Senior Java Engineer

La Fosse Associates Limited; Greater London; Hybrid; GBP 80,000 - 100,000; Full time

Job summary

A recruitment agency in the tech sector is looking for an Integration Engineer for a 6+ month contract based in London. The candidate will focus on designing and building the Middleware layer that connects Shopify with enterprise Back End systems. Key responsibilities include developing custom Shopify app logic, integrating data flows, and collaborating with Back End engineers. Important skills include expertise in Java, REST, and API design. The position pays £400 per day outside IR35.

Qualifications

• Experience with Shopify integrations and middleware design.
• Strong focus on API design and architecture best practices.
• Ability to troubleshoot and optimize integration processes.

Responsibilities

• Develop and maintain custom Shopify app logic and Middleware services.
• Design and implement data flows using REST/GraphQL APIs.
• Collaborate with Back End engineers on integration endpoints.

Skills

Backend Development (Micronaut preferred)

Java

REST

Kafka

API Design & Integration

Unit tests

Tools

Dynatrace

New Relic

Azure Monitor

Job description

We're currently working with our client to seek an Integration Engineer to design and build the Middleware layer connecting Shopify with enterprise Back End systems such as OMS, ERP, and WMS. This role focuses on technical integration and data flow rather than Front End or theme development. You'll work closely with their Back End engineers (primarily Java-based) to ensure robust, scalable, and observable data exchange between Shopify and other platforms.

This is a 6+ month contract position paying £400 per day outside IR35 with 3 days onsite in Paddington, London

Responsibilities

• Develop and maintain custom Shopify app logic and Middleware services for system-to-system integration.
• Design and implement data flows using REST/GraphQL APIs, webhooks, and event-driven patterns (eg Kafka).
• Define and manage data contracts, schema mappings, and transformation logic between Shopify and Back End systems.
• Collaborate with Back End engineers to design integration endpoints, manage authentication, and handle errors.
• Implement observability and monitoring for integration APIs (using tools like Dynatrace, New Relic, or Azure Monitor).
• Troubleshoot and optimise data exchange processes across multiple systems.
• Support testing, validation, and refinement of end-to-end integration flows.

Experience required

• Focus: Architecture, API design, mentoring, delivery - Shopify experience
• Core Skills: Backend Development (Micronaut preferred): Java, Gradle, REST & Kafka scaffolding, Health checks
• API Design & Integration: OpenAPI/AsyncAPI specs, Shopify integration patterns
• Testing & Quality: Unit tests, code coverage, mocking strategie, Contract testing, test data generation
• Architecture & Patterns: Domain-driven design, event-driven architecture, Reusable components (eg, Catalogue Validator)
• Dev Standards & Governance: Linting, formatting, secure coding practices.