Java conferences seems to go on for ever! Previously we've covered Spring I/O, KotlinConf, Devoxx, JavaOne and Voxxed. However, the series wouldn't be complete without JCON EUROPE 2025, which took place between May 12–15 in Cologne.

Lots of speakers, lots of talks, lots of attendees; a recipe for success. Speaker all star, Ivar Grimstad, Marc Philipp, Martin Lippert, Alina Yurenko, Cay Horstmann were in place; and workshops and talks were of the highest quality too.

While the usual Core Java, Serverside Java, APIs, and Frameworks were covered, this year's conference's focus was on Java-Cloud-Native and Microservices, an area where
Java occupies the throne. Other than that, the event coincided with Java's 30th birthday something that rendered the atmosphere vibrant.

The event as well as an in-person conference, was also streamed. Therefore we now have the privilege to watch the talks on demand, available on Youtube. At the time of writing
47 talks were available while 21 videos were hidden, therefore unavailable, but we assume that they'll appear at a later date.
But since the talks were aplenty, we've made an attempt to single the most noteworthy out.

So since the conference was all about Cloud Native aka making Java start faster, the first talk we'll look at is "Duke on CRaC with Jakarta EE" by Ivar Grimstad which talks about one alternative super fast way to start Java applications, looked upon from a Jakarta EE point of view. This is CraC and we've looked at this technique in the past in "Azul Zulu OpenJDK 17 Build Now Comes With CRaC" :

CRaC stands for Coordinated Restore at Checkpoint. It is an API that helps to coordinate the JDK and an application's resources under a checkpoint/restore mechanism. It allows applications to, for instance, close open files, dump their cache, and snapshot the required state for them to come alive when restored back. As such the primary aim of the project is to offer a standard mechanism-agnostic API to notify Java programs about the checkpoint and restore events.

The session goes through the evolution of J2EE finally becoming Jakarta EE, then describes what CraC is and goes on to show how to use the API from your code.

Along those lines and in complementing the aforementioned talk, Mark Stoodley's "Comparing Java startup performance options with Quarkus" enumerates all the alternative ways that Java can be become faster, including CraC, but from a Quarkus perspective. Of course we are talking micro-seconds here but the delay can make a big difference when trying to spin VMs on the Cloud to run Microservices.

A great session was certainly "Java Meets AI: Empowering Developers to Build Intelligent Apps" by Timo Salm & Sandra Ahlgrimm. It goes into the Java frameworks that Spring developers can use to build AI applications. These are LangChain4j, SpringAI and Semantic Kernel. Going along the basic concepts of LLMs, the speakers also compare the frameworks when building a GenAI powered recipe application and tip when to use each.

Finally, Nicolai Parlog's Advanced "Java 101" was a great session that talks about how to make Java easier to learn for beginners. We've recently explored the issue in "Making Java Easier For The Beginner" :

Java is an intimidating language for the complete beginner, but now there is hope of simplification in the recently proposed JEP512. And the fact that it is 512 must count for something - right?

Nicolai demonstrates the complex concepts a beginner to the language should go through by starting out with the notorious "Java Hello World" example which utilizes System.out.println:

public class HelloWorld {
   public static void main(String[] args) {
     System.out.println("Hello, World!");
   }
}

There is a lot here that the beginner is going to struggle to understand and indeed most of the time the whole thing is just wished away with a "you don't need to know about that". But even if the beginner is wimpy enough to accept the boilerplate, they generally can't help but ask what System.out.println is all about? The problem is that all of the boilerplate is about programming in the large and has nothing to add to the simple Hello World in the small.

Nicolai demonstrate show much easier the same Hello World can get implemented when the JEP will be absorbed in Java version 25:

void main() {
   IO.println("Hello, World!");
}

Fantastic, but that's not all. Beginners should also find it easier to build and run code, therefore they also need easy to use tooling. For that there's now the official Java playground where without having to set anything up students can run their code inside their browser. And JSheel provides another alternative.

Yet another obstacle in learning Java, is that the concepts of OOP are coupled to teaching the language's constructs. Nicolai argues that we have to decouple teaching the principles of Object oriented programming from the teaching of the language itself. Therefore he advocates the writing of quick simple programs that do something tangible without getting deep into OOP, suggesting how to go about it:

To sum it up, JCON proves once more why it occupies a top spot in the Java conferences hall of fame. Great speakers, great talks, great attendance. Enjoy the sessions!

More Information

JCON EUROPE 2025 Youtube playlist

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