Senior Java Developer

We are looking for an experienced Java developer to join our team and work on a mature high-load backend platform serving web and mobile applications. The project includes a large monolithic Java application with legacy web components and a set of backend APIs used by mobile clients. The main focus of the role is maintaining business-critical functionality while gradually modernizing the architecture and introducing new services. The role also involves participation in new AI-driven initiatives, including backend integrations with modern LLM-based services and internal automation tools. Responsibilities • Develop and maintain backend functionality for web and mobile applications • Work with a large legacy Java codebase and participate in gradual refactoring • Design and implement new REST APIs for mobile clients • Migrate legacy modules to modern Java stack • Integrate AI-powered services into existing products and internal workflows • Build backend services interacting with LLM APIs and AI-based data processing pipelines • Optimize performance of backend services and database interactions • Participate in architectural decisions for modernization of the monolith • Investigate production issues and improve system reliability • Work with cloud infrastructure and distributed caching solutions Tech stack • Java 17 / 21 • Apache Tomcat • Legacy Struts-based monolith • Spring / Spring MVC (migration in progress)  • JavaScript / React  • MySQL / Percona Server • AWS (EC2, EBS, OpenSearch, S3) • Distributed caching (Apache Ignite) • Gradle • REST APIs • AI integrations (LLM APIs, AI-assisted internal tools) • Git Requirements • 5+ years of commercial Java development experience • Strong knowledge of core Java, multithreading, collections, concurrency • Strong understanding of full web application architecture, including Java backend and JavaScript-based frontend • Experience with large legacy systems and refactoring • Strong SQL skills and experience with MySQL or similar relational databases • Experience building and supporting REST APIs • Experience with application performance tuning and troubleshooting • Familiarity with Linux production environments Nice to have • Experience with legacy frameworks (Struts, Servlet API) • Experience migrating monoliths to Spring Boot or microservices • AWS production experience • Experience with distributed cache systems (Ignite, Redis) • Experience supporting mobile backend APIs • CI/CD and infrastructure automation • Experience building AI-assisted product features • Experience with prompt engineering or AI workflow automation What makes this role interesting • Work on a real-world high-scale product used by both web and mobile users • Modernization project: transforming a mature monolith into a more modern architecture • Combination of legacy engineering challenges and new development • Significant influence on technical decisions and architecture evolution Conditions & Benefits: • Competitive salary, depending on experience • Product company – focus deeply on a single product with no outsourcing, clients, or rushed projects • Challenging, stable, and long-term work — building modern, complex Health & Fitness apps for over 17 years • Direct involvement in product growth and development • Flexible schedule with the option to work remotely or from a coworking space • Paid vacation and sick leave • Performance-based bonuses and salary reviews • Strong, experienced team located in Poland and the USA • Top-tier Apple equipment provided (the latest MacBook Pro, monitor, iPhone and other devices) About the company: MyNetDiary is a U.S.-based product company specializing in Health & Fitness apps. Since the very launch of the App Store, our apps have been repeatedly featured by Apple and Google for their quality and innovation. We’ve also been recognized by top publications including Forbes, The Wall Street Journal, Women’s Health, and USA Today. Our mission is to create high-quality, user-focused products built on decades of expertise, leveraging the latest technologies available on modern mobile platforms like iOS and Android. We work in agile, highly skilled teams with zero bureaucracy, dedicated to writing clean, reliable, and minimalistic code. You’ll work with experienced colleagues who communicate effortlessly and take pride in their craft.