Argument Parsing

Minecraft’s Brigadier system includes a powerful argument parser that Sponge can take advantage of. It converts the string input to java base types (integer, booleans, string) or game objects (players, worlds, block types, …). Sponge’s system also supports optional arguments and flags. It also handles suggestions of arguments.

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

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

When creating a command, consider whether the argument could return multiple values, for example whether a player argument could support multiple players when using a selector. If you support multiple values, the users need to type only one command, and can use an easier command sytax, e.g /tell @a Who took the cookies?

To create a new Parameter (argument), use the Parameter class that will give you many Builder options. Each parameter will need its Builder#key(String) filled out before being built.

Apply the Parameter to the command builder with the Command.Builder#addParameter(Parameter) method. It is possible to pass more than one Parameter to the method, thus chaining multiple arguments. Example /msg <player> <msg>. This has the same effect as wrapping the Parameter objects in a Parameter#seq(Iterable<Parameter>) element.

Example: Building a Command with Multiple Arguments

import org.spongepowered.api.command.parameter.CommandContext;
import org.spongepowered.api.command.parameter.Parameter;
import org.spongepowered.api.command.Command;
import org.spongepowered.api.command.CommandResult;
import org.spongepowered.api.entity.living.player.server.ServerPlayer;

public Command.Parameterized createMessageCommand(){
    Parameter.Value<ServerPlayer> playerParameter = Parameter.player().key("player").build();
    Parameter.Value<String> messageParameter = Parameter.remainingJoinedStrings().key("message").build();

    return Command
        .builder()
        .executor((CommandContext context) -> {
            ServerPlayer player = context.requireOne(playerParameter);
            String message = context.requireOne(messageParameter);

            player.sendMessage(Component.text(message));
            return CommandResult.success();
        })
        .addParameter(playerParameter, messageParameter)
        .build();
}

Nota

The example above uses CommandContext#requireOne(Parameter.Value<T>), this is for arguments that must be provided. Use CommandContext#one(Parameter.Value<T>) for optional arguments

Overview of the Parameter Command Elements

Parameter	Descrizione	Value Type & Amount
string	Require the argument to be a string.	one String
remainingJoinedStrings	Concatenates all remaining arguments separated by spaces (useful for message commands).	one String
bool	Require the argument to be a boolean.	one Boolean
integer	Require the argument to be a integer.	one Integer
rangeInteger	Require the argument to be a integer between two values.	one Integer
doubleNumber	Require the argument to be a double.	one Double
rangeDouble	Require the argument to be a double between two values	one Double
player	Require the argument to be a player. May return multiple players!	multiple ServerPlayer instances
playerOrTarget	Like player, but returns the sender of the command if no matching player was found.	mutiple ServerPlayer instances
user	Require the argument to be a user. May return multiple users!	multiple User instances
world	Require the argument to be a world (only loaded worlds)	multiple ServerWorld instances
location	Require the argument to be a location	one ServerLocation
vector3d	Require the argument to be a vector	one Vector3d
rotation	Require the argument to be a vector, but returns the senders rotation if no value was specified	one Vector3d
registryElement	Require the argument to be the resoure key of one of the specified elements	multiple matching elements of the specified registry type
choices	Returns an argument that allows selecting from a limited set of values	one specified value
literal	Require the argument to match one of the specified literals	one specified literal
enumValue	Require the argument to be a enum	one Enum
seq	Builds a sequence of commands	inherited

Suggerimento

See the Javadocs for Parameter for more information

Avvertimento

Don’t expect that a Parameter will only ever return a single value, a lot of them support multiple return values; some might support regular expressions or use command selector. This is intentional as it makes commands easier to use, e.g /tell @a BanditPlayer has cookies!.

Custom Parameter

It is possible to create custom command elements; for example, Vector2i. This is done though the Parameter#builder(Class) method, which returns a Parameter where all data the parameter neededs should be provided. Once done call the build method to build the parameter.

When building a new parameter, only the parser and key are required for build. The parser contains the logic for mapping the String input to the desired value.

Example: Creating a Custom Parameter

In this example we will make a Vector2i parameter. This requires reading two Integers and converting them to a Vector2i.

Parameter.Value<Vector2i> vectorParameter = Parameter
  .builder(Vector2i.class)
  .addParser((
    Parameter.Key<Vector2i> parameterKey,
    ArgumentReader.Mutable reader,
    CommandContext.Builder context) -> {
      int x = reader.parseInt();
      int y = reader.parseInt();
      return new Vector2i(x, y);
  })
  .key("vector")
  .build();

Suggerimento

When building a new parameter, you can base your parameter on a exsiting parameters. Example: taking Parameter#string() and giving it client suggestions.