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Java Forum / General / January 2007Possible to test if file is open?
I need to test if a file is open by another process. The "other process" will always be another instance of my program, possibly running on a physically separate server, and accessing the file on a shared drive. Is this possible in Java? > I need to test if a file is open by another process. > [quoted text clipped - 3 lines] > > Is this possible in Java? You can try FileChannel lock. But whether it will work as you want depends on the operating system and the software providing the shared drive. Arne On Windows, you can try to delete it, sicne Windows won't let you delete an open file. This approach does have certain disadvantages. On Jan 1, 3:00 am, "Mike Schilling" <mscottschill...@hotmail.com> wrote: > On Windows, you can try to delete it, sicne Windows won't let you delete an > open file. > > This approach does have certain disadvantages. Not necessary. Try this out on windows. Open any text document in notepad, and then try to delete. Document gets deleted. Cheers, Ck http://www.gfour.net > On Jan 1, 3:00 am, "Mike Schilling" <mscottschill...@hotmail.com> > wrote: [quoted text clipped - 5 lines] > Not necessary. Try this out on windows. Open any text document in > notepad, and then try to delete. Document gets deleted. And what does that prove ? Most likely that notepad does not keep the file open (in the meaning of "open file" used by programmers). Arne Arne Vajh?j wrote: > > On Jan 1, 3:00 am, "Mike Schilling" <mscottschill...@hotmail.com> > > wrote: [quoted text clipped - 12 lines] > > Arne Well I did not try to prove anything. The question was can we do check if the file is open by another process or not, so there could be a lot of other process (like notepad) which might use the file without locking out the file. Cheers, Ck http://www.gfour.net "Mike Schilling" wrote: >> On Windows, you can try to delete it, sicne Windows won't let you delete an >> open file. >>> Not necessary. Try this out on windows. Open any text document in >>> notepad, and then try to delete. Document gets deleted. Arne Vajhøj wrote: >> And what does that prove ? >> >> Most likely that notepad does not keep the file >> open (in the meaning of "open file" used by programmers). > Well I did not try to prove anything. The question was can we do check > if the file is open by another process or not, so there could be a lot > of other process (like notepad) which might use the file without > locking out the file. The question, as you pointed out, is whether the file is *open* by another process or notl your example did not actually address that issue. If notepad is not holding the file open, as Arne explained, then it is not part of the scenario in question. "Mike Schilling" wrote: >> On Windows, you can try to delete it, sicne Windows won't let you delete an >> open file. >> >> This approach does have certain disadvantages. You did realize that this was not actually a serious suggestion, right? - Lew > "Mike Schilling" wrote: >>> On Windows, you can try to delete it, sicne Windows won't let you [quoted text clipped - 9 lines] >>> Most likely that notepad does not keep the file >>> open (in the meaning of "open file" used by programmers). Experience says that most ASCII text editors (notepad, vi, microEmacs. PFE etc) do not hold files open. Each load and save operation typically opens the file, does what it needs to do and closes it again. Many word processors, OTOH, seem to hold files open. I think Word falls into this class but can't prove it. But, why just speculate about this when you can easily try an experiment. All you need is a simple CLI program whose logic is something line: open a file write a prompt to the console read the response to the prompt close the file exit The program could have options to write or read the file. Its benefit is that, unlike using some program with unknown characteristics, with this you *KNOW* that the file is open once you've seen the prompt but haven't yet responded to it. At this point you can run other commands or even (shock, horror!) code that you think should check whether the file is in use or not. Running tests is the only safe way to go because actual behavior is likely to be platform-specific. I'd guess that File.canRead() and File.canWrite() may detect file locks under most Unices, MVS or Guardian, because these OSen have kernel support for file locking, but probably do not under Windows. I may be wrong here because I haven't seriously programmed for that environment since Win 95: IIRC there is no kernel level locking in Win 95 or its associated version of DOS.  Signaturemartin@ | Martin Gregorie gregorie. | Essex, UK org | > Experience says that most ASCII text editors (notepad, vi, microEmacs. > PFE etc) do not hold files open. Each load and save operation typically > opens the file, does what it needs to do and closes it again. I am not sure about vi either. It gives a warning if you try to open an already open file. # E325: ATTENTION # Found a swap file by the name ".s6.c.swp" # Swap file ".s6.c.swp" already exists! I guess its not due to lock but due to existence of a swap file. Cheers, Ck > # E325: ATTENTION > # Found a swap file by the name ".s6.c.swp" > # Swap file ".s6.c.swp" already exists! > > I guess its not due to lock but due to existence of a swap file. Yes. A quick glance at the manpage says that vi uses it primarily for recovery after a crash. There will always be a swap file (unless the user invoked the option to disable it) BUT it isn't the same as the file being edited. Its name is the same as the file being edited with ".swp" appended. At least, that applies to vim but may not apply to other implementations like stevie and elvis. he lightweight vi clone pvic doesn't use a swap file. Signaturemartin@ | Martin Gregorie gregorie. | Essex, UK org | > I need to test if a file is open by another process. > [quoted text clipped - 3 lines] > > Is this possible in Java? Open it with exclusive access? I'm not sure if its possible in Java, but I'd be surprised if it wasn't. Check out this URL: http://java.sun.com/j2se/1.5.0/docs/api/java/nio/channels/FileChannel.html FileChannel.tryLock() FileChannel.lock() These won't tell you if another process has the file open non-exclusively, but they will tell you if they are open by a process exclusively. Mearvk Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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