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SimpleHAN

Dev Team Backend Engineer

2021.07 — 2022.03

Custom software consulting firm

Highlights

  • Manual learning management (attendance, completion, progress tracking) — Built LMS full-stack (QR attendance, PDF certificates, Excel bulk registration), Digitized operations for 300+ students per semester
  • New matching and counseling features had to be added to a legacy PHP system, while direct changes carried high regression risk — Integrated an independent Spring Boot app through a constrained iframe/postMessage boundary and implemented a weighted-average matching algorithm, Launched the JOB Agent service while isolating the legacy-system impact surface

Projects

Learning Management System (LMS) Development

2021.07 ~ 2022.03

Resolved manual learning management (attendance, completion, progress) causing low operational efficiency and frequent errors at educational institutions

  • Manual attendance tracking prone to duplicates and errors — Built QR attendance API with date+userID composite unique key preventing duplicate check-ins, Digitized real-time attendance for 300+ students per semester
  • Manual member registration causing data inconsistency — Built Apache POI-based Excel bulk registration with row-by-row sequential processing, Ensured data consistency for batch member registration
  • Manual certificate generation workflow — Built JasperReports-based PDF auto-generation API, Automated dynamic certificate creation

Tech Rationale

Selected Java/Spring Boot as enterprise standard for educational institution delivery. Enforced QR attendance dedup via DB composite unique key (date+userID). Used JasperReports for template-based bulk PDF certificate generation.

Contribution: Directly implemented core features over 10 months: QR attendance, Excel batch registration, PDF certificates, progress tracking. Backend lead in 6-person full-stack team.
JavaSpring BootMyBatisMySQLApache POIJasperReports

Incheon Smart Green Industrial Complex Control Center

2022.01 ~ 2022.03

Resolved fragmented reservation, monitoring, and SMS systems preventing unified management at industrial complex control center

  • Scheduling conflicts from concurrent facility reservations — Built real-time booking API with time+location composite unique key, Prevented scheduling conflicts at the database level
  • Synchronous SMS sending blocking reservation confirmation flow — Implemented Bizppurio SMS API + @Async non-blocking notification, Achieved non-blocking reservation confirmation notifications

Tech Rationale

Enforced meeting room booking conflict prevention via DB composite unique key (time+location). Used @Async for SMS to resolve API response delay — separate message queue deemed over-engineering for the traffic scale.

Contribution: Backend lead over 4 months. Directly implemented reservation API, dashboard monitoring API, and async SMS integration.
JavaSpring BootMySQLBizppurio SMS API

Future Service JOB Agent Development

2021.07 ~ 2022.03

Resolved legacy PHP system's extensibility limitations and lack of structured scoring and counseling management

  • Legacy PHP system could not be extended for new features — Embedded Spring Boot independent app via iframe integration, minimizing legacy impact, Launched JOB Agent service without disrupting existing system
  • No structured scoring system for multi-dimensional assessments — Implemented weighted average-based composite scoring algorithm, Delivered standardized multi-dimensional assessment scoring

Tech Rationale

Embedded independent Spring Boot app via iframe for non-invasive legacy PHP system extension. Used postMessage API for cross-frame communication. Implemented weighted average algorithm for multi-dimensional evaluation scoring.

Contribution: Backend lead over 10 months. Designed iframe integration, implemented weighted scoring algorithm, postMessage state sync, and counselor back-office.
JavaSpring BootMySQL

kfriends Member Management System

2021.09 (3 weeks)

Resolved lack of unified authentication requiring separate logins across 5 country-specific distributed websites

  • Separate logins required across 5 country-specific websites — Built unified auth server with Spring Security + JWT-based centralized authentication, Enabled single sign-on across all 5 country sites

Tech Rationale

Resolved fragmented login across 5-country websites with centralized JWT-based unified auth server. Configured CORS multi-domain handling for cross-origin authentication.

Contribution: Independently implemented over 3 weeks. Built entire unified auth server.
JavaSpring BootSpring SecurityJWTMySQL

Internal Tech Blog Renewal

2021.09 (3 weeks)

Resolved hosting cost burden and manual deployment workflow of WordPress-based blog

  • WordPress hosting cost burden and manual deployment workflow — Migrated WordPress → Jekyll with static site generation, Eliminated 100% hosting costs with automated deployment
JekyllLiquidTravis CIGitHub Pages

Technical Skills

JavaSpring BootSpring SecurityMySQLMyBatisApache POIJasperReportsAWS EC2RDSS3Travis CIJekyllJWTGitHub Pages