why "package org.apache.commons.io" does not exist?

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Hi,

I am running somebody's code. The code has import at the top:

import org.apache.commons.io.FileUtils;


But the compiler complains that "package org.apache.commons.io does not
exist". I want to add classpath to point to it. But I don't know where
this package is located. How can I find out where it is located? Can you
give me a hint?

Thank you very much.