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Creating QRCodes in Kotlin and Java is harder than it should be. QRCode-Kotlin aims to bring a simple, straightforward and customizable way to create QRCodes into the JVM domain, especially in the backend.

Advantages of QRCode-Kotlin

Pure Kotlin: Reimplemented on pure Kotlin from a reference implementation of the QRCode spec by Kazuhiko Arase
Lightweight: No dependencies*, ~65KB and it does what it says on the tin.
Easy to use: Instantiate an object, invoke a method, and you're done :)
Compact: Doesn't add any bloat like when using libraries like Google's ZXing (which do way more than generate QRCodes)
Customizable output: Want to make a colorful QRCode? We got you! A round one? Sure! Maybe use a drawing library? All good as well!
Server friendly: This isn't a library for Mobile applications, but it is extensible. This is a library thought by backend developers for backend developers.
Android is Supported: Since this library is now a Kotlin Multiplatform one, Android is now natively supported as well!
JavaScript is Supported: Now a Browser-Compatible JavaScript version is also available. Check an example here!

* Well, except maybe the org.jetbrains.kotlin:kotlin-stdlib-jdk8 one if you use Java...

Installation

This library is available from Maven Central, so you can add QRCode-Kotlin to your project as a dependency like any other:

Now this is a Multiplatform lib: Starting from version 3.0.0 this library became a Kotlin Multiplatform library. We hope that to you using the library the only change is to declare either qrcode-kotlin-jvm or qrcode-kotlin-android as the dependency.

If you're using Maven - pom.xml:

<!-- Use this one for normal applications -->
<dependency>
    <groupId>io.github.g0dkar</groupId>
    <artifactId>qrcode-kotlin-jvm</artifactId>
    <version>3.3.0</version>
</dependency>



<!-- Or this one for Android apps 👀 -->
<dependency>
    <groupId>io.github.g0dkar</groupId>
    <artifactId>qrcode-kotlin-android</artifactId>
    <version>3.3.0</version>
</dependency>

If you're using Gradle:

// Kotlin ❤️
// Use this one for normal applications
implementation("io.github.g0dkar:qrcode-kotlin-jvm:3.3.0")
// Or this one for Android apps 👀
implementation("io.github.g0dkar:qrcode-kotlin-android:3.3.0")



// Groovy
// Use this one for normal applications
implementation 'io.github.g0dkar:qrcode-kotlin-jvm:3.3.0'
// Or this one for Android apps 👀
implementation 'io.github.g0dkar:qrcode-kotlin-android:3.3.0'

Or if you're using it on your Browser:

<!-- Step 1: Import the library -->
<script src="qrcode-kotlin.min.js"></script>

<!-- Step 2: Recommended to do this to make it easier to use -->
<script>
    const QRCode = window['qrcode-kotlin'].io.github.g0dkar.qrcode.QRCode
</script>

Examples and Usage

Here are a few examples of how to use the library to achieve some nice results. If you are interested in more advanced uses and/or fancier QRCodes, please read the documentation :)

New: There's a new example showing how to create an SVG QRCode!

Also, make sure to check our examples folder for codes in Kotlin and Java, and the resulting QRCodes!

Just a plain, simple QRCode, nothing fancy

To generate a simple QRCode:

// By default, the writeImage() method outputs PNGs
val fileOut = FileOutputStream("example01.png")

QRCode("https://github.com/g0dkar/qrcode-kotlin").render().writeImage(fileOut)

Same code as above, but in Java:

// By default, the writeImage() method outputs PNGs
FileOutputStream fileOut = new FileOutputStream("example01-java.png");

new QRCode("https://github.com/g0dkar/qrcode-kotlin").render().writeImage(fileOut);

A QRCode, but bigger

The render() function can receive a cellSize to adjust the size of the resulting QRCode. This parameter represents the size in pixels of each square of the resulting QRCode. Its default value is 25:

val fileOut = FileOutputStream("example02.png")

QRCode("https://github.com/g0dkar/qrcode-kotlin")
    .render(cellSize = 50)
    .writeImage(fileOut)

In Java:

FileOutputStream fileOut = new FileOutputStream("example02-java.png");

new QRCode("https://github.com/g0dkar/qrcode-kotlin")
    .render(50)
    .writeImage(fileOut);

Just like Google's ZXing one!

As of the time of writing, Google's ZXing library is widely used to render QRCodes. Its rendering of QRCodes usually adds a "border" (aka "margin") around the QRCode, usually equal to 1 cell. The render() function can receive a margin parameter as well, which is how many pixels we want to have as a margin around our QRCode. By default, the margin parameter is equal to 0.

