From hands-on workshops to live coding on the big screen to the new mentoring revolution – JCON EUROPE 2025 in Cologne was a celebration for Java enthusiasts from around the globe.
A global gathering of the Java community
From May 12–15, 2025, Cologne became the epicentre of the international Java community. For the tenth edition of JCON EUROPE, developers from more than 60 countries across five continents gathered at the Cinedom to celebrate 30 years of Java. The atmosphere? Euphoric, collaborative – with plenty of good humour.
“30 years of Java. 10 years of JCON. The spirit of celebration was everywhere,” one attendee wrote on social media. Another summed it up: “JCON feels more like a reunion of old friends.”
Honoring JCON: 10 years of innovation recognized by Oracle
A standout moment of the conference: Oracle honored the JCON team for ten years of continuous commitment to the Java community. The award was personally presented by Sharat Chander (Java Community Lead at Oracle) to Markus Kett (Founder of JCON) and Richard Fichtner (Co-Organizer of JCON).
This recognition highlights JCON’s central role in the global Java community – not just as a conference, but as a platform for innovation, exchange, and learning.
Workshops: An In-Depth Introduction to Key Topics
On Monday, the conference kicked off with a full day of hands-on workshops. In small groups, participants engaged in intensive coding, testing, and discussions. Topics ranged from Testing (Christian Stein, Marc Philipp), Java Performance and Caching (Florian Habermann, Christian Kuemmel), AI-powered application development (Marta Tolosa, Sydney Nurse, Sven Ruppert), to efficient deployment and startup optimization (Mark Stoodley). Parallel to this, the full-day Java Luminaries Summit brought together leading Java experts for in-depth exchange.
The workshops provided an excellent opportunity to explore cutting-edge technologies and work directly with thought leaders in the field. Attendees particularly appreciated the mix of theory, practical exercises, and room for individual questions.
Many used the workshop day as the perfect launch into the conference week, reporting “valuable aha moments” and “immediately actionable learnings” for their teams.
AI & GenAI: Java’s next frontier
AI has firmly arrived in the Java community – and the potential is enormous. Especially in the enterprise space, where Java is a leading force, modern AI technologies now meet vast, mature datasets – a treasure trove waiting to be unlocked.
It’s no surprise that Generative AI was one of the hottest topics at JCON 2025. Numerous high-profile talks and sessions showcased how GenAI can seamlessly integrate into Java ecosystems: from LangChain4J to vector embedding models to AI-driven application development and business process optimization.
The message was clear: Java and GenAI are a powerful combination – unlocking enormous potential for the next generation of enterprise applications.
Conference with cinema glamor
Instead of sterile conference rooms, live coding sessions lit up the big cinema screens. The idea of staging tech talks with Slido Q&A in a cinema setting is now a well-established JCON tradition – and it continues to captivate.
Each day of JCON EUROPE 2025 featured an inspiring keynote that reflected the diversity and future focus of the Java world.
On Tuesday, Markus Kett opened the conference with “Java’s Ignored Potential,” demonstrating how Java-native in-memory data processing can drastically improve the performance of data-intensive applications – a topic that resonated widely with attendees. On Wednesday, Sharat Chander, the face of the global Java community, took the stage with “Happy Birthday, Java!” – an emotional and informative look back at three decades of Java’s legacy, from powering the Mars Rover to the Olympic Games. The final keynote on Thursday was presented by Mark Stoodley (Chief Architect Java at IBM) and Markus Kett with “Rethinking Microservice Persistence” – a revolutionary new approach to database architectures: microservice-based data systems moving away from database monoliths, offering up to 80% savings in compute, energy, CO2 emissions, and cloud costs.
Beyond the keynotes, the program delivered impressive technical depth, dynamic live coding, and a highly engaged community. Cay Horstmann offered deep insights into Virtual Threads and Project Valhalla, Alina Yurenko guided attendees through the world of GraalVM. At the same time, François Martin, Lize Raes, and Andres Almiray brought topics such as Testing, Security, and Generative AI with Java to life. The lineup was rounded out by sessions from community leaders like Brian Vermeer, Sandra Ahlgrimm, Simon Martinelli, Ana-Maria Mihalceanu, and many others – transforming the cinema experience into a true Java festival.
