Write to a file in Kotlin

This article covers different ways to write data to a text file in Kotlin. The solution should truncate the file before writing or create a new file if it doesn’t exist.

1. Using `File.writeText()` function

The standard approach to set the file’s content is with the File.writeText() function. The data is encoded using the default UTF-8 or the specified charset.

import java.io.File

fun main() {

val file = File("foo.out")

val text = "Some log…"

file.writeText(text, Charsets.UTF_8)

}

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2. Using PrintWriter

The PrintWriter is the recommended class that requires writing characters rather than bytes.

import java.io.File

import java.io.PrintWriter

fun main() {

val file = File("foo.out")

val text = "Some log…"

PrintWriter(file, Charsets.UTF_8).use { it.print(text) }

}

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3. Using `Files.newBufferedWriter()` function

The Files.newBufferedWriter() function returns a BufferedWriter that may be used to write text to the file efficiently.

import java.nio.file.Files

import java.nio.file.Paths

fun main() {

val path = Paths.get("foo.out")

val text = "Some log…"

Files.newBufferedWriter(path, Charsets.UTF_8).use { it.write(text) }

}

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4. Using OutputStreamWriter

Since FileOutputStream is meant for writing streams of bytes, you can construct an OutputStreamWriter for writing streams of characters. To improve efficiency, it is advisable to wrap a BufferedWriter around OutputStreamWriter.

import java.io.BufferedWriter

import java.io.File

import java.io.FileOutputStream

import java.io.OutputStreamWriter

fun main() {

val file = File("foo.out")

val text = "Some text"

FileOutputStream(file).use { fos ->

OutputStreamWriter(fos, Charsets.UTF_8).use { osw ->

BufferedWriter(osw).use { bf -> bf.write(text) }

}

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5. Using FileWriter

The FileWriter is a convenience class for writing streams of characters using default character encoding. We can use this as:

import java.io.File

import java.io.FileWriter

fun main() {

val file = File("foo.out")

val text = "Some log…"

FileWriter(file).use { it.write(text) }

}

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6. Using `File.bufferedWriter()` function

It is advisable to wrap BufferedWriter around file writer as its write operations are very costly. We can do this with the File.bufferedWriter() function, which returns a new BufferedWriter for writing this file’s content.

import java.io.File

fun main() {

val file = File("foo.out")

val text = "Some log…"

file.bufferedWriter().use { bw -> bw.write(text) }

}

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7. Using PrintStream

A PrintStream can be used to add functionality to an output stream. But all characters printed by a PrintStream are converted into bytes using the platform’s default character encoding.

import java.io.File

import java.io.FileOutputStream

import java.io.PrintStream

fun main() {

val file = File("foo.out")

val text = "Some log…"

FileOutputStream(file).use { fos ->

PrintStream(fos).use { out -> out.print(text) }

}

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That’s all about writing to a file in Kotlin.

1. Using File.writeText() function

2. Using PrintWriter

3. Using Files.newBufferedWriter() function

4. Using OutputStreamWriter

5. Using FileWriter

6. Using File.bufferedWriter() function

7. Using PrintStream

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1. Using `File.writeText()` function

3. Using `Files.newBufferedWriter()` function

6. Using `File.bufferedWriter()` function