Check if file changed name

Question

I wrote a Java program which watches a directory for changes. I keep a list of files (String[]) and at every x seconds I get a new list and compare them to find which files were added and which ones were removed.

The problem is that if I rename a file, it would appear as a removal of a file with the old name and then as an addition of a file with the new name.

What could I do to keep track of name changes?

EDIT: I would like to find a solution for Java 6. Code:

public void run() {
    int ok;
    while(true) {
        // verify if modified from last check
        if(modified != file.lastModified()) {
            Date d = new Date();
            list = file.list();
            // look for new files
            for(String x : list) {
                ok = 0;
                for(String y : old) {
                    if(x.equals(y)) {
                        ok = 1;
                    }
                }
                if(ok == 0) {  
                    display.setText(display.getText() + "Created file " + x  + " at " + d.toString() + "\n");
                }
            }
            // looking for old files
            for(String x : old) {
                ok = 0;
                for(String y : list) {
                    if(x.equals(y)) {
                        ok = 1;
                    }
                }
                if(ok == 0) {
                    display.setText(display.getText() + "Deleted file " + x + " at " + d.toString() + "\n");
                }
            }
        }
        old = file.list();
        modified = file.lastModified();
        try {
            Thread.sleep(f * 1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Also, in this code, if I want to write old = list (to keep the last list), i get a NullPointerException at line for(String y : old). Why?

Do you have code to share, so we know how you're currently accomplishing this? — Eric Wich, Jun 12 '13 at 16:02
are you based on name of the files? instead of name, may be you can use id sort of thing in file system... in that way even if a file is rename it's id is not changed..... http://stackoverflow.com/questions/8289598/file-id-for-keeping-track-of-file-changes-in-java — pinkpanther, Jun 12 '13 at 16:04
Depending on the ammount of files you could make the CRC o MD5 of the files and keep checking against these hashes so you will know for sure if a file is deleted or not. — Averroes, Jun 12 '13 at 16:12

Stephen C · Answer 1 · 2013-06-12T16:41:14.577

I don't think there is a way to do this that is both portable, reliable and efficient.

Reading the file content is expensive and can be unreliable. (For instance, it will break if you have two files with the same content.
Relying on file timestamps can be unreliable. (You could have different files with the same timestamps.)
I don't think that a WatchService can detect files that are renamed within a directory. (It can detect a rename in or rename out, but not this case ... according to this javadoc.)
The reliable and efficient way to do it (on Linux systems at least) is to either use the native Linux watch service (which supports more FS events), or a combination of the inode numbers and the native file creation timestamp. But these both involve using native code to make the relevant system calls.

Check if file changed name

1 Answers1