Locking and unlocking files using the java API

Question

One of our clients is using some Novel security software that sometimes locks some .class files that our software creates. This causes some nasty problems for them when thi

Answer 1

File.canWrite() has the race condition that Asaph mentioned. You could try FileChannel.lock() and get an exclusive lock on the file. As long as the .class is on your local disk, this should work fine (file locking can be problematic on networked disks).

Alternatively, depending on how the .class name is discovered, you could create a new name for your .class each time; then if the anti-virus software locks your initial class, you can still create the new one.

Answer 2

Before attempting to write to a file, you can check if the file is writable by your java application using File.canWrite(). However, you still might run into an issue if the 3rd party app locks the file in between your File.canWrite() check and when your application actually attempts to write. For this reason, I would code your application to simply go ahead and try to write to the file and catch whatever Exception gets thrown when the file is locked. I don't believe there is a native Java way to unlock a file that has been locked by another application. You could exec a shell command as a privileged user to force things along but that seems inelegant.