Process the command line with CLI in Java

by David Petersheim | Aug 08, 2005 7:00:00 AM

Tags: Jakarta Commons, David Petersheim, Java, BasicParser, HelpFormatter, CommandLine, command line argument, Command Line Interface, line argument, Java Tips Newsletter

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Takeaway: Writing code to parse command line arguments is still necessary sometimes. When you need to examine command line arguments, see how and why you should use your open source Java toolkit and use Command Line Interface.

Writing code to parse command line arguments isn't the most exciting job, but sometimes it's still necessary. The next time you need to examine command line arguments and things get a little complex, whip out your trusty open source Java toolkit, and use Command Line Interface (CLI).

Jakarta Commons hosts the CLI project. While it's overkill if you only have one or two arguments, it's essential if your application takes most of its settings from the command line.

To use CLI, you need to create an instance of the Options class:

Options opt = new Options();

With this instance of Options, you define the command line arguments that your application will accept. One way to do this is by using the addOption() method of the Options class. Call this method once for each option that your application can accept.

opt.addOption("h", false, "Print help for this application");
opt.addOption("u", true, "The username to use");
opt.addOption("dsn", true, "The data source to use");

Once you define your classes' arguments, create a CommandLineParser, and parse the String array that was passed to your main method.

BasicParser parser = new BasicParser();
CommandLine cl = parser.parse(opt, args);

Now that all of the arguments are parsed, you can examine the CommandLine instance returned by the parser to determine what arguments and values were supplied by the user.

if ( cl.hasOption('h') ) {
    HelpFormatter f = new HelpFormatter();
    f.printHelp("OptionsTip", opt);
}
else {
    System.out.println(cl.getOptionValue("u"));
    System.out.println(cl.getOptionValue("dsn"));
}

As you can see from above, you can use the HelpFormatter class to automatically generate usage information for your program.

Here's the entire code:

// OptionsTip.java
import org.apache.commons.cli.BasicParser;
import org.apache.commons.cli.Options;
import org.apache.commons.cli.CommandLine;
import org.apache.commons.cli.HelpFormatter;
import org.apache.commons.cli.ParseException;

public class OptionsTip {
    public static void main(String args[]) {
        try {
            Options opt = new Options();

            opt.addOption("h", false, "Print help for this application");
            opt.addOption("u", true, "The username to use");
            opt.addOption("dsn", true, "The data source to use");

            BasicParser parser = new BasicParser();
            CommandLine cl = parser.parse(opt, args);

            if ( cl.hasOption('h') ) {
                HelpFormatter f = new HelpFormatter();
                f.printHelp("OptionsTip", opt);
            }
            else {
                System.out.println(cl.getOptionValue("u"));
                System.out.println(cl.getOptionValue("dsn"));
            }
        }
        catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

CLI takes a tedious chore off your hands and makes parsing command line arguments a simple task. For more information, check out the documentation.

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