Christian Grümme
Senior Full-Stack Java Freelancer
Berlin, Germany
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Christian Grümme is a freelance full-stack Java developer with over sixteen years of professional experience with Java EE and Spring Boot. He has held various roles in the software development process, for example, as a team lead and Scrum Master. He is particularly interested in overseeing the entire lifecycle of software projects, from conception to operation, but especially in development.
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What Happens on Your Laptop Stays on Your Laptop: Building Java Applications with a Local LLM
Every prompt you send to a cloud coding assistant takes your source code, customer data and secrets with it. So I started building Java applications with a language model running on my own laptop, with no cloud account and no dedicated graphics card. This talk shares what I learned along the way, and shows how to do it well.
Starting from nothing, I'll set up llama.cpp, pick a model that fits the hardware, and connect a coding agent. Then we'll build a small Java application live, with the network unplugged to prove that nothing leaves the machine.
You'll see what makes the difference in practice: how to choose a model, how to work within a small context window, how to keep the agent on track with tests and small steps, and how to review what it produces.
I'll also be honest about the limits: local models are slower and weaker than the big cloud services, they make mistakes you need to catch, and an agent with tools or web access can still leak your data. You'll leave with a setup you can try yourself, realistic expectations and a clear idea of when local is and isn't the right choice.
From Reacting to Leading Under Pressure: A Hands-on Workshop for Tech Leads
A deadline slips, a stakeholder turns on the charm, a colleague gets angry. Most of us have a default reaction in these moments, and it rarely helps. Technical skill won't get you through them, but they can be practiced.
In this hands-on workshop for tech leads, senior developers and anyone who leads without the title, you'll work on what happens to you under pressure. You'll identify your own pattern in conflict using a real situation from your work, collect tools to regulate yourself in the moment, and learn why holding space often works better than rushing to solve the problem.
Then you'll practice. In changing pairs, you'll work through two pressure scenarios, one driven by charm and one by anger, using a simple sequence: notice, regulate, make contact, get clear. Short sharing rounds after each exercise help you take in what you noticed.
You'll leave knowing your own pattern, with tools you've tried yourself and a clear idea of what you'll do differently next time. No prior experience needed, and you decide how much you share.
Spring Boot vs Quarkus - A Comparison
In this talk, I compare Spring Boot and Quarkus, two of the leading, modern frameworks in Java development.
I will present the core functionalities of both frameworks and demonstrate how they differ in terms of functionality and development. A key aspect of my comparison is the suitability of both frameworks about future-proofing, as well as their suitability for migrating legacy software. Using a practical example from my work, I demonstrate the implementation of an application in both frameworks to highlight the differences in practice. This presentation aims to help other Java developers gain insights into the advantages and disadvantages of Spring Boot and Quarkus.
Leading with Presence and Radical Honesty: Communication and Authentic Leadership in Technical Teams
Technical leadership today requires more than logic and process. It calls for presence, empathy, and the courage to be honest.
This talk explores how nonviolent communication, awareness of different learning styles, and embodiment help leaders build trust and handle difficult conversations with authenticity.
Through real examples, we will look at how radical honesty can transform team communication by combining clarity with compassion. Participants will gain new perspectives on how to speak truthfully, stay grounded under pressure, and lead in a way that feels both human and powerful.
Lessons Learned: Building Efficient Team Workflows and Pipelines
In this lightning talk, I share practical lessons and proven patterns for developing software efficiently in a team environment with modern CI/CD pipelines. Based on real project experience, the session walks through how disciplined branching, fast merging and automated checks can dramatically improve both quality and developer productivity.
We’ll look at a streamlined pipeline setup that includes compilation, tests, code formatting, security scans with Trivy and static analysis with SonarQube. The goal is to show how small automation steps and a clear team workflow can create a faster, more reliable and enjoyable development process.
Clean Code 101
Have you ever looked at code you wrote six months ago and thought, “What was I thinking?” Maybe it felt like you were reading a foreign language, or worse—an alien language! Fear not, you're not alone. In this session, I’ll teach you how to avoid writing code for that you will need a decoder ring to understand. Learn the secrets of clean code, from naming things sensibly (goodbye, "temp1"!) to keeping functions small and sweet. With hands-on examples and real-world tips, you’ll leave this talk knowing how to write code that's not only easy to understand but also easier to maintain. Let’s stop writing code that makes us facepalm later!
Building a Cloud-Native Application with Spring Boot and the 12-Factor Principles
In this hands-on workshop, participants will build a complete cloud-native application using Spring Boot 3. Starting from a simple REST API, we will add persistence, configuration management and containerization while applying the 12-Factor App principles at every step.
The workshop focuses on practical implementation: environment-based configuration, stateless services, health checks, logging and deploying the application as a container image. By the end, participants will have a working project that demonstrates how to develop, configure and deploy modern Spring Boot applications that are ready for the cloud.
Advanced SSLContexts in Spring Boot: mTLS, BouncyCastle and Brainpool in Practice
SSL, mTLS and certificate handling often become a source of frustration for Java developers, especially when different protocols and cryptography providers are involved.
This talk demonstrates how to implement advanced security scenarios in Spring Boot with multiple SSLContexts running in parallel. It shows how to integrate X.509 certificates for REST and SOAP services, how to set up mutual TLS (mTLS), and how to use alternative providers such as BouncyCastle, including Brainpool curves as used in infrastructures like the German healthcare TI network.
The session is practical and code-oriented. It focuses on real implementations, typical pitfalls, debugging techniques and proven patterns for creating secure and production-ready Spring Boot bapplications.
From Java EE 6 to Quarkus: A Migration Journey with OpenRewrite
In this session, I will take participants on a live journey of migrating an old Java EE 6 application running on GlassFish 3 and JSF to a modern Quarkus application.
Using a concrete legacy project as an example, I will demonstrate step by step how I automated and accelerated the migration process with the help of OpenRewrite. I will address typical challenges that arise during migration, such as outdated libraries, API incompatibilities, and configuration-related obstacles. During the live demonstration, I will share my experiences, highlight potential pitfalls, and explain how I successfully overcame them.
The goal of this session is to provide participants with practical insights into migrating legacy applications and to demonstrate how the transition to a modern stack can be achieved. This talk is aimed at anyone tasked with modernizing existing applications and offers valuable inspiration for their own migration process.
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