Java commons-cli, options with list of possible values

Question

How can I make an option accept only some specified values like in the following example:

$ java -jar Mumu.jar -a foo
OK
$ java -jar Mumu.jar -a bar
OK
$ java -jar Mumu.jar -a foobar
foobar is not a valid value for -a

Answer 1

I've wanted this kind of behaviour before, and never came across a way to do this with an already provided method. That's not to say it doesn't exist. A kind of lame way, is to add the code yourself such as:

private void checkSuitableValue(CommandLine line) {
    if(line.hasOption("a")) {
        String value = line.getOptionValue("a");
        if("foo".equals(value)) {
            println("OK");
        } else if("bar".equals(value)) {
            println("OK");
        } else {
            println(value + "is not a valid value for -a");
            System.exit(1);
        }
     }
 }

Obviously there would be nicer ways to do this than the long if/else, possibly with an enum, but that should be all you'd need. Also I've not compiled this, but I reckon it should work.

This example also does not make the "-a" switch mandatory, since that wasn't specified in the question.