What is the best way to generate a unique and short file name in Java

Question

I don\'t necessarily want to use UUIDs since they are fairly long.

The file just needs to be unique within its directory.

One thought which comes to mind is

Answer 1

Problem is synchronization. Separate out regions of conflict.

Name the file as : (server-name)_(thread/process-name)_(millisecond/timestamp).(extension)
example : aws1_t1_1447402821007.png

Answer 2

I use the timestamp

i.e

new File( simpleDateFormat.format( new Date() ) );

And have the simpleDateFormat initialized to something like as:

new SimpleDateFormat("File-ddMMyy-hhmmss.SSS.txt");

EDIT

What about

new File(String.format("%s.%s", sdf.format( new Date() ),
                                random.nextInt(9)));

Unless the number of files created in the same second is too high.

If that's the case and the name doesn't matters

 new File( "file."+count++ );

:P

Answer 3

I use current milliseconds with random numbers

i.e

Random random=new Random();
String ext = ".jpeg";
File dir = new File("/home/pregzt");
String name = String.format("%s%s",System.currentTimeMillis(),random.nextInt(100000)+ext);
File file = new File(dir, name);

Answer 4

I'd use Apache Commons Lang library (http://commons.apache.org/lang).

There is a class org.apache.commons.lang.RandomStringUtils that can be used to generate random strings of given length. Very handy not only for filename generation!

Here is the example:

String ext = "dat";
File dir = new File("/home/pregzt");
String name = String.format("%s.%s", RandomStringUtils.randomAlphanumeric(8), ext);
File file = new File(dir, name);

Answer 5

This works for me:

String generateUniqueFileName() {
    String filename = "";
    long millis = System.currentTimeMillis();
    String datetime = new Date().toGMTString();
    datetime = datetime.replace(" ", "");
    datetime = datetime.replace(":", "");
    String rndchars = RandomStringUtils.randomAlphanumeric(16);
    filename = rndchars + "_" + datetime + "_" + millis;
    return filename;
}

// USE:

String newFile;
do{
newFile=generateUniqueFileName() + "." + FileExt;
}
while(new File(basePath+newFile).exists());

Output filenames should look like :

2OoBwH8OwYGKW2QE_4Sep2013061732GMT_1378275452253.Ext

Answer 6

It looks like you've got a handful of solutions for creating a unique filename, so I'll leave that alone. I would test the filename this way:

    String filePath;
    boolean fileNotFound = true;
    while (fileNotFound) {
        String testPath = generateFilename();

        try {
            RandomAccessFile f = new RandomAccessFile(
                new File(testPath), "r");
        } catch (Exception e) {
            // exception thrown by RandomAccessFile if 
            // testPath doesn't exist (ie: it can't be read)

            filePath = testPath;
            fileNotFound = false;
        }
    }
    //now create your file with filePath