We can use the flatten method in Groovy to flatten a collection that contains other collections into a single collection with all elements. We can pass a closure as extra argument to the flatten method to transform each element that is flattened. The argument of the closure is the element from the original collection.

The December 2019 release of Apache Kafka 2.4.0 saw usability improvements in TopologyTestDriver, with the addition of new TestInputTopic and TestOutputTopic classes. These offer typesafe methods to easily produce and consume messages for your Kafka Streams tests. In this post we’ll explore these new classes in the context of Avro messages, which requires a small trick to get working.

In a previous post we learned about callouts in Asciidoctor to add explanation to source code. While surfing the Internet I came upon the following blog post by Alex Soto: Auto-numbered Callouts in Asciidoctor. I turns out that since Asciidoctor 1.5.8 we can use a dot (.) instead of explicit numbers to have automatic increasing numbering for the callouts.

When using Springfox you can annotate your endpoints to automatically generate OpenAPI docs for your clients.
This blogpost will show how you can prevent Springfox generating a model on an endpoint with ResponseEntity as return type.
I’ll also cover how to prevent generating default responses.

Adding Spring Security to an existing application can be quite a daunting prospect. Merely adding the required dependencies to your project sets off a chain of events which can break your application and tests.

In a previous post I’ve shown how to use ZIO environments to provide your program with dependencies, or modules. While using environments at the customer I’m currently working for, we found out that the logic to get a database session object using a module would run over and again. This makes sense, since a ZIO[R, E, A] is a prescribed way of getting an A, and the result is not cached. Our application was reading configuration files and creating SQL sessions on every module call, while the resulting object was obviously constructed from the same underlying values. There are multiple ways to solve this:

When combined with Spring Security 5.2+ and an OpenID Provider such as Keycloak, one can rapidly setup and secure Spring Cloud Gateway for OAuth2 resource servers.

This is an overview of some optimization techniques used by Hotspot JVM to increase performance. I will start by giving a small example of how I ran into these optimizations while writing a naive benchmark. Each optimization is then explained with a short example and ends with some pointers on how to analyze your own code.

You might have a need for a custom access decision voter when security decisions are made based on who is accessing what domain object. Luckily Spring Security has quite a few options for such implement such access control list (ACL) constraints.

ZIO is a type-safe, composable library for asynchronous and concurrent programming in Scala (from: The ZIO github). The library copes with functional IO, like many Functional Programming libraries do. The added value of ZIO is that the ZIO[R, E, A] type-constructor (the main IO monad of the library) acts as an IO monad, an error handling monad, and a reader monad. A functional programming style often needs a combination of these three types to cope with the most common problems when creating an application: