Part 1: GraphQL with Spring Boot, JPA and Kotlin

| renekloth

GraphQL is a query language for dynamic queries on linked data. In the GraphQL world, there are many tutorials and documentation that illustrate the concrete introduction to GraphQL. Since getting started requires a lot of explanation, regular tutorials usually have a simple setup, which does not reflect the real world complexity. If additional technologies are added or the complexity of the project increases, these “Hello World” examples are usually no longer so helpful.

This article introduces GraphQL on the technology Spring Boot with JPA and Kotlin. I also present some best practices which I have learned while I have worked with it. You can find the source code here: https://github.com/akquinet/kotlin-spring-graphql

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Unbounded Functional Loops in Kotlin

| tnfink

This article is a follow-up to this previous article about bounded loops. Bounded loops are cool because they always terminate and usually it is pretty easy to estimate the computational time. But as every computer scientist, who had to understand the halting problem, knows, there is a big class of algorithms which are harder. These are known as the class of μ-recursive functions. Here, unbounded loops exists which can run forever. I will introduce how IMHO unbounded loops can be implemented in Kotlin in a functional way. And, of course, I could not resist and did some measurements…

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Conditional evaluation in Docker files

| M. Dahm

In general, a Docker build file (Dockerfile) should be usable on any Docker server. In some cases however, you would like to have something like a conditional ‘IF’ statement in your Dockerfile. To give an example: It is common usage to use apk/apt-get/curl or any other tool in your build that needs to download data from the Internet.
Alas, in some networks the use of a HTTP(S) proxy is mandatory and thus an impediment.

In this article we will show how to run a proxy-agnostic Docker build. The described mechanism is also usable for other circumstances.

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Java Optional and Kotlin Nullable

| Martin Schröder

We are using Kotlin and Spring Boot in one of our projects. This includes Spring Boot Jpa Repositories. We are using a CrudRepository that provides basic functionalities like save(), delete(), findById() etc. This library is written in Java, hence method signatures look like this:

Optional<T> findById(ID var1);

Using this API out of the box would force us to deal with cumbersome Java Optionals. Since we are implementing in Kotlin we would like to use Kotlin Nullables instead and as it turned out we can achieve this very easily.

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Logging with Azure Application Insights – Part 1: Spring-Boot

| Daniel Bremer-Tonn

When developing and running apps inside Microsoft Azure you have to deal with the topics like monitoring and logging. Azure provides a central solution for that question which is Application Insights. AppInsights (for short) is the central hub to get metrics and log data from our applications and let you access these data within the azure portal in an easy and convenient way. While the metric aspect is well documented, how to connect your favorite application logger to AppInsights it is not.

In this blog post we will show you how to enhance your typical Spring-Boot application to have all the logging data send to Azure AppInsights automatically. In a followup post we will show the same for a typical nodejs based application.

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Multi-target compilation with Kotlin

| M. Dahm

Kotlin allows to compile application code for different platforms, namely into JVM (byte code), JavaScript and native binaries. In one of our projects we were facing the challenge to use the same source code as well in a Java client as in a web application written in TypeScript/Angular. The main reason not to just copy the code and convert it manually to TypeScript is maintenance, i.e. the code is expected to evolve over time.

Thus we came up with the solution to convert the original Java code to Kotlin and compile it for both platforms.

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