Senior Java Developer

NTIATIVE IT Recruitment; Warszawa; On-site; PLN 240,000 - 320,000; Full time

Job summary

NTIATIVE IT Recruitment is seeking an experienced backend engineer to design and implement features in a high-scale billing platform. You will work in a hybrid environment on Monolith + Microservices, ensuring data integrity and reliability for a global client base.

Required are 5+ years of Java backend experience, Spring Boot expertise, and hands-on work with Kafka, Redis, MySQL 8, Hibernate. Strong testing with JUnit 5, Mockito, and Testcontainers is essential, plus Polish and English (B2+).

Qualifications

• 5+ years of backend experience in Java.
• Experience with Spring Boot in a production environment.
• Solid knowledge of relational databases (MySQL 8) and ORM (Hibernate).
• Hands-on distributed systems experience with Kafka and Redis/Redisson.
• Strong automated testing mindset with JUnit 5, Mockito, and Testcontainers.
• Polish language skills and English proficiency (B2+).

Responsibilities

• Design and implement new features within a complex, high-precision billing domain.
• Solve distributed performance and reliability challenges before they hit production.
• Maintain top engineering standards through clean code, testing, and observability.

Skills

Java backend

Spring Boot

Kafka

Redis

JUnit 5

Mockito

Testcontainers

Polish language

English (B2+)

Tools

MySQL 8

Hibernate

Job description

Join the team building a mission-critical billing system for global industry leaders like The Wall Street Journal, BBC, and AXA. We develop a high-scale hybrid platform (Monolith + Microservices) that manages subscription lifecycles and payment processing with zero compromise on data integrity.

What you'll do:

• Design and implement new features within a complex, high-precision billing domain.
• Solve distributed performance and reliability challenges before they hit production.
• Maintain top engineering standards through clean code, testing, and observability.

What we're looking for:

• 5+ years of backend experience with Java (up to v21); experience with Kotlin 2.0 is a strong plus.
• Solid knowledge of Spring Boot and relational databases (MySQL 8, Hibernate)—including transactions, locking, and performance tuning.
• Hands-on distributed systems expertise: Apache Kafka (event-driven architecture) and Redis / Redisson (distributed locks, eventual consistency, idempotency).
• Strong automated testing mindset with JUnit 5, Mockito, and Testcontainers.
• Polish language skills and English proficiency (B2+).

Nice to have:

• Hands-on experience with Observability (Datadog, OpenTelemetry) and Resilience4j.
• Basic AWS/Docker knowledge and experience integrating payment gateways (e.g., Stripe).

Ready to build systems that operate at a global scale?