I’m Mirek Szajner. I build backends in Java and Spring Boot, and I use AI to build them faster, not to think for me.

I’ve been writing Java professionally for 20 years. I started in 2006 at Asseco Poland, building banking web applications (foreign transfers, phone top-ups) and tooling that sped up deployments across more than 200 application instances. Later I spent eight years at Outcom as a Team Leader: talking to clients, turning requirements into specifications, running a Scrum team and evolving an ERP system.

Long before that I was building things for fun: an AVR clock for a school that has been ticking since 2002, a neural network that recognises handwritten digits, a 3D snooker game in OpenGL, a pump controller for wells. Low-level work taught me to care about how things actually behave, not how they look on a slide.

Since 2009 I’ve run REXOFT, where I deliver software for businesses end to end, and since 2019 I’ve also worked as a senior Java developer at HCM Deck on custom integrations (Apache Kafka, Java). My daily tools are Java, Spring Boot, JPA and PostgreSQL, with React and Next.js when a product needs a face.

I publish the parts I keep rebuilding as open source: beanguard for licensing Java applications, beanquery for safe, whitelist-first querying of JPA entities, and beanboot for the backend plumbing every Spring Boot app needs.

I work with AI every day. It writes boilerplate and tests, reviews code statically and describes changes; I keep the architecture and verify that the result matches how I build software. For mostly solo projects I favour a modular monolith, plus a CLAUDE.md and a ROADMAP.md so the AI stays on course. I read and understand everything I ship, because I’m the one accountable for its quality.