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https://github.com/jbock-java/jbock

Reflectionless command line parser
https://github.com/jbock-java/jbock

annotation-processing command-line-parser java

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Reflectionless command line parser

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jbock is a command line parser, which uses the same well-known annotation names as [JCommander](https://jcommander.org/)

and [picocli](https://github.com/remkop/picocli).

It is an

[annotation processor](https://openjdk.java.net/groups/compiler/processing-code.html)

so it doesn't use runtime reflection, but generates a custom parser at compile time instead.



### Quick rundown



Create an abstract class, or alternatively a Java interface,

and add the `@Command` annotation.

In this so-called *command class*, each abstract method



* must return *something* (not `void`),

* must have *no* arguments, and

* must be annotated with either `@Option`, `@Parameter` or `@VarargsParameter`.



The *multiplicity* of options and parameters is determined by the *return type* of their declaring method.

The types `boolean`, `List` and `Optional` (including `OptionalInt`, yada yada) have a special meaning.

See example below.



````java

@Command

abstract class DeleteCommand {



  @Option(names = {"-v", "--verbosity"},

          description = {"A named option. The return type reflects optionality.",

                         "Could use Optional too, but using int or Integer",

                         "would make it a 'required option'."})

  abstract OptionalInt verbosity();



  @Parameter(

          index = 0,

          description = {"A required positional parameter. Return type is non-optional.",

                         "Path is a standard type, so no custom converter is needed."})

  abstract Path path();



  @Parameter(

          index = 1,

          description = "An optional positional parameter.")

  abstract Optional anotherPath();



  @VarargsParameter(

          description = {"A varargs parameter. There can only be one of these.",

                         "The return type must be List-of-something."})

  abstract List morePaths();

  

  @Option(names = "--dry-run",

          description = "A nullary option, a.k.a. mode flag. Return type is boolean.")

  abstract boolean dryRun();

  

  @Option(names = "-h",

          description = "A repeatable option. Return type is List.")

  abstract List headers(); 

  

  @Option(names = "--charset",

          description = "Named option with a custom converter",

          converter = CharsetConverter.class)

  abstract Optional charset();

  

  // sample converter class

  static class CharsetConverter extends StringConverter {

    @Override

    protected Charset convert(String token) { return Charset.forName(token); }

  }

}

````



The generated class is called `DeleteCommandParser`. It converts a string array to an instance of `DeleteCommand`:



````java

public static void main(String[] args) {

  DeleteCommand command = new DeleteCommandParser().parseOrExit(args);

  // ...

}



````



In addition to `parseOrExit`, the generated parser has a basic and side-effect free `parse` method.

This can be used to fine-tune the help and error messages for your users.



### Standard types



Some types don't need a custom converter. See [StandardConverters.java](https://github.com/jbock-java/jbock/blob/master/jbock/src/main/java/net/jbock/contrib/StandardConverters.java).



### Subcommands



The `@SuperCommand` annotation can be used to define a git-like subcommand structure. See [javadoc](https://github.com/jbock-java/jbock/blob/master/jbock/src/main/java/net/jbock/SuperCommand.java).



### Sample projects



* [jbock-maven-example](https://github.com/jbock-java/jbock-maven-example)

* [jbock-gradle-example](https://github.com/jbock-java/jbock-gradle-example)



### Alternatives



* [Tim's list](https://github.com/timtiemens/javacommandlineparser)