10/06/2026 updated
100 % available
Senior Java Backend Developer | Spring Boot | SASS/MVP | Fintech & Payments
Wielkopolskie, Poland
Only remote
About me
When a backend slows down or becomes too risky to change, that's where I'm most useful. 9+ years building Java/Spring Boot systems for fintech and enterprise: payments scaled 1 to 200 TPS, legacy platforms modernized. Send me what you're building or where your system is stuck.
Spring SecuritySpring FrameworkMessaging Application Programming InterfaceSystems IntegrationSpring BootBackendSyntactically Awesome Style Sheets (SASS)Backend ProgrammingFintech
Senior Java Backend Developer with 9+ years of experience building and modernizing Java/Spring Boot systems for fintech, banking, insurance and enterprise products where performance and reliability are critical. Former Principal Software Engineer and Technical Team Lead.
CORE SKILLS
- Java, Spring Boot, Spring Framework, Spring Security, Hibernate/JPA
- REST API development and third-party API integration
- Microservices and event-driven architecture (RabbitMQ)
- Fintech and payment systems: payment processing, mobile wallets, banking integrations, ISO 8583
- Legacy system modernization (AS400/COBOL to Java microservices)
- Backend and database performance optimization, SQL tuning
- Production debugging and system stabilization
- AI integration and automation: Spring AI, OpenAI API, RAG, n8n
TOOLS & TECHNOLOGIES
- Databases: PostgreSQL, Microsoft SQL Server, MySQL, Oracle
- Cloud & DevOps: AWS, Docker, CI/CD, Liquibase
- Messaging: RabbitMQ
INDUSTRY EXPERIENCE
Fintech, banking, insurance, payments, digital wallets, e-commerce, enterprise software
NOTABLE RESULTS
- Scaled payment processing from 1 TPS to 200 TPS using Java, Spring Boot and RabbitMQ
- Cut insurance workflow processing from 4–5 hours to 30–40 minutes for 1,000+ records through SQL optimization and event-driven architecture
- Helped modernize a legacy AS400/COBOL platform into Java-based microservices
- Built payment APIs, wallet transaction workflows, banking integrations and ISO 8583-based systems
HOW I WORK
I take ownership from requirements and technical design through development, integration, optimization and production delivery. I work directly with product and business stakeholders, flag technical risks early, and build maintainable backend systems that run reliably in production.
Experience
Professional experience5 - 10 years
Freelancer since2019
Languages
EnglishFluent
Project history
- Led backend development for enterprise insurance systems using Java, Spring Boot, MSSQL, RabbitMQ and REST APIs
- Modernized a legacy AS400/COBOL platform into Java-based microservices, automating insurance workflows
- Cut workflow processing from 4–5 hours to 30–40 minutes for 1,000+ records through SQL optimization and event-driven architecture
- Built REST APIs for migration and automation of business workflows
- Implemented RabbitMQ event-driven communication between distributed services
- Improved database performance with indexing, multiple database connections and Liquibase migrations
- Worked with product and business stakeholders on requirements and delivery
- Mentored junior engineers, ran code reviews and improved team workflows
- Contributed to the AI Interviewer backend using Spring AI
Tech stack: Java, Spring Boot, MSSQL, RabbitMQ, REST APIs, Liquibase, Hibernate/JPA, Spring Security, Docker
- Built backend services for fintech systems, mobile wallets, payment workflows and banking integrations
- Scaled payment processing from 1 TPS to 200 TPS using Java, Spring Boot and RabbitMQ
- Built payment APIs and wallet transaction workflows using Java, Spring Boot and ISO 8583
- Built real-time payment engine workflows with RabbitMQ
- Migrated the SimSim Wallet to a Lumen/microservices-style backend with REST API integrations
- Contributed to the MyABL Wallet backend (Allied Bank Pakistan): PHP/Laravel, Oracle, MasterPass QR support
- Developed enterprise payroll/HRM workflows in PHP/Laravel, reducing errors by 30%
- Led technical delivery, backend quality and team coordination
Tech stack: Java, Spring Boot, PHP/Laravel, Lumen, RabbitMQ, REST APIs, ISO 8583, AWS, MySQL, Oracle
- Built Magento extensions and e-commerce backend customizations using PHP and JavaScript
- Developed REST API integrations with CRM tools (SugarCRM, FreshSales) for order processing and business automation
- Improved order processing workflows through API integrations and data flow optimization
- Developed plugin/module logic for e-commerce systems
- Worked with teams to keep data flowing smoothly between e-commerce platforms and CRM systems
Tech stack: PHP, Symfony, Magento, JavaScript, REST APIs, SugarCRM, FreshSales