Senior Backend Engineer | Java, Spring Boot | Scalable & AI-Integrated Systems I am a Senior Backend Engineer with experience building secure, scalable, and production-grade backend systems across financial and AI-driven platforms. In my full-time role, currently I work on real-world financial systems where accuracy, validation logic, performance, and reliability are critical. My responsibilities include complex business rule implementation, currency and IBAN validation, stored procedure optimization, secure integrations, and microservices-based architecture using Java and Spring Boot. In parallel, I have delivered two complete freelance backend projects end-to-end: 🛒 Multi-Vendor Marketplace Platform Architected and implemented a full backend system supporting authentication (OTP-based), role-based access (buyer/seller/admin), vendor approval workflows, product lifecycle management, order processing, reporting dashboards, and structured API documentation. 🧬 AI-Powered Biomarker Analysis Platform Built an AI-driven backend using FastAPI, LangChain, and OpenAI (GPT-4) to analyze biomarker data and generate structured 90-day health plans. The system includes PDF lab report parsing, structured prompt orchestration, JSON validation with retry handling, and consistent multi-batch plan generation. Core Expertise REST API Design & Clean Architecture Microservices (Spring Boot) Complex Validation & Business Logic Database Design & Optimization (PostgreSQL, SQL Server) Stored Procedures & Performance Tuning Secure Authentication & Authorization Docker, Kubernetes, CI/CD & Azure I focus on building production-ready systems — not prototypes — with clean architecture, strong validation, and long-term maintainability. If you need a backend engineer who understands both scalable systems and AI integrations, I’m ready to help.

I’m a Top-Rated (5⭐️) Full Stack Engineer with over 4+ years of experience delivering high-quality backend systems, APIs, and full-stack web applications. I specialize in Java/Kotlin with Spring Boot on the backend and Vue/Nuxt on the frontend, supported by modern DevOps and cloud-native practices. I help teams build reliable, scalable, and maintainable software systems, whether it's creating new applications from scratch or improving and refactoring existing codebases for better performance and maintainability. 🔧 My Expertise Covers 🔹 Building RESTful APIs and microservices using Spring Boot (Java/Kotlin) 🔹 Real-time web applications using WebSocket (e.g., chat, live updates) 🔹 Implementing secure authentication & SSO with OAuth 2.0 and OpenID Connect 🔹 Full-stack development with Vue.js, Nuxt.js, Tailwind CSS, and Bootstrap 🔹 Working with relational (PostgreSQL, MySQL), in-memory (Redis), and graph (Neo4j) databases 🔹 Automating CI/CD workflows using GitHub Actions and Docker 🔹 Provisioning and deploying to GCP services (Cloud Run, Cloud SQL, GCS, Cloud Tasks, Cloud Scheduler, Load Balancer) 🔹 Deploying and managing applications on Linux VPS (Ubuntu) 🚀 What I Bring 🔹 Clean, modular, and well-documented codebases 🔹 End-to-end ownership from architecture to deployment 🔹 Real-time, scalable solutions tailored to your product needs 🔹 Proactive communication and on-time delivery 🔹 Strategic insight to improve features, reliability, and scalability Whether you need a full-stack developer to take your product from idea to launch, or a backend specialist to build real-time APIs and services, I’m ready to contribute to your success. Let’s build something exceptional.

Hello and welcome to my profile! My name is Vadym. I'm a skilled Java and Python developer from 🇺🇦 My expertise is Backend development. But also I have experience with Angular 2+. I continue to improve my skills and already know that the best way to learn something new and evolve as a professional is to work on the projects as a part of a team. My main areas of expertise: Backend: Python, Java Frontend: HTML/CSS –basic, Angular 2+ Frameworks: FastAPI, Spring Framework (SpringMVC, Spring Boot, Spring Data, Spring Security) ORM: Hibernate Testing: pytest, FastAPI TestClient, JUnit, JMeter VCS: Git (GitHub) Databases: PostgreSQL, MySQL, MongoDB, SQLite, MS SQL Server, Supabase Build automation tools: Maven, Gradle API documentation tools: OpenAPI, Swagger IDE: Cursor, PyCharm, IntelliJ IDEA Other: REST API, Lombok, Docker, Postman, Pydantic, Heroku, Stripe, Amazon APIs (general familiarity) Ready for any skills evaluation, test task, technical interview. My main goal is to find an interesting project, so if you need a talented developer with technical background let's discuss our cooperation!

