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Samuel LissnerSL

Samuel Lissner

Lead Java Software Engineer • 10+ YoE

€600/day
Barcelona, ES
8-15 years

Average response time: 1 hour

About Samuel

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 a Chemical comp, Wüstenrot & Württembergische, 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 other JVM languages), Spring Boot, Postgres, and modern JavaScript/TypeScript frontends (Angular, React, Vue, Elm)
- 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: Java (JVM languages like Scala or Kotlin), Spring Boot, PostgreSQL, 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

🌍 International & Remote:

Based near Barcelona (Spain), fluent in 🇩🇪 German (native), 🇬🇧 English, 🇪🇸 Spanish, Catalan, 🇫🇷 French
  • German

    Native or bilingual

  • English

    Fluent

  • Spanish

    Fluent

  • Catalan

    Fluent

  • French

    Conversational

Remote only
Primarily works remotely

Experience

  • Global Chemical Company
    Senior Back-end Developer (Java) and Technical Consultant
    CHEMICAL
    October 2024 - Today (1 year and 8 months)
    Madrid, Spain
    • Senior Back-end Java Developer for an intercontinental software project of a DAX listed industry giant corporate
    • Optimizing Performance and Observability of a Redis Search application
    • Scala Parser / Generator of a proprietary query language
    • System design draft, architecture and estimation for integrating the application with a bulk Generative AI service, prompt engine to mass create LLM prompts
    • Domain: Intellectual Property, Chemical Industry
    Spring boot Java Redis PostgreSQL Microsoft Azure
  • Thüga SmartService GmbH
    Apache Cassandra Consultant
    ENERGY AND UTILITIES
    June 2024 - July 2024 (1 month)
    Naila, Germany
    • Improving database performance in a production Cassandra cluster
    • Created a technical report and analysis of the performance issues of the Apache Cassandra cluster
    • Consulting the tech lead and operations lead on a roadmap how to solve the root causes
    • Monitoring the operations of the Apache Cassandra cluster
    Apache Cassandra Apache Spark Apache Kafka Java
  • W&W Interaction Solutions GmbH
    Migration of authentication systems
    BANKING AND INSURANCE
    January 2024 - June 2024 (5 months)
    Múnich, Germany
    Migrate applications away from a Keycloak-Identity-Provider to Ping-Identity. Reconciling authentication with the insurance corporate.
    Keycloak Typescript Capacitor Elm AngularJS

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Education

  • Master of Science*
    FernUniversität in Hagen
    Master of Science - MS, Applied Computer Science *not yet graduated! Courses: Interactive Systems (signal processing and computer vision), Information retrieval, Industry 4.0 and IIoT, IT Security, Decision Theory (Computational Social Choice and blockchain consensus algorithms), Pending: master thesis
  • Academy Studies, Mathematics and Computer Science
    FernUniversität in Hagen
    2020
    Academy Studies, Mathematics and Computer Science

Skill set

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