Senior Java Engineer (WebFlux)

Job Description

Senior Java Engineer (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 worlds 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 are 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