Java: Make sure Files.list() returns only “complete” files
In my application I watch a directory for new files.
I keep an array of current files obtained with Files.list(dir), process this list one file after another, and then reload the directory with Files.list() again.
While I have never encountered the problem myself, a coworker told me that the predecessor software had an additional check that the file is older than 3 seconds (calculated with (Files.getLastModifiedTime(path) - System.currentTimeMillis()) > 3000) because there were issues that incomplete transferred (or better: not yet fully transferred) files went into processing.
Can I make any assumptions that the files returned by Files.list() were copied fully into the directory I am watching?
Is there a cleaner way to check if a file is complete? The 3 seconds check is more like a hack, a file with multiple GB in size could be copied over a slow connection (network) and may not be fully transfered even after 3s have passed.
java filesystems nio
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
|
show 1 more comment
In my application I watch a directory for new files.
I keep an array of current files obtained with Files.list(dir), process this list one file after another, and then reload the directory with Files.list() again.
While I have never encountered the problem myself, a coworker told me that the predecessor software had an additional check that the file is older than 3 seconds (calculated with (Files.getLastModifiedTime(path) - System.currentTimeMillis()) > 3000) because there were issues that incomplete transferred (or better: not yet fully transferred) files went into processing.
Can I make any assumptions that the files returned by Files.list() were copied fully into the directory I am watching?
Is there a cleaner way to check if a file is complete? The 3 seconds check is more like a hack, a file with multiple GB in size could be copied over a slow connection (network) and may not be fully transfered even after 3s have passed.
java filesystems nio
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
stackoverflow.com/questions/1390592/… ?
– user202729
Nov 21 '18 at 15:33
I don't see how this answers my question.
– a.ilchinger
Nov 21 '18 at 15:40
Usually the copier program will keep a file open. If the file is not open, then it's likely that the "copy" is finished. I don't know if it's the case for your copy program.
– user202729
Nov 21 '18 at 15:42
Another approach is to watch files with a particular extension or naming convention. The process creating the file initially names the file something like file1.in.progress, and the last step of that process renames the file to something like file1.dat. Similarly, another approach is for the creator process to add a 0 byte flag file, for example when file1.dat is complete the process also adds file1.ready as a flag for your process.
– Andrew S
Nov 21 '18 at 16:01
These are all good ideas, and rather simple too. Unfortunately, I cannot control the copying process. There are multiple instances of this software running and the "ingest" is different everywhere and not under my supervision.
– a.ilchinger
Nov 21 '18 at 17:00
|
show 1 more comment
In my application I watch a directory for new files.
I keep an array of current files obtained with Files.list(dir), process this list one file after another, and then reload the directory with Files.list() again.
While I have never encountered the problem myself, a coworker told me that the predecessor software had an additional check that the file is older than 3 seconds (calculated with (Files.getLastModifiedTime(path) - System.currentTimeMillis()) > 3000) because there were issues that incomplete transferred (or better: not yet fully transferred) files went into processing.
Can I make any assumptions that the files returned by Files.list() were copied fully into the directory I am watching?
Is there a cleaner way to check if a file is complete? The 3 seconds check is more like a hack, a file with multiple GB in size could be copied over a slow connection (network) and may not be fully transfered even after 3s have passed.
java filesystems nio
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
In my application I watch a directory for new files.
I keep an array of current files obtained with Files.list(dir), process this list one file after another, and then reload the directory with Files.list() again.
While I have never encountered the problem myself, a coworker told me that the predecessor software had an additional check that the file is older than 3 seconds (calculated with (Files.getLastModifiedTime(path) - System.currentTimeMillis()) > 3000) because there were issues that incomplete transferred (or better: not yet fully transferred) files went into processing.
Can I make any assumptions that the files returned by Files.list() were copied fully into the directory I am watching?
Is there a cleaner way to check if a file is complete? The 3 seconds check is more like a hack, a file with multiple GB in size could be copied over a slow connection (network) and may not be fully transfered even after 3s have passed.
java filesystems nio
java filesystems nio
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
asked Nov 21 '18 at 15:30
a.ilchingera.ilchinger
256
256
stackoverflow.com/questions/1390592/… ?
