Senior Java Engineer

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

Job summary

A leading recruitment agency seeks an Integration Engineer for a 6+ month contract in Greater London. The candidate will design middleware to connect Shopify with backend systems. Key responsibilities include developing integration logic, implementing data flows using REST/GraphQL, and collaborating with backend engineers. Essential skills include backend development, Java, and API design. The position offers £400 per day, with 3 days onsite in Paddington.

Qualifications

• Experience with Shopify integration patterns and architecture design.
• Strong skills in backend development and API design.
• Familiarity with testing standards and governance.

Responsibilities

• Develop and maintain custom Shopify app logic and middleware services.
• Design and implement data flows using REST/GraphQL APIs.
• Collaborate with backend engineers for integration endpoint design.

Skills

Backend Development (Micronaut preferred)

Java

REST

Kafka

API Design

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 backend 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 backend 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 (e.g. Kafka).
• Define and manage data contracts, schema mappings, and transformation logic between Shopify and backend systems.
• Collaborate with backend 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 (e.g., Catalogue Validator)
• Dev Standards & Governance: Linting, formatting, secure coding practices.