How to check if a file is open by another process (Java/Linux)?

Question

I am trying to check if a certain java.io.File is open by an external program. On windows I use this simple trick:

try {
    FileOutputStream fos = new FileOutputStream(file);
    // -> file was closed
} catch(IOException e) {
    // -> file still open
}

I know that unix based systems allow to open files in multiple processes... Is there a similar trick to achieve the same result for unix based systems ?

Any help / hack highly appreciated :-)

Solution 1

Here's a sample how to use lsof for unix based systems:

public static boolean isFileClosed(File file) {
    try {
        Process plsof = new ProcessBuilder(new String[]{"lsof", "|", "grep", file.getAbsolutePath()}).start();
        BufferedReader reader = new BufferedReader(new InputStreamReader(plsof.getInputStream()));
        String line;
        while((line=reader.readLine())!=null) {
            if(line.contains(file.getAbsolutePath())) {                            
                reader.close();
                plsof.destroy();
                return false;
            }
        }
    } catch(Exception ex) {
        // TODO: handle exception ...
    }
    reader.close();
    plsof.destroy();
    return true;
}

Hope this helps.

Solution 2

You can run from Java program the lsof Unix utility that tells you which process is using a file, then analyse its output. To run a program from Java code, use, for example, Runtime, Process, ProcessBuilder classes. Note: your Java program won't be portable in this case, contradicting the portability concept, so think twice whether you really need this :)

Solution 3

This one should also work for Windows systems. But attention, does not work for Linux!

     private boolean isFileClosed(File file) {  
            boolean closed;
            Channel channel = null;
            try {
                channel = new RandomAccessFile(file, "rw").getChannel();
                closed = true;
            } catch(Exception ex) {
                closed = false;
            } finally {
                if(channel!=null) {
                    try {
                        channel.close();
                    } catch (IOException ex) {
                        // exception handling
                    }
                }
            }
            return closed;
    }

Solution 4

Thanks for the original suggestion. I have one small upgrade that is somewhat important to that method:

FileOutputStream fos = null;
try {
    // Make sure that the output stream is in Append mode. Otherwise you will
    // truncate your file, which probably isn't what you want to do :-) 
    fos = new FileOutputStream(file, true);
    // -> file was closed
} catch(IOException e) {
    // -> file still open
} finally {
    if(fos != null) {
    try {
        fos.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Cheers, Gumbatron

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