– user202729
Nov 21 '18 at 15:33
I don't see how this answers my question.
– a.ilchinger
Nov 21 '18 at 15:40
Usually the copier program will keep a file open. If the file is not open, then it's likely that the "copy" is finished. I don't know if it's the case for your copy program.
– user202729
Nov 21 '18 at 15:42
Another approach is to watch files with a particular extension or naming convention. The process creating the file initially names the file something like file1.in.progress, and the last step of that process renames the file to something like file1.dat. Similarly, another approach is for the creator process to add a 0 byte flag file, for example when file1.dat is complete the process also adds file1.ready as a flag for your process.
– Andrew S
Nov 21 '18 at 16:01
These are all good ideas, and rather simple too. Unfortunately, I cannot control the copying process. There are multiple instances of this software running and the "ingest" is different everywhere and not under my supervision.
– a.ilchinger
Nov 21 '18 at 17:00
|
show 1 more comment
stackoverflow.com/questions/1390592/… ?
– user202729
Nov 21 '18 at 15:33
I don't see how this answers my question.
– a.ilchinger
Nov 21 '18 at 15:40
Usually the copier program will keep a file open. If the file is not open, then it's likely that the "copy" is finished. I don't know if it's the case for your copy program.
– user202729
Nov 21 '18 at 15:42
Another approach is to watch files with a particular extension or naming convention. The process creating the file initially names the file something like file1.in.progress, and the last step of that process renames the file to something like file1.dat. Similarly, another approach is for the creator process to add a 0 byte flag file, for example when file1.dat is complete the process also adds file1.ready as a flag for your process.
– Andrew S
Nov 21 '18 at 16:01
These are all good ideas, and rather simple too. Unfortunately, I cannot control the copying process. There are multiple instances of this software running and the "ingest" is different everywhere and not under my supervision.
– a.ilchinger
Nov 21 '18 at 17:00
stackoverflow.com/questions/1390592/… ?
– user202729
Nov 21 '18 at 15:33
stackoverflow.com/questions/1390592/… ?
– user202729
Nov 21 '18 at 15:33
I don't see how this answers my question.
– a.ilchinger
Nov 21 '18 at 15:40
I don't see how this answers my question.
– a.ilchinger
Nov 21 '18 at 15:40
Usually the copier program will keep a file open. If the file is not open, then it's likely that the "copy" is finished. I don't know if it's the case for your copy program.
– user202729
Nov 21 '18 at 15:42
Usually the copier program will keep a file open. If the file is not open, then it's likely that the "copy" is finished. I don't know if it's the case for your copy program.
– user202729
Nov 21 '18 at 15:42
Another approach is to watch files with a particular extension or naming convention. The process creating the file initially names the file something like file1.in.progress, and the last step of that process renames the file to something like file1.dat. Similarly, another approach is for the creator process to add a 0 byte flag file, for example when file1.dat is complete the process also adds file1.ready as a flag for your process.
– Andrew S
Nov 21 '18 at 16:01
Another approach is to watch files with a particular extension or naming convention. The process creating the file initially names the file something like file1.in.progress, and the last step of that process renames the file to something like file1.dat. Similarly, another approach is for the creator process to add a 0 byte flag file, for example when file1.dat is complete the process also adds file1.ready as a flag for your process.
– Andrew S
Nov 21 '18 at 16:01
These are all good ideas, and rather simple too. Unfortunately, I cannot control the copying process. There are multiple instances of this software running and the "ingest" is different everywhere and not under my supervision.
– a.ilchinger
Nov 21 '18 at 17:00
These are all good ideas, and rather simple too. Unfortunately, I cannot control the copying process. There are multiple instances of this software running and the "ingest" is different everywhere and not under my supervision.
– a.ilchinger
Nov 21 '18 at 17:00
|
show 1 more comment
1 Answer
1
active
oldest
votes
It is not safe to assume that a file is complete if it is in a directory. There could still be a lock associated with another process that could be writing to it or holds the lock for a different reason.