To have one of these nice looking and spaced QRCode, try doing this:

val fileOut = FileOutputStream("example03.png")
val cellSize = 30 // pixels

QRCode("https://github.com/g0dkar/qrcode-kotlin")
    .render(cellSize, margin = cellSize)
    .writeImage(fileOut)

In Java:

FileOutputStream fileOut = new FileOutputStream("example03-java.png");
int cellSize = 30; // pixels

new QRCode("https://github.com/g0dkar/qrcode-kotlin")
    .render(cellSize, cellSize);
    .writeImage(fileOut);

A splash of Color

Want to have a colorful QRCode? Easy-peasy! The render() function also have the brightColor, darkColor and marginColor parameters just for that. Their default values are Black-and-White squares with a White margin.

Starting from v2.0.0 these are simply Int values in the RGBA space. These can be created with either the new Colors helper class or if you are running in the JRE with plain, (very) old java.awt.Color classes :)

For fun, this will make a QRCode with GitHub's Dark Mode colors:

import io.github.g0dkar.qrcode.render.Colors

val background = Colors.css("#8b949e")
val foreground = Colors.css("#0d1117")
val fileOut = FileOutputStream("example04.png")

QRCode("https://github.com/g0dkar/qrcode-kotlin").render(
    brightColor = background, // Background
    darkColor = foreground,   // Foreground (aka the "black squares")
    marginColor = background  // Margin (ignored since margin = 0)
).writeImage(fileOut)

In Java:

import java.awt.Color;

Color background = new Color(13, 17, 23);
Color foreground = new Color(139, 148, 158);
FileOutputStream fileOut = new FileOutputStream("example04-java.png");

new QRCode("https://github.com/g0dkar/qrcode-kotlin")
    .render(25, 0, background.getRGB(), foreground.getRGB(), background.getRGB())
    .writeImage(fileOut);

Specifying your own data type

If you don't want to rely on the basic data-type identification logic implemented by the library, you can specify what is the type of data that your input string is composed of. You can pass it as the dataType parameter in the constructor of the QRCode class like this:

// Create a "String" typed QRCode instead of a "Number" (which would be automatically identified)
QRCode("42", dataType = QRCodeDataType.DEFAULT)

Spring Framework and/or Spring Boot

One of the main reasons I developed this library was to use it on a Spring Boot API that needed to generate QRCodes. So it is only natural to show how to do that :)

import org.springframework.core.io.ByteArrayResource
import org.springframework.http.HttpHeaders.CONTENT_DISPOSITION
import org.springframework.http.MediaType.IMAGE_PNG_VALUE

@GetMapping("/qrcode")
fun generateQrCode(content: String): ResponseEntity<ByteArrayResource> {
    val imageOut = ByteArrayOutputStream()

    QRCode(content).render().writeImage(imageOut)

    val imageBytes = imageOut.toByteArray()
    val resource = ByteArrayResource(imageBytes, IMAGE_PNG_VALUE)

    return ResponseEntity.ok()
        .header(CONTENT_DISPOSITION, "attachment; filename=\"qrcode.png\"")
        .body(resource)
}

License

QR Code is trademarked by Denso Wave, inc.

Thanks and Acknowledgements

Kazuhiko Arase: For his reference implementation!
Paul Varry: for opening the first few issues on the repo and helping to make the library even better for everyone! 😁
Renan Lukas: For his friendship, patience and help with Android, Gradle and a bunch of other stuff during the development of v2.0.0 and v3.0.0!
Doomsdayrs: For pointing out how the library could be improved using Kotlin Multiplatform, and helping out implementing it into the project.

Support and Links

If you found any bugs, please open an Issue 😁
Have any suggestions? You can make them as well!

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README_v3.md

README_v3.md

Table of Contents

Advantages of QRCode-Kotlin

Installation

Examples and Usage

Just a plain, simple QRCode, nothing fancy

A QRCode, but bigger

Just like Google's ZXing one!

A splash of Color

Specifying your own data type

Spring Framework and/or Spring Boot

License

Thanks and Acknowledgements

Support and Links

Files

README_v3.md

Latest commit

History

README_v3.md

File metadata and controls

Table of Contents

Advantages of QRCode-Kotlin

Installation

Examples and Usage

Just a plain, simple QRCode, nothing fancy

A QRCode, but bigger

Just like Google's ZXing one!

A splash of Color

Specifying your own data type

Spring Framework and/or Spring Boot

License

Thanks and Acknowledgements

Support and Links