Where should my application save its data files?

Question

Every operating system has a preferred default folder for saving data files generated by an application. On my Mac, it is users/<username>/library/application support/<application name>. On Windows, it is somewhere inside Documents and Files.
Is there a way to determine this folder in Java?
If at all possible I want my application to automatically load its data files at start up, and save them on exit, without prompting the user for a location. But the default folder appears to be the folder containing the jar, which is not the best choice for the platform.
-Ron.

Answer 1

There is a system property called user.home that will point you to the right folder. You'll still have to do a bit of platform specific code if you want to it correctly, though. Here's a method I use in my private toolbox (SysInfo is also private, but i guess you'll see what is does from the code):
     * Returns the appropriate working directory for storing application data. The result of this method is platform
     * dependant: On linux, it will return ~/applicationName, on windows, the working directory will be located in the
     * user's application data folder. For Mac OS systems, the working directory will be placed in the proper location
     * in "Library/Application Support".
     * <p/>
     * This method will also make sure that the working directory exists. When invoked, the directory and all required
     * subfolders will be created.
     * @param applicationName Name of the application, used to determine the working directory.
     * @return the appropriate working directory for storing application data.
public static File getWorkingDirectory(final String applicationName) {
        final String userHome = System.getProperty("user.home", ".");
        final File workingDirectory;
        switch (SysInfo.getPlatform()) {
            case LINUX:
            case SOLARIS:
                workingDirectory = new File(userHome, '.' + applicationName + '/');
                break;
            case WINDOWS:
                final String applicationData = System.getenv("APPDATA");
                if (applicationData != null)
                    workingDirectory = new File(applicationData, "." + applicationName + '/');
                else
                    workingDirectory = new File(userHome, '.' + applicationName + '/');
                break;
            case MACOS:
                workingDirectory = new File(userHome, "Library/Application Support/" + applicationName);
                break;
            default:
                return new File(".");
        if (!workingDirectory.exists())
            if (!workingDirectory.mkdirs())
                throw new RuntimeException("The working directory could not be created: " + workingDirectory);
        return workingDirectory;
    }