10/15/2026 updated
100 % available
Senior Java / Spring Boot Engineer – Banking & Payments (ISO 20022, PostgreSQL) – 100% remote
Kraków, Poland
Only remote
M.Sc. Applied Computer Science, AGH University of Science and Technology, KrakowAbout me
Senior Java/JVM engineer since 2008, mostly banking and funds (UBS, State Street, Rabobank). Lately led NatWest and Lloyds payment integrations (ISO 20022, OAuth2, mTLS, reconciliation). Looking for remote Java/Spring Boot projects in banking, payments or fintech. Available now, B2B, CET.
OAuth 2.0GitHub ActionsJava (Programming Language)Amazon Web ServicesBankingBanking SoftwarePayment SystemsGradleSpring FrameworkJUnitPostgreSQLApache MavenMongoDBMySQLPayment Gateway
Java/JVM Backend Development
Java backend development since 2008, mostly in banking and investment-fund systems. Spring, Spring Boot, Hibernate and microservice architecture.
Payment Systems & ISO 20022 Integration
Lead engineer on direct payment integrations with NatWest and Lloyds: ISO 20022 (pain.001/pain.002), OAuth2 with JWT-signed client auth, mTLS,
webhook certificate validation, idempotent submission with deduplication, automated reconciliation, SEPA cross-border payments. Familiar with PSD2
/ open banking.
Quality Assurance & Mutation Testing
Mutation testing (PIT) held at 100% on payment-critical paths, WireMock integration suites against bank API contracts, detailed code reviews and
documentation.
Database Technologies
PostgreSQL (primary OLTP and pgvector), Oracle, MySQL, MongoDB, DynamoDB, Redis, SQL.
Cloud & DevOps
AWS, Azure / Azure DevOps, Docker, Jenkins, CircleCI, GitHub Actions, git. Kubernetes: tooling familiarity.
Performance Optimization
JVM profiling with JProfiler and YourKit, caching with Ehcache and Redis: response times down, user experience up 30% (Rabobank).
AI-Assisted Development
Claude Code / Codex agent workflows with review gates in daily implementation and test work.
Banking Facade & Audit Architecture
Co-designed a banking-facade service with sole custody of bank credentials, webhook subscriptions and an append-only audit log for all bank-facing
calls. Extracted a reusable Spring Boot payment-providers client library shared across services.
TDD & Software Craftsmanship
Test-driven development, code-review discipline, documentation for onboarding and long-term maintainability.
Experience
Professional experience10+ years
Freelancer since2025
Languages
EnglishFluentPolishNative speaker
Project history
Lead engineer on direct integrations with NatWest and Lloyds commercial payment APIs: ISO 20022 pain.001 submission and pain.002 status webhooks, OAuth2 with JWT-signed client auth, mTLS transport, webhook client-certificate validation, idempotent submission with deduplication, automated reconciliation, and SEPA cross-border payments. Co-designed an internal banking-facade service with an append-only audit log. Designed a PostgreSQL-backed matching pipeline (pgvector) for automated bank-statement reconciliation. Embedded Claude Code agent workflows with review gates into daily implementation and test work.
Led design and development of scalable Java applications on Spring and microservice architecture. Conducted performance profiling, tuning, and caching with Ehcache and Redis, improving response times and user experience by 30%. Maintained high code quality through detailed code reviews and comprehensive documentation. Stack: Java, Python, Spring, Spring Boot, MongoDB, PostgreSQL, Azure DevOps.
Developed backend features for NAV-calculation dashboards with accurate real-time reporting. Mentored junior developers. Performed JProfiler/YourKit performance analysis and technical-debt reduction. Stack: Java, SQL, Spring, Spring Boot, Hibernate, Jenkins, Maven, Gradle, Docker.
Certificates
Oracle Certified Professional Java SE 8 Programmer
Oracle2017
Oracle Certified Professional Java SE 8 Programmer
Oracle2016
Oracle Database SQL Certified Expert
Oracle2016