How to make a folder which contains many files in Java?

Question

I want to make a folder which contains files that my program made. For example (this example doesn't represent the things that my program actually does):

private static HashMap<LocalDate,Number> numbers = new HashMap<>();
private static ListIterator li;
public static void saveIndividually(){
    try{
    if(!numbers.isEmpty()){
        ArrayList<LocalDate> lista= new ArrayList<LocalDate>(numbers.keySet());
        li=lista.listIterator(); 
        while (li.hasNext()){
            Number number=numbers.get(li.next());
            FileOutputStream ostreamPassword = new FileOutputStream(number.getDate()+".dat");
            ObjectOutputStream oosPass = new ObjectOutputStream(ostreamPassword);
            oosPass.writeObject(number);
            ostreamPassword.close();     
        }
    }
} catch (IOException ioe) {
        System.out.println("Error de IO: " + ioe.getMessage());
    } catch (Exception e) {
        System.out.println("Error: " + e.getMessage());
    }
}

- My program makes random numbers combination. - Every combination is stored in a HashMap like so( I've added new code): And now I want to make a .txt document individually for every number in the HashMap, with the name datetime(when the number was created).txt, and introduce all of them in a folder to make it easy for the user to read the combination without starting my program. Is it possible to do that in Java?

Answer 1

Let's answer "How to make a folder - in java". There are several ways to do this. Let's create an output folder on the Desktop for demonstration.

public static File createOutputFolder() {
   final File desktop = new File(System.getProperty("user.home"), "Desktop")
   final File output = new File(desktop, "output");

   if (!output.exists()) {
          // The directory does not exist already, we create it
          output.mkdirs();
    } else if (!output.isDirectory()) {
          throw new IllegalStatexception("The output path already exists but is no directory: " + output);
    }

    return output;
}

Our method also returns the output directory. You may now pass this File object to your FileOutputStream and create new files like that:

File output = createOutputFolder();
FileOutputStream ostreamPassword = new FileOutputStream(new File(output, number.getKey()+".dat"));

Hopefully this answered your question. If not, please be more specific about the problem.