns:

“Ahoy!, I’m Captain Jack Sparrow”

To your implementation of PirateTranslator, create a brand new file named DefaultPirateTranslator.kt and place it below src/principal/kotlin/com/raywenderlich. Add the category DefaultPirateTranslator:

// src/principal/kotlin/com/raywenderlich/DefaultPirateTranslator.kt
bundle com.raywenderlich

class DefaultPirateTranslator : PirateTranslator

// 1
val replacements = mapOf(“Hey” to “Ahoy!”, “Sure” to “Aye!”, “Sure, Captain!” to “Aye Aye!”)

override enjoyable translate(message: String): String

On this code:

You create a Map with some pirate translations.
You exchange any occurrences within the enter string with pirate lingo.

Take a look at the PirateTranslator

Subsequent you’ll add a check for the PirateTranslator. Create a file below src/check/kotlin/com/raywenderlich and identify it PirateTranslatorTest.kt.

Add your check class:

bundle com.raywenderlich

import kotlin.check.Take a look at
import kotlin.check.assertEquals

class PirateTranslatorTest
// 1
@Take a look at enjoyable testPirateTranslator()

Right here you:

Annotate the tactic with @Take a look at.
Instantiate the category below check.
Create assertions to confirm the anticipated habits.

To run the check, in Terminal within the mission root listing, run the next command:

$ ./gradlew check –tests=com.raywenderlich.PirateTranslatorTest

You need to see a BUILD SUCCESSFUL message if the check passes. If the check failed, you’d see an exception. You can too run the check in IntelliJ IDEA, by urgent the inexperienced run button subsequent to the check technique.

Create an AWS Lambda RequestHandler

Your mission wants to simply accept enter, cross it to the pirate translator, and reply with the translated output. You’ll do that with an AWS Lambda RequestHandler.

Create a category named HandlerInput below src/principal/kotlin/com/raywenderlich. This class will encapsulate the message you’ll enter into your Discuss like a pirate serverless operate. Arrange the category like this:

// src/principal/kotlin/com/raywenderlich/HandlerInput.kt
bundle com.raywenderlich

class HandlerInput

Be aware that you’re not utilizing a Kotlin information class for the enter, as that will trigger points when utilizing it to bind JSON within the AWS Lambda RequestHandler.

Now create a Kotlin information class named HandlerOutput below src/principal/kotlin/com/raywenderlich. This class will encapsulate the interpretation you’ll obtain from the Discuss like a pirate serverless operate. The information class ought to appear like this:

// src/principal/kotlin/com/raywenderlich/HandlerOutput.kt
bundle com.raywenderlich

information class HandlerOutput(val message: String, val pirateMessage: String)

Now it’s essential to add the AWS Lambda dependency. Modify the file construct.gradle.kts, by including the next dependency within the dependencies block:


The aws-lambda-java-core dependency is a minimal set of interface definitions for Java help in AWS Lambda.

Open the Gradle tab in IntelliJ IDEA and hit the sync button to synchronize the dependencies.

Syncing dependencies

Exchange the contents of src/principal/kotlin/com/raywenderlich/App.kt with the next:

bundle com.raywenderlich

import com.amazonaws.providers.lambda.runtime.Context
import com.amazonaws.providers.lambda.runtime.RequestHandler

// 1
class App : RequestHandler
// 2
val translator : PirateTranslator = DefaultPirateTranslator()

// three
override enjoyable handleRequest(enter: HandlerInput?, context: Context?): HandlerOutput

Right here you do the next:

Create a RequestHandler. Lambda stream request handlers implement AWS Lambda Perform utility logic utilizing enter and output streams.
Instantiate a PirateTranslator.
Override handleRequest which takes a HandlerInput and responds with a HandlerOutput.
Use the translator to populate pirateMessage, the second argument of the HandlerOutput constructor.

Exchange the contents of src/check/kotlin/com/raywenderlich/AppTest.kt with:

bundle com.raywenderlich

import kotlin.check.Take a look at
import kotlin.check.assertEquals

class AppTest
@Take a look at enjoyable testAppHasAGreeting()

The above check verifies that given a HandlerInput with a message of worth “Hey”, the response (the HandlerOutput) incorporates a pirateMessage with worth “Ahoy!”.

Go forward and run the check the identical approach as earlier than, both from a Terminal utilizing gradlew, or proper in IntelliJ IDEA.

