01 / Java Backend Developer

Java that ships.
Owned past the merge.

Java backend developer with 3.5 years of commercial experience, building production services at urmate.ai - Java 21, Spring Boot, REST APIs and PostgreSQL. I take features from refinement to production support: Docker images, Jenkins pipelines, Kubernetes on AWS and Google Cloud, Prometheus monitoring and the incidents that follow.

About me

Backend, owned end to end.

I'm a Java backend developer with 3.5 years of commercial experience, based in Łódź and open to remote, hybrid or on-site work. At urmate.ai I build and maintain production services in Java 21 and Spring Boot - REST APIs, distributed services, PostgreSQL with Flyway migrations, Spring Security, Resilience4j and Bucket4j.

I own my changes past the merge: container images, Jenkins CI/CD pipelines, Kubernetes releases on AWS and Google Cloud, Linux/VPS deployments and the production incidents that follow. When an endpoint gets slow I profile the hot path, fix it and verify the fix against Prometheus and Grafana metrics - not against a hunch.

Quality is part of the definition of done, not a phase at the end: JUnit and Mockito unit tests, integration tests against real dependencies, coverage gates, code review and static analysis with Spotless, PMD and Checkstyle. Security gets the same treatment - auth flows, input validation and dependency vulnerabilities are fixed, not postponed.

On the AI side I built a production RAG platform on PostgreSQL and pgvector with hybrid search and RRF fusion (Spring AI, LangChain4j), measurably more accurate than plain vector search. Python for data processing, Claude Code with my own workflow of agents, skills and review prompts, and enough React and React Native to debug a feature across the whole stack. Keep calm and just drink Java.

Currently: Java Backend Developer, urmate.ai
Experience: 3.5 years commercial
Focus: Java 21 · Spring Boot · cloud
Location: Łódź · remote / hybrid / on-site
Studying: CS, Lodz University of Technology
Languages: PL · EN B2+ · DE · ES

From refinement to production support.

What I actually do day to day on a Java backend - not a tool list. Every area below covers design, tests, deployment and what happens after release, because that is where the cost of a bad decision shows up.

Java & Spring Boot

I build and maintain the Java back end: Java 21 with virtual threads, Spring Boot and WebFlux, JSON REST APIs, PostgreSQL with Flyway migrations and Spring Security. Resilience is designed in, not bolted on after the first outage.

REST APIs on Spring Boot and WebFlux, Java 21 with virtual threads
PostgreSQL with Flyway migrations and bound queries only
Spring Security, JWT and role-based access control
Resilience4j retries, circuit breakers, fallbacks and Bucket4j rate limiting

Architecture & distributed services

I design end to end: data model, service boundaries and deployment topology. Highly available REST services following microservice patterns, running on Docker and Kubernetes in AWS and Google Cloud.

Data model, service boundaries and deployment topology
Microservice patterns and distributed, highly available services
Docker and Kubernetes on AWS and Google Cloud
Stable contracts across services and clients

Testing, quality & security

Quality gates belong in the definition of done. Unit and integration tests, coverage thresholds, code review and static analysis on every pull request; vulnerabilities in code and dependencies get triaged and remediated.

JUnit and Mockito unit tests, integration tests on real dependencies
Coverage gates, code review and a pull request workflow
Spotless, PMD, Checkstyle and Husky pre-commit hooks
Auth flows, input validation and dependency vulnerability remediation

CI/CD, monitoring & performance

A feature is done when it runs and stays up. Jenkins pipelines, container images, Kubernetes and Linux/VPS releases with server hardening - then metrics to prove the change did what it promised.

Jenkins CI/CD pipelines, container images and releases
Kubernetes and Linux/VPS deployments with server hardening
Prometheus, Grafana and Micrometer on every change
Profiling slow endpoints and SQL, indexes, caching, hot-path rewrites

AI in production

RAG and AI agents wired into the product and treated like any other production dependency: PostgreSQL and pgvector with hybrid search and RRF fusion, with cost, latency and answer quality kept under control.

Production RAG on PostgreSQL and pgvector, hybrid search with RRF fusion
Spring AI and LangChain4j inside Spring Boot services
Cost, latency and answer quality measured, not assumed
Python for data processing; Claude Code with my own agents and skills

From an internship in Spain to production Java.

10.2024 - presentJava Backend Developer (full-stack)urmate.aiJava 21, Spring Boot, WebFlux and PostgreSQL with Flyway; architecture, tests, security and code quality; Jenkins CI/CD, Kubernetes on AWS and Google Cloud, Prometheus and Grafana. RAG and AI agents in production, React and React Native on the same APIs. Wrocław / remote.
03.2023 - 10.2024Full-Stack Developer (Java)FreelanceShort contracts for several software houses - joined existing teams, picked up their stack and shipped in their sprint, pull request and code review rhythm. Back-end authentication and authorisation for a finance app (Spring Security, JWT, RBAC), Java, React and PostgreSQL projects end to end, releases on Docker and Linux/VPS. Remote.
09.2022 · 04.2024Frontend Developer, internships (incl. Erasmus+)InfmovilwebSchool internships in Corralejo, Spain, in a Spanish- and English-speaking team. React, Next.js, TypeScript and Sass; the SSR I introduced shortened load times and improved SEO.

In numbers

API response time (4.7 s → 1.7 s): −64%
monthly running cost (~1,000 PLN → ~70 PLN): −93%
languages I work in: 4

Technologies I work with.

The stack behind the services I ship - Java and Spring at the core, PostgreSQL, Docker and Kubernetes around it, plus the testing, monitoring and AI tooling that keeps every change verifiable.

Java & Spring: Java 21
Virtual threads
Spring Boot
Spring Framework
Spring Security
Spring WebFlux
Resilience4j
Bucket4j
Maven
Architecture & data: PostgreSQL
SQL
REST
Flyway
pgvector
Testing & quality: JUnit
Mockito
Vitest
Playwright
Spotless
PMD
Checkstyle
Husky
DevOps & cloud: Docker
Kubernetes
Jenkins
AWS
Google Cloud
Linux
Git
GitHub
Reliability & security: Prometheus
Grafana
Micrometer
JWT
RBAC
Python, AI & frontend: Python
Spring AI
LangChain4j
Claude Code
Cursor
React
React Native
TypeScript
Next.js
Node.js

Watch me build.

On @oliwier.markiewicz I publish material about programming and working in IT - Java and Spring Boot, backend engineering, testing, AI in production and the parts of the job that never make it into a job ad. Practical knowledge from real projects, not documentation read out loud.

Java
Spring Boot
Backend
PostgreSQL
DevOps
AI
Testing
Career

Subscribe - @oliwier.markiewicz

youtube.com/@oliwier.markiewicz

Built and shared.

Outside production code I build and maintain CodeLinesJs, a platform for learning programming, publish a free e-book on web design and record on YouTube - plus two competition awards from before all of that.

ProjectCodeLinesJs - a platform for learning programmingcodelinesjs.pl
E-bookPractical tips: what to watch out for when designing a websiteFree e-book
AwardKonkurs Młody InformatykCertification
Award„Pomóż ocalić życie bezbronnemu” - XXI editionCertification

Hiring for a Java backend?

I'm open to Java backend roles and contracts - Spring Boot, distributed services, cloud and everything that keeps them running in production. Based in Łódź, available remote, hybrid or on-site; English B2+, used daily in an international team. Write and I'll get back to you.

oliwier.markiewicz.dev@gmail.com GitHub LinkedIn YouTube

Open to work

Java that ships.Owned past the merge.