Filename, Dates

A program generates a file on a regular time schedule. We can use the current date and time as a filename. This avoids file system conflicts.

With a format string, we create a filename String. We specify that the year, month, day, hour, minute and second is present.

Example program

This program first calls Calendar.getInstance to access a calendar. It then sets the time to the current instant—it uses the now() method.

import java.time.Instant;
import java.util.Calendar;
import java.util.Date;

public class Program {
    public static void main(String[] args) {

        // Get a Calendar and set it to the current time.
        Calendar cal = Calendar.getInstance();
        cal.setTime(Date.from(Instant.now()));

        // Create a filename from a format string.
        // ... Apply date formatting codes.
        String result = String.format(
                "file-%1$tY-%1$tm-%1$td-%1$tk-%1$tS-%1$tp.txt", cal);

        // Display our result filename.
        System.out.println("Filename:");
        System.out.println(result);
    }
}
Filename:
file-2015-05-04-16-07-pm.txt

Program result

The program generated a string with a filename that could be used to store time-sensitive information. It contains the date, month, year, hour, minute and seconds.

Format strings are concise

With the format string in this example we can add six time fields to a filename in one line of code. The symbols are hard to read, but can be learned.

For log files, or files that are written on a timed basis, this approach to generating filenames is useful. It avoids conflicts which could caused at a loss.