[cli] A weakness of parser

I found a weakness of Jakarta Commons CLI and want to explain it with a simple
example:

Our program provides 2 options:

1. -a or --algo <name>: The -a option requires an argument.
2. -k or --key <value>: The -k option requires an argument too.

a)

If you pass the following command line arguments everything will be ok:
-a Caesar -k A

After evaluation:

• "Caesar" is the parameter of the -a option and
• "A" is the parameter of the -k option.

b)

However an org.apache.commons.cli.MissingArgumentException: no argument for:k is
thrown if you pass the following input:

-a Caesar -k a

The Parser assumes that the argument "a" after the -k option, is the -a option
missing the hyphen. At the end of this description there is Java code for
executing this problem.

Information:

The handling of this command line

-a Caesar -k a

works in Getopt without any problem:

• "Caesar" is the parameter of the -a option and
• "a" of the -k option.

After parsing a valid option Getopt always takes the next (available) command
line argument as the option's parameter if the option requires an argument -
means if you pass to the command line

-k -a Caesar

After evaluation:

• "a" is the parameter of the -k option
• the "Caesar" argument is just ignored

If the option's parameter (<value>) represents an optional argument the next
argument is not required, if it represents a valid option - means if you pass to
the command line

-k -a Caesar

After evaluation:

• "Caesar" is the parameter of the -a option
• k option is set without a parameter - in this case a default value makes sense.

Last but not least here is the code snippet for the CLI Test:

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

public class TestCommonsCLI {

/**

• @param args
  */
  public static void main(String[] args) {

Options options = new Options();

Option algorithm = new Option("a" , "algo", true, "the algorithm which it to
perform executing");
algorithm.setArgName("algorithm name");
options.addOption(algorithm);

Option key = new Option("k" , "key", true, "the key the setted algorithm uses
to process");
algorithm.setArgName("value");
options.addOption(key);

CommandLineParser parser = new PosixParser();

try {
CommandLine line = parser.parse( options, args);

if(line.hasOption('a'))

{ System.out.println("algo: "+ line.getOptionValue( "a" )); }

if(line.hasOption('k'))

{ System.out.println("key: " + line.getOptionValue('k')); }

} catch (ParseException e)

{ // TODO Auto-generated catch block e.printStackTrace(); }

}

}