Gradle Shadow Plugin

Earlier than deploying to AWS, apply the Gradle Shadow Plugin – a Gradle plugin for collapsing all dependencies and mission code right into a single Jar file.

Modify the file construct.gradle.kts once more, this time so as to add to the plugins block:

id(“com.github.johnrengelman.shadow”) model “”

Go forward and sync the mission Gradle recordsdata yet another time for enjoyable! :]

Deploying to AWS Lambda

Now that you’ve your Kotlin pirate translator mission arrange, it’s time to deploy it to AWS Lambda! :]

Login to your AWS Console and go to

Create a Perform

You’ll be taken to the Capabilities display:

AWS Lambda Functions screen

Click on on Create operate, and also you’ll see the Create operate display:

Create function screen

On this display:

Choose Creator from scratch.
As Perform identify enter pirate-translator.
For Runtime, choose Java eight.
Choose Create a brand new Function with Fundamental Lambda permissions

Click on on Create Perform.

You’ll be taken to your new AWS Lambda operate pirate-translator:

Pirate translator screen

Domestically in a Terminal, from the mission root folder run ./gradlew shadowJar.

That generates a JAR file construct/libs/pirate-translator-all.jar.

Again in AWS, on the pirate-translator display:

Add the JAR file as operate bundle.
For the Handler, enter: com.raywenderlich.App::handleRequest.
Click on Save within the higher proper.

Take a look at Your Perform

Subsequent you’ll create a check occasion in your operate. Choose Configure check occasions from the dropdown:

Configure test event dropdown

That may present the Configure check occasion dialog:

Configure test event dialog

On the dialog:

For Occasion identify enter PirateHello

As content material enter:

Click on Create.

Now be sure the PirateHello occasion is chosen and click on Take a look at. You need to then see a profitable run of the check:

Test success

Congratulations! Your Kotlin Pirate Translator works with AWS Lambda!

Add an API-Gateway Set off

The subsequent step is to create an AWS API Gateway Set off. Amazon API Gateway is a totally managed service that makes it simple for builders to create, publish, preserve, monitor, and safe APIs at any scale.

You’ll create an API in entrance of your AWS Lambda making it clear to the shoppers of the API which expertise you used to energy your pirate translator.

Within the AWS Lambda console, in your pirate-translator display, click on the Add set off button:

Add a trigger

You’ll be taken to the Add set off display:

Add trigger screen

On this display:

Select API Gateway from the primary dropdown.
Choose Create a brand new API.
Choose Open for Safety.
For the API identify, go away pirate-translator-API.
For Deployment stage, go away default.

Depart the remaining with the default values as effectively and click on Add.

You’ll be taken again to the display in your operate:

Back to your function screen

Click on the API identify to go to the Amazon API Gateway UI. From right here, choose the tactic ANY and within the Actions dropdown choose Delete Technique. Then affirm the delete.

Select Delete Method Action

Open the Actions dropdown and choose Create Technique:

Select Create Method Action

Choose POST and click on the checkmark:

Select POST method

Select Integration kind Lambda Perform. Enter pirate-translator for the operate identify. Kind p and you must be capable of choose utilizing auto-completion. Then click on Save within the decrease proper, and ensure on the dialog that seems.

Setting up the POSE

Then click on Take a look at:

Test the POST method

Enter the Headers:

Settle for:utility/json
Content material-Kind:utility/json

And for the Request Physique use:

“message”: “whats up”

Then click on Take a look at and you will notice the pirate translation because the Response Physique. Aye!

Running the test

Now open the Actions dropdown once more and select Deploy API.

Select Deploy API

Choose default because the Deployment stage, and click on Deploy:

Deploying the API

As soon as, it’s deployed you’ll get a Invoke URL which you’ll be able to train with a cURL command in Terminal:

$ curl -X “POST” “” -H ‘Settle for: utility/json’ -H ‘Content material-Kind: utility/json’ -d $”

(Remember to substitute in your Invoke URL.)

You’ll get a response like this:

Congratulations! You may have created an API in entrance of an AWS Lambda operate written with Kotlin!

Writing the Perform with Micronaut

Micronaut is a a contemporary, JVM-based, full-stack framework for constructing modular, simply testable microservice and serverless purposes. On this part, you’ll see easy methods to create the identical pirate translator utilizing Micronaut.