I build payment systems and backend infrastructure that handle serious scale. At Paytm (300M+ users), I designed the UPI Mandate Platform from scratch - coordinating directly with NPCI and integrating 4 major banks. At Ola Financial Services, I built EMI and wallet systems processing 100,000 EMIs per month at 14,000 requests per minute. 5+ years in production Java systems. Fintech, payments, microservices, and AI agents. Most clients come to me when: - They need payment infrastructure built properly - UPI, mandates, bank settlements, or gateway integrations - Their Java backend is hitting performance limits at scale - They need an AI agent built on real LLM infrastructure - not a chatbot wrapper - They need full-stack backend engineering: Spring Boot, Laravel, Python, AWS, DevOps - They need someone who has shipped at enterprise scale, not just side projects WHAT I HAVE BUILT IN PRODUCTION UPI Mandate Platform - Paytm (300M+ users): Designed from scratch. Coordinated directly with NPCI. Integrated SBI, HDFC, Axis, and Yes Bank. Built complete mandate lifecycle APIs. Integrated Mindgate, Juspay, and built TSP for Yes Bank settlement. EMI and Wallet Platform - Ola Financial: 14,000 requests per minute. 100,000 EMIs per month. Architecture reused by Ola Electric. Migrated 200,000+ users from Mastercard to RuPay with zero downtime. FinOps AI Agent (Production): LangChain, Claude API, RAG on compliance docs. Reduced incident resolution from 45 minutes to 8 minutes. 60% reduction in manual ops. Multi-model orchestration: Claude Opus and GPT. Runs in production. B2B Trading Platform (Saudi Arabia ZATCA Compliance): Government integration, cryptographic stamping at full scale, fault-tolerant CRON job management. WHAT I BUILD Payment Systems and Fintech - UPI mandates, payment gateway integration, bank settlement, multi-bank API orchestration - EMI systems, wallet platforms, recurring payments with NPCI and RBI compliance - High-throughput Java backends: 14K+ req/min, built for millions of users Java and Spring Boot Backend - Spring Boot microservices with Kafka event-driven architecture - Redis, MySQL, PostgreSQL at scale. AWS: EC2, ECS, S3, Lambda, RDS - REST APIs, Spring Security, OAuth2, JWT, full observability: Grafana, Prometheus AI Agent Development - LangChain and LangGraph multi-agent systems, RAG pipelines - Claude API and OpenAI API integration, tool-use agents, human-in-the-loop - pgvector and Pinecone vector databases Laravel, PHP and Python Backend - Laravel REST APIs, microservices, third-party integrations - Python for AI pipelines, automation, and backend scripting DevOps and Cloud - Full AWS stack, Docker, Kubernetes, GitHub Actions, GitLab CI/CD - Zero-downtime deployments, staging-to-production pipelines PROOF POINTS 14K req/min throughput - 300M+ user platform - 200K zero-downtime migration - 4 banks integrated - 45min to 8min AI resolution - Patent filed - Springer published researcher TECH STACK Backend: Java 17, Spring Boot, Laravel, PHP, Python, Dropwizard, Hibernate Databases: MySQL, PostgreSQL, MongoDB, DynamoDB, Redis Messaging: Apache Kafka, AWS SQS Cloud: AWS (EC2, ECS, S3, Lambda, RDS), Docker, Kubernetes AI/LLM: LangChain, LangGraph, Claude API, OpenAI API, RAG, pgvector, Pinecone Observability: Grafana, Prometheus, OpenTelemetry Available 30+ hours per week. Send me your requirements - I respond within hours. - Raj Keywords: Java Spring Boot Developer, Java Developer, Spring Boot Microservices, Payment Gateway Integration, Fintech Developer, UPI Payment Integration, NPCI API Integration, Microservices Architecture, Apache Kafka Developer, High Throughput Backend, LangChain Developer, AI Agent Developer, RAG Development, LLM Integration, Claude API Integration, OpenAI Integration, Multi-Agent Orchestration, Laravel Developer, PHP Developer, REST API Development, AWS Developer, DevOps Engineer, Docker Kubernetes, CI/CD Pipeline, Redis Caching, MySQL Optimization, PostgreSQL Developer, Java Backend Developer, Payment Processing API, Bank API Integration, Event-Driven Architecture, Spring Security, Python Developer

