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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
  • Legacy PHP system extensibility limits — Embedded Spring Boot app via iframe + weighted-average matching algorithm, JOB Agent service launched

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.
Java Spring Boot MyBatis MySQL Apache POI JasperReports

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.
Java Spring Boot MySQL Bizppurio 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.
Java Spring Boot MySQL

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.
Java Spring Boot Spring Security JWT MySQL

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
Jekyll Liquid Travis CI GitHub Pages

Technical Skills

Java Spring Boot Spring Security MySQL MyBatis Apache POI JasperReports AWS EC2 RDS S3 Travis CI Jekyll JWT GitHub Pages