Picocli: how to make subcommands required - command-line-arguments

Question

I have a command with subcommands. In my application I want it mandatory for the user to specify a subcommand. How should I do this?
(See also https://github.com/remkop/picocli/issues/529)

Answer 1

Update: this is now documented in the picocli manual: https://picocli.info/#_required_subcommands
Prior to picocli 4.3, the way to achieve this would be to show an error or throw a ParameterException if the top-level command is invoked without subcommand.
For example:
#Command(name = "top", subcommands = {Sub1.class, Sub2.class},
synopsisSubcommandLabel = "COMMAND")
class TopCommand implements Runnable {
#Spec CommandSpec spec;
public void run() {
throw new ParameterException(spec.commandLine(), "Missing required subcommand");
}
public static void main(String[] args) {
CommandLine.run(new TopCommand(), args);
}
}
#Command(name = "sub1)
class Sub1 implements Runnable {
public void run() {
System.out.println("All good, executing Sub1");
}
}
#Command(name = "sub2)
class Sub2 implements Runnable {
public void run() {
System.out.println("All good, executing Sub2");
}
}
From picocli 4.3, this can be accomplished more easily by making the top-level command not implement Runnable or Callable.
If the command has subcommands but does not implement Runnable or Callable, picocli will make subcommands mandatory.
For example:
#Command(name = "top", subcommands = {Sub1.class, Sub2.class},
synopsisSubcommandLabel = "COMMAND")
class TopCommand {
public static void main(String[] args) {
CommandLine.run(new TopCommand(), args);
}
}