: 간단한 커뮤니티 구조의 백엔드 API 서버를 구현했습니다.(Webflux패턴 기반)

: Simple Social network stuff Structure based Back-end API server using Spring Webflux pattern.

• 개인 포트폴리오가 전부 상업용 프로젝트이기도 하고 백엔드 관련한 개인적인 repo가 충분하지 않았다.(My portfolio is full of commercial projects that cannot show to others. so tried to make public one)
• 개인적으로 만들고 있는 프로젝트(InteractiveERD)에서 백엔드를 뭘로 할지 고민을 하고 있었다.(Need to select proper backend language and frameworks to be used in my private projects which named 'InteractiveERD')
• 지인중 한 분이 본인 팀에서 Spring Webflux를 사용한다고 하길래 트랜드인가 싶어 익숙한 kotlin으로 공부해보면 좋겠다는 생각이 들었다.(옷은 트랜드를 안 따라가더라도 프로그래밍은 못참지)(Some of my X co-worker told me that Spring Webflux pattern used in IT major company in these days. so tried to study this pattern for catching up with IT trends for fun.)
• reactive 패턴은 이전에 rxdart로 질리도록 해봐서 재밌을거라 생각했다.(I get used to reactive pattern because used rxdart before in other company to make flutter app.)

: Found out some issues during making Webflux pattern project.

1. Reactor pattern(using Mono, Flux) can reduce code readability.(callback hell like before async/await pattern popped out in Node.js)

• Resolved by using kotlin coroutine.(persist non-blocking)

1. It's not an ORM(need to write raw query and mapper in some cases)
2. Recommend to use R2DBC because of blocking issue when using JDBC(it's blocking API) instead.
   • Could not take advantage of confidence when using JPA.
3. R2DBC does not support relation mapping like ORM (No plan for it)
4. Performance issues when using Postgresql driver compared to JDBC
   • ref : spring-projects/spring-data-r2dbc#203
5. Pagination with sort and offset need to use databaseClient(raw query). It won't work with @Query annotation.
   • ref: spring-projects/spring-data-r2dbc#596
   • Resolved by Fluent API in R2DBC.(can put sort or offset stuffs using Fluent API template.)
6. There's other relation mapping support(alternatives) on reactive db connection API which called Hibernate Reactive(can use with Hibernate ORM) and Kotlin JDSL Reactive
7. [221223 UPDATE] QueryDsl could resolve relation mapping issue
8. [221223 UPDATE] What about java-dataloader to resolve n+1 issue when want to fetch join data not using join functionality.

• Kotlin 언어 사용(이전에 안드로이드 개발을 kotlin으로도 했고 꽤나 열심히 언어공부를 했던 언어이기에 선택함.)
• gradle 빌드 방식 적용(안드로이드에 익숙함)
• Webflux 패턴 채택
• 함수형(Functional) 프로그래밍 적용
• Postgresql driver 사용(원래는 mysql이 익숙한데 tokenizing때문에 postgresql을 공부하기로 맘먹음)
• 논블로킹을 위해 JPA가 아닌 R2DBC 채택 (ORM이 아니라서 고민중)
• 클라우드는 GCP를 사용 for file upload

• 관계 테이블 커스텀 쿼리 적용
• kotlin coroutine 적용(코드 가독성을 위해)
• R2DBC OneToMany, OneToOne, ManyToMany mapping 적용(속도 저하 이슈로 로우쿼리로 전환)
• 로깅 적용(logging)
• 클라우드 저장소 이미지 파일 업로드
  • ISSUE > 8MB 이상 파일 업로드시 inputStream 데이터 비는 현상 개선
• 서버 에러 핸들링(error handling)
• Webflux Security 적용(간단한 정도의 인증/인가 미들웨어 구현) (apply auth middleware)
• Proxy based AOP(Aspect oriented programming) 적용(메서드별 소요시간측정)
• 테스트 코드 작성(test code) -> kotest
• 배포 자동화 CI/CD (profile 환경별 빌드 및 배포, build and deploy by each profile)
• (microservice는 손이 너무 많이 가서 일단 보류...)

: application.yaml 파일을 .gitignore 처리를 했지만 아래와 같이 적으면 문제 없이 실행할 수 있습니다. 혹시나 다른 데이터베이스 드라이버를 사용하시는 경우라면 datasource파일 및 gradle을 수정할 필요가 있습니다.

