Cannot resolve symbol 'IOUtils'

For Android Studio:

1. File -> Project Structure... -> Dependencies
2. Click '+' in the upper right corner and select "Library dependency"
3. In the search field type: "org.apache.commons.io" and click Search
4. Select "org.apache.directory.studio:org.apache.commons.io:<X.X>

Or

Add implementation 'org.apache.directory.studio:org.apache.commons.io:2.4 to the build.gradle file

Right clicking on the commons-io-2.4.jar file in project navigator and clicking 'Add to project' solved the issue.