Kotlin: How to Print Colored Text in the Console

Introduction

A common requirement in many applications is to enhance the readability of console outputs by adding colors. This is particularly useful in logging, troubleshooting, or simply making the interaction with CLI applications more engaging. In Kotlin, several methods can be used to print colored text to the console. The following sections will explore these options, providing solutions with sample code and discussing the advantages and disadvantages of each.

Solution

Using ANSI Escape Codes

ANSI escape codes are a popular way to color terminal output because they are widely supported and straightforward to implement.

Sample Code

fun main() {
    val ANSI_RESET = "\u001B[0m"
    val ANSI_RED = "\u001B[31m"
    val ANSI_GREEN = "\u001B[32m"
    val ANSI_BLUE = "\u001B[34m"

    println("${ANSI_RED}This text is red!${ANSI_RESET}")
    println("${ANSI_GREEN}This text is green!${ANSI_RESET}")
    println("${ANSI_BLUE}This text is blue!${ANSI_RESET}")
}

Output

This text is red!
This text is green!
This text is blue!

Advantages

• Simple and Direct: Requires no additional libraries.
• Widely Supported: Works on most Unix-like systems and some Windows terminals.

Disadvantages

• Limited Control: Complex color manipulation (e.g., backgrounds, bold, etc.) can become cumbersome.
• Compatibility Issues: Not all terminal emulators support ANSI codes equally well.

Using JANSI Library

JANSI is a library specifically designed for ANSI escape codes, making it easier to work with colors in Java and Kotlin applications.

Sample Code

import org.fusesource.jansi.AnsiConsole
import org.fusesource.jansi.Ansi.ansi

fun main() {
    AnsiConsole.systemInstall()

    println(ansi().fgRed().a("This is red text").reset())
    println(ansi().fgGreen().a("This is green text").reset())
    println(ansi().fgBlue().a("This is blue text").reset())

    AnsiConsole.systemUninstall()
}

Output

This is red text
This is green text
This is blue text

Advantages

• Ease of Use: Simplifies the usage of ANSI codes.
• Feature-Rich: Provides additional formatting options like bold, underline, etc.

Disadvantages

• Third-Party Dependency: Adds an external dependency to the project.
• Heavier: Slightly more heavyweight compared to raw ANSI codes.

Using Kotlinx-cli Library

Kotlinx-cli is a library designed by JetBrains to simplify command-line parsing and enhance CLI applications.

Sample Code

import kotlinx.cli.*

fun main(args: Array<String>) {
    val parser = ArgParser("example")
    val red: Boolean by parser.option(ArgType.Boolean, shortName = "r", description = "Print text in red").default(false)

    parser.parse(args)

    if (red) {
        println("\u001B[31mThis text is red!\u001B[0m")
    } else {
        println("This text is default color.")
    }
}

Output

$ java -jar example.jar -r
This text is red!
$ java -jar example.jar
This text is default color.

Advantages

• Enhanced CLI Features: Provides robust command-line argument parsing.
• Modular: Can be easily integrated with other Kotlin multiplatform projects.

Disadvantages

• Learning Curve: Requires understanding of the library and its syntax.
• Limited Color Control: Primarily aimed at argument parsing rather than text formatting.

Similar Topics

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