Senior Java Engineer – Reactive (Spring WebFlux)
London – Hybrid (1 day per week onsite)
Are you a senior, hands-on Engineer who thrives in event-driven, asynchronous environments? Do you enjoy building low-latency, high-throughput distributed systems where correctness, resilience, and performance really matter?
This is an opportunity to work at the core of real-time payments infrastructure, helping to power instant transactions for some of the world’s largest banks.
We’re hiring on behalf of a leading payments consultancy delivering mission-critical, event-driven platforms that integrate deeply with bank infrastructure to enable secure, real-time payments at global scale.
What You’ll Be Doing
You’ll play a senior individual-contributor role within a high-performing engineering team, building asynchronous, message-driven systems designed for scale, resilience, and near-zero downtime.
* Design and implement high-throughput, low-latency systems processing millions of real-time payment events
* Build event-driven architectures using modern Java and reactive frameworks
* Work extensively with non-blocking I/O, asynchronous flows, back-pressure, and concurrency
* Contribute to system and API design, focusing on scalability, fault tolerance, and observability
* Collaborate closely with architects, engineers, and client teams across Europe
* Operate in Agile environments (Scrum / Kanban) with a strong engineering culture
Tech Stack (current & evolving):
Java 17+, Spring WebFlux, Akka, Kafka, reactive streams, distributed messaging, cloud-native tooling
What You Bring
We’re looking for engineers who enjoy thinking in events, streams, and asynchronous workflows, and who take pride in building systems that perform under pressure.
* Strong hands-on experience with Java 11+ (ideally Java 17) in production environments
* Deep understanding of asynchronous and reactive programming models
* Proven experience with event-driven architectures and real-time messaging (Kafka, JMS, Akka, etc.)
* Solid grasp of distributed systems concepts: concurrency, idempotency, fault tolerance, and resilience
* Experience building and testing production-grade systems using TDD/BDD and CI/CD pipelines
* Comfortable working on complex, long-lived systems where performance and reliability are critical
Bonus (not essential):
Experience in banking, payments, or financial systems, or if you’ve built real-time platforms at scale.
What’s In It for You
* £100,000 – £115,000 base salary (DOE)
* 20% annual bonus
* Work on event-driven, real-time systems with global impact
* Hybrid working – 1 day a week onsite (more if you prefer)
* Exposure to major international banks and payment networks
* A product-led, engineering-first environment where technical decisions matter