purkkafi / jarpa

Java program arguments parser

Jarpa – Java ARguments PArser

A lightweight parser of command line arguments.

Features

• Very lightweight
• Only throws JarpaExceptions with friendly error messages – you can catch them and show the user the message
• Completely typesafe – handles parsing for you
• Extensible in the previous regard

Quick Examples

Note that the following examples use the static import fi.purkka.jarpa.JarpaArg.* to make the code shorter.

Everything begins by obtaining a JarpaArgs instance; args is of type String[]. JarpaArgs implements AutoCloseable to permit use in try-catch blocks; the close() method calls finish() which makes sure that the user hasn't entered any unknown arguments.

try(JarpaArgs jargs = JarpaParser.parsing(args).parse()) {
    // code
} catch(JarpaException e) {
    // handle errors
}

JarpaArgs has a get() method that takes a JarpaArg. The static methods of JarpaArg provide facilities for obtaining values of different types.

String string = jargs.get(string("--name"));
int integer = jargs.get(integer("--id"));
double decimal = jargs.get(decimal("--weight"));
String[] strings = jargs.get(stringArray("--versions"));

Flags are special types of JarpaArg. They are associated with a boolean value that indicates whether they are present. Unlike other types, they will not cause an exception to be thrown if missing).

boolean hasFlag = jargs.get(flag("-f"));

Kind of like flags, optional arguments can freely be omitted. They provide access to an Optional instance.

int repeat = jargs.get(integer("--repeat").optional()).orElse(1);

Aliases can be used to allow the user use shorter or longer versions of arguments as they wish. Only one given alias may be used at the same time; otherwise, an exception is raised.

boolean verbose = jargs.get(flag("--verbose").alias("-v"));

Other types of JarpaArg can be used if a parse method is provided.

MyClass myClass = jargs.get(object("--myclass", MyClass::parse));

Licence

Jarpa is licenced with the Unlicence.