Command Not Found

在默认情况下，缺失的命令由 CommandNotFoundResultHandler 处理，并输出一条简单消息：

shell:>missing
No command found for 'missing'

在内部，CommandNotFoundResultHandler 使用 CommandNotFoundMessageProvider，它是一个简单函数，可以将 ProviderContext 作为输入，并返回一条文本消息。以下是自定义消息提供程序可能的样子之一。

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可以通过将其定义为一个 bean 来更改此实现。

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CommandNotFoundResultHandler 是一个函数式接口，因此它可以作为 lambda 来编写。

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