Question

A program we have erred when trying to move files from one directory to another. After much debugging I located the error by writing a small utility program that just moves a file from one directory to another (code below). It turns out that while moving files around on the local filesystem works fine, trying to move a file to another filesystem fails.

Why is this? The question might be platform specific – we are running Linux on ext3, if that matters.

And the second question; should I have been using something else than the renameTo() method of the File class? It seems as if this just works on local filesystems.

Tests (run as root):

touch /tmp/test/afile

java FileMover /tmp/test/afile /root/
The file move was successful

touch /tmp/test/afile

java FileMover /tmp/test/afile /some_other_disk/
The file move was erroneous

Code:

import java.io.File;

public class FileMover {
    public static void main(String arguments[] ) throws Exception {
        boolean success;
        File file = new File(arguments[0]);
        File destinationDir = new File(arguments[1]);
        File destinationFile = new File(destinationDir,file.getName() );
        success = file.renameTo(destinationFile);
        System.out.println("The file move was " + (success?"successful":"erroneous"));
    }
}

Answer 1

Java 7 and above

Use Files.move(Path source, Path target, CopyOption... opts).

Note that you must not provide the ATOMIC_MOVE option when moving files between file systems.

Java 6 and below

From the docs of File.renameTo:

[…] The rename operation might not be able to move a file from one filesystem to another […]

The obvious workaround would be to copy the file “manually” by opening a new file, write the content to the file, and delete the old file.

You could also try the FileUtils.moveFile method from Apache Commons.