QR Code Generator in Kotlin: ZXing Library and Implementation Tips

QR Code Generator in Kotlin Using ZXing

QR codes (Quick Response) have become an integral part of the modern digital world. They are used for quickly sharing links, contact information, Wi-Fi passwords, and other data. If you are developing an application in Kotlin — whether for Android, server-side (Ktor, Spring), or desktop (Compose Desktop) — you may need to embed QR code generation functionality. In this article, we will look at how to create a simple and effective QR code generator in Kotlin using the popular ZXing (Zebra Crossing) library.

Why ZXing?

ZXing is a multifunctional library for reading and writing barcodes and QR codes. It is written in Java, making it perfectly compatible with Kotlin. Key advantages:

• Support for various formats: QR Code, Data Matrix, Aztec, PDF417, and others.
• High performance and customizability.
• Active community and regular updates.
• Easy integration into Kotlin projects.

Adding the Library

To start, add the dependency to your build.gradle.kts (if you are using Gradle):

dependencies {    implementation("com.google.zxing:core:3.5.3")    implementation("com.google.zxing:javase:3.5.3") // for working with BufferedImage}

If you are writing a server application in Ktor or Spring, these dependencies will work. For Android, you can use the android-core module, but in most cases core is sufficient.

Basic QR Code Generator

Let's create a class QRCodeGenerator that will accept text and return a QR code image as a BufferedImage.

import com.google.zxing.BarcodeFormatimport com.google.zxing.EncodeHintTypeimport com.google.zxing.qrcode.QRCodeWriterimport com.google.zxing.common.BitMatriximport java.awt.image.BufferedImageimport java.util.*

class QRCodeGenerator {

    fun generateQRCode(text: String, width: Int = 300, height: Int = 300): BufferedImage {        // Setting encoding and error correction level        val hints = EnumMap<EncodeHintType, Any>(EncodeHintType::class.java).apply {            put(EncodeHintType.CHARACTER_SET, "UTF-8")            put(EncodeHintType.ERROR_CORRECTION, com.google.zxing.qrcode.decoder.ErrorCorrectionLevel.H) // High            put(EncodeHintType.MARGIN, 1) // Margins around the QR code        }

        val writer = QRCodeWriter()        val bitMatrix: BitMatrix = writer.encode(text, BarcodeFormat.QR_CODE, width, height, hints)

        // Converting BitMatrix to BufferedImage        val image = BufferedImage(width, height, BufferedImage.TYPE_INT_RGB)        for (x in 0 until width) {            for (y in 0 until height) {                image.setRGB(x, y, if (bitMatrix.get(x, y)) 0xFF000000.toInt() else 0xFFFFFFFF.toInt())            }        }        return image    }}

Explanation:

• QRCodeWriter — ZXing class responsible for creating the dot matrix.
• BitMatrix — a binary matrix where true means a black pixel.
• We set UTF-8 encoding and the maximum error correction level (H — 30% damage).
• The image is saved in ARGB format with a black and white color scheme.

Saving to a File (PNG)

To save the generated QR code to a file, use javax.imageio.ImageIO:

import java.io.Fileimport javax.imageio.ImageIO

fun saveQRCodeToFile(text: String, filePath: String) {    val generator = QRCodeGenerator()    val image = generator.generateQRCode(text)    val outputFile = File(filePath)    ImageIO.write(image, "png", outputFile)    println("QR code saved: ${outputFile.ab