Example picocli-based CLI application

FileList.java

/* STEPS FOR CREATING NATIVE IMAGE (MacOS, Linux):

# download this file
mkdir picocli-demo
cd picocli-demo
wget --quiet --show-progress https://gist.githubusercontent.com/remkop/4d0339d9a7f80fa848735bec745d203a/raw/8a3fcaf698b44a3a721e1ba800674cbb1a435e29/FileList.java

# download dependencies
wget --quiet --show-progress https://github.com/remkop/picocli/releases/download/v4.1.4/picocli-4.1.4.jar
wget --quiet --show-progress https://github.com/remkop/picocli/releases/download/v4.1.4/picocli-codegen-4.1.4.jar

# compile and generate native-image configuration files
mkdir classes
javac -d classes -cp picocli-4.1.4.jar:picocli-codegen-4.1.4.jar FileList.java

# inspect result
tree

# build native image
native-image -cp classes:picocli-4.1.4.jar FileList

# execute: basic usage
./filelist -h
./filelist --version
./filelist
./filelist -r -S SIZE

# install command line completion for this command
. <(./filelist generate-completion)

# use completion
./filelist -<TAB>

*/
import picocli.AutoComplete;
import picocli.CommandLine;
import picocli.CommandLine.Command;
import picocli.CommandLine.Option;
import picocli.CommandLine.Parameters;

import java.io.File;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Date;
import java.util.concurrent.Callable;
import java.util.function.Consumer;

@Command(name = "filelist", mixinStandardHelpOptions = true,
        description = {
                "List information about the <file> (the current directory by default).",
                "Sort entries alphabetically if no other sort order is specified." },
        version = {
                "filelist 2.0",
                "Picocli " + picocli.CommandLine.VERSION,
                "JVM: ${java.version} (${java.vendor} ${java.vm.name} ${java.vm.version})",
                "OS: ${os.name} ${os.version} ${os.arch}"},
        subcommands = AutoComplete.GenerateCompletion.class)
public class FileList implements Callable<Integer> {

    @Parameters(index = "0", defaultValue = ".", description = "The file to list.")
    private File file;

    @Option(names = {"-S", "--sort"},
            description = "Sort order. One of: ${COMPLETION-CANDIDATES}. Default value: ${DEFAULT-VALUE}.")
    private Sort sort = Sort.NAME;

    @Option(names = {"-r", "--reverse"}, description = "Reverse order while sorting.")
    private boolean reverse;

    public static void main(String... args) {
        System.exit(new CommandLine(new FileList()).execute(args));
    }

    @Override
    public Integer call() throws Exception {
        Comparator<File> order = reverse ? sort.order.reversed() : sort.order;
        Arrays.stream(file.listFiles()).sorted(order).forEach(f ->
                System.out.printf("%2$10d %3$tb %3$2te %3$tY %3$tH:%3$tM %1$s%n",
                        f.getName(), f.length(), new Date(f.lastModified()))
        );
        return 0;
    }

    enum Sort {
        NONE((f1, f2) -> 0),
        SIZE((f1, f2) -> Long.compare(f1.length(), f2.length())),
        NAME((f1, f2) -> f1.getName().compareTo(f2.getName())),
        TIME((f1, f2) -> Long.compare(f1.lastModified(), f2.lastModified())),
        ;
        public final Comparator<File> order;
        Sort(Comparator<File> c) { order = c; }
    }
}