Senior Java Developer

Sii Ukraine is a subsidiary of Sii Poland — the leader in IT, engineering, and consultancy services with over 7500 IT experts in Poland and more than 250 prestigious customers. We are looking for ambitious and top-quality professionals to join our project teams.

As a Senior Java Developer, you will join an exciting long‑term project for one of our clients, a leading global provider of technology solutions in the online trading domain. The main focus of the project is the development and enhancement of Price Alerts functionality, enabling users to receive real-time notifications when financial instruments reach predefined price levels.

The role involves working on a high-performance, distributed system that integrates APIs, real-time market data, and frontend applications within a unified platform. Due to the financial and time-sensitive nature of the product, reliability, scalability, and performance are critical.

Responsibilities:

• Design, develop, and maintain backend services and microservices supporting Price Alerts functionality
• Deliver scalable, maintainable solutions following clean architecture principles
• Build secure and reliable APIs to support system functionality and integrations
• Integrate with internal and external services and support asynchronous communication patterns
• Handle data processing, transformation, and integration across multiple sources
• Ensure high performance, reliability, and fault tolerance in a high-load, real-time environment
• Collaborate closely with cross-functional teams including frontend, QA, architects, and stakeholders
• Write and maintain automated and acceptance tests to ensure solution quality
• Participate in code reviews, technical design discussions, and continuous improvement initiatives
• Document solutions and contribute to knowledge sharing within the teamKey Requirements:

Key Requirements:

• 5+ years of experience as a Java Backend / Software Engineer
• Expert-level knowledge of Java 17+ and Spring Boot 3.x
• Hands-on experience with Hexagonal architecture (mandatory)
• Strong expertise in Spring Security, OAuth2, JWT (JWKS)
• Experience with Feign, Resilience4j, and AMQ messaging systems
• Proficiency in XML processing and JAXB marshalling
• Solid testing experience with JUnit 5 and Mockito
• Strong understanding of microservices, distributed systems, and high-availability architectures
• Experience in high-load, real-time environments (finance/trading is a plus)
• Strong analytical, problem-solving, and collaboration skills
• Fluency in English
• Tax residence in Ukraine is required