Hi, I'm Bui Minh Toan 👋

Java Backend Engineer · Spring Boot · Microservices · Fintech

Building reliable backends for financial systems — from e-commerce APIs running inside 20+ banking apps
to a double-entry core ledger and an ISO 20022 payment gateway.

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🧑‍💻 About me

• ⚙️ 3+ years shipping production backend services with Java & Spring Boot
• 🏦 Built core-business APIs for an e-commerce platform distributed inside 20+ banking applications
• 🔨 Currently building core banking systems: double-entry ledger, ISO 20022 gateway, Saga-based distributed transactions
• ✍️ Writing about backend & fintech on Substack
• 🌱 Open to Java backend roles — view my CV

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🛠️ Tech stack

Language
Backend
Data
Messaging
DevOps
Frontend
Testing

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📌 Featured projects

Project	What it is	Stack
🏦 core-banking-system	Double-entry core ledger with pessimistic locking, audit trail, DDD aggregates, Outbox pattern + Kafka and Redis caching — runs on PostgreSQL or Oracle	Java 17 · Spring Boot · Kafka · Redis
📄 banking-portfolio-docs	Architecture docs, ADRs, roadmap & devlog for the banking systems — read online	Docs · ADR
☕ JavaCore	Notes & exercises on Java fundamentals	Java

🤝 Open source

• Spring Framework — reported a generic-type resolution bug in InvocableHandlerMethod
• Spring Cloud Gateway — analysed and reported an API-gateway configuration defect affecting microservice routing
• Stack Overflow — resolved an Asia/Saigon timezone defect affecting legacy database systems

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💬 "Consistency beats intensity."