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Java Developer · Lublin, Poland

Jarosław Juś

I build high-performance microservices in Spring Boot, from banking systems to a production ticketing platform.

Four years in banking and fintech, and projects taken end to end: design, code, tests, deployment and monitoring.

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Developer.java

public record Developer() {

  String stack  = "Java 25 · Spring Boot 4";
  String data   = "PostgreSQL · Oracle";
  String infra  = "OpenShift · Docker";
  String tests  = "Spock · Testcontainers";
  String motto  = "pragmatic and readable";
}

4 years

in banking and fintech

microservices in coordinated testing

720+

tests in the ticketing project

~85%

line coverage

01 / About

An engineer with a head for business

I am a backend developer with four years of experience in banking and fintech. I work on Spring Boot microservices deployed cloud-native on OpenShift for a global financial institution.

Outside the banking project, I designed, built and deployed a bus ticketing and fleet management platform on my own. It runs in production and is now being rolled out for a second client.

Before software, I spent eight years creating 3D models for games, which taught me attention to detail and optimization. My background in management makes it easy to bridge business and engineering. I favor solutions that are pragmatic and easy to maintain.

02 / Skills

Technologies I work with

Core

Java 11 / 17 / 21+ Virtual threads Spring Boot 2, 3, 4 Spring MVC WebFlux Spring Data JPA Hibernate Spring Security JWT OAuth2 / OIDC Groovy

Architecture

Microservices REST API Event-driven DDD Design patterns Server-Sent Events ShedLock JGroups

Messaging

Apache Kafka RabbitMQ JMS / ActiveMQ

Data

PostgreSQL Oracle SQL Liquibase Flyway Apache POI

Testing

Spock JUnit 5 Mockito Testcontainers JaCoCo SonarQube / SonarCloud

DevOps

OpenShift Docker / Compose Jenkins GitHub Actions Bitbucket Gradle Maven Nexus Checkmarx Caddy

Monitoring

Prometheus Grafana Loki Alloy Alertmanager Micrometer Splunk

Frontend and tools

Angular PrimeNG Tailwind CSS IntelliJ IDEA Git Jira Confluence Postman Claude Code

03 / Featured project

Bus ticketing and fleet management platform

A production system for a Polish passenger carrier: reservations, ticket packages, online payments, fiscal compliance and an admin panel. Designed and built on my own, now being rolled out for a second client.

gemini.org.pl ↗

Reservations without overselling

Seat tracking at the level of individual stops prevents double sales on partial route segments.

Event-driven payments

PayNow API v3 with webhook validation, asynchronous status checks and refunds.

Fiscal compliance

Novitus fiscal printer via a reactive WebClient with retry and backoff, e-receipts and KSeF e-invoices.

Quality and observability

Over 720 tests, around 85% coverage, a CI quality gate and a full Grafana stack with alerting.

Security

JWT with a refresh token in an HttpOnly cookie, Google OAuth2/OIDC, e-mail verification and password reset.

Web and mobile clients

An Angular app with an admin panel and a Flutter app for iOS and Android, both on the same API.

Java 25 Spring Boot 4 PostgreSQL Flyway Spock Testcontainers Docker Compose GitHub Actions Grafana · Loki · Prometheus Angular Flutter

04 / Experience

Career so far

04.2025 – present

Full-Stack Developer (Freelance)

Bus ticketing and fleet management platform

Architect and developer of a production platform for a Polish passenger carrier: backend, payments, fiscal compliance, infrastructure and client apps.

01.2023 – present

Software Engineer

Sii Polska · banking system for a global financial institution

Optimized an active-passive JGroups cluster and reduced the split-brain problem, protecting the integrity of financial data.
Sped up Excel report exports with JPA projections, batch pagination, database-side aggregation and streamed file generation using Apache POI SXSSF.
Led the migration from Spring Boot 2 to 3, from Java 11 to 17 (now 21), and from Maven to Gradle.
Added real-time notifications with Server-Sent Events.
Coordinated testing of 16 microservices across three teams and prepared the production rollout.

08.2022 – 12.2022

Java Developer (internship)

Sii Polska

A conference management system: two Spring Boot services communicating over RabbitMQ, event registration, e-mail notifications and payment integration (Ingenico, Adyen).

08.2014 – 06.2022

3D Artist

Artists Entertainment / Freelance

Complete 3D models for mobile and PC games: high-poly and low-poly meshes, LODs optimized for the game engine and prepared for animation.

Education: Master's in Management and Marketing, and Engineer's degree in Management, Lublin University of Technology

Languages: Polish (native), English (advanced)

05 / Contact

Let's talk

I am looking for new challenges as a Java developer. Write to me if you have an interesting project or team.

jarek.jus@pm.me GitHub ↗ LinkedIn ↗