Senior Java Developer

About Company:
Piano’s Digital Revenue Optimization solution helps digital services grow revenue by better
understanding and influencing their customers’ behavior. Piano unifies analytics, segmentation, and
commercial personalization in one AI-driven application, enabling sites and apps to efficiently
maximize the value of every user visit. Headquartered in Amsterdam with offices in the Americas,
Europe, and Asia-Pacific, Piano serves a global client base including the BBC, Deutsche Telekom,
Nikkei, AXA and the Wall Street Journal. For more information, visit piano.io.

About the project:
You’ll join a team working on a high-complexity system in the billing & subscription management
domain. The platform uses a hybrid architecture (monolith + selected microservices) and a hybrid
technology stack, requiring strong engineering judgment around consistency, correctness, reliability,
and scalability.
 Critical domain: billing cycles, and subscription lifecycles across multiple payment providers.
Precision and data integrity are non-negotiable.
 Distributed architecture: event-driven patterns (Kafka), Outbox patterns, and distributed
coordination (Redis/Redisson distributed locks).
 Hybrid ecosystem: mix of Spring Boot + Jersey + Guice, split between Java 21 and Kotlin
2.0.
 Scale & resilience: resilience patterns (Resilience4j), observability (Datadog/OpenTelemetry),
and scheduling (Quartz).

What you’ll do:
 Collaborate with technical leaders and architects to efficiently deliver new functionalities in a
complex domain.
 Plan, design, and implement new features with a strong focus on reliability, consistency, and
maintainability.
 Solve production problems before they affect customer experience (root-cause analysis,
mitigation, and long-term fixes).
 Contribute to engineering: testing strategy, performance, observability, and operational
readiness.

Expected qualifications:
 5+ years of experience as a Java Developer (enterprise systems preferred).
 Strong proficiency in Java (up to v21) and plus would be a solid experience with Kotlin.
 Experience with Spring Boot (2.7+) / Spring Framework.
 Good level of understanding of SQL (MySQL 8) and ORM (Hibernate), including: transaction
isolation and locking strategies; performance tuning
 Hands-on distributed systems experience: Kafka (event design, consumer reliability,
exactly/at-least-once thinking); Redis / Redisson (distributed locks, concurrency handling);
designing for eventual consistency, idempotency, and failure scenarios
 Strong automated testing culture: JUnit 5, Mockito, Testcontainers
 Polish, English (B2)

Nice to have:
 Cloud/infra: Basic understanding of AWS, Docker/Docker Compose.
 Observability: Datadog, OpenTelemetry, distributed tracing/metrics-first mindset.
 Payments: experience integrating Stripe
 Computer Science degree
 Selenium experience

Current Tech stack:
 Languages: Java 21, Kotlin2.0
 Frameworks: Spring Boot, Guice, Jersey (JAX-RS)
 Data: MySQL 8.0, Redis (Redisson), Hibernate 5.6, DynamoDB
 Messaging: Apache Kafka
 Resilience / Scheduling: Resilience4j
 Observability: Datadog, OpenTelemetry
 Build: Gradle (KotlinDSL)
 Infrastructure: Docker, AWS, Kubernetes