I use the following method to check if a file is ready (this uses java 1.8)
public static boolean isFileReady(Path file) {
try(FileChannel ch = FileChannel.open(file, StandardOpenOption.WRITE, StandardOpenOpption.APPEND); FileLock lock = ch.tryLock()) {
if (lock == null) return false;
return true;
} catch (IOException ex) {
return false;
}
}
This will try to open the file for appending (open for normal writing will erase all its content) and create a lock. If the lock is established then we are good to go otherwise we are not.
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
add a comment |
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It is not safe to assume that a file is complete if it is in a directory. There could still be a lock associated with another process that could be writing to it or holds the lock for a different reason.
I use the following method to check if a file is ready (this uses java 1.8)
public static boolean isFileReady(Path file) {
try(FileChannel ch = FileChannel.open(file, StandardOpenOption.WRITE, StandardOpenOpption.APPEND); FileLock lock = ch.tryLock()) {
if (lock == null) return false;
return true;
} catch (IOException ex) {
return false;
}
}
This will try to open the file for appending (open for normal writing will erase all its content) and create a lock. If the lock is established then we are good to go otherwise we are not.
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
add a comment |
It is not safe to assume that a file is complete if it is in a directory. There could still be a lock associated with another process that could be writing to it or holds the lock for a different reason.
I use the following method to check if a file is ready (this uses java 1.8)
public static boolean isFileReady(Path file) {
try(FileChannel ch = FileChannel.open(file, StandardOpenOption.WRITE, StandardOpenOpption.APPEND); FileLock lock = ch.tryLock()) {
if (lock == null) return false;
return true;
} catch (IOException ex) {
return false;
}
}
This will try to open the file for appending (open for normal writing will erase all its content) and create a lock. If the lock is established then we are good to go otherwise we are not.
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
add a comment |
It is not safe to assume that a file is complete if it is in a directory. There could still be a lock associated with another process that could be writing to it or holds the lock for a different reason.
I use the following method to check if a file is ready (this uses java 1.8)
public static boolean isFileReady(Path file) {
try(FileChannel ch = FileChannel.open(file, StandardOpenOption.WRITE, StandardOpenOpption.APPEND); FileLock lock = ch.tryLock()) {
if (lock == null) return false;
return true;
} catch (IOException ex) {
return false;
}
}
This will try to open the file for appending (open for normal writing will erase all its content) and create a lock. If the lock is established then we are good to go otherwise we are not.
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
It is not safe to assume that a file is complete if it is in a directory. There could still be a lock associated with another process that could be writing to it or holds the lock for a different reason.
I use the following method to check if a file is ready (this uses java 1.8)
public static boolean isFileReady(Path file) {
try(FileChannel ch = FileChannel.open(file, StandardOpenOption.WRITE, StandardOpenOpption.APPEND); FileLock lock = ch.tryLock()) {
if (lock == null) return false;
return true;
} catch (IOException ex) {
return false;
}
}
This will try to open the file for appending (open for normal writing will erase all its content) and create a lock. If the lock is established then we are good to go otherwise we are not.
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
answered Nov 21 '18 at 15:58
locus2klocus2k
1,022613
1,022613
add a comment |
add a comment |
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stackoverflow.com/questions/1390592/… ?
– user202729
Nov 21 '18 at 15:33
I don't see how this answers my question.
– a.ilchinger
Nov 21 '18 at 15:40
Usually the copier program will keep a file open. If the file is not open, then it's likely that the "copy" is finished. I don't know if it's the case for your copy program.
– user202729
Nov 21 '18 at 15:42
Another approach is to watch files with a particular extension or naming convention. The process creating the file initially names the file something like file1.in.progress, and the last step of that process renames the file to something like file1.dat. Similarly, another approach is for the creator process to add a 0 byte flag file, for example when file1.dat is complete the process also adds file1.ready as a flag for your process.
– Andrew S
Nov 21 '18 at 16:01
These are all good ideas, and rather simple too. Unfortunately, I cannot control the copying process. There are multiple instances of this software running and the "ingest" is different everywhere and not under my supervision.
– a.ilchinger
Nov 21 '18 at 17:00