warning

There is a pending German patent application with the application number 10 2023 125 012.4. In order to use the TREND watermarker Software in the form published here, a patent license is required in addition to the license for the Software. See LICENSE for more information. In case of any questions or uncertainties, please contact us at trend@isst.fraunhofer.de.

Kotlin

If you want to use watermarking inside your Kotlin project, this page gives you the necessary information.

Compile the Library

See Installation.

Example: Watermarking Text with Text

Below you can see an example project that inserts a text as a watermark into a cover text and then extracts the watermark from the watermarked text.

1. Add Library as Dependency

Line 12 is the important line that adds our library as a dependency into the project. Currently, we are working with local deployment, so you will have to add mavenLocal() as repo (line 8) and publish the library to mavenLocal (see Installation).

build.gradle.kts

plugins {
    id("org.jetbrains.kotlin.jvm") version "2.0.0"
    application
}

repositories {
    mavenCentral()
    mavenLocal()
}

dependencies {
    implementation("de.fraunhofer.isst.trend:watermarker:0.1.0-SNAPSHOT")
}

application {
    mainClass.set("MainKt")
}

2. Use the Library

The extension functions handle() and unwrap() are optional for easy error handling with our custom return types (see Concepts for more details).

Watermark extraction can be customized for different use cases using optional Boolean parameters (see Watermarker for more details)

src/main/kotlin/Main.kt

import de.fraunhofer.isst.trend.watermarker.Watermarker
import de.fraunhofer.isst.trend.watermarker.returnTypes.Result
import de.fraunhofer.isst.trend.watermarker.returnTypes.Status
import de.fraunhofer.isst.trend.watermarker.watermarks.TextWatermark
import kotlin.system.exitProcess

fun main() {
    // *********************
    // ***** INSERTION *****
    // *********************

    // the coverText to be enhanced with a watermark
    val coverText =
        "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor " +
            "incididunt ut labore et dolore magna aliqua. Blandit volutpat maecenas " +
            "volutpat blandit aliquam etiam erat velit."
    // the watermark text that will be included in the coverText above
    val watermarkText = "Test"

    // prepare watermarker
    val watermarker = Watermarker()

    // creating a watermark with watermarkText as content
    val watermark = TextWatermark.new(watermarkText)

    // inserting the watermark into the cover text and handling potential errors and warnings
    val watermarkedText = watermarker.textAddWatermark(coverText, watermark).unwrap()

    // print the watermarked text
    println("watermarked text:")
    println(watermarkedText)
    println()
    
    // **********************
    // ***** Extraction *****
    // **********************

    // extract the watermark from the watermarked text
    val extractedWatermarks = watermarker.textGetTextWatermarks(watermarkedText).unwrap()
    check(extractedWatermarks.size == 1)
    val extractedWatermark = extractedWatermarks[0]

    // print the watermark text
    println("Found a watermark in the text:")
    println(extractedWatermark.text)


    // *******************************
    // ***** Multiple watermarks *****
    // *******************************

    // for multiple watermarks in a single text an additional parameter 'singleWatermark = false'
    // can be passed to the extraction function alongside the watermarked text, details are linked 
    // above this code block 

    // a second Watermark to illustrate multiple watermark extraction
    val secondWatermarkText = "Okay"

    // creating the second watermark
    val secondWatermark = TextWatermark.new(secondWatermarkText)

    // inserting the second watermark into the coverText
    val secondWatermarkedText = watermarker.textAddWatermark(coverText, secondWatermark).unwrap()

    // combining the watermarked texts to get two different watermarks in one Text
    val combinedText = watermarkedText + secondWatermarkedText

    // extract the watermarks from the watermarked text
    val extractedMultipleWatermarks =
        watermarker.textGetTextWatermarks(combinedText, singleWatermark = false).unwrap()

    // print the watermarks found
    for (extracted in extractedMultipleWatermarks) println("Found watermark: $extracted")

}

/**
 * Handles a status depending on its variant:
 * Variant Error:
 *  - print error and exit with code -1
 * Variant Warning:
 *  - print warning
 * Variant Success:
 *  - nop
 */
fun Status.handle() {
    if (isSuccess && !this.hasCustomMessage) {
        return
    }

    println(this)

    if (isError) {
        exitProcess(-1)
    }
}

/**
 * Unwraps a Result depending on its variant:
 * Variant Error:
 *  - print error and exit with code -1
 * Variant Warning:
 *  - print warning
 *  - return non-null value
 * Variant Success:
 *  - return non-null value
 */
fun <T> Result<T>.unwrap(): T {
    status.handle()
    checkNotNull(value) {
        "A Result with a Status of type Success or Warning is expected to have a value"
    }

    return value!!
}