For those unable to attend in person: all sessions and keynotes are available on the official JAVAPRO YouTube channel.
Mentoring Hub: Deep conversations beyond the stage
Another standout feature was the new Mentoring Hub format: here, experienced developers connected with newcomers and early-career professionals. In small groups, participants engaged in coaching, discussions, and idea-sharing – a format that moved beyond the traditional conference model. Rather than passively listening, attendees engaged in direct dialogue with seasoned Java experts.
Whether in sessions with Bruno Souza, discussions about “Next Steps for Developers,” or exploring what it means to become a “mature developer,” the feedback was overwhelmingly positive. “It added a kind of depth and connection that went beyond the usual conference experience,” one participant remarked.
A statement in print: JAVAPRO returns to paper
Another highlight: the return of JAVAPRO in print. The special edition “30 YEARS OF JAVA” was completely snapped up within just two hours – not a single copy remained at the booth. The revival of JAVAPRO as a print magazine was seen not only as a surprise but as a strong signal: technical journalism for developers remains as relevant as ever.
For those who missed out, the articles will be published gradually online at javapro.io.
The limited special edition is also being distributed at selected conferences and features articles on Core Java, GenAI, Microservices, Architecture, Frameworks & APIs, Testing, Security, Cloud, retrospectives on 30 years of Java, and future topics such as “GenAI with Java” and new JVM languages. Those eager for more can subscribe to the free PDF editions.
Community spirit & late-night talks
Beyond the technical program, JCON 2025 also shone on the human side. The “Hallway Track,” spontaneous networking between sessions, and 1:1 speaker meetings were all buzzing with activity. Many attendees described the event as a “conference family” rather than just a professional gathering.
A social highlight was the VIP dinner on Wednesday evening – attended by members of the Java community, speakers, sponsors, and the organizing team. In a relaxed atmosphere, conversations were had, toasts raised, and visions for Java’s future shared. The dinner reinforced the event’s spirit of connection – and provided space for personal exchanges on equal footing.
And of course, there was celebration too: 30 years of Java – in great style. The community toasted three decades of innovation and collaboration – complete with a specially designed anniversary cake, shared and enjoyed together at the VIP dinner. A sweet moment that strengthened the sense of community even further.
Alongside expert talks and in-depth discussions, small playful details added to the fun: the colorful ribbons were especially popular. Those proudly wearing a rainbow of badge extensions like “JVM,” “Star Trek,” and “Maven” (or similar) demonstrated humor, broad technical knowledge – or simply that they’d had a great week.
Every year, the new JCON T-shirts are eagerly anticipated. This year’s special 10th anniversary edition was highly sought after and proudly worn by many attendees during the conference. For some, these shirts have long become collector’s items — and anyone who secured a limited edition now owns a piece of JCON history.
JCON goes to the USA
But that wasn’t all. Officially announced on stage in Cologne, and already sparking excitement: with the first U.S. edition of JCON @ IBM TechXchange from October 6–9, 2025 in Orlando, Florida, the successful JCON format will cross the Atlantic for the first time. Another milestone in its evolution – and a clear sign that the community spirit knows no borders.
An anniversary that connects – and leaves us wanting more
Ten years of JCON, 30 years of Java, four inspiring days. JCON EUROPE 2025 was a resounding success – both organizationally and in terms of content. It vividly demonstrated just how modern, diverse, and forward-looking the Java community is. A huge thank you to all participants, volunteers, and the entire organizing team, and especially to our fantastic speakers, partners, exhibitors, and sponsors who made JCON EUROPE 2025 possible.
The combination of innovation, practical relevance, mentoring, and genuine community spirit makes JCON far more than just a developer conference – it’s a true home for Java enthusiasts. If you missed it, you definitely missed out.
Good news: the recap video is online, and the session videos are now being released step by step. Many talks are already available to stream — an excellent opportunity to revisit the highlights or discover sessions you may have missed.
Save the Date:
The next JCON EUROPE will take place from April 20–23, 2026, once again at the Multiplexkino Cinedom in Cologne.
More info: https://jcon.one
