Kotlin Bootique Workshop

Introduction

Welcome to the Kotlin Bootique Workshop. The Kotlin Bootique application provides a very minimalistic implementation of a RESTful API for building a Webshop. The application consists of the following endpoints:

Uri	HttpMethod	Description
/products	GET	retrieve product and price information
/baskets/{id}	GET	retrieve a shopping basket
/baskets/{id}/items	POST	adding an item to a basket

Throughout this workshop you are going to convert this Spring Boot based application written in Java to the Kotlin equivalent. You will be guided through some of the challenges you as a developer will be facing while migrating existing applications to Kotlin.

If you are able to successfully complete this workshop, you should have enough knowledge to start using Kotlin in any of your (existing) Java projects.

Prerequisites

This tutorial assumes that you at least have some basic knowledge about Java 8, Maven, Git and Spring Boot.

Git

Download and install git from https://git-scm.com/downloads

Java

Make sure you have at least JDK 11 installed. You can check which version is installed by executing in your terminal:

java -version

Should output something similar like:

java -version
openjdk version "11.0.5" 2019-10-15
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.5+10)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.5+10, mixed mode)

Java can be downloaded from the AdaptOpenJDK website: https://adoptopenjdk.net/. Or, if you really need to, from the Oracle website: http://www.oracle.com/technetwork/java/javase/downloads/index.html.

IDE - IntelliJ

In this tutorial we assume that you will be using IntelliJ because of it`s excellent Kotlin support! That makes sense considering Kotlin was invented and created by JetBrains, the creator of IntelliJ.

IntelliJ Ultimate Edition is preferred but IntelliJ Community will also work. IntelliJ can be downloaded from: https://www.jetbrains.com/idea/download/.

Sources

The Kotlin Bootique exercises can be found in a separate git repository. Please clone the source to your local machine from github:

git clone https://github.com/sourcelabs-nl/kotlin-bootique-exercises

Keep this documentation open in your browser while completing the exercises.

Build the application

Open the project in IntelliJ ( File > Open... ) or navigate with your favorite terminal application to the location where you just cloned the project.

You can build the project using maven by executing the following command:

./mvnw clean install

mvnw is no typo, this makes sure you are using the maven wrapper file. If you experience issues with you existing maven settings file you can use the provided settings.xml inside the project. Or temporarily renamed your settings.xml to settings.tmp.

./mvnw -s settings.xml clean install

Run the application

You can launch the BootiqueApplication by running the project using the spring-boot maven plugin. Execute the following maven command:

./mvnw spring-boot:run

Exploring the API

The Kotlin Bootique application exposes a Swagger endpoint that allows you to explore the API: http://localhost:8080/swagger-ui.html

Alternatively you can also execute request inside IntelliJ against the API using the provided HTTP Request files in the /http folder or by using curl on the command-line.

Products

You can list all the products using your browser, Swagger or curl

curl -X GET http://localhost:8080/products

Basket

You can view the content of your basket using your browser, Swagger or curl

curl -X GET http://localhost:8080/baskets/1

Adding items

You can add items to the basket using Swagger or curl

curl -H "Content-Type: application/json" -X POST -d '{"productId":"1","quantity":2}' http://localhost:8080/baskets/1/items
curl -H "Content-Type: application/json" -X POST -d '{"productId":"2","quantity":4}' http://localhost:8080/baskets/1/items

Next steps

This workshop consist of several exercises that will guide you through the process of converting the Java code to Kotlin. Each of the exercises are in the kotlin-bootique-exercises project on an separate git branch.

By checking out each exercise branch, you will start of with a working implementation of the previous exercise.

You can start your journey now by switching to the exercise-1 branch, either by using IntelliJ or, by issue the following command in your terminal:

git checkout exercise-1

Please keep this documentation open in your browser while completing the exercises. The lines marked with: Exercise are the task that need to be performed!

The documentation for the first exercise can be found here: exercise-1.md

Enjoy the ride!