Command Catalog

The CommandCatalog interface defines how command registrations exist in a shell application. It is possible to dynamically register and de-register commands, which gives flexibility for use cases where possible commands come and go, depending on a shell’s state. Consider the following example:

CommandRegistration registration = CommandRegistration.builder().build();
catalog.register(registration);

Command Resolver

You can implement the CommandResolver interface and define a bean to dynamically resolve mappings from a command’s name to its CommandRegistration instances. Consider the following example:

static class CustomCommandResolver implements CommandResolver {
	List<CommandRegistration> registrations = new ArrayList<>();

	CustomCommandResolver() {
		CommandRegistration resolved = CommandRegistration.builder()
			.command("resolve command")
			.build();
		registrations.add(resolved);
	}

	@Override
	public List<CommandRegistration> resolve() {
		return registrations;
	}
}

A current limitation of a CommandResolver is that it is used every time commands are resolved. Thus, we advise not using it if a command resolution call takes a long time, as it would make the shell feel sluggish.

Command Catalog Customizer

You can use the CommandCatalogCustomizer interface to customize a CommandCatalog. Its main use is to modify a catalog. Also, within spring-shell auto-configuration, this interface is used to register existing CommandRegistration beans into a catalog. Consider the following example:

static class CustomCommandCatalogCustomizer implements CommandCatalogCustomizer {

	@Override
	public void customize(CommandCatalog commandCatalog) {
		CommandRegistration registration = CommandRegistration.builder()
			.command("resolve command")
			.build();
		commandCatalog.register(registration);
	}
}

You can create a CommandCatalogCustomizer as a bean, and Spring Shell handles the rest.