Backend Developer focused on transaction processing systems and core financial logic.

I am interested in how financial systems guarantee atomicity, consistency, and data integrity under concurrent transaction environments.
Through implementing core banking features and migrating legacy systems, I have developed a strong interest in building reliable and maintainable financial software.

Repository: https://github.com/zzzyoonnn/FinFlow-backend

A backend application that simulates core banking operations with a focus on transactional integrity.

Designed and implemented essential banking operations including:

• Deposit
• Withdrawal
• Transfer
• Transaction history management

• Managed withdrawal and transfer operations within a single @Transactional boundary to ensure atomicity
• Delegated validation logic (ownership, password verification, balance checks) to the Account domain entity
• Prevented negative balances through explicit business rule enforcement
• Recorded transaction history with balance snapshots at the time of execution for auditability
• Structured flow clearly as: validation → state mutation → persistence → response

Through this implementation, I became particularly interested in how financial systems prevent data inconsistency, race conditions, and double execution under concurrent requests.

👉 Core Banking Service Implementation: AccountService.java

• 계좌가 많아질 경우, 어떻게 설계하면 좋을까?🤔
• N+1은 왜 발생할까?🤔(Fetch Join 적용 전후 성능 비교)
• N+1은 왜 JPA에서 발생할까?🤔(JPQL)
• N+1은 메모리에 어떤 영향을 미칠까?🤔
• 영속성 컨텍스트는 N+1과 어떤 관계가 있을까?🤔

Repository: https://github.com/zzzyoonnn/Servlet2Spring

This project reflects my growth in understanding backend architecture evolution and framework-driven design.

Started with a JSP-based architecture and progressively evolved it into Spring MVC and Spring Boot.

• Refactored the application into a clearer layered architecture
• Improved separation of concerns between controller, service, and domain layers
• Simplified configuration using Spring Boot auto-configuration
• Enhanced security structure using Spring Security
• Reduced boilerplate code and improved maintainability
• Improved deployment and dependency management with Maven

This migration process taught me the importance of modernizing systems without compromising stability, especially in environments where reliability is critical.

Backend

• Java 21
• Spring Boot
• Spring Data JPA
• Spring Security (JWT)

Database

• MySQL
• H2 (for testing)

Infrastructure

• AWS (EC2, RDS, S3)

Build Tool

• Maven

• Core Banking Systems
• Transaction Processing
• Financial Data Integrity
• High-reliability Backend Systems

I aim to build backend systems where correctness and reliability are prioritized over feature speed — especially in domains where data integrity is critical.