Write Lock in Java

Question

I have a file say text.csv from which my java programs tries to read/write.

Is there a way in Java to detect if this file is opened for writing when the file has been opened by some user by "double clicking"? If so , how? I'm looking for this kind of code:

if(isOpenForWrite(File file){
//say text.csv is already opened ...
}

Any helpful documentation or other resources is welcome.

http://www.linuxtopia.org/online_books/programming_books/thinking_in_java/TIJ314_030.htm — StanislavL, Feb 26 '14 at 07:05
@StanislavL Does that locking interfere with other processes accessing files? — Sotirios Delimanolis, Feb 26 '14 at 07:07
@Kunal Krishna Have you read this "http://stackoverflow.com/questions/1390592/java-check-if-file-is-already-open" — saravanakumar, Feb 26 '14 at 07:08
@StanislavL FileLock is made for suncing acces inside java, it can't detect if the file is locked with some other application — crzbt, Feb 26 '14 at 07:08

score 0 · Answer 1 · answered Feb 26 '14 at 07:04

0

Best way to check this is checking if you can rename the file

String fileName = "C:\\Text.xlsx";
File file = new File(fileName);

// try to rename the file with the same name
File sameFileName = new File(fileName);

if(file.renameTo(sameFileName)){
    // if the file is renamed
    System.out.println("file is closed");    
}else{
    // if the file didnt accept the renaming operation
    System.out.println("file is opened");
}

or use Apache Common IO library

answered Feb 26 '14 at 07:04

crzbt

183
4
14

1

Note that the rename can work and _then_ a user could open the file. – Sotirios Delimanolis Feb 26 '14 at 07:05
@SotiriosDelimanolis same can happen with any check, so i don't think this is a problem of implementation. – crzbt Feb 26 '14 at 07:19
I just don't think it will be very reliable. – Sotirios Delimanolis Feb 26 '14 at 07:20
@SotiriosDelimanolis that's still the only way that working for me when checking MS Office files for being opened. Only other way is Commons IO but using library only for this seems strange for me. Especially if you can do the same with 4 lines of code. – crzbt Feb 26 '14 at 07:25
How often do you loop to check? – Sotirios Delimanolis Feb 26 '14 at 07:26
@SotiriosDelimanolis i was checking it every time i needed to export data to file. And it's not in loop, it checks every time we need to edit file. – crzbt Feb 26 '14 at 07:34

score 0 · Answer 2 · answered Feb 26 '14 at 07:11

I would use the FileChannel.lock to do this.

try { // Get a file channel for the file 
    File file = new File("text.csv");
    FileChannel channel = new RandomAccessFile(file, "rw").getChannel();

    // Blocks until it can retrieve the lock. 
    FileLock lock = channel.lock(); 
    // Try acquiring the lock without blocking. 
    // lock is null or exception if the file is already locked. 

    try { 
        lock = channel.tryLock();
    } catch (OverlappingFileLockException e){}


    lock.release(); // Close the file 
    channel.close();
} catch (Exception e) { 
}

score 0 · Answer 3 · edited May 23 '17 at 10:31

Source : Java: Check if file is already open

Use this i found this in above commanded link

    boolean isFileUnlocked = false;
    try {
     org.apache.commons.io.FileUtils.touch(yourFile);
    isFileUnlocked = true;
    } catch (IOException e) {
    isFileUnlocked = false;
    }

    if(isFileUnlocked){
    // Do stuff you need to do with a file that is NOT locked.
    } else {
    // Do stuff you need to do with a file that IS locked
    }

Write Lock in Java

3 Answers3