Backend developer (Java & Spring Boot)

Job Description

Join us as a Backend Developer specializing in Java and Spring Boot, where you will play a pivotal role in building and enhancing a modern debt-management and debt-registering platform used by Norwegian social welfare offices and institutional partners. Your day-to-day responsibilities will include developing backend microservices using Java 21, Spring Boot 3.x, WebFlux, and Project Reactor, ensuring the system is high-performing and reactive to process large volumes of sensitive documents efficiently. You will write clean, maintainable, and scalable code, backed by comprehensive unit and integration testing, while collaborating closely with both KOIA engineers and our Norwegian fintech client. The role involves engaging in system modernization and scalability efforts, maintaining a client-focused approach with clear and frequent communication. You will work onsite or hybrid from the Tricity area, participating in core CET business hours and occasionally traveling to Norway or our Polish office for in-person meetings.

Your qualifications

You might be the perfect match if you are/have:  

•  3+ years of experience as a Backend Java Developer

• Strong proficiency in Java 17+ (we use Java 21)

• 2+ years of hands-on experience with Spring Boot 3.x and Spring Core (DI, configuration, application structure)

• Understanding and practical exposure to reactive programming with Spring WebFlux and Project Reactor (Mono/Flux),

• Understanding of backpressure and non-blocking I/O

• Experience working with SQL databases (MariaDB/MySQL/PostgreSQL), R2DBC (reactive database connectivity), schema design, and performance optimization

• Experience building and consuming REST APIs

• Knowledge of microservices architecture and distributed-systems fundamentals

• Experience with Message-Driven Architecture, including:

  • Apache Kafka

  • Event-driven patterns

  • Asynchronous messaging

• Familiarity with Spring Ecosystem

• Familiarity with Gradle and Git workflows and Monorepo/multi-module project management

• Ability to write clean, maintainable code, including unit and integration tests (JUnit 5, TestContainers, WireMock)

• Analytical thinking, attention to detail, and strong problem-solving skills

• Excellent communication skills, clear, concise, and straightforward

• A proactive, accountable mindset, comfortable working in a small, highly skilled team

• Ability to work onsite/hybrid from the Tricity area (required)

• Nice to have (not required, but a strong plus):

  • Redis,

  • Docker,

  • Kubernetes/EKS,

  • AWS (S3, RDS, Lambda),

  • Liquibase,

  • MongoDB,

  • Spring Security/OAuth2,

  • Maintaining Node.js/TypeScript legacy services.

  • Knex.js/Prism

Tech stack you’ll work with

• Backend: Java 21, Spring Boot 3.x, WebFlux, Project Reactor, R2DBC

• Messaging: Kafka

• Databases: MariaDB/MySQL/PostgreSQL, Redis

• Infrastructure: AWS (S3, RDS, Lambda), Docker, Kubernetes (EKS)

• Testing: JUnit 5, TestContainers, WireMock

• Legacy components: Node.js/Express, TypeScript

• Project Management: Jira

• Time Tracking: Toggl

• Version Control: GitHub

You will

• Develop backend microservices using Java 21, Spring Boot 3.x, WebFlux, and Reactor

• Work on high-performance, reactive systems processing large document volumes

• Ensure high code quality by writing unit and integration tests

• Contribute to system modernization and scalability efforts

• Collaborate closely with KOIA engineers and the client’s technical team

• Work from the Tricity area, with the option to use our Gdańsk Wrzeszcz office regularly

• Participate in a hybrid workflow with onsite collaboration when needed

• Maintain a client-focused approach with regular communication

• Work during core CET business hours

• Occasionally travel to Norway or our Polish office for in-person meetings

• Contribute to high-impact, mission-critical fintech solutions

• Maintain a client-focused approach and engage in frequent client communication.

• Pay attention to detail and ensure the quality of development work.

Offer description

KOIA is not just a software development house. We are a crew creating amazing solutions that serve businesses.

A cool mix of people here makes KOIA packed with experience and talent. We are learning from each other and working not only on interesting but also on revolutionizing (even life-changing) sustainable projects every day. We love challenges. If you love them also - then we make a perfect match.

That's what has made our past and current projects successful and incredibly rewarding.

• Decent Salary: in KOIA, we value our talents. We understand that Pizza Days will never replace high respect and reward. So we prefer the last one.20-24 EURO/H + VAT (B2B contract, rate based on programming proficiency)

• Dynamic Work Environment: an invigorating workspace with a mix of Norwegian and Polish innovation focused on smart software solutions.

• Team Culture: Here, we respect maturity, conversations, and intelligent working (which means not overwork but taking care of ourselves along the way). We see the value in effective listening, so your thoughts and ideas matter to us.

• Continuous Learning: We support continued learning and offer learning opportunities as well as access to any tools you might need

• Sustainable Life Concept: It is not only about work. We care about body, mind, and spirit, organize events for meeting together, etc.

• Self-Development Days: We care about your growth. We offer mentorship opportunities.

• Excellent Office Space: Although we are remote-first, our office offers a comfortable and adjustable workspace with plants, bike parking, and a loaded kitchen.

• Fantastic Partners: You'll have the chance to work with innovators in the fintech and climate-tech scenes in the Scandinavian region.

By joining KOIA, you will join a successful team committed to creating meaningful solutions and promoting a healthy and fulfilling work environment.

Hiring Process

At KOIA, we value a clear and efficient recruitment journey. Here’s what to expect:

• Email with Clarifying Questions After submitting your application, you’ll receive an email with a few additional questions to better understand your experience and skills.

• Video Call with HR A 1 hour conversation with our HR team to discuss your background, expectations, and company culture fit.

• Pair Programming Video Call A hands-on coding session with one of our engineers and/or our CTO, where you’ll collaborate on a real-world problem to assess your technical and problem-solving skills. Please note: Due to the Christmas break, all technical interviews will be scheduled from January onward.

• Offer If everything aligns, you’ll receive a job offer and details about the next steps in joining KOIA!

Regardless of the final decision, we will always contact you with feedback and close the process transparently.