# src/main/resources/application.yaml
spring:
  config:
    activate:
      on-profile: local
  server:
    port: 8000
  r2dbc:
    protocol: r2dbc:postgresql
    host: localhost
    port: 5432
    username: postgres
    password: postgres
    database: postgres
  storage:
    cred-path: <YOUR CONFIG CREDENTIAL FILE PATH>
    project-id: <YOUR GCP STORAGE PROJECT ID>
    bucket-name: <YOUR GCP STORAGE BUCKET NAME>

# Itellij Configuration > VM option 
-Dspring.profiles.active=<YOUR PROFILE>

# Use Command line to run build jar file
java -jar -Dspring.profiles.active=<YOUR PROFILE> path/to/app.jar

: 공부하면서 참고한 링크는 아래에 모두 기록할 예정입니다. 프로젝트 코드보다 개념이 필요하신분들은 아래 링크들에 잘 기록되어있을테니 참고하시면 되겠습니다.(주의 : 개념이 없는 링크들도 있을수도 있음.)

(Warning: it's almost Korean blog links. )

• URL : https://github.com/piomin/sample-spring-data-webflux
• URL : https://docs.spring.io/spring-data/r2dbc/docs/current-SNAPSHOT/reference/html/#reference
• URL : https://www.vinsguru.com/spring-data-r2dbc/
• URL : https://github.com/hantsy/spring-r2dbc-sample
• URL : https://medium.com/bliblidotcom-techblog/reactive-spring-boot-application-with-r2dbc-and-postgresql-849fc7811135
• URL : https://github.com/kakaohairshop/spring-r2dbc-study

• URL : https://docs.spring.io/spring-boot/docs/1.5.6.RELEASE/reference/html/boot-features-external-config.html

• URL : https://1minute-before6pm.tistory.com/12

• URL : spring-projects/spring-framework#28603

• URL : https://www.baeldung.com/spring-webflux-errors

• URL : https://github.com/kamalhm/spring-boot-r2dbc/tree/master/src/main/java/com/khm/reactivepostgres

(공식적으로 r2dbc는 관계relation를 지원하지 않는다.)

지원하고 있지 않다는 이슈

• URL : spring-projects/spring-data-r2dbc#99
• URL : spring-projects/spring-data-r2dbc#352

관계 매핑 구현방법

• URL : https://tolkiana.com/introduction-to-spring-data-r2dbc-with-kotlin/
• URL : https://heesutory.tistory.com/33
• URL : https://heesutory.tistory.com/35
  • Lombok의 @Builder 대신 kotlin으로 해결(URL : https://levelup.gitconnected.com/kotlin-makes-lombok-obsolete-9ed3318596cb, https://stackoverflow.com/questions/36140791/how-to-implement-builder-pattern-in-kotlin)
• URL : https://binux.tistory.com/156
• URL : https://medium.com/pictet-technologies-blog/reactive-programming-with-spring-data-r2dbc-ee9f1c24848b
  • Combinations of repo query to make join relations
• URL : https://www.sipios.com/blog-tech/handle-the-new-r2dbc-specification-in-java
  • Raw query join and aggregate cause blocking issue

• URL : https://techblog.woowahan.com/7349/
• URL : https://appleg1226.tistory.com/16
• URL(coRouter 구현) : https://veluxer62.github.io/tutorials/spring-web-flux-functional-endpoint-api/
• URL : https://umbum.dev/1047

• URL : https://spring.io/blog/2019/05/16/reactive-transactions-with-spring

• URL : https://jsonobject.tistory.com/500
• URL : https://www.reddit.com/r/Kotlin/comments/8gbiul/slf4j_loggers_in_3_ways/

• URL : https://medium.com/geekculture/spring-data-jpa-spring-data-r2dbc-hibernate-reactive-bcc43e321566

• URL : https://hantsy.github.io/spring-puzzles/hibernate-reactive.html
• URL : https://hibernate.org/reactive/
• URL : https://itnext.io/integrating-hibernate-reactive-with-spring-5427440607fe

: official docs가 아주 잘 되어있음.

• URL : https://github.com/kotest/kotest-examples-spring-webflux
• URL : https://velog.io/@revimal/Kotlin-Kotest%EC%99%80-MockK%EB%A1%9C-Spring-Boot%EC%97%90%EC%84%9C-Kotlin-%EC%8A%A4%ED%83%80%EC%9D%BC-%ED%85%8C%EC%8A%A4%ED%8A%B8-%EC%9E%91%EC%84%B1
• URL : https://github.com/HomoEfficio/dev-tips/blob/master/Kotlin-Coroutine-Spring-WebFluxTest.md