Antaes, Kotlin overview

Kotlin is an object-oriented and functional programming language created by JetBrains. It is the (other) official language for Android development.

Key features

• Interoperability with JVM
• Cross-platform
• Statically typed with type inference
• Object-oriented
• Functional
• Target JVM or JS
• One of the fastest growing language
• Open-source
• Fully supported by IntelliJ with code conversion from/to Java
• Already a lot of dedicated tools, frameworks

Code sample

fun main() = println("Hello")

Some nice stuff

• Null safe by default
• Extension function
• Complex switch cases
• if...else and try...catch (and a lot more) are instructions with a return value, making the java ternary operator obsolete.
• Ranges (1..10 for instance)
• Data classes
• Object (singleton)
• Companion object
• Delegated properties
• Default value for method parameters
• Named arguments
• let keyword allowing object initialization and configuration in a single block
• Destructuring declaration

Useful links

• Language documentation
• Nice overview of the language with some editable code samples
• Online editor for a simple Kotlin file
• Training with a set of exercises to complete
• The sources of Kotlin

Exercises

Compiling and running the exercises can be achieved with gradle:

./gradlew run

Then a Micronaut server will start.

• Base address is http://localhost:8080
• Remote port is 8000
• Health check is http://localhost:8080/health
• OpenAPI file is http://localhost:8080/openapi/kotlin-training-1.0.yml

REST Web server with Micronaut

Fill the HelloController class to make it answer the following JSON:

{
  "content": "Hello world!"
}

Create a new POST endpoint

Create a new /companies POST endpoint that will take a JSON like

{
  "name": "Antaes"
}

and return the following response:

{
  "self": "http://localhost:8080/companies/1",
  "name": "Antaes"
}

Create a new GET endpoint

Create a new /companies GET endpoint that will return the location of recorded companies:

[
  "http://localhost:8080/companies/1",
  "http://localhost:8080/companies/2"
]

Create a new PUSH endpoint

Create a new /companies/{id} PUSH endpoint that will update the corresponding company data and returns it:

{
  "name": "Antaes Consulting S.A.",
  "creationYear": 2007
}

Response:

{
  "self": "http://localhost:8080/companies/1",
  "name": "Antaes Consulting S.A.",
  "creationYear": 2007
}