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Java Forum / General / February 2006Watching for new files
Is there a better way to watch a directory for new files than to simply poll it and compare against a list? I have a security Cam programming running on a windows box, and I would like to watch for appearance of new files and then quickly upload them to an FTP server. A unique image file will be generated every time movement is detected on the camera. It is likely I can figure out the FTP itself on my own - but polling every few seconds for new files sounds less than desirable.  SignatureLTP :) > Is there a better way to watch a directory for new files than to simply > poll it and compare against a list? [quoted text clipped - 8 lines] > It is likely I can figure out the FTP itself on my own - but polling every > few seconds for new files sounds less than desirable. the simplest way is to keep directory empty. Just move files after upload to another directory SignatureAndrey Kuznetsov http://uio.imagero.com Unified I/O for Java http://reader.imagero.com Java image reader http://jgui.imagero.com Java GUI components and utilities >> Is there a better way to watch a directory for new files than to simply >> poll it and compare against a list? [quoted text clipped - 11 lines] > the simplest way is to keep directory empty. > Just move files after upload to another directory That is a good idea. Is there a way to check to make sure the file isn't open - since it is at least possible, if not likely that a file will be detected while it is in the process of being writen. Perhaps moving it and copying it can be part of the same operation - and if moving fails, then it can be assumed that the file is not yet ready to be copied. This is still polling - but requires no memory of which files have been transfered and resolves the issue of trying to transfer files which are still open. -- LTP :) >>> It is likely I can figure out the FTP itself on my own - but polling >>> every few seconds for new files sounds less than desirable. [quoted text clipped - 4 lines] > That is a good idea. Is there a way to check to make sure the file isn't > open... File.canWrite(); SignatureAndrey Kuznetsov http://uio.imagero.com Unified I/O for Java http://reader.imagero.com Java image reader http://jgui.imagero.com Java GUI components and utilities > Is there a better way to watch a directory for new files than to simply poll > it and compare against a list? [quoted text clipped - 10 lines] > > :) Not using the Java platform. Other platforms permit you to register a callback for notification of changes - this is the correct way of avoiding a busy/wait (or as you put it, "polling"). SignatureTony Morris http://tmorris.net/ >> Is there a better way to watch a directory for new files than to simply > poll [quoted text clipped - 21 lines] > it, > "polling"). That's what I was afraid of. I've never been to good with any of this windows messaging crap. SignatureLTP :) >> Not using the Java platform. >> Other platforms permit you to register a callback for notification of [quoted text clipped - 4 lines] > That's what I was afraid of. I've never been to good with any of this > windows messaging crap. Search for ReadDirectoryChangesW on Windows, or FAM on Linux, etc. At any rate it's system specific and will require JNI or an external helper. /gordon Signature[ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > Is there a better way to watch a directory for new files than to simply poll > it and compare against a list? > > I have a security Cam programming running on a windows box, and I would like > to watch for appearance of new files and then quickly upload them to an FTP > server. The real problem might not be to figure out if there is suddenly a new file, but if it has been completely written by the camera. If you start to early with the download of the file you might miss parts of the file. So you probably don't want to "quickly upload" them. > A unique image file will be generated every time movement is detected on the > camera. You probably need to wait until there are two or more such files, and then upload all except the latest one (which might be incomplete). This assumes that the camera only starts to write a new file after it has completed the previous one. Which is likely. Or you need to have some other way to check the integrity of a file. > It is likely I can figure out the FTP itself on my own - but polling every > few seconds for new files sounds less than desirable. If the camera doesn't provide any notification mechanism this is probably the only way to do it. /Thomas SignatureThe comp.lang.java.gui FAQ: ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq http://www.uni-giessen.de/faq/archiv/computer-lang.java.gui.faq/ On Wed, 1 Feb 2006 15:15:46 -0700, "Luc The Perverse" <sll_noSpamlicious_z_XXX_m@cc.usu.edu> wrote, quoted or indirectly quoted someone who said : >Is there a better way to watch a directory for new files than to simply poll >it and compare against a list? See http://mindprod.com/projects/filefinder.html That is a student project that tackles your same problem in a more generic way. In particular check the reference to Sysinternals Filemon. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > Is there a better way to watch a directory for new files than to simply poll > it and compare against a list? [quoted text clipped - 8 lines] > It is likely I can figure out the FTP itself on my own - but polling every > few seconds for new files sounds less than desirable. How about querying file.lastModified() and keeping the timestamp of the latest file? This way you: - don't have to keep track of all files to compare - know when a new file has arrived (by looping through the directory for files with a higher lastModified() value) - can repeat this forever if you adjust lastModified() to the newest file after the copy process has ended Just a thought. I don't see any problems with it at the moment, but if someone else does, I'd like to know them out of curiosity. Kind regards, JC -- http://jcsnippets.atspace.com a collection of source code, tips and tricks >> Is there a better way to watch a directory for new files than to simply > poll [quoted text clipped - 24 lines] > Just a thought. I don't see any problems with it at the moment, but if > someone else does, I'd like to know them out of curiosity. If would require a discretization since 1 second is the minimal amount of time. This is one possibility that I did look at. It wouldn't be too hard as long as new files weren't being added in the second that you are x-ferring. This is easy if you put in a delay -- LTP :) 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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