How to Use the DefaultParser in Apache Commons CLI?

Question

How do I utilize the DefaultParser class in Apache Commons CLI for parsing command-line arguments?

// Example of using DefaultParser in Apache Commons CLI
import org.apache.commons.cli.*;

public class CommandLineParserExample {
    public static void main(String[] args) {
        Options options = new Options();
        options.addOption("h", "help", false, "Show help");
        options.addOption("f", "file", true, "Input file");

        CommandLineParser parser = new DefaultParser();
        try {
            CommandLine cmd = parser.parse(options, args);
            if (cmd.hasOption("h")) {
                HelpFormatter formatter = new HelpFormatter();
                formatter.printHelp("Utility-name", options);
                System.exit(0);
            }
            if (cmd.hasOption("f")) {
                String fileName = cmd.getOptionValue("f");
                System.out.println("Input file: " + fileName);
            }
        } catch (ParseException e) {
            System.out.println(e.getMessage());
            HelpFormatter formatter = new HelpFormatter();
            formatter.printHelp("Utility-name", options);
            System.exit(1);
        }
    }
}

Answer

The DefaultParser in Apache Commons CLI is a powerful utility for handling command-line arguments in Java applications. It allows developers to craft complex command-line interfaces with ease, parsing user input and handling errors during parsing.

// Potential parsing exceptions handler
try {
    CommandLine cmd = parser.parse(options, args);
} catch (ParseException e) {
    System.err.println("Parsing failed.  Reason: " + e.getMessage());
}

Causes

User input not matching defined options.
Incorrect configuration of options and parameters in the CLI.

Solutions

Verify that all defined options in the Options object match the expected user input.
Utilize the HelpFormatter to provide clear usage instructions to users and to troubleshoot input mistakes.

Common Mistakes

Mistake: Failing to define options before parsing.

Solution: Always define your options in the Options object before attempting to parse the command-line arguments.

Mistake: Not handling ParseException correctly.

Solution: Implement a catch block for ParseException to inform users of parsing errors and provide usage details.

Helpers

Apache Commons CLI
DefaultParser
command-line arguments
Java CLI parsing
Apache Commons
Java command-line interface