✅ JAVA ✅ Spring ✅ Thymeleaf ✅ Rest API I am a solutions provider, share with me your requirements and I will give you a complete solution, front-end to back-end. I'll take care of the whole building process. You just sit, drink a beer and enjoy your app I have experience working as a developer, team leader, and project manager. As a developer I make modular, clean, object-oriented and well-commented code, always aiming quality and intelligence in the solutions. My solutions are complete, front-end to back-end. I have experience with: java, swing, J2EE mobile development (android - java native) spring boot, spring MVC, spring roo,spring-security, spring data, thymeleaf ... HTML, CSS,javascript,angular SQL databases like MySQL, PGSQL, SQL server and ORACLE NoSQL databases like MongoDB, Cassandra JPA, hibernate elasticsearch, kibana, Redis maven, Gradle, GIT, Jira, Jenkins, docker, kubernetes 🌟 WHY CHOOSE ME OVER OTHER FREELANCERS? 🌟 ✅ Client Reviews: I focus on providing VALUE to all of my Clients and Earning their TRUST. The Client Reviews and Feedback on my Profile are immensely important to me and the value that I provide. ✅ Over-Delivering: This is core to my work as a Freelancer. My focus is on GIVING more than what I expect to RECEIVE. I take pride in leaving all of my Clients saying "WOW" ✅ Responsiveness: Being extremely responsive and keeping all lines of communication readily open with my Clients. ✅ Resilience: Reach out to any of my Current of Former Clients and ask them about my Resilience. Any issue that my Clients face, I attack them and find a SOLUTION. ✅ Kindness: One of the biggest aspects of my life that I implement in every facet of my life. Treating everyone with respect, understanding all situations, and genuinely wanting to IMPROVE my Client's situations. I am eager to work with you, to provide reliable, consistent, and High-Level solutions to design/development challenges. Please contact me, so we can discuss how we can work together to FULLY meet your Business Needs!

💼 8+ Years Building Production-Grade Java Backends for Enterprise & Startups 🤝 Worked with Macy's · Backcountry · Agrobank · Dubai Islamic Bank 🛠️ Spring Boot · Microservices · AWS · PostgreSQL · Docker · React · Full-Stack When It Counts I'm a Senior Java Backend Engineer specializing in building secure, scalable, production-grade systems using Java, Spring Boot, and microservices architecture for enterprise eCommerce, digital banking, and government platforms across the US and UAE. I've built systems serving millions of users at Macy's, delivered nationally regulated banking infrastructure at Agrobank. Every system designed with security, scalability, and long-term maintainability at the core. When the project demands it, I extend into the full stack with React, Next.js, and TypeScript delivering end-to-end without losing the backend focus. 𝐓𝐞𝐜𝐡𝐧𝐢𝐜𝐚𝐥 𝐄𝐱𝐩𝐞𝐫𝐭𝐢𝐬𝐞 Backend (Core): Java · Spring Boot · Spring Security · Spring Cloud · Spring Data JPA · Hibernate · Microservices · REST API · GraphQL · OAuth2 · JWT · Apache Kafka · RabbitMQ · Maven · Gradle · Lombok · Liquibase · Flyway Frontend: React.js · Next.js · TypeScript · JavaScript · Redux · Zustand · React Query · Axios · Tailwind CSS · Material UI · Node.js · Vite Databases: PostgreSQL · MySQL · MongoDB · Redis · Firebase Cloud & DevOps: AWS (EC2, S3, SNS) · Azure · Docker · Kubernetes · CI/CD · GitHub Actions Testing & Docs: JUnit · Jest · Postman · Swagger 𝐖𝐡𝐚𝐭 𝐈'𝐯𝐞 𝐃𝐞𝐥𝐢𝐯𝐞𝐫𝐞𝐝 𝗠𝗮𝗰𝘆'𝘀 | eCommerce Platform Built Java Spring Boot microservices for catalog, promotions, and cart operations serving tens of millions of shoppers annually. Optimized performance through Redis caching and CDN integration, reducing response times across high-traffic retail events including Black Friday. 𝗕𝗮𝗰𝗸𝗰𝗼𝘂𝗻𝘁𝗿𝘆 | Online Retail Platform Developed Java backend services for product catalog, inventory management, and order processing at scale. Implemented Redis caching and CDN integration that cut API response times during peak retail traffic. 