picocli

A one-file framework for creating Java command line applications with almost zero code.

Website | Source

Example: Fully-functional checksum application

import picocli.CommandLine;
import picocli.CommandLine.Command;
import picocli.CommandLine.Option;
import picocli.CommandLine.Parameters;

import java.io.File;
import java.math.BigInteger;
import java.nio.file.Files;
import java.security.MessageDigest;
import java.util.concurrent.Callable;

@Command(name = "checksum", mixinStandardHelpOptions = true, version = "checksum 4.0",
         description = "Prints the checksum (SHA-256 by default) of a file to STDOUT.")
class CheckSum implements Callable<Integer> {

    @Parameters(index = "0", description = "The file whose checksum to calculate.")
    private File file;

    @Option(names = {"-a", "--algorithm"}, description = "MD5, SHA-1, SHA-256, ...")
    private String algorithm = "SHA-256";

    @Override
    public Integer call() throws Exception { // your business logic goes here...
        byte[] fileContents = Files.readAllBytes(file.toPath());
        byte[] digest = MessageDigest.getInstance(algorithm).digest(fileContents);
        System.out.printf("%0" + (digest.length*2) + "x%n", new BigInteger(1, digest));
        return 0;
    }

    // this example implements Callable, so parsing, error handling and handling user
    // requests for usage help or version help can be done with one line of code.
    public static void main(String... args) {
        int exitCode = new CommandLine(new CheckSum()).execute(args);
        System.exit(exitCode);
    }
}

Example: Same, as Kotlin

import picocli.CommandLine
import picocli.CommandLine.Command
import picocli.CommandLine.Option
import picocli.CommandLine.Parameters

import java.io.File
import java.math.BigInteger
import java.nio.file.Files
import java.security.MessageDigest
import java.util.concurrent.Callable
import kotlin.system.exitProcess

@Command(name = "checksum", mixinStandardHelpOptions = true, version = ["checksum 4.0"],
    description = ["Prints the checksum (SHA-256 by default) of a file to STDOUT."])
class Checksum : Callable<Int> {

    @Parameters(index = "0", description = ["The file whose checksum to calculate."])
    lateinit var file: File

    @Option(names = ["-a", "--algorithm"], description = ["MD5, SHA-1, SHA-256, ..."])
    var algorithm = "SHA-256"

    override fun call(): Int {
        val fileContents = Files.readAllBytes(file.toPath())
        val digest = MessageDigest.getInstance(algorithm).digest(fileContents)
        println(("%0" + digest.size * 2 + "x").format(BigInteger(1, digest)))
        return 0
    }
}

fun main(args: Array<String>) : Unit = exitProcess(CommandLine(Checksum()).execute(*args))

Dependency:

dependencies {
    implementation 'info.picocli:picocli:4.7.7'
}

Enabling the annotation processor:

dependencies {
    implementation 'info.picocli:picocli:4.7.7'
    annotationProcessor 'info.picocli:picocli-codegen:4.7.7'
}


compileJava {
    options.compilerArgs += ["-Aproject=${project.group}/${project.name}"]
}

Tags: library   console   jvm  

Last modified 28 April 2025