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<Hyun/>

Hi, I'm

Hyun Lee

Backend Engineer · Kotlin/Spring Boot & FastAPI

I build and run production systems for small businesses: a retailer's purchasing platform and a laundromat's ordering and payment backend.

Open to backend engineering roles working with Kotlin or Java and Spring Boot, or Python and FastAPI.

  • AWS Certified DevOps Engineer – Professional
  • Software Developer at SB Trading
  • Merged PRs in Spring Boot, MockK & Redisson
View projectsResume (PDF)

By the numbers

PROJECTS

Production · Jun 2025 – May 2026

Bellight

Laundromat Ordering & Payments

Laundromat backend for tap-to-pay washers and Uber Direct laundry pickup, delivery and status tracking.

  • ~150 payments processed
  • 524 → 0 module violations
  • 1,340 automated tests
  • Integrated Stripe Terminal and Stripe Connect behind a database-backed idempotency layer that replays stored responses
  • Built MQTT machine control and persisted machine state for recovery after restarts
  • Scheduled Uber Direct pickup and return delivery, with courier details, ETAs and delivery-status tracking
  • Kotlin
  • Spring Boot
  • Spring Modulith
  • MySQL
  • Kafka
  • MQTT
  • +3
Demo: BellightLive site: Bellight. Opens the operator console, which needs a sign-in. The demo below shows the backend. (opens in a new tab)
Production · 2026–present

SB Trading

Purchasing & Inventory Platform

Purchasing workspace for replenishment and allocation across four retail stores (staff login required).

  • 83,412 formula cells reproduced
  • 5,949 rows, 100% match
  • 695 pytest + 79 Playwright tests
  • Moved Excel-based ordering into a React and FastAPI app with configurable rules and vendor exports
  • Separated calculations into durable workers so review screens remain responsive
  • Added role-based approval, quantity-change history, and BigCommerce order lookup and refunds
  • React
  • TypeScript
  • FastAPI
  • Python
  • SQLite
  • Docker
  • +3
Explore features: SB TradingLive site: SB Trading. Staff sign-in required; the interface is in Korean. (opens in a new tab)
Java · Kotlin · Spring Boot
Open source · 2026

Open Source Contributions

Merged pull requests to Java and Kotlin open-source projects in September 2026.

  • 7 merged PRs
  • Spring Boot: fixed cookie handling in the reactive Apache HttpComponents client (#51724)
  • MockK: negative verifications now wait out the whole timeout, closing an issue open since 2019 (#1559)
  • Redisson: added Redis server TIME to RKeys across sync, async, Reactive and RxJava APIs (#7358)
  • Java
  • Kotlin
  • Spring Boot
  • Redis
  • JUnit
  • Gradle
Explore features: Open Source ContributionsMerged PRs: Open Source Contributions (opens in a new tab)

More projects

Personal · 2026

JobPilot

Personal Job Search Dashboard

A personal dashboard that brings job discovery, resume matching, and application tracking into one workflow.

  • Next.js
  • TypeScript
  • SQLite
  • Drizzle
  • Python
  • Playwright
  • +1
Explore features: JobPilot
Earlier team projects (4)
Team project · 2025

CodeMate

Personal Code Mentor System

Code-mentoring web app from a team project. I built the Spring Boot back end that analyzes a GitHub repository with SonarQube.

  • Java
  • Spring Boot
  • Spring Data JPA
  • SonarQube
  • Auth0
  • React
  • +3
Explore features: CodeMate
More on GitHub(opens in a new tab)

EXPERIENCE

Software Developer, Operations Automation

  • SB Trading Corporation
  • May 2026 – Present
  • Kansas City area, USA
  • Built a React/TypeScript and FastAPI platform that replaced an Excel ordering workflow across four retail stores.
  • Implemented configurable replenishment rules and vendor-specific Excel exports.
  • Validated the results against the master workbook: 5,949 rows matched 100%, and 83,412 formula cells were later reproduced.
  • Separated calculation workers from the API, with durable job tracking, duplicate-request protection, and auditable quantity changes.
  • Integrated BigCommerce order lookup and allocation cart previews behind a shared request-coalescing cache.
  • Added approval-gated store-credit refunds batched across stores, and report emails with role-based access.
  • Covered the platform with 695 pytest and 79 Playwright tests.
Case study: SB Trading Corporation