𝗔𝗴𝗿𝗼𝗯𝗮𝗻𝗸| Digital Banking Platform Architected the backend microservices layer for a nationally regulated digital banking platform using Java, Spring Boot, and PostgreSQL covering account management, transactions, and financial reporting under strict compliance requirements. 𝗗𝘂𝗯𝗮𝗶 𝗜𝘀𝗹𝗮𝗺𝗶𝗰 𝗕𝗮𝗻𝗸 | Investor Relations Portal Built secure Java Spring Boot backend APIs for one of the world's largest Islamic banks. Delivered financial reporting endpoints with compliance-grade data security for institutional stakeholders. 𝐇𝐨𝐰 𝐈 𝐖𝐨𝐫𝐤 🔹 Architecture designed before a single line of code is written 🔹 Clean, maintainable Java with documentation built in 🔹 Security and scalability from day one, not retrofitted later 🔹 Full ownership from architecture through deployment 🔹 Proactive updates and clear communication throughout I work with modern development tooling and productivity practices to maintain high output and code quality, with rigorous human review and production standards applied to every deliverable, no exceptions. 🚀 𝐋𝐞𝐭'𝐬 𝐓𝐚𝐥𝐤 𝐀𝐛𝐨𝐮𝐭 𝐘𝐨𝐮𝐫 𝐏𝐫𝐨𝐣𝐞𝐜𝐭: Whether you're building a Java backend from scratch, scaling a system that's hitting its limits, or need a full-stack engineer who leads with architecture, I'm here to make it production-ready. Send me a message and let's get started.

I bring over 10 years of full-stack development experience in the Java-Spring-Web ecosystem and Node.js. My expertise extends to front-end development, where I utilize React, Angular and Flutter frameworks. With a strong background in Java and NodeJS, I have contributed to various projects in fintech, telecommunications, insurance, and e-learning industries. I’m passionate about system design and clean, maintainable architecture, and I enjoy working in agile teams where collaboration is important. I focus on building reliable and scalable solutions that deliver real value. I’m also always learning and exploring new technologies, especially in areas like AI, distributed systems, and modern backend development, and I try to apply them in practical ways to improve systems. I consistently adhere to SOLID principles in my work. Software patterns play a crucial role in my approach, as they effectively address various challenges in object-oriented design. I am confident that my skills align well with your business needs. If given the opportunity, I am certain that I can deliver successful projects and supports. Backend : ✔ Java/Android ✔ Maven/Gradle ✔ Spring - Spring Cloud - Spring Boot - Spring MVC ✔ Rest APIs ✔ Hibernate ✔ Docker ✔ Git - Github - Gitlab - Bitcbucket ✔ Junit - Mockito ✔ Elastic Search ✔ Node.js ✔ Express.js Frontend Skills : ✔ Javascript ✔ React - Redux ✔ Angular Mobile : ✔ Flutter - Dart ✔ Firebase/Firestore Business Flow: ✔Jira - Confluence - Miro Databases : ✔ Mysql - Mongo - Oracle - IBM DB2 - PostgreSql I also use Copilot and Claude Code to deliver the best solutions. ✔ LLM integrations (OpenAI, Claude, etc.) ✔ AI-assisted workflow automation ✔ Prompt engineering & optimization ✔ AI code acceleration using tools like Cursor

Java sits at the center of the platforms I build. Spring Boot runs the backend services and APIs, handling business logic, data access, and the core behavior of the system. Many of these platforms pair a Spring Boot backend with Angular on the frontend, forming structured web applications such as internal dashboards, operational platforms, and SaaS systems used by teams every day. Angular provides the application interface while the Java backend manages services, data, and integrations behind the scenes. Python also comes into play when automation or data workflows are needed. Small services and scripts written in Python handle background tasks, integrations, and operational processes that support the main platform. Java and Spring Boot handle the backend services, Angular runs the platform interface, and Python supports automation and background tasks.

