Code Challenge: Watermark Service

• Note: there is a kafka-based implementation in progress: https://github.com/bastman/codechallenge-watermark-service-kafka

Run

$ ./gradlew bootRun

... and then open http://localhost:8080 in your browser

Test

$ ./gradlew clean build test

Api Endpoints

- POST /api/watermark-job/submit
- GET /api/watermark-job/{ticketId}/status
- GET /api/watermark-job/{ticketId}/download

Gradle Modules

• rest-service: contains spring-boot application
• common: contains core domain logic (no dependency to spring)

Coding flavour

• (threadsafe) immutable data structures
• sealed class hierarchies
• composition over inheritance
• functional over classic oop-style

Features

• spring boot, swagger-ui, undertow, jackson, caffeine, junit5
• gradle-multimodule-project (common, rest-service)
  • the core domain logic resides in common-module
  • you may want to reuse core domain logic within different services/projects (e.g. a kafka-based pipeline)

Testing

• data-driven testing (junit5: @TestFactory)
• schema-based testing (https://jsonschema.net)

Concurrency

• lightweight threading provided by kotlin coroutines, similar to ...
  • quasar fibers (https://github.com/puniverse/quasar)
  • golang goroutines (https://www.golang-book.com/books/intro/10)
• threadsafe immutable data structures
• immutable message passing via coroutine channels
  • similar to golang channels (https://gobyexample.com/channels)

Drawbacks (Things that can be improved)

• the solution provided will not scale horizontally, since:

  • application uses local in-memory-cache
  • there is no chance to re-process jobs (in case of failure/re-deploy)

  => a kafka-based solution with dedicated microservices (api, job-processor) is preferable for real-world deployments => https://github.com/bastman/codechallenge-watermark-service-kafka

• api's are not secured by any auth-strategy

• submit-api currently does not check for having enough capacity to add new jobs

• no request validation

• no proper exception handling

Why Kotlin? Kotlin ...

• is like SWIFT (ios)
• is like Scala, but easy to learn
• is much more type safe than Java - No NullPointerException ;)
• is fully compatible to Java, but less verbose
• has first class support for closures
• is based on "Effective Java"
• is used in production, by e.g. JetBrains
• coding is pure fun :)

Kotlin extensions are available for

• spring (https://github.com/sdeleuze/spring-kotlin)
• gradle (https://github.com/gradle/gradle-script-kotlin)
• mockito (https://github.com/nhaarman/mockito-kotlin)
• vert.x (https://github.com/vert-x3/vertx-lang-kotlin)
• quasar (https://github.com/puniverse/quasar/tree/master/quasar-kotlin)
• jackson (https://github.com/FasterXML/jackson-module-kotlin)
• and many more ...