Technologies

  • Python
  • FastAPI
  • React
  • TypeScript
  • SQLite
  • BigCommerce API
  • Docker
  • Render
  • pytest
  • Playwright

Backend Engineer

  • Bellight LLC
  • Jun 2025 – May 2026
  • Built the backend for a laundromat ordering and payment platform using Kotlin 2.0 on Java 21, Spring Boot, and MySQL.
  • Integrated Stripe Terminal (M2) and Stripe Connect to initiate payments. Built a database-backed idempotency layer that validates requests and replays stored responses to prevent duplicate charges on retries and webhook redelivery. Added a reconciliation job to repair orders whose status had drifted from their payment records.
  • Replaced 11 synchronous calls between modules with Spring Modulith events, reducing module-boundary violations from 524 to 0 in CI. Published cross-module events to Kafka through a transactional outbox with deduplication keys and dead-letter replay.
  • Evolved the MySQL schema through 79 Flyway migrations. Used optimistic locking (@Version) and pessimistic row locks to protect concurrent payment updates. Built order search with QueryDSL.
  • Wrote Bash scripts for deployment and MySQL backup and restore rehearsals. Monitored payment and webhook flows with Prometheus and Alertmanager. Wrote 1,340 automated tests using JUnit 5 and Testcontainers and required them to pass before GitHub Actions releases.
Case study: Bellight LLC

Technologies

  • Kotlin
  • Java
  • Spring Boot
  • Spring Modulith
  • Spring Security
  • MySQL
  • Kafka
  • Stripe
  • Flyway
  • QueryDSL
  • Resilience4j
  • Prometheus
  • JUnit
  • Testcontainers
  • GitHub Actions
  • Bash

Website Coordinator Intern

  • TRTCLE
  • Jan 2025 – May 2025
  • Remote
  • Five-person agile team
  • Replaced a manual Excel workflow for 300+ course records with Python automation.
  • Worked on legal-education website content and navigation.

Technologies

  • Python
  • Excel
  • Jira
  • Confluence

Software Engineer Intern

  • Seoul St. Mary's Hospital, The Catholic University of Korea
  • Jun 2024 – Dec 2024
  • Remote
  • Two backend engineers, one frontend engineer
  • Co-built the Spring Boot backend of an ERAS surgical-checklist system with another backend engineer.
  • Implemented patient registration, checklists through discharge, filtered views, and per-patient Excel exports to replace paper records.
Case study: Seoul St. Mary's Hospital, The Catholic University of Korea

Technologies

  • Java
  • Spring Boot
  • Spring Data JPA
  • MySQL
  • Apache POI
  • Docker
  • GitHub Actions

Education & Certifications

Education

  • University of VirginiaB.S. Computer Science · Aug 2021 – May 2025
  • Johnson County Community CollegeA.S. Computer Science · Aug 2018 – May 2021

Certifications

  • AWS Certified DevOps Engineer – ProfessionalAmazon Web Services
  • AWS Certified Developer – AssociateAmazon Web Services

SKILLS

Languages
  • Kotlin
  • Java
  • Python
  • TypeScript
  • SQL
Backend
  • Spring Boot
  • Spring Modulith
  • Spring Security
  • JPA / Hibernate
  • FastAPI
  • Kafka
  • REST APIs
  • Stripe
  • BigCommerce API
Data
  • MySQL
  • PostgreSQL
  • SQLite
  • Redis
Infrastructure
  • Docker
  • GitHub Actions
  • AWS (EC2, RDS, S3, SES, SNS)
  • Cloudflare Workers
  • Render
  • Linux
Testing
  • JUnit 5
  • Testcontainers
  • pytest
  • Playwright
Frontend
  • React
  • Next.js
  • Tailwind CSS
Also used
  • JavaScript
  • Angular
  • MongoDB
  • Querydsl
  • HTML / CSS
  • Figma

CONTACT

I'm open to backend engineering roles and collaborative projects. Based in Overland Park, Kansas.

Email meResume (PDF)LinkedIn(opens in a new tab)

Or write to [email protected]