Senior Java Integration Developer

Quick Facts

• Role: Senior Java Integration Developer

• Industry: Fintech

• Work mode: Hybrid (3 days in office, rest remote)

• Location: Warsaw

• Start: December 2026

• Engagement: B2B

• Duration: Minimum 6 months, with possible extensions

Description

You will develop enterprise integration layers for payment-related initiatives, combining Java/Spring Boot development with contract-first REST API design and asynchronous messaging. The role connects modern digital solutions with backend and mainframe systems and includes end-to-end technical ownership from API contracts to implementation, deployment, and knowledge transfer.

Responsibilities

• Design and develop REST APIs using Java and Spring Boot

• Use contract-first API development with OpenAPI/Swagger

• Translate API contracts into reliable, production-ready implementations

• Build integration and transport services connecting digital applications with backend and mainframe systems

• Develop integrations using IBM MQ or comparable enterprise messaging technologies

• Implement reliable asynchronous message exchange

• Design data mappings and transformation logic between systems

• Implement validation, error handling, and appropriate failure scenarios

• Support deployment within containerized and PaaS environments

• Support potential migration from a single-cluster to a multi-cluster platform

• Troubleshoot integration and production issues

• Take technical ownership end-to-end (design → implementation → deployment)

• Share technical knowledge, mentor, and train team members

• Prepare clear technical documentation and structured handover materials

Requirements

• Strong hands-on experience with Java and Spring Boot

• Senior-level backend or integration development experience

• Strong experience designing and implementing REST APIs

• Very good knowledge of OpenAPI/Swagger and API contract work

• Practical experience with IBM MQ or comparable enterprise messaging technology

• Good understanding of asynchronous communication and enterprise integration patterns

• Experience with data mapping, validation, and error handling

• Experience deploying applications in containerized or PaaS environments

• Strong troubleshooting and analytical capabilities

• Ability to work independently and take technical ownership

• Willingness and ability to mentor developers and transfer knowledge

• Good English communication skills

Benefits

• Hybrid work model (Warsaw: 3 days in office, remaining time remote)

• B2B engagement starting December 2026

• Minimum 6-month assignment with possible extensions

• Hands-on, end-to-end technical ownership with documentation and knowledge transfer