Temporary Files And Directories in Kotlin

Throughout program execution, we often want to create data that isn’t needed after the program exits. Temporary files and directories are useful for this purpose since they don’t pollute the file system over time.

import java.io.File
import kotlin.io.path.createTempDirectory
import kotlin.io.path.createTempFile

fun check(e: Exception?) {
    e?.let { throw it }
}

fun main() {
    // The easiest way to create a temporary file is by using
    // createTempFile. It creates a file *and* opens it for
    // reading and writing. We provide null as the first argument,
    // so createTempFile will create the file in the default
    // location for our OS.
    val f = createTempFile(prefix = "sample", suffix = null)
    check(null)

    // Display the name of the temporary file. On
    // Unix-based OSes the directory will likely be `/tmp`.
    // The file name starts with the prefix given as the
    // first argument to createTempFile and the rest
    // is chosen automatically to ensure that concurrent
    // calls will always create different file names.
    println("Temp file name: ${f.absolutePath}")

    // Clean up the file after we're done. The OS is
    // likely to clean up temporary files by itself after
    // some time, but it's good practice to do this
    // explicitly.
    f.toFile().deleteOnExit()

    // We can write some data to the file.
    f.toFile().writeBytes(byteArrayOf(1, 2, 3, 4))
    check(null)

    // If we intend to write many temporary files, we may
    // prefer to create a temporary *directory*.
    // createTempDirectory's arguments are similar to
    // createTempFile's, but it returns a directory *name*
    // rather than an open file.
    val dname = createTempDirectory("sampledir")
    check(null)
    println("Temp dir name: ${dname.absolutePath}")

    dname.toFile().deleteOnExit()

    // Now we can synthesize temporary file names by
    // prefixing them with our temporary directory.
    val fname = File(dname.toFile(), "file1")
    fname.writeBytes(byteArrayOf(1, 2))
    check(null)
}

When you run this program, you’ll see output similar to:

Temp file name: /tmp/sample3521276550293018817.tmp
Temp dir name: /tmp/sampledir3521276550293018818

In this Kotlin version:

We use kotlin.io.path.createTempFile and kotlin.io.path.createTempDirectory to create temporary files and directories.
Instead of using a custom check function to handle errors, we use Kotlin’s built-in exception handling. The check function is kept for consistency with the original example, but it throws the exception if it’s not null.
We use deleteOnExit() to ensure temporary files and directories are deleted when the program exits.
File operations are performed using Kotlin’s File API, which provides a more idiomatic way to work with files in Kotlin.
We use Kotlin’s string interpolation (${...}) for easier string formatting.

This example demonstrates how to work with temporary files and directories in Kotlin, which is useful for creating data that isn’t needed after the program exits.

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Temporary Files And Directories in Kotlin