I’m a Senior Software Engineer with over 4 years of experience delivering secure, scalable, and high-performance software solutions for startups, SMEs, and enterprises across industries such as e-commerce, fintech, blockchain, edtech, and food & beverage. My core focus is on backend development, API engineering, cloud-native applications, workflow automation, and AI-powered solutions, but I also bring full-stack expertise to deliver complete, production-ready systems. I hold a Bachelor’s degree in Computer Science and specialize in building robust, maintainable, and efficient backend architectures using Java, Spring Boot, Node.js, and TypeScript, integrated with high-performance databases like PostgreSQL, MySQL, MongoDB, and Redis. I’m highly skilled in RESTful API development, microservices architecture, asynchronous processing, and secure authentication (JWT, OAuth2, SSO). Core Technical Skills: Backend Development: Java, Spring Boot, Spring MVC, Jakarta EE, JavaFX, Node.js, Express.js, Python, Golang Frontend Development: React, Angular, Next.js, Thymeleaf, JSP/JSTL, Bootstrap, HTML5, CSS3, JavaScript, jQuery Databases: MySQL, PostgreSQL, MongoDB, Redis (NoSQL & SQL database design, query optimization, indexing, caching) Cloud & DevOps: AWS (EC2, S3, RDS, Lambda), Google Cloud Platform (GCP), Microsoft Azure, Docker, Kubernetes, CI/CD pipelines Messaging & Integration: RabbitMQ, Kafka, WebSockets, API Gateway integrations, GraphQL Automation & AI: n8n, Make (Integromat), Apify, PhantomBuster, OpenAI API, AI model integration, workflow orchestration Version Control & Collaboration: Git, GitHub, GitLab, Bitbucket, Agile/Scrum methodologies Achievements & Project Highlights: ✔ Built an e-commerce platform capable of handling 500+ daily transactions, reducing load times by 30% and lowering infrastructure costs by 15% through database optimization and caching strategies. ✔ Led a cloud migration project from legacy infrastructure to AWS, reducing operational costs by 25% while improving scalability and uptime. ✔ Developed an AI-powered study assistant for neurodivergent students, winning the AI for Social Good hackathon and improving engagement and retention rates. ✔ Created a data automation pipeline that processed and scored 1,300+ startup applications for Pitch2Win, enabling quick finalist selection and improving investor matching efficiency. ✔ Engineered a grant-winning platform for Babcock University’s community health project, helping secure $80K in funding. What I Bring to Your Project: ✔ Expert in API-first development, secure authentication, and microservices architecture ✔ Strong track record with data enrichment, web scraping, and workflow automation tools like n8n and Apify ✔ Proven ability to design cloud-native, fault-tolerant, and cost-optimized applications ✔ Deep experience in AI integration for lead generation, data analysis, and personalized user experiences ✔ Commitment to clear communication, on-time delivery, and scalable, future-proof code If you’re looking for a results-driven software engineer who can handle everything from custom backend architecture to AI-driven automation systems, I’d love to collaborate. Let’s discuss how I can turn your requirements into a solution that’s efficient, secure, and built for growth.

