04/30/2026 updated
Premium member
100 % availableSenior Java Software-Entwickler | Spring Boot, Performance & Architektur
Capçanes, Spain
Germany +4
MSc Praktische Informatik (Fernstudium läuft noch), BA, MA, LLMinfo: Germany, Austria, Spain, France, Netherlands
About me
Senior Java/Kotlin-Entwickler & Tech Consultant | 10+ Jahre Erfahrung | BASF, W&W, Thüga | Spring Boot, PostgreSQL, Cloud/DevOps | Architektur, Performance, Teamführung | Remote & vereinzelt vor Ort | DE/EN/ES
Java (Programming Language)JavaScriptSpring SecurityApache ActiveMQAmazon Web ServicesArchitectureAuditingMicrosoft AzureConsultingContract ManagementDevOpsGitHubApache HadoopIntellectual PropertiesJava Virtual Machine (JVM)
I help tech teams cut through complexity and deliver high-performance, scalable software — fast.
Over the past 10+ years, I’ve worked on complex international IT projects for major players like BASF, Wüstenrot & Württembergische AG, and Thüga SmartService, helping their development teams navigate technical complexity and deliver high-quality systems at scale:
- Legacy codebases that are hard to maintain or scale
- Poorly structured architectures leading to instability or low velocity
- Difficulty finding the right senior expertise when it’s needed most
What I Do:
- Freelance Contracting: Clean, production-ready code in Java (and related JVM languages like Kotlin and Scala), Spring Boot, Postgres and many other technologies
- Technical Consulting: Architecture reviews, performance tuning, DevOps improvements, mentoring and code quality audits
- Project Leadership: As a lead developer and technical product owner, I’ve successfully led cross-functional teams of 5+ developers
✅ What You Get:
- Fast onboarding and impact — no hand-holding required
- Structured, methodical approach to software challenges
- Strategic input, not just execution — I give clear, honest, and actionable feedback
- Results-oriented delivery with a focus on long-term maintainability and system performance
Technologies I Work With:
Backend (focus): Java, Kotlin, Scala, Spring Boot, PostgreSQL, Apache Cassandra, Redis, Keycloak, ActiveMQ Artemis, SpringAI
Frontend: TypeScript, JavaScript, Angular, React, Vue, Elm
DevOps: GitLab CI, GitHub Actions, Azure DevOps, Prometheus/Grafana, Azure, Hetzner, minor AWS
Domains: FinTech, Insurance, AdTech, Intellectual Property, Energy (minor)
International & Remote: Based near Barcelona (Spain), fluent in German (native), English, Spanish, Catalan, French — available for remote freelance contracts and consulting engagements across Europe and beyond.
Always happy to meet on-site and in person, of course!
Let’s talk about how I can support your next project: https://cal.com/slissner
Check my market availability: https://slissner.com/availability/
Languages
GermanNative speakerEnglishFluentFrenchGoodSpanishFluent
Project history
- Fixen kritischer Performance-Probleme in einem produktiven Cassandra Cluster
- Tiefgreifende Analyse über die Ursachen der Performance Probleme angefertigt
- Roadmap erstellt für den Tech Lead und Operations Lead zur Lösung der Probleme
- Neuntwicklung des Firmenkundenportal Front-ends
- Integration der Anforderungen zu „Firmenkunden“ in die bestehende Architektur
- Betreuung von bis zu acht internen und externen Entwicklern im Projektverlauf