java-flags

Light-weight command-line flags using an easy-to-use static binding approach. It provides annotations to describe classes and flags and tools to generate program usage documentation from sources at runtime.

Usage

To use a command-line flag value you need to create an accessor for it. This is done by Flags.create() method or by one of the specific variants:

class ReadmeExample {
    static final Flag<String> input = Flags.create("");
}

The name argument must match the flag name as specified on command-line (without '--' prepended), i.e.:

java ProgramRunner --input input.txt

In your program main() method pass the command-line arguments to Flags:

public class ProgramRunner {
    public static main(String[] args) {
            Flags.parse(args, ImmutableList.of("com.github.yin.flags.example"));
        // ....
    }
}

To access the flag value, use the accessor get() method. This is typically done in the constructor, or in a Guice Module Provider:

public class ReadmeExample {
    static final Flag<String> input = Flags.create("");
    private final String inputfile;
    // ...

    ReadmeExample() {
	this.inputfile = input.get();
    }
}

Generating command-line usage help

And finally, to attach some docs and generate the documentation, you just use the @FlagDesc annotation:

@FlagDesc("This class is an example how to print files")
public class ReadmeExample {
    @FlagDesc("Specifies path to input file")
    static final Flag<String> input = Flags.create("");
    // ...
}

... and call the printUsage() method for you program package:

@FlagDesc("This class is an example how to print files")
public class ReadmeExample {
    // ...
    public static void main(String[] args) {
        try {
            Flags.parse(args, ImmutableList.of("com.github.yin.flags.example"));
        } catch (Flags.ParseException e) {
            System.err.println(e.getMessage());
            Flags.printUsage("com.github.yin.flags.example");
            System.exit(1);
            return;
        }
        ReadmeExample re = new ReadmeExample();
        re.run();
    }
    // ...
}

Validators

public class ProgramRunner {
    static final Flag<String> input = Flags.create("")
            .validator((String path) -> {
                if (path == null || path.isEmpty()) {
                    throw new Flags.ParseException("Input path is empty");
                }
            });
}

Installation

Just grab the package from Maven Central:

<dependency>
    <groupdId>com.github.yin.flags</groupId>
    <artifactId>java-flags</artifactId>
    <version>0.3.0-beta1</version>
</dependency>

Building

Easy, use this GitHub repository and Maven:

git clone https://github.com/yin/java-flags.git java-flags
cd !$
mvn install

License

MIT License, (C) 2016-2017 Matej 'Yin' Gagyi