Command Not Found

On default a missing command is handled via CommandNotFoundResultHandler and outputs a simple message:

shell:>missing
No command found for 'missing'

Internally CommandNotFoundResultHandler is using CommandNotFoundMessageProvider which is a simple function taking a ProviderContext and returning a text message. Below is an example what a custom message provider might look like.

class CustomProvider implements CommandNotFoundMessageProvider {

	@Override
	public String apply(ProviderContext context) {
		// parsed commands without options
		List<String> commands = context.commands();
		// actual error, usually CommandNotFound exception
		Throwable error = context.error();
		// access to registrations at this time
		Map<String, CommandRegistration> registrations = context.registrations();
		// raw text input from a user
		String text = context.text();
		return "My custom message";
	}
}

It’s possible to change this implementation by defining it as a bean.

@Bean
CommandNotFoundMessageProvider provider1() {
	return new CustomProvider();
}

CommandNotFoundResultHandler is a functional interface so it can be writter as a lambda.

@Bean
CommandNotFoundMessageProvider provider2() {
	return ctx -> "My custom message";
}