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React At Light Speed
// Stephen White
One of the things I love, appreciate, respect, adore … about Callista is our focus on learning and our ability to go on conferences! It’s essential in helping us grow and stay current with tech trends and mingle with other like-minded tech geniuses …
Having got back from AppConf.js in Kraków at the end of May I felt compelled to do something fun for the React Gothenburg meetup.
First AI-fokus
// Ove Lindström
The team behind our favorite Java conference most likely played around with ChatGPT and came up with the idea of having an AI-focused conference. As with all conferences, it focuses around the coffee breaks, so these are my coffee break reflections and highlights.
Kafka utan partitioner?
// Andreas Mossljung
När man bygger integrationer med Kafka och ska sätta upp sina topics ställs man alltid inför samma val: Hur många partitioner ska jag välja? Det är relativt enkelt att utöka med fler, svårare att minska antalet och det är vettigt att ha samma som liknande befintliga topics. Resultatet brukar bli en grov uppskattning, och kanske tar man i lite extra för säkerhets skull. 12 kan vara en bra utgångspunkt, då kan lasten fördelas jämnt över 1, 2, 3, 4, 6, eller 12 konsumenter.
Photo Collage Generation Using Genetic Algorithms
// Marcus Cedergren
Photo Collage Generation Using Genetic Algorithms
This post explores an automated approach to creating high-quality photo collages from large image collections, a journey that began out of frustration with existing tools. The solutions I found, whether manual or automated, often created repetitive patterns, ugly image overlaps, and offered only a fixed set of layouts. This led me to explore a new approach, leveraging a Genetic Algorithm (GA), to efficiently generate large collage layouts. I’ll present an overview of the algorithm and a custom implementation written in Kotlin.
Why Your APIs Should Be RESTful (and Not Just CSV Dumps)
// Ove Lindström
In today’s digital landscape, APIs are the backbone of modern software systems. But not all APIs are created equal. Dive into this blog post and discover why RESTful APIs with structured data and DTOs are vastly superior to database-centric, CSV-driven approaches. We’ll explore the flexibility, scalability, and security benefits that make REST the clear winner for your next integration project. Don’t let clunky APIs hold you back! Read more to learn how to build APIs that developers (and your business) will love. And, there is a twist at the end.
NixOS meets MacOS
// Henrik Starefors
After starting my NixOS journey and embracing Flakes in my previous two posts, it’s now time to set my eyes on a new frontier: MacOS and Nix-Darwin.
Next step in Nix: Embracing Flakes and Home Manager
// Henrik Starefors
In this post, I’ll talk about Nix, provide an overview of Nix flakes, explain their benefits, describe how I migrated my existing setup, and share the code structure I settled on.
Real-Time Q&A Moderation with AI at CADEC 2025
// Andreas Tell
Last year, we introduced the CADEC App — a custom-built iOS and Android mobile app that let attendees submit and upvote questions during each talk. The most popular questions were addressed live in the Q&A session.
For 2024, we relied on manual moderation, but sifting through questions manually just didn’t feel right for 2025. Enter AI-powered moderation: designed to filter out off-topic or inappropriate questions in real time.
This retrospective explores the technical implementation, challenges, and lessons learned.
A Go optimization journey, part 3
// Erik Lupander
An update on the journey of optimizing a text-similarity HTTP request handler with the new swissmap map implementation introduced in Go 1.24.
Faster startup with Spring Boot and CRaC, part 3 - Automated build process
// Magnus Larsson
This is the third part of the blog series “Faster startup with Spring Boot and CRaC”, where we will learn how to automate the build process for creating Docker images for CRaC-enabled applications, including how to warm up the application before the checkpoint. We will create CRaC images for reactive microservices based on Project Reactor and Kafka.
Jfokus 2025
// Ove Lindström
Den 19:e upplagan av Jfokus är slut och nu ser vi fram emot det stora jubileumet nästa år. Eftersom jag verkar finnas med på inventarielistan var jag på plats även i år och såg till att alla talarna fick hjälp av scenvärdar. Årets upplaga var en av de bästa jag varit på och det finns många intryck att smälta. Det här är några av intrycken från konferensen.
The Laws That Secretly Control Your Software Delivery
// Nils Janson
So you think you are in control of your software delivery process? What if I told you that your software delivery process is governed by laws just as the physical world you are living in? In this article, I will explore these often-hidden principles, helping you better understand the challenges and frustrations you may encounter in your daily work. I will offer practical strategies and suggestions to overcome these challenges and improving your teams ability to deliver software successfully.
A Go optimization journey, part 2
// Erik Lupander
Continuing the journey of optimizing a text-similarity HTTP request handler.
Year of the homerow mods
// Henrik Starefors
Today i will share my initial experinces with adding modifers to my keyboards homerow keys. Aka Homerow Mods.
A Go optimization journey
// Erik Lupander
The journey of optimizing a Go web service.
Kroxylicious, Kafka Record Encryption and the Power of Proxies
// Martin Holt
In this blog we will take a look at one way to encrypt your Kafka records using Kroxylicious. This blog post is supported by a working example with source code in this GitHub repository.
Från hålkort till moln - reflektioner från 50 år i IT-branschen
// Peter Hernfalk
50 år i IT-branschen – och fler ska det bli :-)
I år har jag arbetat 50 år i IT-branschen. Under detta halvsekel har jag hunnit med lågt räknat 80 000 arbetstimmar. Jag som verkligen gillar att lära mig nya saker har svårt att tänka mig ett roligare jobb. Det är faktiskt så roligt att jag också har det som hobby.
Ännu en "Alt-conference" på Callista
// Mats Ekhammar
Vad är en alt-conference?
Under och strax efter Covid hade vi börjat gå på online konferenser och känt att de oftast var rätt OK, men vi saknade att komma iväg på riktigt med kollegor. När det sedan blev OK att åka ut igen på konferenser kom många iväg, men några av oss kom inte riktigt till skott igen.
DTO or not DTO?
// Ove Lindström
In this blog we dive into the concept of Data Transfer Objects (DTOs), providing a detailed explanation of their use, design best practices, and how they relate to other object patterns like Value Objects (VO), Domain Objects (DO), and Business Objects (BO). You will gain the understanding that the key to effective use of DTOs lies in their purpose: transferring data efficiently while keeping domain logic separate and testable.
My declarative journey with NixOS
// Henrik Starefors
In this post, I will share my journey of setting up and configuring NixOS as a daily driver from scratch. These are my first steps with NixOS, and they are neither a comprehensive guide nor a tutorial on correct usage; instead, they are stories about how I stumbled through the Nix landscape.