The simplest approach to set up Micronaut is through SDKMan:

$ sdk set up micronaut

Or as a substitute through the use of Homebrew:

$ brew set up micronaut

Create a brand new listing named pirate-translator-mn. In that listing run:

$ mn create-function –inplace –lang=kotlin –test=spek

Like earlier than, you may open the mission in IntelliJ IDEA 2019.2 or later.

Copy the recordsdata PirateTranslator.kt, DefaultPirateTranslator.kt and HandlerOutput.kt, HandlerInput.kt from the earlier mission to src/principal/kotlin/com/raywenderlich within the Micronaut mission.

For the Micronaut model of the mission, the HandlerInput is usually a information class. Exchange the content material of HandlerInput.kt with:

bundle com.raywenderlich

information class HandlerInput(val message: String)

Exchange the contents of src/principal/kotlin/com/raywenderlich/AppFunction.kt with :

bundle com.raywenderlich;

import io.micronaut.operate.executor.FunctionInitializer
import io.micronaut.operate.FunctionBean;
import java.util.operate.Perform;

// 1
class AppFunction : FunctionInitializer(), Perform

* This principal technique permits operating the operate as a CLI utility utilizing: echo ” | java -jar operate.jar
* the place the argument to echo is the JSON to be parsed.
enjoyable principal(args : Array)
val operate = AppFunction(), context -> operate.apply(context.get(

The code is nearly similar to the earlier mission, however as a substitute of implementing com.amazonaws.providers.lambda.runtime.RequestHandler, you implement java.util.operate.Perform. That may assist you to swap a serverless supplier comparable to AWS Lambda with one other serverless supplier simply.

Delete src/principal/kotlin/com/raywenderlich/App.kt from the mission, since you employ HandlerInput and HandlerOutput.

Exchange the contents of src/principal/check/kotlin/com/raywenderlich/AppClient.kt with:

bundle com.raywenderlich

import io.micronaut.operate.consumer.FunctionClient
import io.micronaut.http.annotation.Physique
import io.reactivex.Single
import javax.inject.Named

// 1
interface AppClient

This code does the next:

Making use of the @FunctionClient annotation implies that strategies outlined by the interface develop into invokers of distant or native features configured by the appliance.
The worth of @Named should match the worth of the @FunctionBean annotation within the AppFunction class.
You outline a way returning a ReactiveX Single kind. Micronaut implements the tactic for you.

Exchange the contents of src/principal/check/kotlin/com/raywenderlich/AppFunctionTest.kt with:

bundle com.raywenderlich

import io.micronaut.context.ApplicationContext
import io.micronaut.runtime.server.EmbeddedServer
import org.jetbrains.spek.api.Spek
import org.jetbrains.spek.api.dsl.describe
import org.junit.jupiter.api.Assertions.assertEquals

// 1
class AppFunctionTest: Spek()

Right here you do the next:

Take a look at utilizing Spek– a specification framework that lets you simply outline specs in a transparent, comprehensible, human readable approach.
Begin a Netty embedded server inside your check.
Retrieve the declarative consumer to devour the operate.
For the reason that consumer returns a blocking kind, you name blockingGet to acquire a solution.

Generate one other shadow JAR with ./gradlew shadowJar from the pirate-translator-mn root.

Now it’s essential to replace your AWS Lambda operate to make use of the Micronaut model of the mission. Return to the AWS Lambda console, and on the display in your pirate-translator operate:

Add the JAR
Change the Handler to
Click on Save.

Uploading the Micronaut JAR

Go forward and run the identical cURL command you ran earlier than as a check.

Congratulations! You may have deployed your first Micronaut operate written with Kotlin to AWS Lambda.

Micronaut affords lots of options comparable to dependency injection, declarative HTTP shoppers, bean validation, and many others., which you haven’t used on this tutorial however which may vastly enhance your efficiency and code high quality when creating real-world serverless features.

The place to Go From Right here?

Congratulations once more on deploying two variations of an AWS Lambda operate written in Kotlin, and making the serverless operate accessible in an API! :]

You may obtain each remaining initiatives utilizing the Obtain Supplies button on the prime or backside of the tutorial.

For additional studying:

You may have simply scratched the floor of what’s doable with AWS Lambda and serverless features, however I hope it opens a world of prospects in your cellular app API back-ends.

When you’ve got any questions or feedback, please don’t hesitate to hitch the discussion board dialogue beneath.

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