Command Line Interface

A small Java library, featuring a Command Line Interface and a custom JSON Parser.

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Command Line Interface

The CLI is split into options and the command line.

Creating an option

You’ll have to create a new Option using the OptionBuilder. An example implementation would be:

private static final Option INPUT = new OptionBuilder().setAbbreviation("-i").addAlias("--input").setRequired(true).setTakesInput(true).setDescription("Input file").create();
  1. Command Line Interface
    1. Creating an option
    2. Creating a CLI parser
    3. Parsing Arguments
    4. Help Page
  2. JSON Parsing
    1. Parsing
    2. Encoding

The aliases are optional, but each option requires an abbreviation. You can also toggle, whether an option is required and/or reads the following parameter as argument.

Creating a CLI parser

Next, you’ll need to create an CommandLine object, allowing you to parse args. Again, here’s an example implementation, using the CmdLineBuilder class:

private static final String CMD_BASE = "java -jar program.jar";
private static final String DESCRIPTION = "Magic Tool doing something special.";
private static final String COPYRIGHT = "Copyright (c) 2024 To_Craft. Licensed under the Crafted License 1.0";
private static final CommandLine CMDLINE = new CmdLineBuilder().setCmdBase("java -jar program.jar").setHeader(DESCRIPTION).setFooter(COPYRIGHT).setForceArgInput(false).addOptions(INPUT).create();

If forceArgInput is set to true, other options can be read as input for other options.

You’ll notice that you can define the base command. Every command option will then be amended to it on the help page. Every required argument is enclosed by brackets: [-i]. Moreover, every option that takes an input has <arg amended. The description for each option will be added to the more detailed help view. The Description/Header for the CommandLine will be added between the command and the detailed explanation. The Footer/Copyright will be added as the last line of help page.

The help page for the example above will look like this:

usage: java -jar program.jar -i <arg>
Magic Tool doing something special.
-i,--input <arg>       Input file
Copyright (c) 2024 To_Craft. Licensed under the Crafted License 1.0

If you add more options, you might see a help page, similar to this one:

usage: java -jar program.jar -i <arg> -o [-s <arg>] [-d] [-b <arg>]
Magic Tool doing something special.
-i,--input <arg>       Input file
-o,--output            Output if specified
-s,--second <arg>      Define a second input
-d,--directory,--dir   Do it in a directory
-b <arg>               Do it vise-versa
Copyright (c) 2024 To_Craft. Licensed under the Crafted License 1.0

Parsing Arguments

You can parse arguments by using CommandLine.parseArgs(String[]);. Assuming you have a String Array called args:

Map<Option, String> parsedArgs = CMDLINE.parseArgs(args);

parseArgs returns null, if there was an error parsing the args.

Each option will be mapped to an input value. If no input value is required, it will be mapped to null. Therefore, check if an option is present by using:

boolean inputIsPresent = parsedArgs.containsKey(INPUT);

Help Page

You can get the help page as a String by calling cmdLine.getHelpPage();.

JSON Parsing

The CLI library also contains a logic for parsing and encoding JSON.

Parsing

Assuming you have a String json, you can call JsonParser.parseJson(json); to get a JsonElement. Depending on what type of json you parsed, you can call one of the following methods, where each one throws a JsonParseException if the json String is of another type:

  • jsonElement.asBool() — returns a JsonBool, where you can call jsonBool.get() to get the value
  • jsonElement.asDouble() — returns a JsonDouble, where you can call jsonDouble.get() to get the value
  • jsonElement.asInt() — returns a JsonInt, where you can call jsonInt.get() to get the value
  • jsonElement.asInt() — returns a JsonInt, where you can call jsonInt.get() to get the value
  • jsonElement.asString() — returns a JsonString, where you can call jsonString.get() to get the value
  • jsonElement.asArray() — returns a JsonArray, which you can use like an ArrayList<JsonElement>
  • jsonElement.asObject() — returns a JsonObject, which you can use like a HashMap<String, JsonElement>

Each of these types is a descendant of JsonElement.

Encoding

If you have a JsonElement jsonElement, you can simply call jsonElement.toJson(); in order to get a compacted JSON String. To get a pretty JSON, just call jsonElement.toPrettyJson(); and you will get a pretty JSON String.