Kotlin ?
Pourquoi Kotlin ?
Environnement
Où l'utiliser ?
- Développement mobile
- Développement back
- Développement front
1 langage
2 paradigmes
Quelques bases
Inférence de type
var myVariable : String = "ma première chaine"
var myVariable2 = "ma seconde chaine"
Typage fort
fun add(param1: Int, param2: Int ) : Int
{
return param1 + param2
}
Null Safe
class HelloWorld {
fun displayNullableMessage(message: String?) {
print(message)
}
fun displayMessage(message: String) {
print(message)
}
}
fun main(args: Array<String>) {
val service = HelloWorld()
val s : String? = null
service.displayMessage(s) //does not compile
if( s != null ){
service.displayMessage(s) //compile
}
service.displayNullableMessage(null)
}
Immutabilité
var myVariable : String = "ma variable"
myVariable = "ma variable mis à jour"
val myConst = "ma constante"
myConst = "ma constante mise à jour" // does not compile
Concis
fun add(a: Int, b: Int): Int {
return a + b
}
fun add(a: Int, b: Int) = a + b
fun displaySize(x: Any) {
if (x is String) {
print(x.length)
} else{
print("Not a String")
}
}
fun getCity(p: Person?): String {
return p?.address?.city
}
fun getCityWithNPE(p: Person?): String {
return p!!.address!!.city
}
fun getAddress(p: Person?): Address {
return p?.address ?: Address()
}
Null Safe
Elvis Operator
Pour les nostalgiques
listOf("Tintin", "Asterix", "Milou")
.map { it -> it.toUpperCase() }
.forEach { it -> println(it) }
listOf("Tintin", "Asterix", "Milou")
.map { it.toUpperCase() }
.forEach { println(it) }
Un peu de fonctionnel
Utilisation avec Spring
<build>
<sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
<testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<artifactId>kotlin-maven-plugin</artifactId>
<groupId>org.jetbrains.kotlin</groupId>
<configuration>
<compilerPlugins>
<plugin>all-open</plugin>
<plugin>spring</plugin>
<plugin>jpa</plugin>
</compilerPlugins>
<pluginOptions>
<option>all-open:annotation=com.zenika.SimpleAnnotation</option>
<option>all-open:annotation=com.zenika.ComplexAnnotation</option>
</pluginOptions>
</configuration>
<dependencies>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-allopen</artifactId>
<version>${kotlin.version}</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>
@SpringBootApplication
class MatinaleSpringApplication
fun main(args: Array<String>) {
runApplication<MatinaleSpringApplication>(*args)
}
@RestController
class SampleController(val sampleService: SampleService?) {
@GetMapping("/hello/{name}")
fun hello(@PathVariable name: String): String {
sampleService?.greet()
return "Hello $name"
}
}
interface CompanyRepository : CrudRepository<Company, UUID> {
fun findAllByOrderByNameAsc(): Iterable<Company>
}
@Entity
@Table(name = "companies")
data class Company(@Id var id: UUID = UUID.randomUUID(),
var name: String = "",
val state: Boolean = true)
beans {
bean<UserHandler>()
bean<Routes>()
bean<WebHandler>("webHandler") {
RouterFunctions.toWebHandler(
ref<Routes>().router(),
HandlerStrategies.builder().viewResolver(ref()).build()
)
}
profile("foo") {
bean<Foo>()
}
}
router {
accept(TEXT_HTML).nest {
GET("/") { ok().render("index") }
GET("/sse") { ok().render("sse") }
}
"/api".nest {
accept(TEXT_EVENT_STREAM).nest {
GET("/users", userHandler::stream)
}
}
resources("/**", ClassPathResource("static/"))
}
Spring-kotlin-functional
Differents runtimes
- Java
- Javascript
- Native (LLVM)
- Android
Web Assembly
By erwann thebault
Web Assembly
- 491