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