Our client's development team is looking for an experienced Kotlin/Java engineer to help evolve and modernize a core application landscape. You’ll work in a cross-functional Agile team situated close to the business, building and maintaining product applications in Java and Kotlin. A major focus for 2026 is the progressive decomposition of a legacy monolith into clear, well-defined domains.
This role combines hands-on engineering, architectural input, pair/mob programming, and coaching of other developers in modern engineering practices.
What you’ll do
- Build new features and adapt existing Kotlin and Java code.
- Refactor legacy components into maintainable, testable modules.
- Write and run unit tests and component tests.
- Deploy new and updated functionalities in a controlled, incremental way.
- Refine functional and non-functional requirements into user stories.
- Propose and evaluate solution options.
- Contribute to domain and architectural design — with a focus on clean, hexagonal patterns.
- Coach teammates in Agile XP practices such as pairing, mobbing, TDD and katas.
- Ensure high code quality, performance and maintainability.
What are we looking for?
- Strong hands-on experience with Java and Kotlin (incl. coroutines, Result4k).
- Solid understanding of object-oriented design, algorithms and technical design diagrams (C4).
- Experience with Spring Boot, hexagonal/clean architecture and domain modelling.
- Production exposure to Java/J2EE ecosystems (Hibernate/ORM, CDI; JBoss is a plus).
- Strong experience with Git and collaborative development workflows.
- Confident with SQL and relational schema understanding.
- Experience with API development (REST, SOAP).
- Experience working with archiving systems and integrations with external platforms (mypension, eBox…).
- Exposure to Angular and Vaadin is a plus.
- Experience with CI/CD pipelines in Jenkins and container-based deployments.
- Experience with monitoring (Prometheus, Grafana).
- Experience with event-driven architectures, AMQ (outbox, deduplication) and event sourcing.
- Familiarity with Selenium or similar test automation tooling.
Engineering practices
- Demonstrated experience coaching teams in Agile and XP.
- Hands-on experience with pair programming, mob programming, and coding katas.
- Advanced TDD mindset and incremental delivery approach.
- Ability to break down complex changes into small, frequent deliverables.
Ways of working
- Able to pair or mob 100% of the time.
- Comfortable reading and understanding complex implementations.
- Skilled in facilitation (retrospectives, reading groups, business workshops).
- Experience using Miro for collaboration.
- Previous experience working in the public sector is required.
What do we offer?
Location: Brussels (Tour du Midi) — hybrid, 2 days/week onsite
Work model: Full-time
Contract: Freelance or Permanent
Start date: 5 January 2026
End date: 31 December 2026 (extendable)
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