MonadicT

I see dead objects!

Commandline parsing in Java

Despite thousands of Java CLI programs written, there is no standard Java library to parse command line arguments. Of course, there are tons of libraries which aim to fill this gap. Here is one that I like for its simplicity and minimal boilerplate requirements while supporting a decent feature set.

We define a class listing all our options. The options are annotated with @Option. An instance of this is passed to CmdLineParser.

/**
 * Class with annotated program options
 */
import org.kohsuke.args4j.Option;

class ProgramOptions {
    @Option(name = "-h", aliases = { "--host" }, required = false,
            usage = "Host URL")
    String option = "localhost";

    @Option(name = "-p", aliases = { "--port" }, required = false,
            usage = "Host port")
    int port = 3018;
}

In our main program, we instantiate ProgramOptions and CmdLineParser. The CmdLineParser's parseArgument method is invoked with args. Upon successful parse, our ProgramOptions object will be set to values that user provided or their default values. Quite nice!

import org.kohsuke.args4j.CmdLineException;
import org.kohsuke.args4j.CmdLineParser;

/**
  * An example command line parser
  */
    public class CommandLineParsing {

    static ProgramOptions opts = new ProgramOptions();

    static void processArgs(String[] args) {
        CmdLineParser parser = new CmdLineParser(opts);

        try {
            parser.parseArgument(args);
        } catch (CmdLineException e) {
            System.err.println(e.getMessage());
            parser.printUsage(System.err);
            System.exit(1);
        }
    }

    public static void main(String[] args) {
        processArgs(args);
    }
}