argvester

ARGument harVESTER - a simple command line parser written with Love and Java 17

Apart from being fun, the code also show how record and sealed types works together.

The argvester uses a record as a meta description of the arguments of the command line. The original idea comes from structopt that uses a struct in C++, so the argvester is a kind of liberal port of structopt in Java.

Argvester supports 3 kinds of arguments

positional argument, argument that are required and in the right order
optional argument, argument that starts with '-' or '--' and can happear anywhere on the command line
variadic argument, one argument at the end that will collect all the arguments that rest

To define the arguments, the following algorithm is used

if the last record component is a collection, it's a variadic argument
if a record component is typed by Optional or a collection, it's an optional argument
otherwise it's a positional argument

Moreover, you can use (it's not a requirement) the annotation Opt to specify additional properties. This annotation is heavily inspired by the project Google Options.

A record as a meta description

First, let us define a record that describes all the arguments of the command line

  enum LogLevel { error, warning }
  record Option(
    // positional argument
    // java MyClass <config_file>
    Path config_file,
 
    // optional argument
    // short or long version
    //   e.g., -b or --bind-address
    // arguments can be delimited by ' ', '=' or ':'
    //   e.g., -b:192.168.0.10
    //   e.g., --bind-address=192.168.0.10
    //   e.g., --bind-address 192.168.0.10
    Optional<String> bind_address,
 
    // use enum to restrict possible arguments
    //   e.g., --log-level error
    Optional<LogLevel> log_level,
 
    // optional flag argument
    //   e.g, -v or --verbose
    Optional<Boolean> verbose,
 
    // variadic argument
    // use a collection like java.util.List or java.util.Set
    List<String> filenames
  ) {}

Then to create an ArgVester on it

  var argVester = ArgVester.create(MethodHandles.lookup(), Option.class);

and use the ArgVester to parse the command line

  var option = argVester.parse(args);

the ArgVester will create an instance of the record populated with the value of the arguments.

forax / argvester

argvester

A record as a meta description

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