build.gradle

buildscript {
    ext.kotlin_version = '1.2.10'

    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

apply plugin: 'java'
apply plugin: 'kotlin'

sourceCompatibility = 1.8

repositories {
    jcenter()
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
    // Errors on Klaxon 2.0.3 as well
    compile 'com.beust:klaxon:2.0.5'
}

Main.kt

import com.beust.klaxon.Klaxon
import data.StockEntry
import java.io.File

fun main(args: Array<String>) {
    val stockFile = File("src/main/kotlin/data/STOCK.json").inputStream()
    val data = Klaxon().parseArray<StockEntry>(stockFile)
    println(data)
}

StockEntry.kt

package data

data class StockEntry(
        val date: String,
        val close: Double,
        val volume: Int,
        val open: Double,
        val high: Double,
        val low: Double
)