Senior Java Developer

Quick Facts

• Role: Senior Java Developer

• Focus: Payment terminal integration module for GPOS (online fiscalization, Self-Checkout)

• Work model: Hybrid (occasional office meetings every 2–3 weeks)

Description

You will develop, test, and deploy backend integration solutions for payment terminals in a payment platform supporting the Greek market, including online fiscalization and Self-Checkout processes. The role emphasizes high code quality, engineering best practices, and strict adherence to architectural standards within a hexagonal architecture approach. You will support production rollout and stabilization after go-live.

Responsibilities

• Develop and maintain payment terminal integration modules

• Implement online fiscalization payment processes

• Build backend applications using Java and Spring Boot

• Integrate with external devices and services via REST, TCP Socket, and binary protocols

• Create and evolve unit, integration, and architectural tests

• Prepare deployment packages

• Support deployments and stabilize the solution post-production

• Ensure implementations comply with agreed architectural standards

• Collaborate with developers, testers, and architects

Requirements

• Minimum 5 years of experience as a Java Developer

• Polish language proficiency at least B2 (B2B)

• Excellent knowledge of Java 21+ and modern concurrency features, including Virtual Threads

• Practical experience with Spring Boot 3.x

• Solid knowledge of Hibernate/JPA and REST APIs

• Experience with Gradle, especially multi-module projects

• Knowledge of Git, Docker, and CI/CD

• Experience with hexagonal architecture (Ports & Adapters)

• Knowledge of plugin patterns and layer separation principles

• Practical experience with ArchUnit

• Experience with TCP Socket, REST Client, and binary protocols (TLV or similar)

• Experience with relational databases and JPA

• Willingness to work with SQLite as an embedded database

• Testing skills: unit tests with Mockito, integration tests with @SpringBootTest, and architectural tests with ArchUnit

Benefits

• Opportunity to work on a strategic pricing/payment platform used by a major European retail group

• Impact on architectural decisions and development of modern microservices-based systems

• Knowledge-sharing, mentoring, and growth of technical and business competencies

• Work on projects involving data, process automation, and AI solutions supporting business