[Java] How to create tmp file name with out creating file.

Question

I write application in Java using SWT. I would like to create unique file name. But I do not want create it on hard drive. Additional functionality: I want to create unique file name in specify folder.

public String getUniqueFileName(String directory, String extension) {
     //create unique file name 
}

Answer 1

Use a timestamp in the filename?

Of course this may not work if you have very high concurrency.

For example:

public String getUniqueFileName(String directory, String extension) {
    return new File(directory, new StringBuilder().append("prefix")
        .append(date.getTime()).append(UUID.randomUUID())
        .append(".").append(extension).toString());
}

AS John Oxley's answer suggests. UUID may be a solution as you can use 4 different schemes to create them. Though there is still a small chance of a collision. If you combine a timestamp with a random UUID the chances of any collision becomes vanishingly small.

Answer 2

Use a GUID

• http://java.sun.com/j2se/1.5.0/docs/api/java/util/UUID.html
• http://en.wikipedia.org/wiki/Globally_Unique_Identifier

Answer 3

You could try using a GUID for the file name.

Answer 4

You can create a file with any name (time, GUID, etc) and then test it to see if it already exists. If it does, then try another name to see if it's unique.

File f = new File(guid);
if (f.exists()) {
  //try another guid
}else{
  //you're good to go
}

Answer 5

From your question I assume you've seen that File.createTempFile() always creates a file rather than just allowing you to generate the name.

But why not just call the method and then delete the temporary file created? createTempFile() does all the work in finding a unique file name in the specified directory and since you created the file you can sure you'll be to delete it too.

File f = File.createTempFile("prefix",null,myDir);
String filename = f.getName();
f.delete();