Java Store UUID

Question

I have a question about storing a UUID. I would like to use Java to generate a UUID and save it so that I can retrieve it the next time the application runs.

In a .NET application I built, I'm doing something similar to this. I'm using the Windows Registry to store the UUID and all other settings. However, this Java application is supposed to be cross-platform compatible. This presents the problem. Obviously on other operating systems I won't have the Windows Registry for such a task, so how would I go about this?

I have one solution for this problem, but I'd like something slightly more sophisticated. My current solution is storing a text file (named something like unique.txt) in the application's directory and then reading it at runtime.

Here are my grievances about that solution:

• If the user moves the application to a new directory, the program has to generate a new UUID and settings file.
• I don't like the fact that the user can see the settings file sitting in their directory.

Here are the conditions I'd like a solution to satisfy:

• The solution should be able to store a UUID value (and possibly other variables) in such a way that they can be retrieved and modified at runtime.
• If the application is deleted and then re-downloaded, the values of the previous installation should still be retrievable.
• The file used to store the values should not appear in the directory of the application (no sense cluttering up the users directory with a settings file).
• If the user moves the application to a different directory, the application should still be able to retrieve the previous settings file. The settings should not be dependent on the directory.

I have thought about storing the settings file in the root directory (/ on unix and C:\ on Windows); however, in my experience, writing to the root directory typically requires elevated permissions. I also feel like the root directory is not the most appropriate location for this.

If Java has a built in method for doing something like this, I would greatly appreciate someone pointing me in the direction of it. Otherwise, if someone could provide some guidance, that would also be great.

I apologize if this question is a duplicate. I've searched for something like this, but I haven't found an answer. If anything about the question is unclear, please add a comment and I'll try to revise the question to clarify.

Thank you in advance.

Answer 1

The Preferences API should provide what you need. If you want common settings for the entire system, check out systemNodeForPackage. Something like this (not tested):

class HardwareId {
    public UUID read() {
        Preferences pref = Preferences.systemNodeForPackage(HardwareId.class);
        String uuid = pref.get("UUID", null);
        if (uuid == null) {
            uuid = UUID.randomUUID().toString();
            pref.put("UUID", uuid);
            pref.flush();
        }
        return UUID.fromString(uuid);
    }
}