This post shows how to leverage Java libraries (from our underlying JVM) to read file line by line from classpath using Kotlin. Also, IntelliJ IDE is used for this post but can easily be replicated in Eclipse.

Requirements

IntelliJ IDEA Ultimate 2016.3
- The Community Edition may be enough but we have not tried it.
Kotlin Version 1.1
Windows 10 Enterprise

IntelliJ Project and Files

We have a very simple project that contains two (2) files – TestData01.txt and EX01.kt.

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Codes and Data File

Here is our Kotlin program.

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package exercise01

import java.io.File

/**
 * Created by Turreta.com on 12/6/2017.
 */

fun main(args: Array<String>) {

    File(ClassLoader.getSystemResource("TestData01.txt").file).forEachLine {
        println(it)
    }
}

package exercise01

import java.io.File

/**

* Created by Turreta.com on 12/6/2017.

fun main(args: Array<String>) {

File(ClassLoader.getSystemResource("TestData01.txt").file).forEachLine {

println(it)

}

If you are really new to Kotlin, the following provide short explanations on how the codes work.

In Java

In Java, the codes are equivalent to:

    public static void main(String... a) {
        String fileName = ClassLoader.getSystemResource("TestData01.txt").getFile();

        /**
         * To remove prefixed "/", e.g., /C:/
         */
        fileName = fileName.substring(1);

        try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
            stream.forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

public static void main(String... a) {

String fileName = ClassLoader.getSystemResource("TestData01.txt").getFile();

/**

* To remove prefixed "/", e.g., /C:/

fileName = fileName.substring(1);

try (Stream<String> stream = Files.lines(Paths.get(fileName))) {

stream.forEach(System.out::println);

} catch (IOException e) {

e.printStackTrace();

}

So, in Kotlin

The codes create a java.io.File object and uses the file property to get the name (path + name) of the file in the file system. The forEach construct, which is from Kotlin, loops through the content of the file.