Java Caching: From HashMap to Redis

Hello Everyone!

A new season of our SKG Java Meetup begins, and we are ready to kick off! 🚀

For our first meetup of the season, we are diving into one of those topics that every backend developer uses at some point:
Caching in Java!

Topic
Caching sounds simple: store something expensive once and reuse it.

In practice, though, things get interesting very quickly.
Where should the cache live? How long should data stay cached? What happens when the application runs on multiple instances? When should we use an in-memory cache such as Caffeine, and when does a distributed cache like Redis make more sense? And what happens behind Spring's @Cacheable annotation?

In this session, we will explore caching from the simplest implementation all the way to production-ready approaches. We will build the examples progressively, starting from a simple cache implementation and moving towards Caffeine, Redis and Spring Cache, while looking at what changes and what does not in our application code.

💡 This will be a presentation and hands-on session, with several switches from slides directly into the IDE. The goal is not just to see caching APIs, but to understand the engineering decisions and trade-offs behind them.

🎤 Speaker
I'll make the start of the season so this time, I, Eleftherios Chrysochoidis (https://www.linkedin.com/in/lefterisxris/), will be taking the stage. Note: As always, our community is open to your ideas and topic suggestions. Everyone is welcome to step up, present something, and share their knowledge and experience with the community. Contact us to set it up.

🎯 Whether you are working with Spring Boot every day, already using Redis in production, or simply want to understand what @Cacheable is actually doing behind the scenes, this session will give you a clearer understanding of caching in Java applications.

Agenda

• 7:00 - 7:15 Arrival / Networking
• 7:15 - 7:20 Meetup Intro
• 7:20 - 8:20 Caching in Java: From HashMap to Redis
• 8:20 - 9:00 Pizza & Networking 🍕

🙏 Voxxed Days Thessaloniki will be sponsoring our pizzas for this meetup! 🍕

Voxxed Days Thessaloniki celebrates its 10th anniversary this year, with the 2026 conference taking place on November 20-21 at the Ioannis Vellidis Congress Center.

As a Java community in Thessaloniki, we are very happy not only to support the event, but also to be part of it. SKG Java Meetup will be present at the Community Corner, of Voxxed Days, where you will be able to find us throughout the conference, meet the community, and chat with us. We will also be taking part in some additional activities, with more details to be announced soon. 🎉

The Voxxed Days team is preparing a particularly strong edition for this milestone year, so if you are part of the developer community in Thessaloniki, this is definitely an event worth having on your radar.
You can find all the details here:
https://voxxeddays.com/thessaloniki/

A big thank you to the Voxxed Days Thessaloniki team for supporting our community and helping us kick off the season! ❤️

Also huge thanks to Ok!Thess and to Δήμος Θεσσαλονίκη for their support and for providing the space for our events! Thanks 🙏

Gifts 🎁
Make sure you RSVP and join the event to get a chance to win:

• 🎟️ 2 tickets for Voxxed Days Thessaloniki!
• 1 JetBrains 100% free license for any product! 🏆

As always, the event is free of charge. Just bring your best mood, your caching questions, and enjoy 🙂

Let's start the new season strong! 🚀

See you all there!
Lefteris, Dimitris