Configuring Logging in a CLI App

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.config.Configurator;
import picocli.CommandLine;
import picocli.CommandLine.Option;

class MyApp {
    private static Logger logger = LogManager.getLogger(MyApp.class);

    @Option(names = {"-v", "--verbose"},
            description = {
                    "Specify multiple -v options to increase verbosity.",
                    "For example, `-v -v -v` or `-vvv`"})
    boolean[] verbosity = new boolean[0];

    private void configureLoggers() {
        if (verbosity.length >= 3) {
            Configurator.setRootLevel(Level.TRACE);
        } else if (verbosity.length == 2) {
            Configurator.setRootLevel(Level.DEBUG);
        } else if (verbosity.length == 1) {
            Configurator.setRootLevel(Level.INFO);
        } else {
            Configurator.setRootLevel(Level.WARN);
        }
    }

    @Override
    public void run() {
        logger.trace("Starting... (trace)");
        logger.debug("Starting... (debug)");
        logger.info("Starting... (info)");
        logger.warn("Starting... (warn)");
    }

    public static void main(String[] args) {
        System.exit(new CommandLine(new MyApp())
                .setExecutionStrategy(parseResult -> {
                    MyApp app = parseResult.commandSpec().commandLine().getCommand();
                    app.configureLoggers();
                    return new CommandLine.RunLast().execute(parseResult);
                }).execute(args));
    }
}