👋 Hey, I'm SangHyun
software engineer
From Spring backends to Flutter apps — I build software that ships as a product
01 — Work
Selected work
HeatTrip
An emotion-centered mobile travel service that recommends destinations based on the user's emotional state and connects itineraries, emotion diaries and retrospectives. I staged the LLM recommendation for cost/failure isolation and designed search, pagination and observability myself.
Staged the LLM recommendation to isolate cost/failure propagation — Excellence Award at the Korea Tourism competition
BARO FARM
Backend for an agri-fisheries commerce service. I owned the auth/authorization flow in a Spring Cloud Gateway·Redis·Kafka·OPA-based MSA, and resolved intermittent 403s at the structural root cause rather than the surface symptom.
Diagnosed intermittent 403s as a "permission-vs-user-state mismatch" structural problem
02 — Writing
Recent posts
ObjectMapper는 단순 JSON 변환기가 아니었다 — Jackson, 리플렉션, 동시성
Tour API 응답을 DTO로 파싱하는 단위 테스트를 짜다가 들여다본 ObjectMapper. Jackson의 계층 구조, treeToValue에 .class를 넘기는 이유(타입 소거)까지 정리했습니다.
2026. 06. 20 · Java
Stream이 뭐였더라? — map, flatMap, 그리고 메모리 구조까지
포트폴리오 프로젝트를 리팩토링하다 만난 Stream 코드. stream/map/flatMap이 무엇인지, List와 무엇이 다른지, 그리고 메모리에는 어떻게 올라가는지까지 파고들어 정리했습니다.
2026. 06. 15 · Java
03 — Elsewhere