KotlinConf 2025 is a real bowl of fresh air for backend Devs
With their keynote that JetBrains intentionally started putting backend developers in the spotlight again. They made big, impactful announcements, both at an ecosystem and language levels and I can't wait to try out all of the new goodies.
TL;DR : After years of focus on the compiler and KMP, The JetBrains folks are coming it out with tons of announcements for server folks too, and that feels great
The past few years
You probably know me by now, I've been liking Kotlin a lot for a long time. Back in 2019 already we were the first at ING moving some of of our production code from Java to Kotlin. Over the past years though, I've also been vocal online about my worries that all of the love was going towards KMP. And Google deciding to sunset the (non Android) Kotlin category has just been another pointer in the same direction. I've even mentioned this exact thing already right after visiting KotlinConf 2023.
Julien
Even with Java releasing more often, and getting more and more new features every iteration I'm still much happier using Kotlin. But for pure backend developers is the developer experience still that differentiating that it makes it worth switching? After all, Java got pretty good records those days. A much better functional programming experience. And virtual threads. The list goes on....
Note : This article is my personal impression based on my usage of the language. Depending what you're working on, your opinion may vary 😊. I've also included many screenshots from the Keynote itself, please watch it for the complete announcements!
Note 2 : There's also been lots of great AI related announcements, but I'll intentionally skip them in this article. I'm generally happy JetBrains picks up the AI wave and innovates while staying open. I'm a mostly happy user of their product myself.
New language features
As a backend engineer, I think the main improvements I've personally seen in Kotlin that made a difference to me the past years are the time API (back in 2021!) and the K2 compiler. Of course, the K2 compiler is a huge (and needed) improvement that came with Kotlin 2.0. But it also didn't bring a huge amount of new language features.
Now, today's keynote was a VERY welcome change to this. Others will do a complete breakdown better than me but here some actual new language features I'm excited about!
- Name-based destructuring to ensure I am grabbing the right properties. An actual improvements compared to the current version.
- Rich errors : an improvement to error handling, sitting on top of the already great null safety features of the language. Not only do we now have complete return types but they also get propagated so we can neatly handle all error cases in a single location.
- Even Kotlin compiler plugins are getting more powerful, with Power Assert offering an expressive and clear error message. Look at this, we're almost topping the already amazing Elm error handling capabilities.
This is developer experience like I haven't seen in a long time from the teams at JetBrains, and it genuinely makes me happy.
Tooling ecosystem, and strategic partnerships
I've already mentioned lately that I was a big fan of Kotlin notebooks. I find them generally amazing, because they combine the unique experience of Python Notebooks with the gigantic JVM ecosystem (and without the Python horrible dependency management issues).
I was legit 🤯 this morning when I saw that the folks at JetBrains combine this already amazing experience together with the ecosystem that pretty much every JVM dev uses on the planet : Spring!
The screenshots aren't doing justice to the announcement, so please just go and have a look at the Keynote yourself. The latest version of notebooks can attach itself to a running Spring kernel and have access to all of its context. And that even for applications that aren't using Kotlin yet.
Again, this is next level for me in terms of developer experience : combining the flexibility of notebooks for experimentation together with the sturdiness of a production like application. With the kandy and dataframe data manipulation capabilities, I can definitely see this speed up my day to day development speed.
And of course, JetBrains also announcing a strategic partnership with Spring on stage shows that they clearly intend to give us "corporate" backend developers some serious love.
Growing Kotlin Foundation
For a long time, Kotlin was completely in the hands of JetBrains. This has massively changed over the past years with the creation of the Kotlin Foundation.
As a professional having to pick a technology, it is crucial to look at how promising its future looks. Seeing that Kotlin is jointly supported by several companies, and especially companies that aren't making a living of the language makes it a much safer business case to adopt inside a company.
Seeing two more companies (and none other than Meta) join the foundation gives a great idea of how bright of a future Kotlin has 😊.
The Kotlin built Java library ecosystem
A few weeks back, I was mentioning that for the first time I found a library that was completely built in Kotlin, but had a clear Java compatibility too. If you're interested, I'm talking about the KBsky.
A Java library, built in Kotlin
Today, I learnt that the two most successful JVM AI libraries (the OpenAI Java SDK and the Anthropic Java SDK) both are actually written in Kotlin.
I find this a great sign for the language. Of course, the amount of Java developers out there is much larger than people writing Kotlin and it makes sense for library builders to want to maximize their reach. But them choosing Kotlin to write the library speaks volume about the quality of the language, but is also a great sign for its future.
The official KOTLIN LANGUAGE SERVER
This is, by far, the announcement I am most excited about and I genuinely didn't see it coming. JetBrains announced the official release of their Kotlin Language Server protocol today.
For those unaware, the language server protocol "defines the protocol used between an editor or IDE and a language server that provides language features like auto complete, go to definition, find all references etc.". Having an official language server protocol implementation basically means that all IDEs (from vim to IntelliJ, or SublimeText) can support the language equally well.
The fact that JetBrains is behind Kotlin always made it rather logical for them to not Open-Source a language server. After all, they're selling their IDEs and that'd pretty much mean they're competing against themselves. And it's always been one of my biggest issues with the language.
Yes, IntelliJ is a great IDE. I use it every single day, have paid for my license for years and I love it. But in simply just don't believe in the success of gated products. More and more people use VSCode every day. People now use Cursor. Or SublimeText. Some still use vim. Forcing folks to use a specific IDE just feels wrong and tames the excitement using a new language should bring.
Yes, there's been community driven language server implementations for Kotlin, but they've always been struggling with support. And literally being a company building IDEs for a living, JetBrains always felt like the best party to handle this properly.
I'm over the moon that JetBrains has the courage to open up and even lead the language server efforts in the future. It shows a strong trust in the future of the language and that can only help drive adoption across the industry.
ING as use case
As I mentioned already, I was part of the first team to start using Kotlin at ING back in 2019. Five years later, adoption has grown a lot internally and I was super happy to see JetBrains offer us to be one of the leading industry use cases for their server side Keynote.
Kotlin powers some of our critical services today, and it's a great symbol of how good and powerful the language is. I can't wait to see where we'll be in 5 years.
I've always been a fan of Kotlin, and it's been an honour to be able to contribute to the content of the program, no matter how small my contribution was.
Conclusion
There's much more I'd like to talk about (amper, klibs, kmp, ...) but I'll keep it to the essential : It feels to me with their keynote that JetBrains intentionally started putting backend developers in the spotlight again. They made big, impactful announcements, both at an ecosystem and language levels and I can't wait to try out all of the new goodies.
Well done JetBrains, well done!