Java's File.renameTo()
is problematic, especially on Windows, it seems.
As the API documentation says,
Many aspects of the behavior of this method are inherently platform-dependent: The rename operation might not be able to move a file from one filesystem to another, it might not be atomic, and it might not succeed if a file with the destination abstract pathname already exists. The return value should always be checked to make sure that the rename operation was successful.
In my case, as part of an upgrade procedure, I need to move (rename) a directory that may contain gigabytes of data (lots of subdirectories and files of varying sizes). The move is always done within the same partition/drive, so there's no real need to physically move all the files on disk.
There shouldn't be any file locks to the contents of the dir to be moved, but still, quite often, renameTo() fails to do its job and returns false. (I'm just guessing that perhaps some file locks expire somewhat arbitrarily on Windows.)
Currently I have a fallback method that uses copying & deleting, but this sucks because it may take a lot of time, depending on the size of the folder. I'm also considering simply documenting the fact that the user can move the folder manually to avoid waiting for hours, potentially. But the Right Way would obviously be something automatic and quick.
So my question is, do you know an alternative, reliable approach to do a quick move/rename with Java on Windows, either with plain JDK or some external library. Or if you know an easy way to detect and release any file locks for a given folder and all of its contents (possibly thousands of individual files), that would be fine too.
Edit: In this particular case, it seems we got away using just renameTo()
by taking a few more things into account; see this answer.
In my case, the error was in the path of the parent directory. Maybe a bug, I had to use the substring to get a correct path.
The above is the simple code. I have tested on windows 7 and works perfectly fine.
The original post requested "an alternative, reliable approach to do a quick move/rename with Java on Windows, either with plain JDK or some external library."
Another option not mentioned yet here is v1.3.2 or later of the apache.commons.io library, which includes FileUtils.moveFile().
It throws an IOException instead of returning boolean false upon error.
See also big lep's response in this other thread.
You may try robocopy. This is not exactly "renaming", but it's very reliable.
See also the
Files.move()
method in JDK 7.An example:
I know it sucks, but an alternative is to create a bat script which outputs something simple like "SUCCESS" or "ERROR", invoke it, wait for it to be executed and then check its results.
Runtime.getRuntime().exec("cmd /c start test.bat");
This thread may be interesting. Check also the Process class on how to read the console output of a different process.