Truncate a File in Kotlin

This post will discuss how to truncate a file to size zero in Kotlin.

1. Using `PrintWriter`

The recommended solution is to create a PrintWriter instance, which results in the specified file being truncated to size zero. Note that if the file doesn’t exist, a new file will be created.

This is demonstrated below with the use function, which automatically takes care of closing the stream:

import java.io.IOException

import java.io.PrintWriter

fun main() {

val fileName = "/user/data/sys.log"

try {

PrintWriter(fileName).use { }

} catch (e: IOException) {

e.printStackTrace()

}

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2. Using `BufferedWriter`

Another option is to create a BufferedWriter using Files.newBufferedWriter(…) and specify the StandardOpenOption.TRUNCATE_EXISTING option to truncate the file to length 0 (if it exists). Its usage is demonstrated below with the use function:

import java.io.IOException

import java.nio.file.Files

import java.nio.file.Path

import java.nio.file.StandardOpenOption

fun main() {

val fileName = "/user/data/sys.log"

try {

Files.newBufferedWriter(Path.of(fileName), StandardOpenOption.TRUNCATE_EXISTING

).use { }

} catch (e: IOException) {

e.printStackTrace()

}

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3. Using `FileChannel`

The FileChannel class contains the truncate() function to truncate a file to the specified size. It can be used as follows:

import java.io.IOException

import java.nio.channels.FileChannel

import java.nio.file.Path

import java.nio.file.StandardOpenOption

fun main() {

val fileName = "/user/data/sys.log"

try {

FileChannel.open(Path.of(fileName), StandardOpenOption.WRITE)

.truncate(0).close()

} catch (e: IOException) {

e.printStackTrace()

}

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Alternately, you can directly specify the StandardOpenOption.TRUNCATE_EXISTING option to the open() function, which results in the file being truncated to a size of 0 (if it exists).

import java.io.IOException

import java.nio.channels.FileChannel

import java.nio.file.Paths

import java.nio.file.StandardOpenOption

fun main() {

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

try {

FileChannel.open(path, StandardOpenOption.WRITE,

StandardOpenOption.TRUNCATE_EXISTING)

.close()

} catch (e: IOException) {

e.printStackTrace()

}

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4. Using `RandomAccessFile`

The RandomAccessFile class provides support for setting the length of a file using the setLength() function. To truncate a file, you can open the file in rw mode and pass the length as 0 to the setLength() function:

import java.io.IOException

import java.io.RandomAccessFile

fun main() {

val fileName = "/user/data/sys.log"

try {

RandomAccessFile(fileName, "rw").use { it.setLength(0) }

} catch (e: IOException) {

e.printStackTrace()

}

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5. Using `FileOutputStream`

The following solution constructs a FileOutputStream instance with append mode as false, which truncates the file to length 0. Here’s how code would look like:

import java.io.FileOutputStream

import java.io.IOException

fun main() {

val fileName = "/user/data/sys.log"

try {

FileOutputStream(fileName, false).use { }

} catch (e: IOException) {

e.printStackTrace()

}

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6. Using `FileWriter`

Finally, you can also create a FileWriter object which would truncate the file if it already exists. This is demonstrated below:

import java.io.File

import java.io.FileWriter

import java.io.IOException

fun main() {

val file = File("foo.out")

try {

FileWriter(file).use { }

} catch (e: IOException) {

e.printStackTrace()

}

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That’s all about truncating a file in Kotlin.

1. Using PrintWriter

2. Using BufferedWriter

3. Using FileChannel

4. Using RandomAccessFile

5. Using FileOutputStream

6. Using FileWriter

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1. Using `PrintWriter`

2. Using `BufferedWriter`

3. Using `FileChannel`

4. Using `RandomAccessFile`

5. Using `FileOutputStream`

6. Using `FileWriter`