默认情况下，缺少的命令是通过处理的，并输出一条简单的消息：CommandNotFoundResultHandler

shell:>missing
No command found for 'missing'

内部正在使用，这是一个简单的函数，获取并返回文本 消息。下面是自定义消息提供程序的示例。CommandNotFoundResultHandlerCommandNotFoundMessageProviderProviderContext

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";
	}
}

可以通过将此实现定义为 Bean 来更改此实现。

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

CommandNotFoundResultHandler是一个功能接口，因此它可以 写成 lambda。

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