Apache POIでExcelファイルを読み書きする方法

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib</artifactId>
    <version>1.2.21</version>
</dependency>

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-ooxml</artifactId>
    <version>3.17</version>
</dependency>

package com.javasampleapproach.kotlin.apachecsv

constructor() {}
constructor(id: String?, name: String?, address: String?, age: Int) {
    this.id = id
    this.name = name
    this.address = address
    this.age = age
}

override fun toString(): String {
    return "Customer [id=" + id + ", name=" + name + ", address=" + address + ", age=" + age + "]"
}