📣 Hello, and welcome! I'm a Senior Software developer with 6 years of commercial experience in Java, Springboot, React, Next.js, React Native, Node.js, Nest.js, and Express.js. I'm oriented on results, motivated, and responsible developer with good analytical skills and attention to detail. I'm well-versed in software development, data structures, algorithms, and object-oriented design principles. I'm skilled in utilizing various tools and technologies. Quick learner. Also, I am an active team player who wants to deliver high-quality work and continue expanding my knowledge and skills in software development. I would be happy to work with E-commerce, Fintech, HealthTech, Blockchain, EdTech, PropTech, CRM, TravelTech, InsurTech, LogistecsTech, and Gambling projects. 📌WHAT I'M OFFER: 💻WEB DEVELOPMENT I'm delivering high-performance, responsive web applications. I specialize in building modern front-end interfaces using React.js and Next.js while handling robust backend systems with Node.js, Express.js, and Nest.js. Full-stack capabilities allow me to craft seamless, end-to-end solutions, from user interfaces to database management. 💻 API DEVELOPMENT & INTEGRATION Design and develop custom RESTful APIs and GraphQL endpoints to connect applications. I integrate third-party services like Stripe, Twilio, Google Maps API, and more, ensuring seamless communication between platforms. I also implement secure authentication and authorization systems using JWT, OAuth, or custom protocols. 💻 ENTERPRISE SOLUTIONS (JAVA) I'm building scalable enterprise applications with Spring Boot or lightweight FastAPI solutions for startups. Develop and deploy microservices architectures, automate workflows, and integrate powerful tools like Kafka and RabbitMQ for real-time processing. 💻 REAL-TIME & eCommerce SOLUTIONS I'm developing real-time applications such as chat apps, live notifications, and streaming platforms using WebSockets. Build custom eCommerce platforms with payment integrations like Stripe, PayPal, and others, providing features like cart management, inventory tracking, and order processing. 💻 CLOUD & DevOps I'm deploying and managing scalable applications on cloud platforms like AWS, Google Cloud, Azure, Heroku, and Vercel. I handle CI/CD pipelines for automated testing and deployment, leveraging Docker and Kubernetes for containerized environments. 💻 DATA-DRIVEN APPLICATIONS I'm creating interactive data dashboards using React tools. I automate data pipelines and web scraping tasks with pandas, NumPy, Scrapy, and Selenium. I also integrate machine learning models into applications for advanced analytics and predictions. 📌 My Javascript Front-end skills: Javascript, Typescript, React.js, Next.js, React Native (CLI/Expo), TailwindCSS, Material UI, Ant Design, SCSS, HTML5, CSS3, Redux Thunk, Redux Saga, Chakra UI, Bootstrap. 📌 My Javascript Back-end skills: Node.js, Nest.js, Express.js, Jest, Fastify, GraphQL, Docker. 📌 My Java skills: Java21, Spring (Boot, Core, MVC, Security, Data, Cloud, Javamail), Concurrency, SOLID, OOP, JakartaEE, JSP, Tomcat, Thymeleaf, JUnit, Mockito, Maven, Gradle. Docker, Lombok 📌 My Database skills: Hibernate, JDBC, Liquibase, SQL, NoSQL, PostgreSQL, MySQL, Objection, Knex, Prisma, MongoDB. 📌Other skills: Stripe, Firebase, Mapbox, GoogleMap, Google Analytics, Google Cloud, KuCoin API, OAuth2, WordPress, AWS. 📌API Tools: Swagger, Postman 📌KEYWORDS: JavaScript, Firebase, Vue.js, Angular, Svelte, D3.js, Chart.js, Three.js, PostgreSQL, React.js, Python, Spring Boot, Docker, Redis, Google Analytics, Kubernetes, Next.js, NumPy, Tailwind CSS, Google Maps API, TensorFlow, AWS S3, JPA, Redux, Material-UI, Selenium, MongoDB, Django, Stripe, Node.js, Jupyter Notebooks, OpenCV, Vercel, Cloudflare, React Native, Celery, ElasticSearch, Hibernate, Express.js, PyTorch, Twilio, Nest.js, pandas, RabbitMQ, Spring Framework, Pipedrive, Google Cloud, GraphQL, scikit-learn, MUI, Azure Functions, Jenkins, Ansible, RESTful APIs, Heroku, Kafka, JSP, OpenAPI, FastAPI, Bitbucket, Gradle, Tomcat, SendGrid, Chakra UI, WebSockets, Java EE, Apache Spark, Servlets, Storybook, Maven, JUnit, SQLite, Scrapy, SQLAlchemy, Apache Kafka, PayPal, Azure DevOps, Microservices, Terraform, Electron.js, Webpack, Babel, ESLint, Vite, Jest, Cypress, Puppeteer, Mocha, Jasmine, Lodash, RxJS, Immutable.js.