Argument Parsing

The Command Builder API comes with a powerful argument parser. It converts the string input to java base types (integers, booleans, strings) or game objects (players, worlds, block types , …). The parser supports optional arguments and flags. It also handles TAB completion of arguments.

The parsed arguments are stored in the CommandContext object. If the parser returns a single object, obtain it with CommandContext#getOne(String). Optional and weak arguments may return Optional.empty().

Many of the parsers may return more than one object (e.g. multiple players with a matching username). In that case, you must use the CommandContext#getAll(String) method to get the Collection of possible matches. Otherwise, the context object will throw an exception!

Suggerimento

You can use the GenericArguments#onlyOne(CommandElement) element to limit the amount of returned values to a single one, so you can safely use args.<T>getOne(String).

To create a new CommandElement (argument), use the GenericArguments factory class. Many command elements require a short text key, which is displayed in error and help messages.

Apply the CommandElement to the command builder with the CommandSpec.Builder#arguments(CommandElement…) method. It is possible to pass more than one CommandElement to the method, thus chaining multiple arguments (e.g /msg <player> <msg>). This has the same effect as wrapping the CommandElement objects in a GenericArguments#seq(CommandElement…) element.

Example: Building a Command with Multiple Arguments

import org.spongepowered.api.Sponge;
import org.spongepowered.api.text.Text;
import org.spongepowered.api.entity.living.player.Player;
import org.spongepowered.api.command.CommandException;
import org.spongepowered.api.command.CommandResult;
import org.spongepowered.api.command.CommandSource;
import org.spongepowered.api.command.args.CommandContext;
import org.spongepowered.api.command.args.GenericArguments;
import org.spongepowered.api.command.spec.CommandExecutor;
import org.spongepowered.api.command.spec.CommandSpec;

CommandSpec myCommandSpec = CommandSpec.builder()
        .description(Text.of("Send a message to a player"))
        .permission("myplugin.command.message")

        .arguments(
                GenericArguments.onlyOne(GenericArguments.player(Text.of("player"))),
                GenericArguments.remainingJoinedStrings(Text.of("message")))

        .executor(new CommandExecutor() {
            @Override
            public CommandResult execute(CommandSource src, CommandContext args) throws CommandException {

                Player player = args.<Player>getOne("player").get();
                String message = args.<String>getOne("message").get();

                player.sendMessage(Text.of(message));

                return CommandResult.success();
            }
        })
        .build();

Sponge.getCommandManager().register(plugin, myCommandSpec, "message", "msg", "m");

Overview of the GenericArguments command elements

Command Element

Descrizione

Value Type & Amount

none

Expects no arguments. This is the default behavior of a CommandSpec.

Java Base Types

string

Require an argument to be a string.

one String

remainingJoinedStrings

Concatenates all remaining arguments separated by spaces (useful for message commands).

one String

bool

Require an argument to be a boolean.

one Boolean

integer

Require an argument to be an integer.

one Integer

doubleNum

Require an argument to be a double.

one Double

Game Objects

player

Expect an argument to represent an online player. May return multiple players!

multiple Player instances

playerOrSource

Like player, but returns the sender of the command if no matching player was found.

multiple Player instances

userOrSource

Like playerOrSource, but returns a user instead of a player.

multiple User instances

world

Expect an argument to represent a world (also includes unloaded worlds).

multiple WorldProperties

dimension

Expect an argument to represent a dimension (END, NETHER, OVERWORLD).

multiple DimensionType instances

location

Expect an argument to represent a Location.

one Location

vector3d

Expect an argument to represent a Vector3d.

one Vector3d

catalogedElement

Expect an argument that is a member of the specified CatalogType.

multiple matching elements of the specified catalog type

Matchers

choices

Return an argument that allows selecting from a limited set of values.

one specified value

literal

Expect a literal sequence of arguments (e.g. "i", "luv", "u": /cmd i luv u). Throws an error if the arguments do not match.

one specified value

enumValue

Require the argument to be a key under the provided enum.

multiple matching elements of the specified enum

Utilities

Can be wrapped around command elements. The value type is inherited from the wrapped element.

seq

Builds a sequence of command elements (e.g. /cmd <arg1> <arg2> <arg3>).

inherited

repeated

Require a given command element to be provided a certain number of times.

multiple inherited

allOf

Require all remaining args to match the provided command element.

multiple inherited

optional

Make the provided command element optional. Throws an error if the argument is of invalid format and there are no more args.

inherited

optionalWeak

Make the provided command element optional. Does not throw an error if the argument is of invalid format and there are no more args.

inherited

firstParsing

Returns a command element that matches the first of the provided elements that parses (useful for command overloading, e.g. /settime <day|night|<number>>).

inherited

onlyOne

Restricts the given command element to only insert one value into the context at the provided key.

inherited

flags

Returns a builder for command flags (e.g. /cmd [-a] [-b <value>]).

See Command Flags

Short Flag: one Boolean

Long Flag: one String

Value Flag: inherited

requiringPermission

Requires the command sender to have the specified permission in order to use the given command argument

inherited

Suggerimento

See the Javadocs for GenericArguments for more information.

Custom Command Elements

It is possible to create custom command elements (e.g. a URL parser or a Vector2i element) by extending the abstract CommandElement class.

The CommandElement#parseValue(CommandSource, CommandArgs) method should fetch a raw argument string with CommandArgs#next() and convert it to an object. The method should throw an ArgumentParseException if the parsing fails.

The CommandElement#complete(CommandSource, CommandArgs, CommandContext) method should use CommandArgs#peek() to read the next raw argument. It returns a list of suggestions for TAB completion.

Example: Vector2i command element definition

The parser in this example reads two input arguments and converts them to a vector.

import com.flowpowered.math.vector.Vector2i;
import org.spongepowered.api.command.args.ArgumentParseException;
import org.spongepowered.api.command.args.CommandArgs;
import org.spongepowered.api.text.Text;
import org.spongepowered.api.command.args.CommandElement;

import java.util.Collections;
import java.util.List;

public class Vector2iCommandElement extends CommandElement {
    CommandArgs errorargs;

    protected Vector2iCommandElement(Text key) {
        super(key);
    }

    @Override
    protected Object parseValue(CommandSource source, CommandArgs args) throws ArgumentParseException {

        // <x> <y>
        errorargs=args;

        String xInput = args.next();
        int x = parseInt(xInput);

        String yInput = args.next();
        int y = parseInt(yInput);

        return new Vector2i(x, y);
    }

    private int parseInt(String input) throws ArgumentParseException {
        try {
            return Integer.parseInt(input);
        } catch(NumberFormatException e) {
            throw errorargs.createError(Text.of("'" + input + "' is not a valid number!"));
        }
    }

    @Override
    public List<String> complete(CommandSource src, CommandArgs args, CommandContext context) {
        return Collections.emptyList();
    }

    @Override
    public Text getUsage(CommandSource src) {
        return Text.of("<x> <y>");
    }
}

Example: Vector2i command element usage

// /plottp <x> <y>
CommandSpec myCommandSpec = CommandSpec.builder()
        .description(Text.of("Teleport to a plot"))
        .permission("myplugin.command.plot.tp")

        .arguments(new Vector2iCommandElement(Text.of("coordinates")))

        .executor(new MyCommandExecutor())
        .build();

Suggerimento

Guarda il codice sorgente della classe``GenericArguments`` per ulteriori esempi.