Simple client server communication with object streams in Kotlin.

SocketExample.kt

import java.io.ObjectInputStream
import java.io.ObjectOutputStream
import java.io.Serializable
import java.net.ServerSocket
import java.net.Socket
import java.util.*

data class Question(val question: String, val answers: List<String>): Serializable

fun main(args: Array<String>) {
    when {
        args.size < 1 -> println("Start with -s for server and -c for client.")
        args[0].toLowerCase() == "-s" -> server()
        args[0].toLowerCase() == "-c" -> client()
    }
}

fun server() {
    val serverSock = ServerSocket(34567)

    while (true) {
        val sock = serverSock.accept()
        val outStream = ObjectOutputStream(sock.getOutputStream())
        val inStream  = ObjectInputStream(sock.getInputStream())

        val question = Question("What day is it?", listOf(
            "February",
            "Orange",
            "A great day!"
        ))
        outStream.writeObject(question)

        val answer = inStream.readObject()
        if (answer is String) {
            println("Client answered with $answer")
        }

        inStream.close()
        outStream.close()
        sock.close()
    }
}

fun client() {
    val sock = Socket("127.0.0.1", 34567)
    val outStream = ObjectOutputStream(sock.getOutputStream())
    val inStream  = ObjectInputStream(sock.getInputStream())

    val question = inStream.readObject()
    if (question is Question) {
        println("Server asked: $question.question")
        outStream.writeObject(question.answers[Random().nextInt(3)])
    }

    outStream.close()
    inStream.close()
    sock.close()
}