Mission-Critical Java Engineer for Financial Transaction and Payment Systems

Budget: $15 - $25/hr

Senior Java Engineer — Core Transaction Systems / Distributed Processing Role Overview

We are seeking a senior Java engineer to build and maintain high-performance, mission-critical backend systems responsible for transaction processing, state management, and data integrity.

This role focuses on deg deterministic execution systems, transactional processing engines, and scalable backend services with strict consistency and audit requirements.

Key Responsibilities Design and implement core backend systems in Java for transaction processing Build and maintain high-performance, stateful processing engines Develop domain-driven models for complex business logic Implement robust data consistency and integrity mechanisms Design and optimize database interactions (PostgreSQL or similar) Build and maintain asynchronous processing systems consuming message queues Implement idempotency, concurrency control, and fault-tolerant processing Develop journaling, logging, and audit frameworks Collaborate with distributed system teams to integrate upstream services Ensure system reliability, scalability, and performance under load Required Qualifications 7+ years of backend development experience with strong Java expertise Experience building high-throughput, low-latency systems Strong understanding of concurrency, multithreading, and synchronization Experience with transactional systems and data integrity patterns Strong experience with relational databases (PostgreSQL preferred) Experience with message-driven architectures (SQS, Kafka, etc.) Solid understanding of object-oriented design and design patterns Experience with Linux-based environments Experience with cloud platforms (AWS preferred) Preferred Qualifications Experience with distributed systems and event-driven architectures Experience with financial transaction systems, ledgers, or accounting systems Experience implementing audit, logging, and traceability frameworks Experience with performance tuning and system optimization Experience with Spring Boot or similar frameworks (optional, not required) Financial services or payment systems experience is a plus What We’re Looking For Strong engineering discipline with focus on correctness and reliability Ability to design deterministic and auditable systems Deep understanding of system behavior under concurrency Ownership mindset with attention to edge cases and failure scenarios