Parsing arguments to a Java command line program

Question

What if I wanted to parse this:

java MyProgram -r opt1 -S opt2 arg1 arg2 arg3 arg4 --test -A opt3

And the result I want in my program is:

regular Java args[]  of size=4
org.apache.commons.cli.Options[]  of size=3
org.apache.commons.cli.Options[] #2 of size=1

I would prefer to use Apache Commons CLI, but the documentation is a little unclear about the case I present above. Specifically, the documentation doesn't tell you how to handle options of the 3rd type I specify below:

1. options with a "-" char
2. options with a "--" char
3. options without any marker, or "bare args"

I wish that Apache Commons CLI would work but STILL be able to pass regular args to the program if those args didn't have a option prefix. Maybe it does but the documentation doesnt say so as I read through it...

Answer 1

I like this one. Simple and you have have more than one parameter for each argument:

final Map<String, List<String>> params = new HashMap<>();

List<String> options = null;
for (int i = 0; i < args.length; i++) {
    final String a = args[i];

    if (a.charAt(0) == '-') {
        if (a.length() < 2) {
            System.err.println("Error at argument " + a);
            return;
        }

        options = new ArrayList<>();
        params.put(a.substring(1), options);
    }
    else if (options != null) {
        options.add(a);
    }
    else {
        System.err.println("Illegal parameter usage");
        return;
    }
}

For example:

-arg1 1 2 --arg2 3 4

System.out.print(params.get("arg1").get(0)); // 1
System.out.print(params.get("arg1").get(1)); // 2
System.out.print(params.get("-arg2").get(0)); // 3
System.out.print(params.get("-arg2").get(1)); // 4

Answer 2

Here is @DwB solution upgraded to Commons CLI 1.3.1 compliance (replaced deprecated components OptionBuilder and GnuParser). The Apache documentation uses examples that in real life have unmarked/bare arguments but ignores them. Thanks @DwB for showing how it works.

import org.apache.commons.cli.CommandLine;
import org.apache.commons.cli.CommandLineParser;
import org.apache.commons.cli.DefaultParser;
import org.apache.commons.cli.HelpFormatter;
import org.apache.commons.cli.Option;
import org.apache.commons.cli.Options;
import org.apache.commons.cli.ParseException;

public static void main(String[] parameters) {
    CommandLine commandLine;
    Option option_A = Option.builder("A").argName("opt3").hasArg().desc("The A option").build();
    Option option_r = Option.builder("r").argName("opt1").hasArg().desc("The r option").build();
    Option option_S = Option.builder("S").argName("opt2").hasArg().desc("The S option").build();
    Option option_test = Option.builder().longOpt("test").desc("The test option").build();
    Options options = new Options();
    CommandLineParser parser = new DefaultParser();

    options.addOption(option_A);
    options.addOption(option_r);
    options.addOption(option_S);
    options.addOption(option_test);

    String header = "               [<arg1> [<arg2> [<arg3> ...\n       Options, flags and arguments may be in any order";
    String footer = "This is DwB's solution brought to Commons CLI 1.3.1 compliance (deprecated methods replaced)";
    HelpFormatter formatter = new HelpFormatter();
    formatter.printHelp("CLIsample", header, options, footer, true);    

    String[] testArgs =
            { "-r", "opt1", "-S", "opt2", "arg1", "arg2",
                    "arg3", "arg4", "--test", "-A", "opt3", };

    try
    {
        commandLine = parser.parse(options, testArgs);

        if (commandLine.hasOption("A"))
        {
            System.out.print("Option A is present.  The value is: ");
            System.out.println(commandLine.getOptionValue("A"));
        }

        if (commandLine.hasOption("r"))
        {
            System.out.print("Option r is present.  The value is: ");
            System.out.println(commandLine.getOptionValue("r"));
        }

        if (commandLine.hasOption("S"))
        {
            System.out.print("Option S is present.  The value is: ");
            System.out.println(commandLine.getOptionValue("S"));
        }

        if (commandLine.hasOption("test"))
        {
            System.out.println("Option test is present.  This is a flag option.");
        }

        {
            String[] remainder = commandLine.getArgs();
            System.out.print("Remaining arguments: ");
            for (String argument : remainder)
            {
                System.out.print(argument);
                System.out.print(" ");
            }

            System.out.println();
        }

    }
    catch (ParseException exception)
    {
        System.out.print("Parse error: ");
        System.out.println(exception.getMessage());
    }

}

Output:

usage: CLIsample [-A <opt3>] [-r <opt1>] [-S <opt2>] [--test]
                 [<arg1> [<arg2> [<arg3> ...
       Options, flags and arguments may be in any order
 -A <opt3>   The A option
 -r <opt1>   The r option
 -S <opt2>   The S option
    --test   The test option
This is DwB's solution brought to Commons CLI 1.3.1 compliance (deprecated
methods replaced)
Option A is present.  The value is: opt3
Option r is present.  The value is: opt1
Option S is present.  The value is: opt2
Option test is present.  This is a flag option.
Remaining arguments: arg1 arg2 arg3 arg4