Retrieving the underlying error when File.listFiles return null

Question

According to the File.listFiles javadoc the method

Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.

I know that I am using a directory, but have received a null result, so an I/O error must've appeared. I'm very much interested in what the error was.

How can I retrieve the error message/code when such a null result is returned?

Answer 1

You can't. Unfortunately the API doesn't provide you with a way to find out about the underlying I/O error.

See also

• Bug 4505804: File.listFiles() requires null check on return value - should have better error handling

  The various listFiles methods of File all have the following annoying feature: they may possibly return null if an I/O error occurs.

  This behavior is very inconvenient, because it means that not only must I have code that handles IOExceptions (which is fine), but I also have to do additional null checks on the result.

  Better behavior would be that if an I/O error occurs, then an IOException always gets thrown. You should not use a distinguished return value to sometimes indicate errors, and then also other times throw Exceptions!

  Evaluation: We plan to address this longstanding problem in the forthcoming new filesystem API.

Answer 2

Use java.nio.file.DirectoryStream (in Java 7+) and you will get proper exceptions.