Working with ZIP/archives in Kotlin: a complete guide

Working with ZIP/archives in Kotlin: a complete guide

In modern Kotlin development (especially for JVM and Android), there is often a need to work with ZIP archives: pack logs, unpack resources, create backups, or transfer data in compressed form. In this article, we will take a detailed look at how to work with ZIP archives in Kotlin using built-in Java capabilities (the java.util.zip package), as well as consider convenient extensions and alternatives.

Why work with archives in Kotlin?

• Saving space — compressing data when storing on disk.
• Convenience of transfer — one archive instead of many files.
• Security — the ability to encrypt (with additional libraries).
• Working with resources — unpacking configurations or updates.

Main Java classes for working with ZIP

Kotlin is fully compatible with Java, so for working with archives we use the following classes from java.util.zip:

• ZipOutputStream — for creating an archive.
• ZipInputStream — for reading an archive.
• ZipEntry — represents an individual file/folder inside the archive.
• ZipFile — a convenient class for reading an existing archive.

Example 1: Creating a ZIP archive in Kotlin

Let's create an archive that contains several files and folders. We use ZipOutputStream and BufferedOutputStream for better performance.

import java.io.*import java.util.zip.*

fun createZipArchive(    filesToZip: List<File>,    outputZipPath: String) {    ZipOutputStream(BufferedOutputStream(FileOutputStream(outputZipPath))).use { zos ->        for (file in filesToZip) {            if (file.isDirectory) {                // Add an empty folder                zos.putNextEntry(ZipEntry("${file.name}/"))                zos.closeEntry()                continue            }            // Add a file            val entry = ZipEntry(file.name)            zos.putNextEntry(entry)            FileInputStream(file).use { fis ->                fis.copyTo(zos)            }            zos.closeEntry()        }    }    println("Archive created: $outputZipPath")}

fun main() {    val files = listOf(        File("document.txt"),        File("image.png"),        File("configs") // folder    )    createZipArchive(files, "output.zip")}

Example 2: Reading the contents of a ZIP archive

To view the list of files inside an archive, it is convenient to use ZipFile.

import java.util.zip.ZipFile

fun listZipContents(zipPath: String) {    ZipFile(zipPath).use { zip ->        println("Contents of archive $zipPath:")        zip.entries().asSequence().forEach { entry ->            val size = if (entry.isDirectory) "folder" else "${entry.size} bytes"            println("- ${entry.name} ($size)")        }    }}

fun main() {    listZipContents("output.zip")}

Example 3: Extracting a ZIP archive

Let's extract all files from the archive to a specified folder. Pay attention to handling nested folders.

import java.io.*import java.util.zip.ZipInputStream

fun extractZip(    zipPath: String,    outputDir: String = "extracted") {    val destDir = File(outputDir)    destDir.mkdirs()

    ZipInputStream(BufferedInputStream(FileInputStream(zipPath))).use { zis ->        var entry = zis.nextEntry        while (entry != null) {            val file = File(destDir, entry.name)            if (entry.isDirectory) {                file.mkdirs()            } else {                // Create parent folders                file.parentFile?.mkdirs()                BufferedOutputStream(Fi